ASME Conference Presenter Attendance Policy and Archival Proceedings

2014;():V003T00A001. doi:10.1115/PVP2014-NS3.

This online compilation of papers from the ASME 2014 Pressure Vessels and Piping Conference (PVP2014) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Design and Analysis: Acoustic Induced Vibration in Piping Systems

2014;():V003T03A001. doi:10.1115/PVP2014-28140.

High acoustic energy is known to cause vibrations in pipes, and in some severe cases acoustic induced vibration can lead to fatigue failure at branch connections with high stress concentration. Industry guidelines suggest using mitigation measures such as fabricated full wrap-around reinforcement pad (re-pad) or Sweepolet fittings at branch connections. Effectiveness of these mitigation measures is evaluated via a finite element analysis of four types of branch connections; (i) Sockolet, (ii) Sockolet with 2″ wide partial re-pad, (iii) Sockolet with full wrap-around re-pad, and (iv) Sweepolet. Four distinct acoustic frequency ranges (1/3 octave bands) with associated sound pressure levels are used as the excitation source. Maximum stress levels in the main header pipe at the branch tie-in are monitored to assess the potential for vibration damage. Of the four branch connections, Sockolet with full wrap-around re-pad is found to be least susceptible to damage, followed by the Sweepolet. Unreinforced Sockolet is most susceptible to damage, and the Sockolet with partial re-pad is only marginally better.

Topics: Fatigue , Acoustics
Commentary by Dr. Valentin Fuster
2014;():V003T03A002. doi:10.1115/PVP2014-28260.

A framework for Acoustic Induced Vibration (AIV) evaluation is outlined which is based on estimating the pipe surface strain for an evaluation framework of structural fatigue. Critical to this approach is that the assessment is implemented with frequency based formulations. The frequency based formulation allows for more accurate determination of the pipe’s structure response and combining different sources, such as the valve and piping elements. The approach relies on internationally recognized standards as the core technology, in particular the IEC 60534-8-3 control valve aerodynamic noise prediction standard and the fatigue assessment in design codes, such as the ASME Boiler and Pressure Vessel code. These are augmented with system noise predictions using a non-dimensional testing based model for piping component noise predictions. Components of this approach have been described in previous papers and are presented here in a more complete form.

Commentary by Dr. Valentin Fuster
2014;():V003T03A003. doi:10.1115/PVP2014-28303.

Finite Element Analysis (FEA) and Statistical Energy Analysis (SEA) methods have been applied recently to the study of acoustic induced vibration (AIV) in piping systems.

In this paper, the acoustic vibration in the piping systems is studied by performing FEA of a model of the structural pipe with the application of the acoustic excitation as stationary acoustic modes to the structural pipe model. This approach provides an alternative to performing FEA using a combined model for the acoustic fluid and the pipe. The analysis is used for the evaluation of the power flow from the acoustic medium to the pipe. The acoustic part of the system is modeled as a series of acoustic modes that are taken to act on the pipe FEA model. The Coupling Loss Factor (CLF), required for the formulation of the SEA model, is identified and plotted against pipe parameters.

Commentary by Dr. Valentin Fuster
2014;():V003T03A004. doi:10.1115/PVP2014-28325.

While finite element modeling analysis is becoming more frequent for analyzing AIV problems, in the absence of experimental data in large diameter pipe, there is no industry wide accepted methodology for representing the pressure excitation for the pipe so accurate cycles to failure may be predicted. The assumptions involved in determining the actual amplitude of the acoustic excitation, which modes may develop and how they couple with the structure all contribute to the overall uncertainty of the problem.

Depending on the degree of correlation assumed between the structural and acoustical mode shapes the results vary dramatically. There are also variations based on the number of participating modes assumed. Relative strengths of a Weldolet®, an Insert Weldolet® that is a variation of Sweepolet® and a Reducing Tee connection were analyzed for a 24×6 inch Sch. 10S and STD connection assuming various degrees of correlation and mode participation. Wide fluctuations in the cycles to failure were observed based on the assumptions; however, the stress ratios between the connections are relatively stable. This suggests the use of an acoustic Stress Intensification Factor (SIF) in conjunction with Fatigue Strength Reduction Factors (FSRF) to determine suitability of connections in AIV service rather than an absolute value of cycles to failure.

Further investigation of the trends in the value of SIF as the D/d (branch to header diameter) and D/t (diameter to thickness) ratios over a range of pipe diameter are required before these SIF’s could be put into use. Experimental data for a few controlled failure cases are required to ground the finite element prediction in reality. As the experiment is more likely to be conducted with air the possible pitfalls in extending the results from air to commonly used process fluid are also discussed.

Commentary by Dr. Valentin Fuster
2014;():V003T03A005. doi:10.1115/PVP2014-28600.

In the flare piping system, it is known that piping vibrations occur caused by Acoustically Induced Vibration (AIV) and Flow Induced Vibration (FIV) corresponding to high flow rate, high pressure drop and relatively thin pipe wall thickness. For FIV, turbulence generated at combining tee with high fluid velocity results in low frequency piping vibration. For AIV, large noise produced through a component with large pressure drop results in high frequency piping vibration. Carucci and Mueller shows the several cases with piping failure due to AIV and most of these cases the piping failure occurred at the combining tee. In these piping failure cases, the velocity at the combining tee would be quite high close or equal to sound speed and this means piping vibrations could occur due to FIV in addition to AIV.

This paper shows the investigation results of FIV at combining tee with 90 degrees using experimental data. The results are compared to the previous study results for 45 degrees combining tee and the difference between 90 and 45 degrees tees are discussed in the view points of pressure fluctuation and piping vibration. This paper also shows that the vibration index proposed by authors is quite effective to evaluate the vibration level caused by FIV for both of 90 and 45 degrees tees. This proposed vibration index is applied to failure and no failure cases presented in Carucci and Mueller paper with some assumptions and it is suggested that the vibration indexes for failure case is relatively higher than those of no failure cases. And this suggests that not only AIV but also FIV could affect the piping failure reported in Carucci and Mueller paper.

Commentary by Dr. Valentin Fuster
2014;():V003T03A006. doi:10.1115/PVP2014-28794.

The prediction of acoustically induced vibration (AIV) failures in the design or redesign of piping systems requires an accurate estimate of the excitation source. Furthermore, the next generation of AIV analysis may require a physics-based noise-generation predictive technique, which entails the need for validation via direct measurements. The noise generated by a pressure relief valve (PRV) during a full-scale AIV blowdown test was measured inside a pipe downstream of the valve. A maximum flow rate of 33.5 kg/s was achieved using nitrogen gas through a 3×4″ relief valve generating a peak dynamic pressure level exceeding 650 kPa and sustained levels of 450 kPa (peak). Measurements are compared to existing noise calculation techniques which appear to under-predict the generated noise.

Commentary by Dr. Valentin Fuster

Design and Analysis: CFD in Design and Analysis

2014;():V003T03A007. doi:10.1115/PVP2014-28382.

In the nuclear power plants, there are many branch pipes with closed-end which are attached vertically to the main pipe. We consider a situation in which the high temperature water is transported in the main pipe, the branch pipe is filled with stagnant water which has lower temperature than the main flow, and the end of the branch pipe is closed. At the branch connection part, it is known that a cavity flow is induced by the shear force of the boundary layer which separates from the leading edge of the branch pipe along the main pipe wall. In cases where the high temperature water penetrates into the branch pipe, there is a possibility that a steep and large temperature gradient field, called “thermal stratification layer” is formed at the boundary between high and low temperature water in the branch pipe. If the thermal stratification layer is formed in a bend pipe, which is used for connecting the vertical branch pipe and to a horizontal pipe, at the same time, the temperature fluctuation by the thermal stratification layer motion occurs, there may cause the thermal stress in the piping material. Furthermore, keeping the piping material under the thermal stress, there might be a possibility of a crack on the surface of the bend pipe. For this reason, the evaluation of the position where the thermal stratification layer reaches is very important during early piping design process. And, deeply understanding regarding the phenomena, is also important. However, because of the complexities of the phenomena, it is difficult to immediately clarify the whole mechanisms of the thermal stress arising due to the temperature fluctuation by the thermal stratification layer change. The complete prediction method for the position of the thermal stratification layer based on the mechanisms that is able to be applied to any piping system, any temperature and any velocity conditions, is also difficult. Therefore, a practical approach is required.

The authors attempt to develop the practical estimation method for the thermal stratification layer position using the three-dimensional Navier-Stokes simulation which was based on the Reynolds-average in order to reduce the computational costs. In this paper, three different configurations of the piping were simulated and the simulation results were compared with the experimental results obtained by the other research group.

Commentary by Dr. Valentin Fuster
2014;():V003T03A008. doi:10.1115/PVP2014-28437.

In a boiling water reactor (BWR) and advanced boiling water reactor (ABWR) a main steam line pipe rupture in the main steam piping system, hereafter called main steam (MS) line, will create a decompression wave and a pressure disturbance that moves through the MS line toward the reactor pressure vessel (RPV). It expands into a large region transmitting a compression wave at acoustic speed and spreads as an acoustic wave over the adjacent dryer plate. The initial acoustic pressure force on the dryer is expected to spread from an origin at the steam line attachment. It reflects back toward the RPV wall and again to the dryer until it dissipates. This is expected in a space that is not of uniform spacing because the dryer surface is nearly flat and the vessel wall is a curved surface. The acoustic load region is bounded by the steam dryer outer surface and RPV inner wall surfaces. In this paper, simplified, conservative modeling is applied in this approach to obtain reasonable bounding loads. The method is compared against the result of a detailed fine-structure Computation Fluid Dynamic (CFD) analysis using the same input data. Therefore, the simplified method may be used to quickly estimate conservative decompression forces on a dryer surface.

Commentary by Dr. Valentin Fuster
2014;():V003T03A009. doi:10.1115/PVP2014-28702.

The working cycle of a reciprocating compressor is characterized by heat generation, mainly due to compression transformation and friction phenomena. The main consequences are a reduction of the volumetric efficiency and an increase in the gas discharge temperature. Current regulations such as API618 for reciprocating compressors require a cylinder cooling system. Therefore, a proper design of the cooling circuit is needed in order to achieve the best balance between refrigerating potential and system capacity.

A systematic methodology for the evaluation of the heat transfer process is essential and since experimental characterization of the circuit is complex and case-dependent, the use of a numerical technique is the most favorable and generalizable approach. Within this scenario, 3D analysis shows a great potential although several phenomena must be accounted for in order to accurately model the system.

In this paper, a conjugate heat transfer (CHT) analysis on a double-acting water-cooled reciprocating compressor cylinder is presented, where the three-dimensional flow field of the water circuit and the thermal conduction inside the solid metal are solved simultaneously. The best practice for the imposition of consistent boundary conditions for the metal body is given with special attention to the heat transfer coefficient values for the suction and discharge gas chambers, the compression chamber and the external ambient. The assessment of the numerical methodology is completed with an investigation on the influence of wall roughness and buoyancy effects.

Commentary by Dr. Valentin Fuster

Design and Analysis: Composite Materials and Structures

2014;():V003T03A010. doi:10.1115/PVP2014-28054.

Composite materials are often utilized in weight-critical applications, owing to their higher specific strength\stiffness characteristics. In addition, composite materials also possess qualities such as better corrosion resistance, lower coefficient of thermal expansion, etc., which makes them a potential material choice for riser systems in high pressure and high temperature environments. However, design certification of risers using the finite element method requires modeling and analysis techniques, centric to the multi-layered nature of composite structures.

Riser systems, owing to their high aspect ratios, have traditionally been modeled with beam elements. The methodology for extracting the stress results and certifying a metallic riser is well established in the Oil and Gas industry. However, for analyzing a composite riser, three-dimensional shell or hexahedral elements are generally required to capture the through-the-thickness (or pipe cross-sectional) variation of structural response, especially in critical regions such as touchdown point, pipe-intersection zones, etc.

In this paper, a method for analyzing a detailed local model (discretized with shell\hexahedral elements) driven by results from a global model (meshed with beam elements) is presented. The global model captures the structural response whereas the local model provides cross-sectional stress\strain information for individual layers. Although the method is illustrated for a composite riser, it is also applicable to metallic structures.

Commentary by Dr. Valentin Fuster
2014;():V003T03A011. doi:10.1115/PVP2014-28130.

The combination of fibre volume fraction, fibre orientation and lay-up sequence in composite materials makes it possible to design a multitude of composite pressure vessels and pipes. Analytical models, based on the classical laminate theory and numerical predictive techniques offer a means to optimize the lay-up sequence in order to maximize the strength to weight / cost ratio. This study looks at the validity of using analytical models prescribed in the design by analysis filament wound composite standards and compares the results with realistic test and numerical models. The results show that the classical laminate theory accurately establishes the design load in symmetric and balanced lay-up laminates when appropriate material properties are assigned. However in the case of asymmetric or unbalanced lay-up sequences, the bending and twisting stiffness geometrically strengthens the pipes such that the classical hoop and axial loading conditions based on isotropic material properties, no longer apply. In such instances the analytical solutions can underestimate the design load by more than 33%. An analytical solution that accurately establishes the loading configuration and magnitude is required. On the other hand numerical models gave good agreement with the experimental test results immaterial of the lay-up sequences, when appropriate end coupling, pressure loading and material properties are applied.

Commentary by Dr. Valentin Fuster
2014;():V003T03A012. doi:10.1115/PVP2014-28439.

The evaluation of external nozzle loading on filament wound Fiber Reinforced Plastic (FRP) storage tanks and pressure vessels can be a challenging task. While established methods for metallic vessels exist, limited guidance is available to account for the unique characteristics of FRP composite materials and standard FRP fabrication practices. Anisotropic material properties can have a significant effect on the stress/strain distribution due to external nozzle loading. Typical FRP nozzle installation practices introduce additional concerns, including the potential for peeling or overstraining the nozzle attachment overlays. In this paper, the effects of various orthotropic material properties of cylindrical vessels with external nozzle loading are explored using finite element analysis and compared with existing methods established for isotropic materials. Modifications to account for the effects of filament wound FRP material properties are proposed. A simplified FRP nozzle load evaluation procedure, along with additional commentary, is presented to address some of the special considerations regarding nozzle load evaluation for FRP storage tanks and pressure vessels.

Commentary by Dr. Valentin Fuster
2014;():V003T03A013. doi:10.1115/PVP2014-28941.

Filament wound composite pipes are being used in more and more applications. However, the impact behavior of these pipes is of particular importance in many applications. The sudden failure of these pipes under low velocity impact loads can be dangerous especially when the medium inside the pipe is hazardous or toxic in nature. The impact response of a composite laminate depends upon various factors such as thickness, stacking sequence and number of layers. The primary focus of this paper is parametric study of low velocity impact damage of CFRP and GFRP pipes under varying design parameters using finite element analysis. The simulation results are then used along with the ANN (Artificial Neural Networks) to fit a function to estimate the amount of absorbed energy.

Commentary by Dr. Valentin Fuster

Design and Analysis: Design and Analysis of Bolted Joints

2014;():V003T03A014. doi:10.1115/PVP2014-28174.

High pressure screw plug (also called breech lock) exchangers are arguably the most complicated bolted connection in a refinery. After traveling around the world helping facilities turn these exchangers from chronic leakers (from internal tubesheet and external diaphragm and B style shell leaks) to one of the most reliable heat exchangers in the plant, it is very clear to me that manufacturers, engineers and mechanics struggle to correctly understand the interactions between gaskets, internal pressure, the two circles of external push bolts that are part of A style exchangers and all the internal parts.

Some manufactuers have given up on trying to make these connections operate leak free, and prefer to weld in the tubesheets and diaphragms. This significantly adds to the cost and time needed to open and close these exchangers, as special equipment is needed to machine out the parts and weld them back together again.

There are a handful of equipment manufacturers that build these exchangers, and while there are differences from one manufacturer to the next, once the basic design is understood, the reader should be able understand that they are all basically the same when it comes to the few critical steps that must be followed when opening and closing these exchangers.

In order to obtain reliable leak free performance, all the basic sealing tools must be employed, including:

1. A spreadsheet that will easily analyze the critical variables;

2. Correct gasket selection;

3. Correct assembly procedures that focus on important steps including proper spacing of internal parts and obtaining consistent thread friction;

4. And finally hot torqueing the exchangers after startup.

The goal of this paper to provide the end-user with a good understanding for how parts interact and how the bolted connections function, so that they might also achieve reliable, leak free performance. This paper will explain:

1. How the connections work;

2. Common misunderstanding about screw plug exchangers;

3. Pressure Testing Screw Plug Exchangers;

4. Analyzing the design and calculating the important variables;

5. The key assembly steps that must be included in all assembly procedures;

6. Important design considerations when building new exchangers.

Commentary by Dr. Valentin Fuster
2014;():V003T03A015. doi:10.1115/PVP2014-28261.

An ASME Class 300 NPS12 flange connection between a control valve and a pipe has been evaluated at a temperature of 1100° F with testing and Finite Element Analysis (FEA). The goal of the testing was to validate the FEA simulation. The valve side of the test sample was a cast structure, the pipe side was a forged flange butt welded to a pipe section, and the gasket was a Thermiculite filled spiral wound gasket. The valve, flange, and piping material are SA-217, SA-182, and SA-335 (2 ¼ Cr – 1 Mo) steel respectively. The bolt length and flange geometry was measured before and after loading the bolts, and before and after heating the sample in order to measure changes in the bolt load and flange rotation which would indicate creep/relaxation in the joint. Tests were run with two types of bolts, B16 (SA-193) and 718 (SB-637), and also with two gasket arrangements, no gasket and then a spiral wound gasket. The results of the completed test and the correlation to an FEA analysis will be presented.

Commentary by Dr. Valentin Fuster
2014;():V003T03A016. doi:10.1115/PVP2014-28304.

The regulatory compliance of the containment system is of essential importance for the design assessment of transport packages for radioactive materials. The requirements of the IAEA transport regulations SSR-6 for accident conditions implies high load on the containment system of Type B(U) packages. The integrity of the containment system has to be ensured under the mechanical and thermal tests.

The containment system of German transport packages for spent nuclear fuel (SNF) and high level waste (HLW) usually includes bolted lids with metal gaskets. BAM Federal Institute for Materials Research and Testing as the German competent authority for the mechanical and thermal design assessment of approved transport packages has developed the guideline BAM-GGR 012 for the analysis of bolted lid and trunnion systems. According to this guideline the finite element (FE) method is recommended for the calculations. FE analyses provide more accurate and detailed information about loading and deformation of such kind of structures. The results allow the strength assessment of the lid and bolts as well as the evaluation of relative displacements between the lid and the cask body in the area of the gasket groove.

This paper discusses aspects concerning FE simulation of lid systems for SNF and HLW transport packages. The work is based on the experiences of BAM within safety assessment procedures. The issues considered are the assessment methods used in the BAM-GGR 012 for bolted lid systems along with the nominal stress concept which is applied for bolts according to that guideline. Additionally, modeling strategies, analysis techniques and the interpretation of the results are illustrated by the example of a generalized bolted lid systems under selected accident conditions of transport.

Commentary by Dr. Valentin Fuster
2014;():V003T03A017. doi:10.1115/PVP2014-28366.

This paper describes and explains the contents of bolt and bolted connection design rules included in the present 2012 edition of the French RCC-MRx code ([1], applicable to nuclear installation components). The aim of this work is to describe the rules and their technical and historical background, owing to the widespread fields of application in a NPP and to the relative complexity of methods; bolted connections have often a major safety-related role.

The domain of the RCC-MRx covers high temperature sodium reactors, experimental nuclear facilities (Jules Horowitz Reactor, research reactor under construction in France), and fusion reactor components (ITER Vacuum Vessel). The first major application is at present for ASTRID (Advanced Sodium Technological Reactor for Industrial Demonstration).

The bolt connection usual domain varies in a wide range, from very complex configurations, like high temperature, pressure retaining under cyclic load, to simpler flanges for low temperature piping.

In order to fulfill such different needs in design, several sets of rules are included at present in RCC-MRx code, issued from the historical development of previous RCC-MR and RCC-MX codes, from which the “RCC-MRx” version is derived.

In the following, the existing four configurations of bolted connections are identified, the respective rules are summarized, and, finally, a short comparison with other nuclear codes and industrial standards is provided. Available rules to-date concern respectively:

1) Preloaded bolts assuring leaktightness (type “B1”)

2) Preloaded bolts not assuring leaktightness (“B2”)

3) Non-preloaded bolts (“B3”)

4) Flange bolts

Topics: Design
Commentary by Dr. Valentin Fuster
2014;():V003T03A018. doi:10.1115/PVP2014-28685.

This paper examines two key themes regarding the use of hydraulic tensioners to assemble pressure boundary bolted joints. The first theme is the amount of overload required to compensate for load loss that occurs due to both nut-to-tensioner mechanical interaction and, in the case of less than 100% tensioning, bolt-to-bolt mechanical interaction during assembly using hydraulic tensioners. The second theme is to examine the effect on the required assembly procedure if the target bolt stress value is close to yield. This paper has practical application for general assembly of large diameter bolts, but in particular for assembly of low strength bolting, such as A193-B8M class 1 and class 2 bolts.

Topics: Manufacturing , Stress
Commentary by Dr. Valentin Fuster
2014;():V003T03A019. doi:10.1115/PVP2014-28956.

A bolted flange joint was in cyclic temperature and pressure service in a natural gas dehydrator (mole sieve) vessel. The flange joint suffered from multiple failures on a frequent (9 month) basis.

This paper details the investigation into the failure and highlights the most probable cause of failure. A finite element analysis of the pressure and temperature transients in the bolted flange joint pointed to the temperature cycle as tending to unload the joint. Then, a parametric study was undertaken to evaluate the effectiveness of potential solutions.

The bolted flange joint was placed back into service and has been operating for more than three times the prior mean time between failures.

Commentary by Dr. Valentin Fuster
2014;():V003T03A020. doi:10.1115/PVP2014-28980.

This paper presents results from analysis and testing of an NPS 20 CL600 ring-joint (RTJ) flange through assembly and a thermal cycle. Using a mock-up assembly, multiple gasket materials and types including conversion gaskets were tested to evaluate relative performance based on amount of bolt preload loss as measured through the use of load-indicating studs. To simulate field geometry, most tests included a spacer in the flange pair, which necessitated use of two (2) gaskets in the joint. ASME PCC-1-2010 [1] Appendix O calculations and finite element analysis (FEA) were also performed for comparison with the test results and for evaluation of options to improve flanged joint performance. Testing and analysis results are discussed, and learnings are documented.

Topics: Flanges , Testing
Commentary by Dr. Valentin Fuster

Design and Analysis: Design and Analysis of Piping and Components

2014;():V003T03A021. doi:10.1115/PVP2014-28044.

In general, there are two methods to pass on design information in a petrochemical plant design: the manual data key-in method and the file data transfer method. The manual data key-in method is a basic method to pass on data; but this method is time consuming to assign data in one by one fashion. The file data transfer method is a mapping file data from one program to another program under certain specific function and criteria.

This paper starts with how to use a file data transfer method to create a stress analysis model, and then proposes an approach to transfer the stress analysis result to a structural analysis program by using the Pipe Loadings Transfer Program.

In a piping design using 3D plant design software for modeling, the piping design information can be directly transferred to the stress input file by using point vectors to create a stress analysis model. The concepts of a pipe support vector and a beam vector were introduced to transfer the pipe loadings from stress analysis results to a structural analysis program.

The advantages of using a file data transfer method are simple, fast, and accurate.

Topics: Plant design
Commentary by Dr. Valentin Fuster
2014;():V003T03A022. doi:10.1115/PVP2014-28125.

This paper describes the results of a Finite Element Analysis (FEA) of a pipe junction consisting of a thermal sleeve subject to rapid temperature changes. The purpose of the analysis was to utilise derived Computational Fluid Dynamic (CFD) temperatures to calculate stresses on the pressure boundary and thermal sleeve of a pipe junction.

Several transient events were modelled and analysed. Work was then carried out in accordance with the relevant articles of the ASME Boiler and Pressure Vessel Code, Section III, sub-section NB. Work included, design, hydrotest, Level A (including fatigue) and simplified elastic plastic assessments, however not presented within this paper.

The likely fracture performance of the pressure boundary was also investigated, however are also not presented within this paper.

Commentary by Dr. Valentin Fuster
2014;():V003T03A023. doi:10.1115/PVP2014-28265.

This paper presents the results of a small sample of ASME B16.9 welding tee burst tests. The intent of this study was to make a comparison between what is commonly accepted in industry as a B16.9 welding tee to the burst test requirements of B16.9 paragraph 9. The tests conducted show that the current fabrication techniques and some accepted criteria for B16.9 certification can produce thin sections in the tee which do not meet the required burst test pressures.

The test descriptions and results are presented as well as recommendations for future study and potential modifications to the ASME B16.9 standard to address the concerns.

Commentary by Dr. Valentin Fuster
2014;():V003T03A024. doi:10.1115/PVP2014-28267.

The 2010 version of B31.3 introduced sustained stress indices (SSI’s) in paragraph 320. Using methods in references [1],[2],[3],[4],[5], and [11], a test procedure was developed to evaluate these SSI’s for standard metallic piping components. The test procedure has been incorporated into draft versions of B31J so that the sustained stress index can be produced at the same time stress intensification or flexibility factor tests are performed for a particular component. This paper describes the sustained stress index and the B31J test procedure used to determine the SSI.

Topics: Stress
Commentary by Dr. Valentin Fuster
2014;():V003T03A025. doi:10.1115/PVP2014-28268.

Part 1 of this paper was presented by Mr. Chris Hinnant at the 2008 PVP Conference in Chicago. Since 2008 additional fatigue test data has become available to the Paulin Research Group (PRG) which includes tests on unreinforced fabricated tees intended to support the fatigue curve approach established in the 2008 paper, and twenty-five additional straight pipe cantilever fatigue tests on carbon, stainless, duplex, CuNi, P91, X42 and X65 materials. These more recent experimental results confirm the fatigue slope recommended for cantilevers in the 2008 paper, but suggest that the original Markl slope may be more suited for some configurations of branch connections. Comparisons of the B31 Code allowable with failure data, tests, reviews of ratcheting behavior in pipe systems, and crack growth monitoring help draw conclusions about design equations in the B31 Codes and fatigue test procedures.

Topics: Fatigue , Stress , Pipes
Commentary by Dr. Valentin Fuster
2014;():V003T03A026. doi:10.1115/PVP2014-28275.

The high temperature steam pipe used in one heavy oil well in China burst. This failure pipe was investigated and analyzed by macroscopic analysis, material tests (including chemical composition, metallurgical analysis & mechanical property) and fracture surface scanning electronic microscopy (SEM) analysis. Then it can be concluded that the mechanical properties of the burst pipe accord with related standards, and that the fracture surface is a typical brittle fracture. The herringbone stripes were found on the fracture surfaces and pointed to a fracture source where there were over 1.6mm deep mechanical damages on the pipe surface. After micro hardness testing near mechanical damage area and the nearby substrate, it was found that the toughness of mechanical damage area was low. The expanding diameter of the burst pipe was also investigated. Because the residual water in the pipe was pushed by high temperature steam when the steam was turned on, the speed of water was very fast, and the stress caused by water hammer were higher than yield pressure of the pipe, which is the internal pressure in the pipe and which could produces a maximum hoop stress in the pipe equal to the yield strength of the pipe material, the pipe would be expanded.

The fracture surface is a typical brittle fracture. There are two mechanical damages on the fracture source, and the pipe burst because of the mechanical damages and huge impact of water hammer.

Commentary by Dr. Valentin Fuster
2014;():V003T03A027. doi:10.1115/PVP2014-28327.

The partial differential equations for curved pipes with fluid structure interaction, including the effects of fluid pressure and Coriolis force, Centrifugal force and migration force caused by flow velocity, etc., were derived. These equations were then solved numerically utilizing the transfer matrix method (TMM) in the frequency domain because of its computational efficiency. The results were compared with those predicted by the finite element method and a discrete model. It is demonstrated that the TMM has high precision in the vibration analysis of fluid-filled curved pipes. Furthermore, the influence laws of geometrical properties on the natural frequencies and frequency responses of pipeline are discussed, which show that the natural frequencies of the fluid do not change with the varying of curvature angle when curved pipe filled with steam. But the resonance frequencies of the out-of-plane vibration and vibration amplitudes of the fluid pressure waves are strongly influenced by the variation of curvature angle.

Commentary by Dr. Valentin Fuster
2014;():V003T03A028. doi:10.1115/PVP2014-28338.

In the primary circuit of PWR, main components composed of ferritic steel, such as the pressure vessel or the pressurizer, are connected to the piping system made of austenitic steel with weld joints. In this paper, we are considering a narrow gap weld made of Inconel 52, typical of the new EPR™ design. Thus, there are two interfaces between the different materials, that is to say Ferritic steel/Inconel 52 and Inconel 52/austenitic steel. For safety purposes, the demonstration of the fracture resistance of this area is necessary. In that frame, a conventional defect is postulated at one of the interfaces and the fracture resistance of the structure is evaluated. To do so, the J parameter is determined and then compared to the material toughness. However, calculation of the J parameter for a crack located at an interface is usually difficult to evaluate depending on the Finite Element (F.E.) code used. As a matter of fact, this configuration is close to the limit of validity of the J formulation since the crack is surrounded by different materials. In general, most of studies are conducted with a conventional defect parallel and close to the interface. This configuration is usually used because the domain of validity of the J parameter is well known in that case. Nevertheless, it is important to be able to evaluate the J parameter for a crack located on the interface since it is more representative of a defect due to the welding process and also easier to mesh. This paper focuses on that particular case and evaluates the validity of the J parameter for such a location of the conventional defect. Using F.E.M. with Systus® and Castem®, the J parameter is calculated for a piping structure containing a narrow gap weld and a defect at the ferritic steel/Inconel 52 interface and around this area. The structure is submitted to different types of loading such as internal pressure, axial force, or thermal shocks. All the different results allow concluding about the continuity of the J parameter through the interface and its numerical validity. Also, it gives interesting information about the size of the integration path to use and the adapted mesh size around the crack.

Commentary by Dr. Valentin Fuster
2014;():V003T03A029. doi:10.1115/PVP2014-28400.

Laser shock peening (LSP) is a surface mitigation technique that can be applied to improve the life of a metallic component through the generation of a compressive surface stress field induced by high-power laser pulses. Numerical simulation of LSP (produced residual stresses) in presence of an initial stress field similar to those obtained under welding has been carried out in nonlinear dynamic by coupling an explicit code (Europlexus) and an implicit one (Code_Aster). In the first step, an axisymetrical model has been validated by comparison with an analytical solution considering an elastic-perfectly plastic behavior law. Then, comparisons with Abaqus calculations have been carried out in terms of displacements and residual stresses using the Johnson-Cook high strain rate constitutive law to validate multi-impact 3D modeling. High strain rate parameter of Johnson-Cook law has been identified using LSP on thin plates. Validations of the simulations are then performed by comparing with experimental determined deformations caused by LSP on thick plates. For 25 overlapped shots, LSP induced residual stresses calculated with and without initial residual stresses similar to those obtain under welding have been compared to adress the effect of initial stresses on final residual fields.

Commentary by Dr. Valentin Fuster
2014;():V003T03A030. doi:10.1115/PVP2014-28401.

The primary objective of the present paper is to depict the mechanical behavior of high density polyethylene, (HDPE), pipes under different loading conditions with different specimen geometries to provide the designer with reliable design data relevant to practical applications. Therefore, it is necessary to study the effect of strain rate, ring configuration, and grip or fixture type on the mechanical behavior of dumb-bell-shaped, (DBS), and ring specimens made from HDPE pipe material. DBS and ring specimens are cut from the pipe in longitudinally, and circumferential (transverse) direction respectively. On the other hand, the ring specimen configuration is classified into two types; full ring, (FR), and notched ring, (NR) (equal double notch from two sides of notched ring specimen) specimens according to ASTM D 2290-12 standard. Tensile tests are conducted on specimens cut out from the pipe with thickness 10 mm at different crosshead speeds (10–1000 mm/min), and ambient temperature, Ta = 20 °C to investigate the mechanical properties of DBS, and ring specimens. In the case of test specimens taken from longitudinal direction from the pipe a necking phenomenon before failure appears at different locations along the gauge section. On the other hand, the fracture of NR specimens occurs at one notched side. The results demonstrated that the NR specimen has higher yield stress than DBS, and FR specimens at all crosshead speeds. The present experimental work reveals that the crosshead speed has a significant effect on the mechanical behavior of both DBS, and ring specimens. The fixture type plays an important role in the mechanical behavior for both FR and NR specimens at all crosshead speeds.

Commentary by Dr. Valentin Fuster
2014;():V003T03A031. doi:10.1115/PVP2014-28426.

Demonstration of large components integrity under seismic loading is based up to now on monotonic tearing resistance curves. However, it is well known that cycles decrease the fracture resistance of the material, mainly according to the loading ratio. Most studies use monotonic methods to analyze reversible cyclic loading and the associated increase of crack propagation: Delta J-R curves are largely used. For monotonic loadings, Turner [1] proposed a decomposition of the rate of dissipated fracture energy. This decomposition led on the determination of an energetic criterion for ductile fracture [2]. This intrinsic criterion allows the fracture prediction on large components. This paper aims to propose an analysis of cyclic ductile fracture which should allow the determination of an energetic criterion under large amplitude cycles. For that purpose, compact tension specimens are taken from a carbon steel pipe (Tu42C) used in the secondary circuit of French PWR. A series of cyclic tearing tests are carried out under quasi-static loadings. The effects of loading ratio and incremental plastic displacement are quickly studied. Here, we present an energetic analysis which take into account the crack closure and crack opening. Indeed, displacement fields around the crack tips are measured with digital image correlation and linked with electric potential measurement. That allows an accurate determination of crack closure and crack opening and let a precise calculation of fracture energy possible. The energetic fracture criterion will be confirmed with crack propagation prediction on different geometry like CT specimen and a through-wall-cracked pipe under cyclic reversed loadings.

Commentary by Dr. Valentin Fuster
2014;():V003T03A032. doi:10.1115/PVP2014-28548.

For corroded piping in low temperature systems, such as service water systems in nuclear power plants, replacement of carbon steel piping with high density polyethylene (HDPE) is a cost-effective solution. Polyethylene pipe can be installed at much lower labor costs than carbon steel pipe and HDPE pipe has a much greater resistance to corrosion. The ASME Boiler and Pressure Vessel Code, Section III, Division 1 currently permits the use of non-metallic piping in buried safety Class 3 piping systems. Additionally, HDPE pipe has been successfully used in non-safety-related systems in nuclear power facilities and is commonly used in other industries such as water mains and natural gas pipelines. This paper presents the results of creep testing of PE 4710 cell classification 445574C pipe compliant with ASME Boiler and Pressure Vessel Code material requirements. This information was developed to support and provide a strong technical basis for material properties of HDPE pipe for use in ASME Boiler and Pressure Vessel Code, Section III New Construction and Section XI repair or replacement activities. The data may also be useful for applications of HDPE pipe in commercial electric power generation facilities and chemical, process and waste water plants via its possible use in the B31 series piping codes. The report provides long term creep and modulus data, as well as an analysis of the stress dependency of both.

Topics: Density , Creep
Commentary by Dr. Valentin Fuster
2014;():V003T03A033. doi:10.1115/PVP2014-28549.

For corroded piping in low temperature systems, such as service water systems in nuclear power plants, replacement of carbon steel piping with high density polyethylene (HDPE) is a cost-effective solution. Polyethylene pipe can be installed at much lower labor costs that carbon steel pipe and HDPE pipe has a much greater resistance to corrosion. The ASME Boiler and Pressure Vessel Code, Section III, Division 1 currently permits the use of non-metallic piping in buried safety Class 3 piping systems. Additionally, HDPE pipe has been successfully used in non-safety-related systems in nuclear power facilities and is commonly used in other industries such as water mains and natural gas pipelines. This report presents the results of updated fatigue testing of PE 4710 cell classification 445574C pipe compliant with the specific Code requirements. This information was developed to support and provide a strong technical basis for material properties of HDPE pipe for use in ASME Boiler and Pressure Vessel Code, Section III New Construction and Section XI repair or replacement activities. The data may also be useful for applications of HDPE pipe in commercial electric power generation facilities and chemical, process and waste water plants via its possible use in the B31 series piping codes. The report provides fatigue data in the form of Code S-N curves for fusion butt joints in PE 4710 cell classification 445574C HDPE pipe.

Commentary by Dr. Valentin Fuster
2014;():V003T03A034. doi:10.1115/PVP2014-28837.

Engineering design must take care of local peaks within stress field, in order to provide relevant forecast of material behavior. Within pipeline girth welds, pipe misalignment is an ordinary cause of significant stress concentrations. The matching of pipe ends depends of the quality of alignment procedure but it is also much influenced by pipe fabrication tolerances. In general, misalignment is estimated considering the maximal and minimal values of each pipe size according to pipe fabrication tolerances. But, in practice, the probability to get a such case is very low. This paper describes how to improve the calculation of stress concentration factor (SCF) through a statistical analysis of pipe dimensions. The use of actual pipe measurements is not necessary even if it provides better SCF estimation. Indeed the distribution of pipe size can be estimated through the fabrication tolerances which require acceptable capacities of the manufacturing system.

Commentary by Dr. Valentin Fuster
2014;():V003T03A035. doi:10.1115/PVP2014-28838.

The 45-degree laterals are widely used in pressure vessel nozzles and piping branch connections. Though the pressure design is always important for the 45-degree laterals, it is not a simple work because it has severe stress concentrations, it is difficult to weld and inspect, and there are some discrepancy between a conventional design and design by linear and nonlinear finite element analysis. In previous papers, authors studied the characteristics of both 90 degree tee and 45 degree laterals using an inelastic finite element analysis based on simplified shell element models and proposed Collapse Strength Reduction Factor (CSRF) based on an inelastic analysis were compared. In this paper, results of the burst test of 45-degree lateral and 90 degree intersection were shown. The fracture surface of 45-degree lateral was different from that of 90-degree intersection. These experimental results are compared with the inelastic finite element analysis results focusing on the local stress and strain behaviors. It was found that the magnitude of the local strain affected the burst pressure. Consideration should be given on the local failure due to excessive plastic strain under high stress triaxiality for the design of the 45-degree lateral by inelastic analysis.

Topics: Collapse , Cylinders
Commentary by Dr. Valentin Fuster
2014;():V003T03A036. doi:10.1115/PVP2014-28920.

In this paper, elbow elements in commercial finite element software ABAQUS are reviewed and two commonly used elements, ELBOW31 (2-node, linear) and ELBOW32 (3-node, quadratic), are numerically tested for two Benchmark examples: a cantilever pipe and an in-plane bending pipe bend. Two main issues are studied through the numerical tests: (1) The effect of the element size and the number of ovalization modes chosen for computation; (2) The accuracy of computed deformation and stresses. To gain an insight into the behavior of these elements, a comparison against published results by experiment and computations using elbow elements in software ADINA and MARC, as well as computations using ABAQUS shell elements, is conducted. It is shown that: (i) these elements predict a good peak stress solution with a reasonably coarse mesh and 6 ovalization modes; (ii) the ovalization and the distribution of stresses predicted around the pipe section show, though using a relatively dense mesh, a notable difference as compared to solutions computed by ABAQUS shell elements; (iii) the ADINA elbow element seems to provide, though using a very coarse mesh, a solution closest to analytic and experimental results. It is concluded that there are great needs for in-depth studies on elbow elements regarding reliability and accuracy issues.

Topics: Pipes
Commentary by Dr. Valentin Fuster
2014;():V003T03A037. doi:10.1115/PVP2014-28985.

In one Ontario CANDU reactor unit, the horizontal feeders are interlinked with feeder spacer rods, which are installed to prevent the contact between adjacent feeders. In the normal operating conditions, spaces do not carry any loads. Therefore, the individual feeder model is used without spacers for the horizontal feeders. This reactor unit is under extensive fuel channel shifting in order to extend the life time. The axial shifting of channels is expected to put additional loads on spacers and may constrain feeder movement. In order to determine how the spacer affects the feeder stress and feeder movement due to the extensive fuel channel shifting, multifeeder models that include spacers are created for stress analysis. Multi-feeder modelling capability is not readily available in AUTOPIPE. A novel approach of inter connecting feeders with structural elements is developed for AUTOPIPE. A significant increase in feeder stress under the extensive fuel channel shift loading condition is found when the feeder spacers are included in the model. However, the feeder stresses for Design, Level A&B loading under fuel channel shift configuration meet the ASME B&PV Code NB-3600 stress limit requirements. The feeder spacer assessment results also show that the structural integrity of feeder spacers is not affected by the fuel channel shifting. In addition, this study confirmed that it is unnecessary to release the feeder spacers to prevent spacer break or feeder overstress during the post fuel channel sifting operation, thus saving significant outage time to achieve shifting configuration.

Commentary by Dr. Valentin Fuster
2014;():V003T03A038. doi:10.1115/PVP2014-29065.

Steam line blowing is an operational cleaning method used to clean steam piping and reheaters prior to turbine powering for steam power plants. This paper focusses on the application and challenges associated with the steam blowing of large solar thermal collection power plants.

The boiler configuration, located atop an over 400 foot tall tower, in a large solar thermal collection plant poses some challenges not associated with other steam supply methods. As a result of the flow path configurations and steam mass required for blowing the cold reheat, reheater, and hot reheat portions of the plant, attemperation is required to control temperatures in the reheater. The use of multiple flow paths and stages through the reheater also requires some additional consideration. Where in a fossil powered plant the losses through the reheater are based on the inlet vs. outlet conditions, additional vendor data is required to model the internal sections of the reheater in greater detail.

Methodologies developed for fossil powered plants can be applied to large solar thermal collectors with special consideration for the unique configurations and constantly changing solar conditions associated with the plants. The smaller margins associated with these plants requires more rigorous modeling of the system components.

Commentary by Dr. Valentin Fuster
2014;():V003T03A039. doi:10.1115/PVP2014-29121.

In power plants, engineering analysis is used to design piping systems for steam and water hammer events. A simple and effective approach based on hand calculation was proposed by E.C. Goodling1 which has been widely used in the industry to estimate fluid loads for pipe stress analysis and design of piping restraints. His approach provides a conceptual understanding of many factors that control fluid loads, which can be used both to perform approximate checks of more detailed computer solutions, and to identify parameters that can be changed to optimize system designs. In Goodling’s work, the possibility of reflection waves affecting fluid loading is mentioned. However, this effect was not explored and is often neglected when simple hand estimates of fluid loads are made. This paper looks at the effects reflection waves from pressure vessels or large headers may have on steam/ water hammer loads. A few sample problems are solved with the aid of a Method of Characteristic (MOC) computer program and compared to solutions found using the Goodling approach. It is shown that neglecting reflection waves may lead to non-conservative loads (by up to a factor of two). The effects of other critical parameters (e.g., pressure pulse rise rate) are also discussed.

Commentary by Dr. Valentin Fuster

Design and Analysis: Design and Analysis of Pressure Vessels, Heat Exchangers and Components

2014;():V003T03A040. doi:10.1115/PVP2014-28075.

In urea plant equipment, particularly those operating in the synthesis cycle, anti-corrosive liner plates are usually applied to the pressure retaining carbon steel vessel walls. Even with the correct material selection, controlled fabrication methods and maintenance, the risk of highly corrosive urea-carbamate solution leaking through these liners always exists in these equipment which might eventually damage the carbon steel walls.

Existing designs of these equipment utilizes “weep holes” to reveal such leakages. Various designs exist, but in general these weep holes are 15–20mm dia. plain openings in the vessel walls connecting the space between the liner and the vessel wall to the outside atmosphere or the leak-detect apparatus.

These equipment operate at high pressures and temperatures and therefore ASME Section VIII Division 2 is normally the preferred design and construction Code.

This Code, earlier to the publication of its Edition 2007, had provisions in it to exempt openings not exceeding certain diameters, from any reinforcement calculations. Traditionally, equipment designers have been applying this clause to seek the exemption of these weep holes from any further calculations.

However, starting with Edition 2007, this Code did away with such exemptions and has made it mandatory to assess openings of all sizes, particularly if they are in the monobloc vessels. Weep holes are no exception.

This paper discusses how the assessment of these weep holes in cylindrical shells can be carried out by applying the “Elastic-Plastic Stress Analysis Method” stipulated in Para. 5.2.4 & 5.3.3 of the ASME Section VIII Division 2 Code. This paper also provides the basis for recommending this method. In the application of this method, the subject is approached as a “shell with opening” and not as conventional “nozzle opening in the shell”.

Commentary by Dr. Valentin Fuster
2014;():V003T03A041. doi:10.1115/PVP2014-28122.

The European unfired pressure vessel code EN13445-3 [1] has been used to design a preliminary prototype of a towfish. The towfish is essentially an underwater vessel equipped with various sensors, cameras, hydroplanes and control systems that are used to capture data on the levels of pollutants in the sea and at the same time monitor plankton and jellyfish levels. The towfish is towed behind a surface ship and is designed to dive to a depth of 50m below sea level. The depth of dive can be controlled by means of hydroplanes. Data, signals and electrical power are transferred from the towfish to the surface ship and vice versa via the towing line. From a structural point of view the towfish is a vessel acted upon by external pressure and local loads. Design by rule (DBR) was first used to calculate some of the various dimensions and thicknesses of the towfish components. The various components were designed mainly to prevent failure due to buckling. Design by analysis (DBA) based on Annex B of the pressure vessel code EN13445-3 [1] was then used to carry out further buckling checks that were not possible to do using design by rule. At the end of the paper the results from the two design approaches are compared and any major differences are highlighted.

Topics: Design
Commentary by Dr. Valentin Fuster
2014;():V003T03A042. doi:10.1115/PVP2014-28182.

Coal gasification is a key technology for clean coal conversion with high efficiency. During the past decade, more than twenty Shell Key Gasification Equipments (SKGE) used in the Shell Coal Gasification Process (SCGP) have been built in coal-to-chemicals industry in China. SKGE comprise the Gasifier and Syngas cooler connected by Transfer duct. The support skirt of the Gasifier base was fixed, while the Syngas cooler side was supported by a constant hanger (floating support). Therefore the design by rule is not applicable to the strength calculation of pressure vessels of the system. In this paper, a FE model of global analysis of the largest SKGE system in China to date was established which considered thirteen loads and twenty-four load combinations. In this model, FEA software ANSYS was used to calculate the global dynamic effect of this 2000-ton system. The whole structural deformation and stress distribution, force and moment on several specified cross sections of SKGE under different load combinations are also determined within this model, which is the prerequisite and foundation for accurate calculation of each key part (e.g. connection between Transfer duct and Gas reversal chamber), and essential safety of SKGE system.

Commentary by Dr. Valentin Fuster
2014;():V003T03A043. doi:10.1115/PVP2014-28373.

Next generation reactors which are subjected to elevated temperatures must be designed to account for inelastic deformation along with elastic one. In order to simplify design analysis of perforated portions, conventionally axisymmetric models with equivalent elastic materials are employed. To extend to inelastic analysis, a method of Effective Stress Ratio (ESR) has been studied in recent years. Previous studies have shown that perforated plates have their own ESR and it is a function of geometry and is independent from their materials.

In this study the only geometry dependence and physical meaning of ESR were clarified. ESR results were compared with Reference Stress Method (RSM) results for unit-ligaments with various ligament efficiencies. It was revealed that RSM results coincide with ESR. First meaning of ESR is stress ratio between solid plate and perforated plate at the same reference stresses. Second meaning of this ratio is how plasticity properties of equivalent solid plate have to be changed to give the same steady state deformation rate at the same mean boundary stress. Moreover, to clarify stress redistribution control mechanism at different ligament efficiencies, simple models were developed and an estimation method based on simple models was proposed for engineering use.

Commentary by Dr. Valentin Fuster
2014;():V003T03A044. doi:10.1115/PVP2014-28383.

The exact analytical approach for stress intensity factor calculation for an arbitrary shape mode I crack loaded by the polynomial stresses is proposed. The approach is based on the calculation of the crack faces displacement at given loading. The displacement field is presented as a shape function multiplied by an adjustment polynomial. At that the key problem is the solution of well-known inverse task: obtaining the stresses field at the crack faces on the base of a given displacements field. Multiply solution of such task for a whole set of certain displacements base functions (e.g., for the single terms of the adjustment polynomial) allows to get analytical expression which connects stresses and displacements fields.

The original semi-analytical technique for integration with subsequent differentiation of well-known singular integral equation of the flat crack problem is developed. The excellent accuracy of the method is confirmed for an elliptic crack as well as for a rectangular one in the infinite 3D body. New results are given for an inner semi-elliptic crack in the infinite body which surfaces are loaded by polynomial stresses up to the 6th order. The importance of choosing the appropriate shape function is demonstrated.

Commentary by Dr. Valentin Fuster
2014;():V003T03A045. doi:10.1115/PVP2014-28391.

During operation of an air separation unit (ASU) a plate fin heat exchanger developed a leak. This apparently simple heat exchanger, exchanging heat between two gaseous streams of air versus nitrogen, was not expected to suffer significant stress levels for producing a damage.

During the analysis of the damage which occurred at the connection welds of three adjacent modules — module construction is widely used in the process industry — an operating situation was discovered leading to high thermal gradients inside the exchanger. It occurred during a stop of the plants nitrogen cycle compressor. The warm flow continued and heated up the exchanger in a very fast way. This led to unacceptably high stresses in the top part of the exchanger. But a more severe situation occurred when the cycle compressor has been restarted. Then cold nitrogen entered the lower end of the exchanger which had been warming up in the meantime.

A finite element analysis based on a modeling technique [4] for brazed plate fin heat exchangers was performed for this dynamic incident showing extreme stress levels at the location of the damage. A fatigue evaluation of the calculated stresses showed that only a few cycles were acceptable for this scenario. As a consequence operational measures have been implemented to protect the exchanger against this severe condition.

Commentary by Dr. Valentin Fuster
2014;():V003T03A046. doi:10.1115/PVP2014-28455.

For the radial flow reactor with a packed catalyst bed, the pressure drop in radial direction will affect bed support stress and load condition significantly. Increased fines due to catalyst attrition during operation will increase the radial pressure drop. For an extreme case, the entire catalyst bed could be pushed inward and pinned to the reactor’s perforated center screen, potentially causing the internal components to be overly stressed by the excessive load. Understanding the impact of radial pressure drop to bed stress and load distribution is very important for reactor internals design and operation. In this study, a generic packed catalyst bed for a radial flow reactor is analytically modeled and examined for stress and load by a classical granular solid material model, i.e., Janssen’s theory, which is further modified to include the pressure drop effects for a radial flow reactor. Interactions between bed stress, load, and radial pressure drop are explored. The critical condition is derived.

Commentary by Dr. Valentin Fuster
2014;():V003T03A047. doi:10.1115/PVP2014-28653.

The seismic safety problem of the spherical tank under seismic load has become one important subject in seismic research of special equipment. Based on the ANSYS finite element software, typical spherical tank mechanics model is established first of all, through precise time history response analysis under the seismic excitation to determine the significant location of the stress. Then, the seismic performance impact of the support structure design parameters is analyzed. Finally, the seismic performance of all kinds of spherical tank, such as the large, medium and small tank, is determined. This paper provides a reasonable basis for the anti-seismic safety security and design of the spherical tank.

Commentary by Dr. Valentin Fuster
2014;():V003T03A048. doi:10.1115/PVP2014-28847.

Pressure vessel towers used in the petrochemical and chemical industry are designed to accommodate numbers of internals including trays and beds resulting in tall vertical structures. Transportation of tall towers from the fabrication shop to the construction site presents challenges that can result in high transportation costs or a logistically impossible task of moving the vessel. One of the solutions to this problem is to shorten the tower for transport by cutting part of the tower skirt and welding it in the field. Depending on the location, welding on site can be expensive, labour intensive and may cause problems in the quality of the weld and the tower being out of level. Using a flanged skirt connection will reduce the field labour spent on connecting the bottom part of the skirt to the rest of the vessel. The challenge that lies in front of designers is that the current codes and available literature do not give a specific design and calculation guidance for implementing such a solution. This paper looks at different analytical methods to be used for the design of a skirt splice. Methods provided by Jawad and Farr, the Canadian Institute of Steel Construction, the American Institute of Steel Construction, and the Peterson Method from the European Commission’s High-Strength Tower in Steel for Wind Turbines (HISTWIN) are analyzed. Based on this analysis, the most optimal and safe design and fabrication methodology for implementing a Flanged Skirt Connection is proposed.

Commentary by Dr. Valentin Fuster
2014;():V003T03A049. doi:10.1115/PVP2014-28852.

This paper focuses on design optimization of brick-lined autoclaves to reduce wall thickness without compromising autoclave integrity. The use of acid resistant, brick lined, horizontal, autoclaves is common for hydrometallurgical processing within the mining industry. To prevent corrosion of the carbon steel pressure boundary, autoclaves are often lined with an acid proof flexible membrane and high nickel alloy overlay localized at nozzle areas. A brick lining protects the membrane against high temperature and abrasive damage that would result in corrosion of the carbon steel pressure boundary. Because of stringent out-of-roundness and deflection requirements, autoclave designers are faced with the challenge of choosing the proper thickness and layout of the autoclaves. Common practice for satisfying stringent requirements is to design much thicker autoclave than what is required to satisfy pressure and temperature conditions. This paper provides a methodology for the design that utilizes stiffening rings for controlling out-of-roundness that results in thinner and lighter autoclaves.

Commentary by Dr. Valentin Fuster
2014;():V003T03A050. doi:10.1115/PVP2014-28897.

10 CFR 50.61 and 10 CFR 50, Appendix G require the evaluation of the unirradiated nil ductility transition reference temperature (RTNDT) determined in accordance with ASME Section III, paragraph NB-2331. For extended operation, components outside of the traditional beltline may require evaluation of RTNDT per NB-2331. Many of these components do not have sufficient test data to determine RTNDT in accordance with NB-2331 due to different test requirements during fabrication. The US NRC has provided methods in Branch Technical Position (BTP) 5-3 of NUREG 0800 to estimate a bounding RTNDT for these components using available test data. This paper compares Branch Technical Position 5-3, paragraph 1.1(4) estimates of RTNDT using 10°F Charpy V-notch data to the ASME B&PV Section III, Paragraph NB-2331 values of RTNDT, for a sample of 35 SA-508 Cl. 2 reactor vessel shell forgings. The BTP 5-3, Paragraph 1.1(4) estimates underestimate NB-2331 values by an average of 13.8°F and by as much as 40°F. This non-conservatism is attributed to the use of 10°F Charpy V-notch data for the BTP 5-3, paragraph 1.1(4) estimate and the difficulty of using only Charpy V-notch data to estimate a parameter based on Charpy V-notch and dropweight data. If BTP 5-3, paragraph 1.1(4) estimates for RTNDT are to be used in 10 CFR 50.61 and 10 CFR 50 Appendix G calculations, the bias and measurement uncertainty of BTP 5-3, paragraph 1.1(4) should be accounted for, such that the estimate of RTNDT bounds the NB-2331 RTNDT with 2σ confidence, as shown in Regulatory Guide 1.99, Revision 2.

Commentary by Dr. Valentin Fuster
2014;():V003T03A051. doi:10.1115/PVP2014-28909.

Mechanical study on a fixed tubesheet which are welded with tube bundles and equipment shell using finite element method is performed. Effects of number of tubes on the strength of tubesheet are studied. Variation of the distributions and magnitudes of the stress and deflection of the tubesheet with the size of the unpierced part of the tubesheet are investigated. Results show with support of tubes, the tubesheet does not behave as a flat solid plate in terms of the stress and deflection distribution features. Specifically, If the tubesheet is partly supported with the tubes in the center, the largest stress intensity occurs at the point which depends on the size of the unpierced region. The maximum deflection is near the unpierced region.

Commentary by Dr. Valentin Fuster
2014;():V003T03A052. doi:10.1115/PVP2014-28957.

The design of tall pressure vessel towers may be affected by transportation limitations on the overall length of the vessel-plus-skirt. Additionally, process considerations set minimum elevations for the pressure vessel, and plant conditions may dictate whether the vessel needs to be set on a foundation or in a structure. Occasionally, these limitations collide, resulting in a requirement for a longer skirt than can be transported. To enable transportation, the vessel skirt may need to be spliced.

There are multiple methods for which the skirt can be spliced: welded or re-welded at site, sleeve-and-bolt, double-sleeve-and-bolt, and flanged. This paper presents these various methods, and presents an overview of the different design methodologies and considerations for the flanged approach. Design considerations and evaluations necessary for the design and consideration of fabrication tolerances are presented. A case study is introduced for context.

Commentary by Dr. Valentin Fuster
2014;():V003T03A053. doi:10.1115/PVP2014-28960.

The performance of a new pressure-relief structure in non-refillable steel welded industry cylinder is evaluated. Instead of a rupture disc welded on the opening of the head, this new pressure-relief structure uses a circular groove which is pressed by a special mold on the dished head. This structure not only avoids opening on the head but also reduces the manufacture cost. To ensure the safety of this pressure-relief structure, the study includes the material tests, tensile tests, hardness tests and burst tests, the limited pressure prediction are carried on. Based on the experimental data and finite element analysis results, an empirical correlation between the limited pressure and the groove pressure is proposed. Furthermore, a probabilistic analysis is performed for the limited pressure.

Topics: Pressure , Steel , Cylinders
Commentary by Dr. Valentin Fuster

Design and Analysis: Fatigue

2014;():V003T03A054. doi:10.1115/PVP2014-28060.

This paper analyses the effect of the cutting method on both the fatigue crack initiation and the fatigue life of steel S355M. The research covers three cutting methods (plasma, laser and oxy-fuel) and two specimen geometries: plain specimens with rectangular section and cut edges, and specimens with machined edges and a cut hole in the middle section. All the specimens were conducted to failure in a resonance machine by applying fatigue cycles, the stress ratio (R) being 0.1, and the corresponding S-N curves were obtained for each combination of cutting method and specimen geometry. The crack initiation time was estimated by analyzing the evolution of the resonance frequency on each specimen. The results show a significant influence of the cutting method on both the crack initiation and the fatigue life of this particular steel.

Commentary by Dr. Valentin Fuster
2014;():V003T03A055. doi:10.1115/PVP2014-28188.

In order to investigate the ultimate strength of structures and components under an unexpected huge earthquake, it is necessary to understand the final fracture condition under static and cyclic loadings. This study compared the crack growth behavior under monotonic and cyclic loading conditions for carbon steel SGV410 used for pressure vessels in nuclear power plants. Fatigue tests were carried out for CT specimens 50 mm wide (1CT), 75 mm wide (1.5CT) and 100 mm wide (2CT) using three kinds of test methods, namely monotonic loading (ML), load line displacement amplitude increasing (V-inc.) and fatigue crack growth (FCG) tests. For the FCG tests, the maximum load was kept constant under cyclic loading with full unloading (R = 0), fully reversed loading (R = −1) and fully reversing the load line displacement (R = −1.5) and the crack growth characteristics were evaluated by the fracture mechanics approach.

Commentary by Dr. Valentin Fuster
2014;():V003T03A056. doi:10.1115/PVP2014-28279.

The influence of mean strain on fatigue life was investigated for Type 316 stainless steel at room temperature in ambient environment. Two types of mean strain were simulated in the fatigue tests: constant and increasing (ratcheting) mean strains. In order to apply the constant mean strain, prestraining was induced prior to fatigue tests. Although the stress amplitudes became larger due to the prestraining, fatigue lives were almost the same as those obtained using non-prestrained specimens for the same strain range. Change in the maximum peak stress and stress amplitude due to the prestraining had little influence on the fatigue life. It was shown that the mean strain showed little influence on the fatigue life under the same strain range. The ratcheting mean strain was observed during the fatigue tests under mean stress. The fatigue life was reduced by applying the mean stress for the same strain range. The degree of the reduction was increased with the magnitude of the ratcheting mean strain. It was deduced that the increasing mean strain enhanced the crack mouth opening and increased the effective strain range. It was concluded that the ratcheting mean strain reduced the fatigue life for the same strain range, and the reduction in fatigue life could be predicted conservatively by assuming the crack mouth was never closed during the fatigue tests.

Commentary by Dr. Valentin Fuster
2014;():V003T03A057. doi:10.1115/PVP2014-28378.

In the process systems of offshore installations, welded small-bore side branches can prove vulnerable to high-cycle fatigue failure due to vibrations. This is especially the case for welded connections at tie-in points to the main pipe which are often critical details. International standards and guidelines therefore provide maximum acceptable vibration levels to ensure long term safe operation. In some guidelines, however, these acceptable vibration levels are phrased in terms of screening levels and in practice can be unduly conservative. Process pipework might then unjustly be regarded as unsafe based on measured vibrations in the field. This is especially true for offshore systems, which are characterized by low mechanical damping in the structure. This may result in overdesigned piping or over-conservative operational limits in order to keep vibration levels within the acceptable range. Furthermore, the screening methods and any detailed fatigue assessments typically use established stress-life (S-N) based fatigue design methods where uncertainty exists in the very high-cycle regime.

This paper describes a novel and advanced tailor-made fatigue assessment method whereby acceptable vibration levels are based on maximum acceptable stress ranges for individual side branches. The acceptable stress ranges for each critical welded connection are based on a fracture mechanics analysis of fatigue crack growth. This method also minimizes the cantilevered (overhung) mass of small-bore side branches, whilst remaining safe for long-term operation.

To illustrate the strength of the assessment methodology in practice, this paper describes the application of the procedure to a 2″ side branch connected to a main piping system. A fracture mechanics model and a detailed 3D finite element model are made. By comparing the stress ranges from the fracture mechanics model with the normalized stress ranges obtained from the dynamic FE analysis, maximum acceptable vibration levels for this particular side branch have been derived. The method is validated with experimental modal analysis and strain gauge measurements.

Commentary by Dr. Valentin Fuster
2014;():V003T03A058. doi:10.1115/PVP2014-28379.

Technical components are subjected to cyclic loading conditions that can be arbitrarily complex in the most general case. For analytical fatigue strength verifications in the finite life regime both the uniaxial material characteristics by means of Wöhler curves as well as a representative equivalent fatigue damage parameter (FDP) for multiaxial cyclic loadings have to be determined. For simple loading conditions, the fatigue assessment can be performed using well-known and verified strength hypotheses for quasi-static loading conditions. However, for complex non-proportional cyclic loading conditions with rotating principle stress directions the application of these hypotheses is not sufficiently verified. Hence, advanced stress, strain or energy based strength hypotheses in critical plane formulation are used. These hypotheses require considerable numerical efforts.

The fatigue concept (MPA AIM-Life) enables an assessment of complex fatigue loading conditions with different advanced strength hypotheses. An interface to the finite element code ABAQUS allows the fatigue assessment of complex component geometries. Based on fatigue tests of specimens made from ferritic and austenitic materials under uniaxial and multiaxial loading conditions (tension/torsion) the accuracy of different strength hypotheses is demonstrated. Therefore the fatigue analysis assessment included in codes and standards is compared to different advanced fatigue damage parameters.

Commentary by Dr. Valentin Fuster
2014;():V003T03A059. doi:10.1115/PVP2014-28409.

In the 2009 version of the ASME BPV Code, a set of new design fatigue curves were proposed to cover the various steels of the code. These changes occurred in the wake of publications [1] showing that the mean air curve used to build the former ASME fatigue curve did not always represent accurately laboratory results.

The starting point for the methodology to build the design curve is the mean air curve obtained through laboratory testing: coefficients are then applied to the mean air curve in order to bridge the gap between experimental testing and reactor conditions.

These coefficients on the number of cycles and on the strain amplitude are equal to 12 and 2 respectively in the 2009 ASME BPV code, using the mean air curve proposal from NUREG/CR-6909 [1]. Internationally, with the same mean air curve, other proposals have emerged and especially in France [2]-[3] where a consensus seems to be reached on the reduction of the coefficient on strain amplitude.

This paper provides statistical analyses of the experimental data obtained in France at high-cycle for austenitic stainless steels. It enables to bring arguments for the selection of a coefficient on strain amplitude in the French RCC-M code, where less scatter on the data is witnessed due to fewer material grades.

Commentary by Dr. Valentin Fuster
2014;():V003T03A060. doi:10.1115/PVP2014-28411.

The present contribution is focused on the experimental investigations and numerical simulations of the deformation behaviour and crack development in the austenitic stainless steel X6CrNiNb18-10 (AISI–347) under thermal and mechanical cyclic loading in HCF and LCF regimes. The main objective of this research is the understanding of the basic mechanisms of fatigue damage and development of simulation methods, which can be applied further in safety evaluations of nuclear power plant components. In this context the modelling of crack initiation and crack growth inside the material structure induced by varying thermal or mechanical loads are of particular interest. The mechanisms of crack initiation depend among other things on the art of loading, microstructure, material properties and temperature. The Nb-stabilized austenitic stainless steel in the solution-annealed condition was chosen for the investigations. Experiments with two kinds of cyclic loading — pure thermal and pure mechanical — were carried out and simulated.

The fatigue behaviour of the steel X6CrNiNb18-10 under thermal loading was studied within the framework of the joint research project [1]. Interrupted thermal cyclic tests in the temperature range of 150 °C to 300 °C combined with non-destructive residual stress measurements (XRD) and various microscopic investigations, e.g. in SEM, were used to study the effects of thermal cyclic loading on the material. This thermal cyclic loading leads to thermal induced stresses and strains. As a result intrusions and extrusions appear inside the grains (at the surface), at which micro-cracks arise and evolve to a dominant crack. Finally, these micro-cracks cause continuous and significant decrease of residual stresses.

The fatigue behaviour of the steel X6CrNiNb18-10 under mechanical loading at room temperature was studied in the framework of the research project [2]. With a combination of interrupted LCF tests and EBSD measurements the deformation induced transformation of a fcc austenite into a bcc α′-martensite was observed in different stages of the specimen lifetime. The plastic zones develop at the crack tips, in which stress and strain amplitudes are much higher than the nominal loading, and enable martensitic transformation in the surrounding of the crack tip. The consequence of this is that cracks grow in the “martensitic tunnels”. The short and long crack growth behaviours of the steel X6CrNiNb18-10 under mechanical loading at room temperature and T = 288 °C were studied for different loading parameters. Moreover, the R-ratio was modified in order to study the effect of crack closure at the crack tip for long cracks.

Several FE-models of specimens with different geometries and microstructures were created and cyclically loaded according to the experimental boundary conditions. A plastic constitutive law based on a Chaboche type model was implemented as a user subroutine in the FE software ABAQUS. The corresponding material parameters were identified using uniaxial LCF tests of X6CrNiNb18-10 with different strain amplitudes and at different temperatures. These calculations aimed in the estimation of stress and strain distributions in the critical areas in which the crack initiation was expected.

Commentary by Dr. Valentin Fuster
2014;():V003T03A061. doi:10.1115/PVP2014-28421.

Fatigue lifetime assessment is essential in the design of structures. Under-estimated predictions may result in unnecessary in service inspections. Conversely, over-estimated predictions may have serious consequences on the integrity of structures.

In some nuclear power plant components, the fatigue loading may be equi-biaxial because of thermal fatigue. So the potential impact of multiaxial loading on the fatigue life of components is a major concern. Meanwhile, few experimental data are available on austenitic stainless steels. It is essential to improve the fatigue assessment methodologies to take into account the potential equi-biaxial fatigue damage. Hence this requires obtaining experimental data on the considered material with a strain tensor in equi-biaxial tension.

The aim of this paper is to present the experimental results obtained with a device “FABIME2” developed in the LISN in collaboration with EDF and AREVA. The specimen geometry is optimized by FEM (Cast3M) simulation in order to obtain a stress concentration localized in the central region during the test. This device allows accurate quantification of the effects of both equi-biaxial strain state as well as structure (such as mean stress) on the fatigue life.

Commentary by Dr. Valentin Fuster
2014;():V003T03A062. doi:10.1115/PVP2014-28633.

ASME III NB-3200 provides a method for carrying out fatigue calculations using a simplified elastic-plastic analysis procedure. This allows a correction to elastic analysis to be performed in place of a full elastic-plastic analysis. Two mutually exclusive factors are described: the Poisson’s ratio correction accounts for surface stress exceeding the yield strength of the material and the Ke factor accounts for gross section plasticity. The recently released ASME Code Case N-779 provides a more complex but less onerous calculation of the Ke factor. Correction factors from the JSME and RCC-M codes have also been considered in this paper.

The conservatism of different plasticity correction factors has been examined by calculating a ratio between the equivalent strain range from elastic-plastic Finite Element (FE) models and the strain range from elastic FE models and comparing this to calculated plasticity correction factors. Results show the potential for both the current ASME and Code Case Ke corrections to under-predict the strains when compared to those from an elastic-plastic FE assessment.

A preliminary investigation has been carried out into an alternative correction factor based on linearised stress and local thermal stress ranges. This addresses the discontinuity between the two correction methods for surface and sectional plasticity which has been identified as a feature of the ASME correction methodology.

Commentary by Dr. Valentin Fuster
2014;():V003T03A063. doi:10.1115/PVP2014-28764.

Fatigue is a common failure mode in mechanical components that are subject to repeated load cycles. In nuclear plants the cyclic loading is usually associated with variations of pressure and temperature. The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code provide fatigue evaluation procedures in ASME III Section NB-3220. It is required to calculate a Cumulative Usage Factor (CUF). The Code criterion for acceptance is that the calculated CUF must be less than one. The ASME method is deterministic and it is assumed that uncertainties are accounted for by largely un-quantified inherent safety margins in the assessment.

The conservatism in the ASME III Code fatigue evaluation methods may come from the assessment procedure used and/or the fatigue design curve. In this paper the inputs to an ASME III fatigue assessment that is based upon a finite element determination of stresses are outlined and assessed. Based upon these inputs possible areas of conservatism within the analysis are then discussed and conclusion drawn on the inherent margins.

In addition a probabilistic model that uses Monte Carlo (MC) methods is developed. By assuming the scatter in the fatigue data, used to generate the design fatigue curve, to be the most significant random variable, the MC model was used to calculate the conditional probability of initiation associated with CUFs from a number of plant representative examples.

Topics: Fatigue
Commentary by Dr. Valentin Fuster
2014;():V003T03A064. doi:10.1115/PVP2014-28787.

Austenitic stainless steel of type X6CrNiNb18-10 (1.4550) is a widely used material in piping and components of nuclear power plants. The fatigue behavior of these components is often operationally determined by thermomechanical strains and corresponding stresses. Welded structures lead to complex stresses in the component and potential fatigue lifetime reductions. Various geometrical and microstructural inhomogeneities in welded structures represent the main factors of influence. Nevertheless, clear identification and quantification of various factors of influence are issues still to be resolved.

Within the framework of an ongoing research project, the experimental investigation comprises uniaxial and biaxial fatigue experiments on welded joints which cover temperatures from 25°C to 350°C. Furthermore, a key issue deals with the thermomechanical fatigue behavior of machined and unmachined butt weld seams. A special focus is set on typical low cycle fatigue (LCF) tests in order to explain the behavior of the base material and the weld material to identify the influence of microstructural inhomogeneities. In addition, specimens manufactured directly from the pipe components are tested to examine the influence of the butt weld seam geometry. For a better understanding of the local strain effects, optical strain field measurements (OSFM) are conducted and used to validate numerical simulation. The finite element method (FEM) is utilized to expand the parameter space and identify the main parameters.

Experimental and numerical results show that fatigue failure occurs either in the base metal in the vicinity of the welded zone or in the top layer of the weld, depending on the loading conditions. This knowledge is used to develop an approach to fatigue lifetime estimation.

Commentary by Dr. Valentin Fuster
2014;():V003T03A065. doi:10.1115/PVP2014-28834.

An analytical method to predict the fatigue crack growth of embedded flaw in metallic structure has been established by using a non-isotropic approach. Within Engineering Criticality Assessment, the embedded flaw is considered as planar elliptical defect located inside of structure wall thickness. In the analytical standard assessment procedure [1], since only the minor ligament (the shortest distance between material surface and embedded crack tip) is applied to calculate the stress intensity factor, the fatigue crack propagation prediction in height direction is symmetrical for each side. Therefore, the crack growth is overestimated when, as it usually is the case, the embedded flaw is not centered and/or submitted to non-uniform stress range in the wall thickness of the structure.

The proposed method allows to predict the fatigue crack propagation rate in asymmetrical way, by taking into account respectively the minor and major ligament, in order to remove the above conservatism and consequently to improve the ECA results for embedded defects.

Topics: Fatigue cracks
Commentary by Dr. Valentin Fuster
2014;():V003T03A066. doi:10.1115/PVP2014-28891.

Feedwater (FW) nozzles are often considered to be locations with the highest cumulative fatigue usage in boiling water reactors (BWRs). Despite the lack of fatigue failures of these components, application of fatigue life environmental correction factors to the usage factors, originally computed by the designers, typically result in environmentally assisted fatigue (CUFen) values greater than 1.0. The reason for this disconnect may be attributable to the differences in analytical methods, as well as the differences in severity between the idealized design transient definitions and the actual transient behavior. This paper investigates these differences by comparing the traditional design fatigue analyses with those computed using modern fatigue monitoring methods. The results support the position that the level of conservatism in those original analyses account for some, if not all, of the environmentally-assisted fatigue effects.

Commentary by Dr. Valentin Fuster

Design and Analysis: Fitness for Service Evaluations and Post Construction Issues

2014;():V003T03A067. doi:10.1115/PVP2014-28019.

Current design standards and codes do not provide specific guidance how to perform engineering criticality assessment with bi-metallic girth weld in lined or clad pipe. Recently, Bonora et al. (Proc. ASME 2013 32nd OMAE conf.) proposed the equivalent material method (EMM) which allows one to still use current design assessment routes. The method consists in considering instead of three materials in the weld joint, a single “equivalent” material with a flow curve defined as the interpolated lower bound of the three weld joint material flow curves. In this work, the applicability of the EMM was verified considering the effect associated to weld residual stresses. To this purpose, two flaw geometry configurations have been investigated. Particular relevance was given to the multi-pass weld process simulation. Numerical results indicate that the EMM always provides reasonable results in terms of applied J with respect to those obtained considering the effective multimaterials configuration in the weld joint.

Commentary by Dr. Valentin Fuster
2014;():V003T03A068. doi:10.1115/PVP2014-28071.

Pressure safety relief valve needs to be designed and operated to assure metal temperatures are not lower than the Minimum Allowable Temperature (MAT) to prevent brittle fractures. Design and fitness for service codes include general procedures to prevent brittle fractures. Design procedures in the codes are very conservative whereas fitness for service codes in some cases lack details. In the absence of a detailed brittle fracture assessment procedure for valves subject to significant low temperatures as a result of either Joule-Thompson effect or auto-refrigeration, an approach involving pressure based stress ratio method of ASME/API 579, Part 3 has been adopted and implemented. The initial and very conservative approach involved a worst case combination of the upstream pressure while calculating the stress ratio and a comparison of the newly established MAT with the downstream temperature. This conservative approach resulted in the disqualification of numerous PSVs studied in this work. Valve replacement and associated lost production time leads to high costs. A sophisticated and appropriately conservative brittle fracture assessment approach involving the use of computational fluid dynamics (CFD) followed by finite element method analysis (FEA) based stress analysis was adopted based on the concepts defined in ASME/API 579 and is presented in this paper.

Predictive CFD analysis establishes more realistic temperatures and pressures in relation to the actual operating conditions. The CFD predicted pressure and temperature field is used to determine the stresses in the valve body using FEA methods. The stress analysis is followed by an intermediate brittle fracture assessment based on the procedures described in API 579 Part 3 using the actual PSV body metal temperatures and stresses established using the stress analysis. A discussion on the allowable stresses and stress components to be used in this intermediate assessment is also presented. If the PSVs cannot be qualified with this intermediate brittle fracture assessment, fracture mechanics evaluations are carried out to establish the limiting flaw sizes for the valves. In addition, the flaw tolerances of the valves are also established using reference flaw approach described in API 579, Part 9.

Commentary by Dr. Valentin Fuster
2014;():V003T03A069. doi:10.1115/PVP2014-28138.

The stress field in and around bulges in cylindrical and oval pressure vessels is examined using linear elastic finite element models. The effects of bulge size and shape on axial and hoop stresses are examined under internal pressure loading. Stress components at the center of the bulge, in the entire bulge, and in the vessel outside the bulge are analyzed both on the inside and outside surfaces of the vessel wall. In addition, the effects of vessel ovality (out-of-roundness) and the location of a bulge relative to ovality on these stress components are studied. This study provides engineers with a detailed look at bulging-induced stresses and the limitations of stress-based fitness-for-service assessment of bulges in pressure vessels such as refinery coke drums.

Commentary by Dr. Valentin Fuster
2014;():V003T03A070. doi:10.1115/PVP2014-28139.

A set of four operating coke drums experienced variable degrees of bulging and bulging-induced cracks. Internal laser scans were obtained for these drums to accurately define their geometry. Then, the severity of bulging was analyzed using stress and strain analysis techniques. In this paper, results of the two methods are presented and compared to failure history.

Topics: Coke , Stress
Commentary by Dr. Valentin Fuster
2014;():V003T03A071. doi:10.1115/PVP2014-28211.

The application of emerging fitness-for-service standards in conjunction with advanced modeling and ultrasonic thickness (UT) inspection is demonstrated with the recent assessment and repair of a CO2 absorber vessel. UT inspection discovered four regions of localized metal loss on the internal surface of a CO2 absorber vessel shell. Of the four regions, two were directly adjacent to major structural discontinuities, including two nozzles, one of which contained a reinforcing plate or repad.

In order to define the critical locations of metal loss and estimate a corrosion rate, thickness data for the regions of metal loss was provided in the form of 1 inch by 1 inch equally-spaced, rectangular thickness grid from two separate inspection dates. Based on the estimated corrosion rate, and the specified operation interval, the rate of metal loss was determined to be significant enough to require repair. This conclusion was based on the fact that in certain locations, the metal loss was estimated to grow through-wall before the end of the specified operation interval.

Computational analysis using guidelines per API 579-1/ASME FFS-1 [1] was used to evaluate an appropriate repair procedure. This included evaluation of repair plate placement and sizing using advanced modeling techniques including elastic-plastic material behavior and contact interaction. The effect of future metal loss was included based the estimated corrosion rate. The result of this assessment was a repair design that provided sufficient protection against excessive plastic deformation and allowed for continued operation through the specified operating interval. Thus, repairing the vessel based on fitness-for-service (FFS) criteria allowed for continued use of the vessel and avoided costly replacement. The lessons learned provide insight into the improved design of vessel repairs.

Commentary by Dr. Valentin Fuster
2014;():V003T03A072. doi:10.1115/PVP2014-28256.

Establishing integrity for piping and pipelines requires an understanding of the specific threats, their relationship to the overall condition of the system, and the mitigating measures required to assure safe operation. In the past, industry has relied on years of research and experience to develop a set of tools to analyze these threats and apply conservative solutions to ensure integrity and fitness for service. An effective integrity management program as discussed in this paper, known as the Engineering Based Integrity Management Program (EB-IMP), provides operators with a resource for integrating inspection results, analysis, and testing to qualify the components within a pressurized system.

This paper presents a detailed discussion on how experience, advances in analytical techniques, experimental methods, and engineering rigor are combined to develop a tool to characterize and ensure system integrity. Several case studies are included to demonstrate how the EB-IMP method was used to evaluate the integrity of a piping system, as well as rail gondola cars used to transport coal. The intent with the approach presented in this paper is to foster further developments for advanced integrity management efforts.

Topics: Pipelines , Pipes
Commentary by Dr. Valentin Fuster
2014;():V003T03A073. doi:10.1115/PVP2014-28528.

Unreinforced branch connections are a typical component of steel pipelines, designed and manufactured according to the piping code standards of reference. These joints are constructed welding together two straight pipes at different angles respect to their axis and the Stress Intensification Factors (SIFs) of the welded area are readily available from the standards for stress analysis purposes. Nevertheless, branches manufactured using elbows are occasionally encountered during Fitness-For-Service evaluations of the older carbon-steel pipelines conveying fluids at low pressure and room temperature. In the present paper the SIFs for these peculiar joints were determined using FEA and compared with those obtained by FEA and by code for the classic 90° unreinforced branch connections manufactured with straight pipes. 42 tees were considered in the analysis with diameters ranging from 3″ to 10″ on the run side and from 2″ to 10″ on the branch side; thicknesses from piping Schedule 10, 40 and 80 were adopted in the investigation and long radius elbows were only considered. The SIFs for the elbow branch tees were found to be 1.1 to 1.35 times those of the standard joints for unitary diameter ratios and 0.8 to 1.1 in the other cases. The maximum SIF (out-of-plane branch) was found to be linearly related to the elbow flexibility. A simple formula was then proposed to conservatively calculate the SIFs of the elbow branch connections using the values provided by the codes for a standard stress analysis where the joint is modeled with straight pipes. Finally, the elbow tees were evaluated against fatigue via solid FEA obtaining a lower estimate of their safe life respect to the standard joints.

Commentary by Dr. Valentin Fuster
2014;():V003T03A074. doi:10.1115/PVP2014-28696.

The failure of burner muffles in shell gasifiers has been a common problem, which directly leads to unexpected shutdown in operation of the gasifier and huge economic losses for the factory. Therefore, the experiment of the failure analysis to the burner muffle was conducted in the current work. The microstructure of the burner muffle after failure was measured by means of optical microscope, SEM (scanning electro-microscope) and X-ray diffraction. The reason of failure was obtained based on the analysis of experimental data together with the structural study of the gasifier. It is indicated that the failure of burner muffle is accounted for slag overflow and “backfire”, which lead to local temperature increasing. Cooling water tubes of Burner muffle were partially melted due to oxidation and sulphidation at high temperature, resulting into water leaks.

Commentary by Dr. Valentin Fuster
2014;():V003T03A075. doi:10.1115/PVP2014-28755.

LOOP is a concept to evaluate corroded or damaged pipelines based on detailed data from UT-pigging. The procedure of LOOP delivers a 3D-model generated from the data of a commercial in-line inspection tools (ultrasonic, magnetic flux). This makes it possible to use the full functionalities of the relevant finite element software like evaluation of wall-thinning (LOOP 1) and fracture mechanics analysis to evaluate cracks in the wall (LOOP 2). In this paper is given the basic ideas of the LOOP concept, where the main focus is directed to the LOOP 1 assessment procedure.

Based on a real example of a corroded pipeline is demonstrated the assessment procedure, which is based on an elastic-plastic analysis of a real inner contour of the corroded surface transferred in the finite element geometry model. The unique element is that the surface data of the UT-pigging is used directly to generate the geometry model in the FE-software ANSYS. The assessment procedure is validated by a burst pressure test of a corroded pipeline. The result of the burst pressure test is compared with the calculated limit load from an elastic-plastic analysis based on measured material properties.

Additionally, the assessment procedure is compared with the results of a limit load analysis based on DIN EN 13445-3 and with the results of the standard assessment procedure. At the end the assessment procedure is compared with the procedure given in API 579-1 standard.

Commentary by Dr. Valentin Fuster
2014;():V003T03A076. doi:10.1115/PVP2014-28958.

Finite element analysis (FEA) is used, with increasing frequency, to supplement or justify the design of an ASME Section VIII, Division 1 or 2 pressure vessel. When this occurs, good engineering practice indicates that a competent engineer should review the finite element analysis report. In some jurisdictions, it is required that a Professional Engineer review and certify the report.

This paper discusses some of the practical aspects of both writing and reviewing a good quality FEA report — both in the context of the technical perspective and in the context of Code compliance. This paper will serve as a practical assistant to an engineer reviewing an FEA report, as well as a guide to an engineer preparing an FEA report. Aspects such as properly following Code requirements, following appropriate Design By Analysis methodologies, and applying good design practices will be discussed.

Commentary by Dr. Valentin Fuster

Design and Analysis: Fracture

2014;():V003T03A077. doi:10.1115/PVP2014-28017.

At present, design standards and prescriptions do not provide specific design routes to perform engineering criticality assessment (ECA) of bimetallic girth welds. Although the authors has shown the possibility to implement ECA in accordance with available prescriptions of such flawed weld joint following the equivalent material method (EMM), when dealing with ductile crack initiation and propagation — as a result of the large scale yielding occurring at the crack tip for high fracture toughness material operating in the brittle-ductile transition region — fracture mechanics concepts such as JIc or critical CTOD may breakdown. In this work, the possibility to accurately determine the condition for ductile crack growth initiation and propagation in bi-metallic girth weld flaws using continuum damage mechanics is shown. Here, the base metal as well as the clad and the weld metal have been characterized to determine damage model parameters. Successively, the geometry transferability of model parameters has been validated. Finally, the model has been used to predict crack initiation for two bi-material interface circumferential crack configurations.

Commentary by Dr. Valentin Fuster
2014;():V003T03A078. doi:10.1115/PVP2014-28033.

Autofrettage is the process to introduce favorable residual compressive hoop stresses on the bore of a pressurized cylinder to enhance its strength and durability. For certain type of pressurized vessels under certain severe operating conditions, erosions and cracks often occur causing significant reduction in pressure vessel fatigue life. Those erosions and cracks are in general 3D geometrical configurations. The Stress Intensity Factors (SIFs) of the cracks are often the key to estimate the fatigue life. However the SIFs are largely dependent on not only the crack geometrical configurations but also the geometrical configurations of the erosions introduced during its operation. The Bauschinger effect on the SIFs further complicates the analysis. In this study, a closer look is taken at how a finite axial erosion in combination with the Bauschinger modified autofrettage properties affect the 3D SIFs. The problem is solved via the finite element method (FEM). The SIFs are evaluated for a variety of relative crack depth, different crack configurations and erosion geometrical configurations including arc erosion, semi-circular and semi-elliptical erosions. We show that the effective SIFs can be increased significantly by any of these factors but the combined effect often worsens the situation.

Commentary by Dr. Valentin Fuster
2014;():V003T03A079. doi:10.1115/PVP2014-28047.

Flaws detected in nuclear power plant components during in-service inspections are typically evaluated based on stress intensity factor influence coefficient databases and solutions from industry standards and public literature (e.g. API-579, ASME Section XI Code, WRC-175 Bulletin, Raju-Newman, etc). For certain components in the Pressurized Water Reactor (PWR) nuclear power plants, such as Bottom Mounted Instrumentation (BMI) nozzles, the cylindrical component geometry may fall outside the applicability limits of stress intensity factor influence coefficient databases. This situation occurs where the thickness to inner radius ratios of the cylindrical geometry is greater than 1.0. Accurate stress intensity factor (SIF) solutions are essential to flaw evaluation since the SIFs are used in the determination of both the allowable flaw size and crack growth in order to determine acceptability of the detected flaw.

In this paper, stress intensity factor influence coefficients are generated based on a three-dimensional finite element analysis for axial flaws located on the inside surface and outside surface of a cylindrical component with thickness to inner radius ratios (t/Ri) of 1, 2, 4, & 6. Non-dimensional influence coefficients are determined at the deepest point of the crack front and the surface point of the flaw based on a 4th order polynomial fit for a through-wall stress profile. The influence coefficients are generated for semi-elliptical flaws with a/c ratios = 0.125 through 2; where a is depth of the elliptical flaw, and c is the half-length of the elliptical flaw. The influence coefficients developed are suitable for calculating stress intensity factors for cylindrical components with high thickness to inner radius ratios.

Topics: Stress
Commentary by Dr. Valentin Fuster
2014;():V003T03A080. doi:10.1115/PVP2014-28099.

The accurate prediction of ductile fracture behaviour plays an important role in structural integrity assessments of critical engineering structures under fully plastic regime, including nuclear reactors and piping systems. Many structural steels and aluminium alloys generally exhibit significant increases in fracture toughness, characterized by the J-integral, over the first few mm of stable crack extension (Δa), often accompanied by large increases in background plastic deformation. Conventional testing programs to measure crack growth resistance (J–Δa) curves employ three-point bend, SEN(B), or compact, CT. However, laboratory testing of fracture specimens to measure resistance curves (J–Δa) consistently reveals a marked effect of absolute specimen size, geometry, relative crack size (a/W ratio) and loading mode (tension vs. bending) on R-curves. These effects observed in R-curves have enormous practical implications in defect assessments and repair decisions of in-service structures under low constraint conditions. Structural components falling into this category include pressurized piping systems with surface flaws that form during fabrication or during in-service operation.

This paper presents the on-going work to study geometry effects (e.g. triaxiality effects) in the brittle to ductile transition of carbon-manganese steels, the basic idea being to compare the results obtained on these specimens with the results obtained on CT specimens.

A preliminary program was previously conducted at room temperature using deeply notched specimens (Le Delliou, 2012). Finite element computations were made to optimize the specimen shape and to develop the η-factor, the shape factor F (to compute K) and the normalized compliance μ.

For the present program, new specimens have been machined with shallower notches (a/W = 0.4), to get a0/W = 0.5 after fatigue pre cracking. Fatigue pre cracking was conducted in 4-point bending to avoid damaging the back of the notch. Moreover, the specimens have been cut in the TS (Transverse-Short) direction of the plate to get lower toughness properties, and less plasticity during the tests.

Tests at room temperature have been conducted first to validate the revised test procedure. Then, the SENT specimens have been tested at −100°C, −60°C, and −40°C, together with CT specimens.

Topics: Brittleness , Geometry
Commentary by Dr. Valentin Fuster
2014;():V003T03A081. doi:10.1115/PVP2014-28155.

This paper presents improvements to the LBB.ENG2 method for predicting the moment-rotation response of a circumferential through-wall cracked (TWC) pipe under combined tension and bending loads. The LBB.ENG2 method provides closed-form equations for J-integral (J) estimation using a load-displacement relationship, where the Mode I stress intensity factor (K) solution, beam differential equations, and limit load solutions are utilized for elastic and plastic displacements under a thin-shell assumption. Due to its good predictions and simplicity, LBB.ENG2 has been incorporated into the recent probabilistic fracture mechanics codes, PRO-LOCA and xLPR.

The LBB.ENG2 method, however, has a limited applicability inherited from the thin-shell assumption and the K solution. That is, it might yield an unrealistic J for a thick pipe, or very short and long cracks. In this study, improvements are made to the method, and the thin-shell assumption is revisited. First, in order to extend the applicability limit of the K solution and, hence, the limit of the LBB.ENG2 method, newly developed and more accurate K solutions are implemented in a suitable form to derive equations explicitly for prediction of the crack instability point. Second, thin-shell and thick-shell assumptions are compared and technical justification for the use of the thin-shell theory is provided. In addition, based on the LBB.ENG2 method, moment-rotation response curves of circumferential through-wall cracked pipes are generated.

Commentary by Dr. Valentin Fuster
2014;():V003T03A082. doi:10.1115/PVP2014-28407.

The main purpose of the present paper is to investigate the effect of strain rate, specimen thickness and welding on the fracture toughness. The material of the investigated pipe is a high-density polyethylene, (HDPE) which is commonly used in natural gas piping systems. The welding technique used in this study is butt fusion (BF) welding technique. The crosshead speed ranged from 5 to 500 mm/min and specimen thickness ranged from 9 to 45mm for both welded and unwelded specimens at room temperature, Ta equal 20 °C. Curved three point bend (CTPB) specimens were used to determine KQ. Furthermore, the results of fracture toughness, KQ, will be compared with the plane strain fracture toughness, JIC, for welded and unwelded specimens. The experimental results revealed that KQ increases with increasing the crosshead speed, while KQ decreases as the specimen thickness increases. The investigation reveals that the apparent fracture toughness, KQ, for HDPE pipe of unwelded specimen is greater than that of corresponding value for welded specimen. The same trend was observed for the plane strain fracture toughness, JIc. At lower crosshead speeds there is a minimum deviation in KQ between welded and unwelded specimens, while the deviation becomes larger with increasing crosshead speed.

Commentary by Dr. Valentin Fuster
2014;():V003T03A083. doi:10.1115/PVP2014-28418.

Cleavage crack propagation has been tested for three different geometries of Compact Tensile (CT) specimens: CT25, CT50 and extended CT25 (CT25 with CT50 width) (Figure 3). The experimental results show that the crack paths are straight for CT25 and CT50, but they are unstable and curved for extended CT specimens (Figure 5 to 7).

Numerical computation had been performed by extended finite element method (XFEM) in CAST3M software. 2D modeling was used in order to predict the crack path. The analysis was based on a local non-linear dynamic approach with a RKR fracture stress criterion depending on temperature and strain rate.

In order to simulate the curvature of the cracks path, a statistical effect was introduced in the model to take into account the spatial distribution of cleavage initiators, which is the characteristic of cleavage fracture. At each step of propagation during the modeling, the direction was randomly chosen, according to a uniform defects distribution.

The numerical results show a good agreement with experience. The different crack paths were curved in extended CT25, but remained almost straight in CT25 and CT50 specimens, despite of the instability introduced in the modeling in the propagation direction. These results show that the statistics of micro-defects can induce, jointly with the geometry of specimen, a large scatter of crack propagation paths.

Commentary by Dr. Valentin Fuster
2014;():V003T03A084. doi:10.1115/PVP2014-28422.

The integrity assessment of Reactor Pressure Vessels is mainly based on crack initiation. Nevertheless, in the frame of component life extension, crack arrest conception is investigated.

This paper presents a local non-linear dynamic model to predict the propagation and arrest of cleavage crack in French PWR vessel steel (16MND5). The propagation criterion used in this model is a Ritchie Knott and Rice (RKR) fracture stress criterion: the crack propagates when the maximum stress ahead of crack tip reaches a critical level, which has been shown to depend on temperature and plastic strain rate.

In the first step, the criterion has been identified from crack growth and arrest analysis on CT specimens at different temperatures. Then it was applied to predict the propagation and arrest of cleavage cracks on pre-cracked rings under mixed mode loading, at three different temperatures: −150°C, −125°C and −100°C.

2D modeling was performed by using extended element method (XFEM) in CAST3M software. The propagation direction on pre-crack rings under mixed mode loading was determined from maximum hoop stress criterion. Numerical computation showed a good agreement with experiments, for both curved crack paths and crack arrest locations. Furthermore it showed that crack paths and crack arrest also depend on the level of the crack loading at initiation.

Commentary by Dr. Valentin Fuster
2014;():V003T03A085. doi:10.1115/PVP2014-28557.

This paper presents a methodology for brittle fracture probability assessment of WWER-1000 RPVs subjected to PTS. The main attention of the study is focused on the definition of the stochastic input data: fracture toughness, CTB, size and shape of the defects.

Fracture toughness of RPV metal in the initial state is determined, separately for the base metal and the welds, as the mean curve lines of relevant experimental data. Metal embrittlement is taken into account by increasing CTB.

Based on the results of the Ukrainian surveillance specimens program, a CTB database of WWER-1000 RPVs is created. As a result of processing these data, the CTB temperature dependence on the neutron fluence and chemical composition are obtained. The probability of the fracture toughness curve position on the temperature axis is defined by the CTB standard deviation in accordance with normal distribution law.

The distribution laws of depth and shapes of defects are taken according to the NRC data and verified on the base of the statistics of the defects, which were found in the WWER-1000 RPVs of the Zaporozhye NPP.

In fact, probabilistic calculation of the RPV brittle fracture is performed similarly to the deterministic one. Fields of temperature and stresses in different RPV zones in each timepoint of considered emergency scenario are calculated by the high-effective variant of transfer matrix method in axisymmetric elastic formulation. Semielliptical axial cracks of different sizes and proportions are conservatively considered on the inner surface of RPV. SIF along the crack front is defined using the original variant of Weight Function Method. The probability of failure of a particular defect is determined as the probability that CTB of the appropriate metal reaches the maximum allowable CTB value for the scenario.

The presented method is used for the renewal of operating licenses process of Unit 2 RPV of the South Ukrainian, and Units 1 and 2 RPVs of the Zaporozhye NPPs.

Commentary by Dr. Valentin Fuster
2014;():V003T03A086. doi:10.1115/PVP2014-28749.

This paper presents the results of a structural integrity assessment of a large-scale test undertaken as part of the EU programme STYLE on a repair welded pipe containing a circumferential through-thickness crack. The pipe was manufactured from two Esshete 1250 stainless steel pipes joined by a girth weld containing a deep repair. A through-thickness circumferential pre-crack was introduced to the centre of the repair prior to testing in four-point bend. The assessment used a finite element model created in Abaqus, with the weld residual stress introduced by an iterative technique. Linear elastic fracture mechanics was used to evaluate the stress intensity factor KI for the defect and elastic-plastic analyses were performed to characterise the crack driving force J along the crack front. The predicted crack mouth opening displacement as a function of load was compared with the test results and the derived variation in J used to predict crack initiation and growth. The results predicted the global behaviour of the test to within approximately 7% at final load, and the position of maximum crack growth. However, the final extent of crack extension is under-predicted. Reasons for this underprediction are suggested.

Commentary by Dr. Valentin Fuster
2014;():V003T03A087. doi:10.1115/PVP2014-28760.

In fracture mechanics, several J-estimation schemes are based on the reference stress approach. This approach has been developed initially in the frame of the R5 rule for creep and R6 rule for elasto-plastic fracture assessments. Later other methods, based on the reference stress concept, where derived like the Js method introduced in the French RSE-M code en 1997 and the Enhanced Reference Stress (ERS) method in Korea around 2001. However these developments are based on the J2 deformation plasticity theory and well established for a pure power hardening law. Even in this latter case, the reference stress depends on the hardening exponent. Js and ERS attempt to minimize this dependence and propose some corrections for recorded behavior laws which cannot be fitted by a power law. However their validation has been established mainly on cases where the material behavior is governed by a Ramberg-Osgood (R0) law. The question may be raised, as for the bilinear hardening law case, of the existence of a reference stress for non RO laws.

Commentary by Dr. Valentin Fuster
2014;():V003T03A088. doi:10.1115/PVP2014-28790.

Welded pipes are widely employed in many oil and gas applications. Engineering Critical Assessment (ECA) shall be performed in order to establish acceptance levels for revealed or postulated flaws in new or existing constructions. Although methods for assessing the acceptability of flaws in all types of structures are presented in codes and standards, such as BS7910 [1], API579-1 [2], R6 [3], DNV OS-F101 [4], the approaches are typically derived by simplified geometries as plate solutions, simplified material assumption, and simplified load condition as uniaxial load condition. Dedicate numerical solution are more accurate and would improve the assessed results. But the use of appropriate conditions in the full ECA requires several specific Finite Element Analysis (FEA) which are able to identify the Crack Driving Force (CDF) for each postulated defect geometry, material assumption and load conditions. The purpose of this paper is to propose a simplified method, into a standard procedure (similar to BS7910 [1]), minimizing numerical analyses, to guaranty the safety against fracture of many kind of weld joint under non-conventional condition (such as generic weld joint geometry and/or weld joint subjected to combined axial force, bending moment and internal over pressure which are not contemplate in current code and for which dedicated FEA are recommended).

Commentary by Dr. Valentin Fuster
2014;():V003T03A089. doi:10.1115/PVP2014-28800.

Engineering Critical Assessments (ECAs) are routinely used to provide defect acceptance criteria for pipelines girth welds. The Failure Assessment Diagram (FAD) concept is the most widely used methodology for elastic-plastic fracture mechanics analysis of structural components and adopted by standards/documents including BS7910 [1], API579-1/ASME FFS-1 [2], R6 [3]. It is defined by two criterion Kr and Lr which describe the interaction between brittle fracture and fully ductile rupture: Kr measures the proximity to brittle fracture whereas Lr reflects the closeness to plastic collapse.

The BS7910 FAD level 2B is the most employed for assessment of flaws under mechanical strain lower than 0.4%, the FAD associated is material-specific and it based on single toughness value obtained from CTOD test, the latter-on gives no information about the tearing initiation.

The objective of this paper is to propose an approach for determination of the critical fracture toughness (associated to zero-tearing: JΔa=0). This approach is based on the comparison between the load-CMOD curve provided from a fracture toughness test to the one obtained by Finite Element Analysis (FEA). The goals is to propose a conservative guidance on how to identify a remote strain level below which it may be considered guaranteed the integrity of the remaining ligament.

Commentary by Dr. Valentin Fuster
2014;():V003T03A090. doi:10.1115/PVP2014-28827.

This paper presents a method in order to plot a simplified toughness resistance curve (R-Curve) from three single conventional toughness tests.

The simplified toughness resistance curve will be used to carry out a tearing assessment as part of Engineering Criticality Assessment (ECA) (ref. to Level 3B, [2]). This level of assessment takes into account of stable tearing in order to reduce over-conservatism, but it usually requires additional toughness tests to identify the toughness resistance curve. This present method allows to reach this assessment level without impacting the welding procedure qualification (WPQ).

Commentary by Dr. Valentin Fuster

Design and Analysis: Inelastic, Nonlinear and Limit Load Analysis

2014;():V003T03A091. doi:10.1115/PVP2014-28214.

Ninety degree back–to–back pipe bends are extensively utilized within piping networks of modern nuclear submarines and modern turbofan aero–engines where space limitation is considered a supreme concern. According the author’s knowledge, no shakedown analysis exists for such structure based on experimental data. In the current research, the pipe bend setup analyzed is subjected to a spectrum of steady internal pressures and cyclic out–of–plane bending moments. A previously developed direct non–cyclic simplified technique, for determining elastic shakedown limit loads, is utilized to generate the elastic shakedown boundary of the analyzed structure. Comparison with the elastic shakedown boundary of the same structure, but subjected to cyclic in–plane bending moments revealed a higher shakedown boundary for the out–of–plane bending loading configuration with a maximum bending moment ratio of 1.4 within the low steady internal pressure spectrum. The ratio decreases towards the medium to high internal pressure spectrum. The simplified technique outcomes showed excellent correlation with the results of full elastic–plastic cyclic loading finite element simulations.

Topics: Pipe bends
Commentary by Dr. Valentin Fuster
2014;():V003T03A092. doi:10.1115/PVP2014-28253.

Components of conventional power plants are subject to three potential damage mechanisms and their combination (accumulation) with impact on lifetime considerations: creep, fatigue and ratcheting. Currently, there is a growing need for advanced material models which are able to simulate these damage phenomena and can be implemented effectively within finite-element (FE) codes. This constitutes the basis of an advanced component design. In this work, a constitutive material model, named as the modified Becker-Hackenberg model, is proposed to simulate the thermo-mechanical behavior of high-Cr steel components subject to complex loading conditions. Both creep and viscoplasticity are taken into account in the model, which are viewed as two different kinds of inelastic mechanisms. The key features of the creep strain, i.e., the minimum creep rate and the average creep rupture time, are evaluated by using two Larson-Miller parameters. The cyclic viscoplastic strain is predicted through the conventional Chaboche-type modeling approach, where suitable constitutive evolution equations are adopted to capture the cyclic softening effect, ratcheting effect, time recovery effect and temperature rate effect. All the material parameters involved in this model are identified by using a strategy of stress-range separation. This constitutive model is further implemented in a commercial FE software to simulate the thermo-mechanical behaviors of high-Cr steel components with technologically relevant dimensions. The strain and stress evolution data obtained from the model can be further used for the fatigue damage assessment of high-Cr steel components subject to creep-fatigue interactions. Within an ongoing work, a multiaxial fatigue analyzer is developed to predict the fatigue lifetime of high-Cr steels subject to cyclic loading conditions respectively — in a further step — creep-fatigue interaction.

Commentary by Dr. Valentin Fuster
2014;():V003T03A093. doi:10.1115/PVP2014-28278.

A thermo-solid coupling model of a gun tube is established. The inner boundary conditions of the tube are obtained by carrying out the computations of the boundary-layer model and the core-flow model of interior ballistics. The finite element method is employed here to numerically solve the thermo-solid coupling model. The transient stress and temperature of the coupling field of gun tube subjected to high-frequency periodic dynamic pressure and thermal pulse are computed. The overall state of the stress field and the thermoelastic coupling effect are attained. The strength of gun tube subjected to dynamic pressure load, thermal load and joint load is analyzed respectively, and the cases under the above three kinds of working conditions are compared. The life of gun tube is also studied. A life test system is set up, and detailed measurements about temperature and erosion are performed. A model to estimate the maximum radial wear rate of gun tube is built. Based on the computational results of temperature, the ablation wear extent and the limit life of a gun tube subjected to successive shooting are computed. The models and the analytical techniques adopted here provide important references for gun-tube design and life improvement.

Commentary by Dr. Valentin Fuster
2014;():V003T03A094. doi:10.1115/PVP2014-28536.

Bends are an integral part of a piping system. Because of the ability to ovalize and warp they offer more flexibility when compared to straight pipes. Piping Code ASME B31.3 [1] provides flexibility factors and stress intensification factors for the pipe bends. Like any other piping component, one of the failure mechanisms of a pipe bend is gross plastic deformation. In this paper, plastic collapse load of pipe bends have been analyzed for various D/t ratios (Where D is pipe outside diameter and t is pipe wall thickness) for internal pressure and in-plane bending moment, internal pressure and out-of-plane bending moment and internal pressure and a combination of in and out-of-plane bending moments under varying ratios. Any real life component will have imperfections and the sensitivity of the models have been investigated by incorporating imperfections as scaled eigenvectors of linear bifurcation buckling analyses. The sensitivity of the models to varying parameters of Riks analysis (an arc length based method) and use of dynamic stabilization using viscous damping forces have also been investigated. Importance of defining plastic collapse load has also been discussed. FE code ABAQUS version 6.9EF-1 has been used for the analyses.

Commentary by Dr. Valentin Fuster
2014;():V003T03A095. doi:10.1115/PVP2014-28666.

Based on the previous limit load analytical modeling for cracked thin-walled pipe [1] the limit load model for thick-walled pipe had developed. There are some additional peculiarities included in proposed model. First, the radial stresses distribution and their accounting for the Tresca’s criterion. Second, the crack location and related to it the interaction of hoop stress (due to the inner pressure) and axial one (caused by local bending moment) in the limit state. Third, hoop stress redistribution with possibility of plastic hinge forming in the zone, which is opposite to the crack zone. Forth, an analysis of derived easy to use analytical formulas by comparing with results of full-scale burst test.

Topics: Stress , Pipes
Commentary by Dr. Valentin Fuster
2014;():V003T03A096. doi:10.1115/PVP2014-28670.

Numerical procedures for calculation of reference stresses for pipelines with circumferential defects, based on simulation of global and local ultimate plastic states are proposed. There are some peculiarities of proposed procedures.

First, the schematic analysis of the deformation process of pipe with surface defects is suggested, based on which two critical cases have been specified: global (the Net-Section-Collapse (NSC) criterion) and local, which are applicable for a very wide surface defect and for a sharp crack, respectively. The global solution also describes behaviour of through wall defects.

Second, within the framework of the available Net-Section-Collapse criterion the unified algorithm for determination of reference stresses (global solution) for irregular-shaped circumferential defects under multifactor loading (internal pressure, axial force, bending moment) is proposed.

Third, according to the local modelling, the restricted capability to resist plastic deformations is takes into account by inserting of artificial symmetrical defect. The unified procedure for calculation of reference stresses (local solution) for pipe with irregular-shaped circumferential defects under multifactor loading is developed.

Forth, an analysis of proposed procedure by comparing with results of full-scale burst tests.

Topics: Stress , Pipes
Commentary by Dr. Valentin Fuster
2014;():V003T03A097. doi:10.1115/PVP2014-28714.

In nuclear power engineering failure has to be excluded for components with high safety relevance. Currently, safety assessments mainly use fracture mechanics concepts. Especially in the transition region of fracture toughness where limited stable crack extension may appear before cleavage fracture the currently applied methods are limited.

This Paper deals with the development and verification of a closed concept for safety assessment of components over the whole range from the lower shelf to the upper shelf of fracture toughness. The results of classical used local damage mechanics models depend on the element size of the numerical model. This disadvantage can be avoided using an element size depending on microstructure. With high stress gradients and small crack growth rates usually smaller elements are required. This is in conflict with an element size depending on microstructure. By including the damage gradient as an additional degree of freedom in the damage mechanics model the results depend no longer at the element size. In the paper damage mechanics computations with a nonlocal formulation of the Rousselier model are carried out for the evaluation of the upper transition area. For the prediction of fracture toughness from the ductile to brittle transition area the nonlocal Rousselier model is coupled with the Beremin model. Thus ductile crack growth and failure by brittle fracture can be described in parallel. The numerical prediction of the behaviour of fracture toughness specimens (C(T)-specimens and SE(B)-specimens with and without side grooves) and the experimental results are highly concordant. The load displacement behavior of the specimens and the developed crack front from the ductile to brittle transition area can be well calculated with the nonlocal damage model. The instability in relation to temperature calculated with the coupled damage mechanics model predicts the variations of the experimental results very well.

For further application of the nonlocal Rousselier model experiments and numerical calculations of specimens with different stress states and multi-axiality are carried out. Modified fracture toughness specimens like CTS-specimens (compact tension shear specimens) are taken to investigate the applicability of the nonlocal damage model of Rousselier to mixed mode fracture.

Commentary by Dr. Valentin Fuster
2014;():V003T03A098. doi:10.1115/PVP2014-28759.

For decades, the PWSCC on the penetration nozzles like BMI and CEDM nozzles are widely occurred all around the world. The PWSCC is dependent on the tensile stress condition, specific materials and chemical environment. Therefore, to evaluate the severity of the PWSCC, prediction of the welding residual stress on the J-groove welding part in the penetration nozzles is essential. Residual stress can be measured by using experimental methods like deep-hole drilling and X-ray diffraction, etc. However, the results of experimental methods are quite doubtable and these methods are hard to apply on the actual equipment. Therefore, computational approach like the FE analysis has been considered. The FE analysis results are very sensitive to the FE model density and analysis conditions. In this paper the optimized FE model for the residual stress analysis will be developed in the case of CEDM penetration nozzle. The optimized parameters contains bead number and mesh density. The bead numbers along the longitudinal and circumferential directions are considered and the mesh density in each the bead is also considered. The model will be verified by numerical error control.

Commentary by Dr. Valentin Fuster
2014;():V003T03A099. doi:10.1115/PVP2014-28963.

This paper introduces the application of Gurson model to simulate the ultimate ductile failure of three types of specimens with different constraints. Fracture tests were conducted using three kinds of notched round bar tensile specimens with different notch radii, a flat plate tensile specimen with a centered semielliptical surface flaw and a 1/2TCT specimen. Using the test results of the notched round bar tensile specimens, the Gurson model parameters were determined from the literatures, fracture observation and experimental design calculations. After fixing the Gurson parameters, they were applied to the flat plate tensile specimen and the 1/2TCT specimen model. As a. result Gurson model could simulate the fracture behavior of the flat plate with good accuracy, on the other hand there was a large difference with the test result of the CT specimen. In order to determine the Gurson model parameters universally and quickly, the blind optimization calculations were performed without arbitrariness. Three of five parameters were in the same order of the parameters by the 1st consideration and the others were in the different order. However the blind optimization parameters could show the similar simulation results of the fracture behaviors of the flat plate and 1TCT specimen as the 1st consideration parameters. The further investigation suggested the reason of the different behavior of the CT specimen model may be the different stress distribution, bending component dominant in the cracked ligament of the CT specimen from those of the other models. Additionally the accuracy of the local strain criteria according to ASME Sec. VIII Division 2 was confirmed.

Commentary by Dr. Valentin Fuster

Design and Analysis: Thermal Stresses and Elevated Temperature Design

2014;():V003T03A100. doi:10.1115/PVP2014-28199.

The requirements of the IAEA safety standards for Type B(U) packages include the thermal test as part of test sequences that represents accident conditions of transport. In comparison to mechanical tests, e.g., 9 m drop onto an unyielding target with short impact durations in a range of approximately 10 ms to 30 ms, the extended period of 30 min is defined in regulations for exposure of a package to a fire environment. Obviously, the required containment capability of the package has to be ensured not only after completing the test sequence but also over the course of the fire test scenario.

Especially, deformations in the sealing area induced by the non-uniform thermal dilation of the package can affect the capability of the containment system. Consequently, thermo-mechanical analyses are required for the assessment.

In this paper some aspects of finite element analysis (FEA) of transport packages with bolted closure systems under thermal loading are discussed. A generic FE model of a cask is applied to investigate the stress histories in the bolts, lid, and cask body as well as the deformations in the sealing area and the compression conditions of the gasket. Based on the parameter variations carried out, some recommendations in regard to modeling technique and results interpretation for such kind of analyses are finally given.

Commentary by Dr. Valentin Fuster
2014;():V003T03A101. doi:10.1115/PVP2014-28545.

In this study, an estimation method of graphite dust production in the pebble-bed type reflector region of Korean HCSB (Helium-Cooled Solid Breeder) TBM (Test Blanket Module) in the ITER (International Thermonuclear Experimental Reactor) project using FEM (Finite Element Method) was proposed and the amount of dust production was calculated. A unit-cell model of uniformly arranged pebbles was defined with appropriate thermal and mechanical loadings. A commercial FEM program, Abaqus V6.10 was used to model and solve the stress field under multiple contact constraints between pebbles in the unit-cell. Resulting normal contact forces and slip distances on contact points were applied into the Archard adhesive wear equation to calculate the amount of graphite dust. The friction effect on contact points was investigated. The calculation result showed that the amount of graphite dust production was estimated to 2.22∼3.67e−4 g/m3 which was almost linearly proportional to the friction coefficient. The analysis results will be used as the basis data for the consecutive study of dust explosion.

Topics: Dust , Graphite
Commentary by Dr. Valentin Fuster
2014;():V003T03A102. doi:10.1115/PVP2014-28607.

This paper shows the concepts for creep test machine. Designed creep machine can be used for tensile dead loading or compressive dead loading for the specimens of plate-type and round-bar types. Applied temperature is up to 1000°C. The developed creep test machine can be applied under the action of dead loading, so that long time measurement is possible. The firm measurement stock shelf is used as the framework of keeping right angle maintenance. The obtained creep test machine is also expected to have the rigidity of long term use. The necessary devises are for general purpose to reduce the cost.

Topics: Creep , Machinery
Commentary by Dr. Valentin Fuster
2014;():V003T03A103. doi:10.1115/PVP2014-28683.

This study aims to investigate buckling behaviors of a slender stainless steel column under compressive loads in severe accident conditions, which addresses the accidents in Fukushima Daiichi nuclear power plants. Firstly, buckling load, defined a load which generates a failure of the column (plastic collapse) was experimentally measured in a wide range of temperatures from 25 °C up to 1200 °C. The buckling load values measured were compared to numerical estimations for both an ideal column and for a column initially bent. Secondly, creep buckling tests were also performed for extremely high temperatures (800 °C, 900 °C, and 1000 °C). Creep buckling was found to occur very quickly compared to general creep times under tensile stresses. Time to creep buckling was exponentially increased with decrease of loads applied. Lateral deflection of a test column was estimated using captured images by a high speed camera. It was suggested to represent creep buckling behaviors as a time-lateral deflection curve. Moreover, an empirical correlation was developed to predict creep buckling time, based on the Larson-Miller model with experimental results obtained in present study.

Commentary by Dr. Valentin Fuster
2014;():V003T03A104. doi:10.1115/PVP2014-28698.

The functional features of the CDM-based damage constitutive model for stress relaxation which has been recently proposed were analyzed. Due to the highly nonlinear hyperbolic sine function adopted in the function and the large difference in the orders of magnitude among the material constants, an efficient genetic algorithm based optimization scheme was applied to obtain the global minima for the least square function. In addition, a procedure for the preliminary evaluation of material constants in the model was developed to better converging to the minima. The user-defined subroutine implementing the damage constitutive model was developed. It is validated that the predicted result provided by the developed ANSYS program agrees well with the experimental data of the stress relaxation for ferritic steels, providing preliminary results for the prediction of reheat cracking.

Commentary by Dr. Valentin Fuster
2014;():V003T03A105. doi:10.1115/PVP2014-28739.

In this work, 2D and 3D Finite Element models to simulate the temperature distribution and residual stress in butt-welded steel plates with the aid of computer simulation, using the commercial software Abaqus®, are developed. The work is carried out in two stages: 1) An analysis of heat transfer in transient state regardless of the structural part is performed, and 2) Thermal and structural responses are sequentially coupled in a thermo-mechanical process simulation in order to determine the final residual stresses induced during progressive heating and subsequent cooling. The results show that for 2D and 3D models the residual stress distribution for relatively thick plate welding can be characterized by a state of stresses plane, dominated by longitudinal stresses. The main difference between both models occurs for transverse stress σY where the values for 3D are significantly greater than for 2D.

Commentary by Dr. Valentin Fuster
2014;():V003T03A106. doi:10.1115/PVP2014-28997.

To determine reactor pressure vessel (RPV) residual lifetime as well as its brittle failure probability at pressurized thermal shock (PTS) conditions the original “indirect” solution method for the nonstationary temperature problem in axisymmetric formulation with the method of further stress calculation is developed. Both methods are based on transfer matrix approach and use exact analytical expressions for the thick-walled cylinders.

The automatic timestep determination method is implemented, which provides maximum calculation speed, but without the loss of the critical timepoints of scenarios under consideration. Also the accuracy of the model is improved by separate temperature calculations for “cold” plume and “hot” rest of the reactor, according to IEAE recommendations. At that axial strain of the “hot” part is used to load “cold” one.

The comparison of the methods with well-known theoretical results as well as with numerical tests demonstrates very high accuracy. It is proved by the methods of shell theory that possible difference with full 3D model of cylinder can’t be essential. Obtained fields of the temperature and stresses can be used for further estimation of the allowable value of the ductile-to-brittle transition temperature.

Commentary by Dr. Valentin Fuster
2014;():V003T03A107. doi:10.1115/PVP2014-29051.

A severe accident management concept, known as ‘in-vessel retention (IVR)’, is widely used in advanced pressurized water reactor, such as AP600, AP1000, and so on. The severe accident management strategy is to flood the reactor cavity, submerging the reactor pressure vessel (RPV). In such condition, the temperature on the inside of RPV may exceed the melting point (about 1327 °C) of RPV material, and results in the localized wall thinning. On the outside, the temperature is remained at about 127 °C, by assuming the flow regime is kept to be nucleate boiling. So it will form a high temperature gradient on the wall, and caused high thermal stress.

It will bring about the local discontinuity on the PRV wall because of the wall molten under the elevated temperature. A cylinder model is established to simulate the local discontinuity. The model is composed of the cylinder with the same external radius, but different wall thickness in the local discontinuity zone. Two elastic perfectly plastic models are used to analyze the stress and strain distributions on the wall and ultimate load capacity, based on the hot tensile curves and isochronous stress-strain curves at 100 hour with the change of temperature. The effect of local discontinuity is discussed, under the case of high temperature gradient and internal pressure. The results show that the Mises stress on the whole wall-thickness in the region of local discontinuity will achieve yield stress, under the high thermal stress. Appling internal pressure, the stress decreases in the zone of local discontinuity. The weakest link takes place in the thin segment of the cylinder model, and the ultimate pressure is obtained.

Commentary by Dr. Valentin Fuster
2014;():V003T03A108. doi:10.1115/PVP2014-29078.

The In-Vessel Retention (IVR) of molten core debris has been part of the severe accident management strategy for advanced pressurized water reactor (PWR) plant. Generally, the pressure is supposed to successfully be released, and the externally cooled lower head wall mainly experiences the temperature difference which may be more than 1000°C. However, the Fukushima accident shows that a certain pressure (up to 8.0MPa) still exists inside the reactor pressure vessel (RPV). Therefore, in order to make the IVR succeed, it is necessary to investigate the structural integrity of the RPV under the combined internal pressure and the thermal load on the lower head.

Therefore, it is supposed that the lower head of RPV is a Hemisphere Shell Structure (HSS) with 2150mm external radius and 25mm wall thickness. Similarly, the outer wall temperature is supposed to be 127°C, the wall temperature difference 1200°C, and the material properties (i.e., thermal conductivity, specific heat capacity, yield strength, and so on) are dependent on the temperature. In this paper, the main subjects discussed are as below.

First, the heat transfer analysis is carried out to obtain the temperature distribution of the HSS wall. Due to the high temperature gradient, there may present different failure modes along the HSS wall thickness, i.e., plastic failure and creep failure. Then, the stress and strain distributions along the wall thickness are analyzed by ANSYS finite element method where the Norton-Bailey type creep law is adopted. The result shows that the stress in the lower temperature part (LTP) whose temperature is lower than 405°C is lower than the yield stress of the material with the corresponding temperature. That is to say, the LTP still can bear a certain internal pressure. At last, to consider the combined impact of internal pressure and temperature difference on the HSS, the finite element analysis is carried out by adopting the isochronous stress-strain curves of the Chinese RPV material. The relationship between the stress in the LTP at 100 hours and the internal pressure is discussed, and the limit internal pressure is determined. It is concluded that HSS still can maintain its integrity under IVR, even if there exists a certain internal pressure.

Commentary by Dr. Valentin Fuster

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