ASME Conference Presenter Attendance Policy and Archival Proceedings

2014;():V002T00A001. doi:10.1115/PVP2014-NS2.

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to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

Computer Technology and Bolted Joints: Assembly of Bolted Joints

2014;():V002T02A001. doi:10.1115/PVP2014-28270.

The three critical components within a bolted, flanged connection are the flanges, gasket, and bolts. Until recently, simplified flange assembly target torque values for ASME B16.5 flanges were routinely determined by considering just one or two of these primary components.

One approach considers only the gasket. Gasket-based target torque values are selected to optimize the gasket’s sealing performance by ensuring compression between minimum and maximum seating stress ranges, or based upon achieving specific levels of gasket Tightness (Tp). Another approach, fastener-based torque values, simply targets a specific bolt preload during assembly, typically some percentage of bolt material yield stress. A third approach optimizes gasket seating stress or tightness within the specific preload stress range of particular grades of fasteners. None of these approaches consider the physical limitations and capabilities of the flange itself, which can result in flange damage due to excessive bolt preload or the lost opportunity to gain fatigue resistance and reliability when low fastener preloads are selected [1].

While detailed Finite Element Analysis (FEA) could meet this objective, cost and time constraints limit the number, size, and materials to be considered. The objective of this method to optimize target assembly torques for B16.5 flanges is to identify the likely maximum safe assembly bolt load not exceeding the compression, yield, or tensile limits of any of the three flange components. It is recognized that some localized yielding does occur. Existing industry efforts to study and optimize target torques are surveyed, reviewed, combined, and extrapolated to determine acceptable torque values that conform to selected component limits. The limits are chosen consistent with normal practice in the chemical, process, and power industries.

Commentary by Dr. Valentin Fuster
2014;():V002T02A002. doi:10.1115/PVP2014-28449.

The buckling of spiral wound gaskets (SWGs) causes turbulence of the fluid flow inside flanges and may result in leakage failure over time due to the unwinding of the spirals. A few limited studies on the lateral forces generated by axial compression of the gasket sealing element which cause this phenomenon are available in the literature. The lateral forces are generated during initial tightening and are not distributed uniformly in the circumferential direction. Hence there is an introduction of concentrated forces in small areas.

The non-uniform gasket contact stress caused by the tightening sequence makes the problem more complex. It is suggested to study experimentally the buckling of spiral wound gaskets by developing a special test bench designed for this purpose. This test bench is able to measure the lateral loads and winding inward displacement during the tightening process. The experimental results are to be compared to those obtained by numerical FE simulation for the purpose of extrapolating for other size gaskets.

Topics: Pressure , Gaskets , Buckling
Commentary by Dr. Valentin Fuster
2014;():V002T02A003. doi:10.1115/PVP2014-28730.

Pipe flange connections with gaskets in chemical plants, electric power plants and other industrial plants are usually exposed to elevated internal pressure with cyclic thermal condition. It is important to investigate the sealing performance of pipe connections under long term severe thermal exposure swings to ensure operational safety. In this study, the effects of cyclic thermal conditions on the sealing performance and mechanical characteristics in larger and smaller nominal diameter of pipe flange connection are examined using FEM calculations. Helium gas leakage is predicted using the contact gasket stress obtained from the FEM results. On other hand, the leakage tests using the smaller nominal diameter of pipe flange connection were conducted to measure the amount of helium gas leakage and to compare with the predicted amount of gas leakage. As the results, the contact gasket stress distributions were changed dramatically under cyclic thermal condition and elevated internal pressure. In the pipe flange connections with smaller nominal diameter, the contact gasket stress was the smallest in the restart condition. On other hand, the minimum contact gasket stress in the pipe flange connection with larger nominal diameter was depending on the materials of connection. In the pipe flange connection with larger nominal diameter, the contact gasket stress distributed and changed in the radial direction due to the flange rotation. A fairly good agreement was found between the experimental leakage result and predicted leakage results.

Commentary by Dr. Valentin Fuster
2014;():V002T02A004. doi:10.1115/PVP2014-28998.

This paper presents information about break out torque and several key elements to consider when specifying joint and disassembly procedures. These key elements include: (1) hardened washer material used, (2) penetrant selection for disassembly, and (3) penetrant application method. This paper also presents experimental K-factor data, including variation recorded from several hardened washer configurations and information from additional K-factor testing.

Topics: Torque , Manufacturing
Commentary by Dr. Valentin Fuster

Computer Technology and Bolted Joints: Computational Topics in Limit Analysis, Elastic-Plastic Analysis and Creep

2014;():V002T02A005. doi:10.1115/PVP2014-28623.

The overpressure fragility of a Mark I boiling water reactor drywell was performed by detailed finite element (FE) analysis. The drywell overpressure capacity is controlled by the onset of leakage in the bolted head flange connection once separation exceeds the capacity of the silicone rubber O-ring seals.

The FE analysis was conducted at 6 discrete accident temperatures, ranging from 150 to 425°C. The overpressure evaluation used an axisymmetric model of the drywell head region for computational efficiency, and verified it by comparing to results from one FE model which used 3D solid elements. The mechanical properties of the steel materials were defined as temperature-dependent linear-elastic.

The median overpressure capacity at each temperature was determined using a 2-step thermal-stress analysis procedure. First, a steady-state heat transfer analysis was conducted to map out the temperature distribution in the drywell wall, which is exposed to the accident temperature on the inside and ambient temperature on the outside. Second, a quasi-static multi-step stress analysis was performed. The vertical differential movement between the flange surfaces was monitored and compared to the O-ring rebound capacity to define the pressure at the onset of leakage. After leakage occurred, the relationship between leakage area and increased pressure was recorded.

The evaluation predicted the median overpressure capacity and the lognormal standard deviation for uncertainty in O-ring rebound capacities, bolt preload, and model sophistication, in addition to the median pressure-leak area relationship.

Commentary by Dr. Valentin Fuster
2014;():V002T02A006. doi:10.1115/PVP2014-28774.

Cold bending, warm bending (bending with local heating) and induction bending are three manufacturing processes widely used to produce pipe bends. The cold and warm bending processes have been used for the fabrication of carbon steel feeder bends for CANDU® reactors, and the induction bending process was considered for the fabrication of stainless steel feeder pipes for an advanced CANDU reactor. Bending processes result in plastic deformation, and inevitably, introduce residual stresses in the deformed pipes. Residual stresses in feeder bends are believed to be a very important contributing factor in feeder cracking. Different bending processes result in widely different residual stress patterns and magnitudes in pipe bends. Hence, it is important to understand the effect of bending processes and the process parameters used on the residual stress distribution in the bent pipes. Numerical models have been successfully developed to predict the residual stresses and the deformed shapes induced by cold, warm and induction bending processes. This paper provides a comprehensive review of the predicted residual stress distributions, ovality and wall-thickness variations of the cold, warm and induction bends. The predicted results were compared to earlier measurements of spare CANDU feeder bends and test bends. Advantages and disadvantages of the three bending processes are summarized. Numerical approaches for the modeling of residual stresses could be of benefit to engineering estimates of residual stresses in feeder pipes for safety evaluation of nuclear reactors.

Commentary by Dr. Valentin Fuster
2014;():V002T02A007. doi:10.1115/PVP2014-28896.

The non-cyclic method of shakedown analysis allows the entire ratchet boundary to be determined for a given set of monotonic and cyclic loads on a component. The method is based on an extension of the lower bound shakedown theorem. Typically, the loading of interest to shakedown consists of cyclic thermal loading acting in conjunction with cyclic and monotonic (mean) primary loads, such as pressure.

To date, a certain class of spatially moving cyclic thermal loads could not be analyzed with numerical implementations of the non-cyclic method. In these cases, the mean thermal load cannot be balanced by a self-equilibrating stress state, and the component can ratchet under a purely thermal load. This paper examines why the restriction on the non-cyclic method and similar other approaches to shakedown analysis exists, and proposes an extension with the help of which an analysis of this class of problems becomes feasible. The method is demonstrated on a number of simple examples.

Commentary by Dr. Valentin Fuster

Computer Technology and Bolted Joints: Design and Analysis of Bolted Flange Joints

2014;():V002T02A008. doi:10.1115/PVP2014-28094.

To assure a leak free scenario when a valve packing is utilized, tests have been developed in order to monitor a group of parameters when service conditions are simulated. These tests enable valve manufactures to have an improved design, and guide end users on efficient packing selection. This paper presents valve packing test devices that provide developers with tools to evaluate properties such as; installation stress, relaxation, stem torque, number of rings and thermal expansion effects. Details of each device are shown, along with typical results of each property evaluated.

Commentary by Dr. Valentin Fuster
2014;():V002T02A009. doi:10.1115/PVP2014-28167.

The european standard EN1591-1 [1], initially published in 2001, defines a calculation method for bolted gasketed circular flanges, alternative to the TAYLOR-FORGE method, used as the basic method in most codes. In 2007, a new part, XP CEN/TS 1591-3 [2], has been added to the EN1591 series. This technical specification enables to take into account the Metal to Metal Contact (MMC), appearing inside the bolt circle on some assemblies. Due to a lack of industrial feedback and detailed validation, this document has not been raised to the standard status.

In that context, under the request of its Pressure Vessel and Piping commission, CETIM has performed a study comparing this calculation method to Finite Element Analysis (FEA) on several industrial configurations. After a description of the XP CEN/TS 1591-3 calculation method, the major results obtained for spiral wound gasketed joints where MMC appears between centering ring and flange facing are presented and compared with FEA results. Moreover, results obtained with other classical analytical calculation methods as TAYLOR FORGE and EN1591-1 on the same Bolted Flange Connections (BFC) configuration are also analysed and compared to XP CEN/TS 1591-3 results.

Commentary by Dr. Valentin Fuster
2014;():V002T02A010. doi:10.1115/PVP2014-28731.

Bolted flange connections with metal gasket have been used at higher pressure under higher temperature condition. Assembly procedures and tightening methods the connections including some types of metal gasket is empirically. Generally, it is known that the bolt preload which is required for satisfying an indicated leak rate in the connections including the metal gasket is not higher than that of the connections including sheet gaskets and spiral wound gaskets. However, no research for the evaluating the sealing performance in the bolted flange connections with metal gaskets has been conducted. In this paper, the leakage tests for the bolted flange connections with the metal flat gasket were conducted in the case where the maximum internal pressure of 7MPa and a bending moment are applied, where the leak rate is measured using the pressure drop method. Then, the sealing performance of the connections with the metal flat gasket was evaluated. In addition, using the FEM stress calculations, the flange stress distributions between the flange surface and the gasket were examined as the evaluation. As the result, it is found that the stress distribution at the contact surfaces between the metal flat gasket and the flange surface under the bending moment and the internal pressure. In the leakage tests, it was observed that the amount of the leakage (He gas) depends on the stress distributions and the plastic deformation of the gasket.

Commentary by Dr. Valentin Fuster
2014;():V002T02A011. doi:10.1115/PVP2014-28771.

Comprehensive testing using various different gasket types and materials was performed in order to determine the best overall performance in gasket suitability and leakage reliability on an IBC (Intermediate Bulk Container), provided by a tank manufacturer. Prior to testing, the tank was filled with water just below the elevation of the manway, and the remaining space was charged with air. Testing was performed in two phases. Phase 1 was conducted as a simple pressure test with the container in a static state. For Phase 2, a test procedure was developed to include temperature and pressure variations, soak and dwell times, torque value calculations, leakage rates, sustainability, and a simulation of artificial vibration effects on bolted flange connections. Utilizing the Phase 2 procedure gives the ability to compare the various gasket materials under real world conditions, which will reveal the optimum gasket that provides the safest and most reliable connections for the transportation industry. Four corrosion resistant polytetrafluoroethylene (PTFE) based gasket materials were selected to be tested on the IBC. The gasket materials included virgin PTFE, glass-filled PTFE, tanged 316 stainless steel reinforced expanded PTFE (ePTFE), and corrugated 316 stainless steel reinforced expanded PTFE. All testing was performed indoors in a controlled environment. Testing on each gasket type was performed using the same equipment, while following the same test procedures.

Commentary by Dr. Valentin Fuster

Computer Technology and Bolted Joints: Explicit and Implicit Nonlinear Finite Element Analysis

2014;():V002T02A012. doi:10.1115/PVP2014-28169.

This paper describes the structure and application of a software system that automates the fatigue initiation and crack propagation analysis based on FEM. The system automatically performs necessary procedures to track propagation history of cracks: insertion of a crack and updating of three-dimensional finite element mesh in accordance with the crack propagation. Most of the meshing is carried out by a Delaunay tessellation method. A tubular hexahedral mesh is generated at the crack front and the fracture mechanics parameters are computed using commercial codes to ensure accuracy. The generation of this tubular hexahedral mesh is fully automatic as well.

The system is equipped with a function to automatically perform fatigue analyses using the stress-strain histories at nodes of a three-dimensional FEM model. The standard low cycle fatigue analysis approach is adopted. Using the function, cumulative fatigue for a given FEM model is provided. Some analyses for several examples were carried out for validation. The important example is the surface crack propagation in steel pipes with residual stress.

Commentary by Dr. Valentin Fuster
2014;():V002T02A013. doi:10.1115/PVP2014-28835.

Profile radial-axial ring rolling is a complex bulk forming used to produce seamless rings for critical structural components in many industries, such as machinery, aeronautics, energy and automotive. The process is characterized by high nonlinearity, unsteady three-dimensional deformation, dynamic contact boundary conditions caused by the rotations of ring and rolls. In this paper, a numerical model based on explicit finite element approach is proposed to simulate and analyze the process. An expanded ring with profile section has been obtained by numerical simulations with the dynamic model based on explicit finite element method.

Commentary by Dr. Valentin Fuster
2014;():V002T02A014. doi:10.1115/PVP2014-28893.

Developing the realistic blast loading associated with an internal detonation occurring within a pressure vessel or heat exchanger is challenging. Unlike evaluation of external blast loading on structures due to far-field explosions, where typical overpressure-time histories can be reasonably defined based on empirical data, investigating confined detonations presents additional complications. The subsequent impulsive peak reflected overpressure from confined detonations acting on a structure can be extremely high due to the close proximity of the blast source to the vessel wall or pressure boundary. This establishes the possibility of significant structural damage for process equipment subjected to an internal detonation, even for relatively modest amounts of concentrated explosive products.

This paper discusses the underlying theory of blast analysis and examines the practical application of non-linear, finite element based, explicit computational techniques for simulating the load acting on a structure due to internal and external blasts. The investigation of a recent, real-life industry failure of a heat exchanger due to a suspected internal detonation is discussed. Explicit, three-dimensional blast analysis is performed on the heat exchanger in question, and an internal detonation is simulated to reasonably replicate the considerable damage actually observed in the field. This analysis permits the determination of an approximate amount of concentrated product that caused the accidental explosion; that is, the plausible equivalent amount of explosives is back-calculated based on the predicted damage to the finite element model of the equipment in question. Computational iterations of varying charge amounts are performed and the predicted amount of permanent damage is documented so sensitivity to the hypothesized charge amount can be quantified. Furthermore, explicit blast analysis of nearby equipment is performed.

In this investigation, computational results for both the heat exchanger (subjected to internal blast loading) and surrounding equipment (subjected to external blast loading) are in good agreement with the measured plastic deformations and failure modes that were actually observed in the field. Commentary on the likely detonation event that caused the significant damage observed is provided. Additionally, an advanced finite element failure criterion that is driven by plastic yielding is employed where portions of the computational model are removed from the simulation once a user-defined strain threshold is reached. This approach facilitates simulation of the gross heat exchanger pressure boundary failure actually observed in this case. The explicit finite element based analyses discussed in this study reasonably predict the structural response and damage characteristics corresponding to a recent, real-life industry failure.

Commentary by Dr. Valentin Fuster
2014;():V002T02A015. doi:10.1115/PVP2014-28894.

A series of tests on small-bore Carbon steel piping specimens with bends has been performed within the Feeder Bend Testing Program. The objective of the tests was to explore the effect of global and local wall thinning on the structural behaviour of feeder pipes in CANDU® reactors. Tests involved both cyclic and monotonic bending loading together with static pressure in order to obtain information about both the ultimate load carrying capacity and the fatigue life.

The specimens were thinned locally to below the NB-3600 pressure based wall thickness within or near the bend. Results of cyclic tests are reported and discussed. For one of the tests, a fatigue crack initiation and a fatigue crack growth analysis were performed. The results have relevance as an evaluation of the conservatism of traditional piping design methods, as well as a benchmark for fitness-for-service approaches, such as flaw tolerance evaluation.

Topics: Pipes , Testing
Commentary by Dr. Valentin Fuster

Computer Technology and Bolted Joints: Leak Tightness and Fugitive Emissions

2014;():V002T02A016. doi:10.1115/PVP2014-28024.

The choice of gasket type for flanged connections has typically been determined on the basis of temperature, pressure, and chemical nature of the contained fluid; sealability; ease of handling and installation; expected service life; comparable cost; and other factors. Of ever increasing importance is the environmental performance of the selected gasket with an emphasis on fugitive emissions reduction. All gaskets have some level of fluid leakage but this may vary significantly depending on the type selected. A practical tool using Microsoft® Excel® has been developed that can help predict anticipated fugitive emissions of gaskets for which Room Temperature Testing (ROTT) data are available. The construction and application of this tool are described and a relative comparison of tightness parameters and projected fugitive emissions for example gasket types are documented.

Topics: Gaskets , Emissions
Commentary by Dr. Valentin Fuster
2014;():V002T02A017. doi:10.1115/PVP2014-28514.

The deflections of gaskets after initial tightening largely affect the residual bolt forces and the tightness of bolted flanged connections. The bolt forces decrease significantly due to the deflections of gaskets after initial tightening in the cases where expanded PTFE gaskets are used. The visco-elastic characteristic of the gaskets is the main cause for the phenomenon. It was shown in the paper PVP2012-78694 that the tightness improved even if the bolt forces reduced in the long term. This is because the gasket becomes packed under a high gasket stress. It is important to estimate the thickness change of gaskets to evaluate the tightness of bolted flanged connections.

In this paper, an analytical model of a bolted flanged connection, in which the flanges, the bolts and the gasket are represented by spring constants, is proposed. Experiments were carried out to measure the creep characteristic of the expanded PTFE gasket. The residual bolt forces and the deflection of the gasket were estimated based on the analytical model of the bolted flanged connection and the creep characteristic of the gasket. Thus, the relationship between gasket deflection and the tightness of the bolted flanged connection are clarified.

Commentary by Dr. Valentin Fuster
2014;():V002T02A018. doi:10.1115/PVP2014-28606.

In the present paper, the gasket stress distributions, hub stress and a variation in axial bolt force in bolted gasketed pipe flange connections under internal pressure are analyzed using elasto-plastic FEM taking into account the nonlinearity of gasket behavior. Non-asbestos spiral wound gaskets were employed. The effect of nominal flange diameter is examined on the gasket contact stress distributions, the hub stress and the variation in axial bolt force (the load factor) is examined. Using the obtained gasket contact stress distribution and the fundamental data of the relationship between gasket compressive stress and gasket leak rate according to JIS B 2490, a method for predicting the leak rate is demonstrated. Experiments to measure the amount of leakage, the hub stress and the variation in axial bolt force when the joint is under internal pressure were carried out. The numerical results of the leak rate, hub stress and the load factor are in a fairly good agreement with the measured results. Then, a method is demonstrated for determining the bolt preload under given conditions, that is, taking into account assembly efficiency, leak rate and internal pressure In addition, bolt preload is determined using the actual gasket contact stress which can be estimated using the value of the load factor. As a design example, the procedure for determining the bolt preload in 3″ and 20″ nominal diameter pipe flange connections is shown for the allowable leak rate of 1.0−3Pa • m3/s. The results are validated by the experiments.

Commentary by Dr. Valentin Fuster

Computer Technology and Bolted Joints: New and Emerging Methods of Analysis and Applications

2014;():V002T02A019. doi:10.1115/PVP2014-28117.

Floating roofs are widely used to prevent evaporation of content in large cylindrical aboveground oil storage tanks. The 2003 Hokkaido Earthquake caused severe damages to the floating roofs due to sloshing. These accidents became a cause to establish structural integrity of the floating roof tanks in sloshing. However, many designers do not have a solution for the sloshing of floating roof tanks except for three-dimensional FEA computer codes. The three-dimensional FEA requires a long computational time and expenses. The sloshing of floating roof tanks is a coupling vibration problem with fluid and structure. The simplified and convenient method has been desired for this solution. This paper presents a simplified development method of a FEA code in the axisymmetric linear problem. It is performed to modify an existing structural analysis code. The fluid behavior is formulated in terms of displacement as the Lagrangian approach.

Commentary by Dr. Valentin Fuster
2014;():V002T02A020. doi:10.1115/PVP2014-28340.

Palladium is capable of storing a large atomic percent of hydrogen at room temperature and allows for hydrogen to diffuse with a high mobility. These unique properties make it an efficient storage medium for hydrogen and hydrogen isotopes, such as tritium, a byproduct of nuclear reaction. Palladium thus can be used for applications where fast diffusion and large storage density are important. Better understanding of molecular level phenomena such as hydride phase transformation in the metal and the effect of defects in the materials provides clues to designing metal hydrides that perform better. Atomic simulations are useful in the evaluation of palladium-hydrogen systems as changes in composition can be more easily explored than with experiments. In this paper, we present the palladium hydride potentials to investigate and identify the relevant physical mechanisms necessary to describe the absorption of hydrogen within a metal lattice.

Commentary by Dr. Valentin Fuster
2014;():V002T02A021. doi:10.1115/PVP2014-28940.

The effect of the effective area of an advanced ePTFE gasket on the EN13555[ 1 ] stress retention (PQR) properties was investigated. It was found that larger areas gave higher PQR values but the systems actually lost more force and gave lower final thickness values. This effect of higher PQR with higher force lost is explained mathematically, and the reason behind the thinner final gaskets is also explained. Further analysis shows that the force loss is linked to the ratio of effective area and stiffness, and this effect can be used to better estimate the PQR values of larger area gaskets.

Commentary by Dr. Valentin Fuster
2014;():V002T02A022. doi:10.1115/PVP2014-29090.

When assembling tubing strings in the oilfields, threaded connections are used to connect the pipes with each other. The possibility to reuse these connections is often required and a certain degree of leak tightness is required, even without the use of a sealing surface or shoulder. For this reason, the total plasticity within the connection should be limited and relative movement between pin and box ought to be restricted.

Within this publication, a finite elements analysis is conducted using a 4.5 inch buttress threaded connection as defined in API 5B together with a connection using the enhanced SR23 buttress thread. In addition, an experimental validation of the make-up stage is conducted by comparing the strains generated during make-up using Digital Image Correlation and infrared monitoring.

In order to determine the optimal make-up, values found in literature are compared with a developed method using the magnitude and size of the plastically deformed zones during make-up. In addition, the effect of external axial and pressure loading is examined to identify the effects and critical areas.

As a result, it is observed that pressure loading and make-up tend to have similar effects and in order to determine the optimal make-up torque, the pressure ratings of the assembly should be taken into account to prevent overtorqueing the connection. For the case of axial loading, a critical zone is visible near the last engaged thread and excessive loading of this thread can cause premature failure within this zone. Overall, the SR23 connection shows limited, yet visible, advantages over the standard BTC connection as described in literature.

Topics: Torque , Pressure , Tension
Commentary by Dr. Valentin Fuster

Computer Technology and Bolted Joints: Threaded Fasteners

2014;():V002T02A023. doi:10.1115/PVP2014-28241.

Fine screw threads are widely used for the bolted joints under severe running conditions. It is well known that they are effective to prevent thread loosening due to fine pitch. As for other mechanical characteristics, it has been reported in the previous paper using complex stress functions that the stress concentration at bolt thread root is higher than coarse screw threads and the fatigue strength of threaded fasteners shows a minimum value for varying pitch. However, the latter is questionable since the calculations were conducted under lots of hypotheses. In this study, stress concentration and stress amplitude along thread root are evaluated by three-dimensional finite element analysis, in which numerical models of the bolted joints are constructed so as to accurately represent the effect of thread helical geometry. It is shown that the stress concentration at thread root of fine screw threads is higher than that of coarse screw threads, and the maximum stress amplitude is likely to be lower on the contrary. Meanwhile, it is sometimes recognized that clamping forces of fine screw threads are smaller comparing to those of coarse screw threads when tightened with same torque. To clarify this contradictory phenomenon, tightening experiments are conducted, and it is found that the difference of the energy needed for tightening screw threads is found to be the major cause.

Commentary by Dr. Valentin Fuster
2014;():V002T02A024. doi:10.1115/PVP2014-28242.

When bolted joints are subjected to thermal load, variations of the bolt clamping force are of great concern from the view point of joint safety. It is considered that titanium and titanium alloy bolts have high possibility for clamping machines and structures subjected to thermal load. Its specific characteristic of low thermal expansion expectantly works well to mitigate the reduction of bolt clamping force caused by thermal expansion. Low weight, low Young’s modulus and high resistance to corrosion of titanium and titanium alloy are also highly attractive.

In this paper, the effectiveness of the numerical method proposed in the previous study is validated by experiments using bolted joints composed of titanium bolts and carbon steel plates. Then, thermal and mechanical behaviors of titanium and titanium alloy bolts are analyzed by finite element analysis in order to examine the applicability of those bolts for the joints under elevated temperature. Numerical analyses are executed as in the manner introduced in the previous paper, i.e., by incorporating the thermal contact coefficient into the finite element formulation. Numerical results suggest that titanium and titanium alloy bolts are favorably applied to the joints made of carbon steel whose clamping forces are likely to decrease under elevated temperature.

Commentary by Dr. Valentin Fuster
2014;():V002T02A025. doi:10.1115/PVP2014-28269.

Experimental and Finite Element methods are used for investigating the effect of cyclic thermal loading on the clamp load decay in preloaded single-lap bolted joints that are made of dissimilar-materials. Joint material combinations include steel and lightweight materials such as aluminum and magnesium alloys, with various different thicknesses. The range of cyclic temperature profile varies between −20°C and +150°C. A computer-controlled environmental chamber is used for generating the desired cyclic temperature profile and duration. Real time clamp load data is collected using high-temperature load cells. Percent clamp load decay is investigated for various combinations of joint materials, initial preload level, and test specimen thicknesses. Thermal and material creep finite element analysis is performed using temperature-dependent mechanical properties. FEA result has provided insight into interesting experimental observations regarding model predictions and the experimental data is discussed.

Commentary by Dr. Valentin Fuster
2014;():V002T02A026. doi:10.1115/PVP2014-28356.

Three dimensional Finite Element model is used to investigate the loosening behavior of countersunk threaded fasteners subjected to cyclic shear loading applied through prescribed transverse excitation to the fastener head. Fasteners with conical head profile require precision machining of both the fastener head and the mating joint hole. Any mismatch between the head and the joint conical angles affects the torque tension relationship as well as the loosening performance. Investigation focuses on the loosening behavior in its early stages. Factors investigated include the effect of the bolt head/joint hole contact location, joint elastic modulus, and tapped hole clearance for different combinations of thread fit, on the loosening performance of preloaded countersunk-head bolts. The FEA model prediction of the self-loosening behavior is experimentally validated.

Commentary by Dr. Valentin Fuster
2014;():V002T02A027. doi:10.1115/PVP2014-28719.

Heavy hex nuts may be selected with similar hardness to the studs to avoid stripping of nut threads for pressure containing (closure bolting) and primary load bearing bolting. However, industry specification for subsea production systems, e.g. such as API Specifications 6A, 16A, 16C, and 17D, allows the use of low strength heavy hex nuts, e.g. ASTM A194 Grade 2HM or 7M, to be applied together with high strength studs, e.g. ASTM A320 Grades L43 or L7. In the refining and chemical industries the common practice is to use ASTM A193 B7 studs with 2H nuts. Calculations and testing of nuts have been performed and capacity formulas have been established for nut structural capacities. Guidance is given on selecting nut strength/hardness to avoid stripping of nut threads. ASTM specifications give minimum quality requirements during manufacture. A brief review of standard quality requirements is given and guidance for additional requirements for high integrity fasteners in order to have equivalent quality as pressure containing forgings is given. The results from this paper may be used as background for requirements in code updates and purchaser specifications.

Topics: Fasteners
Commentary by Dr. Valentin Fuster

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