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Stress Measurements at Hot Spots Using StressProbe

[+] Author Affiliations
I. Lotsberg

DNV, Oslo, Norway

M. M. Salama

ConocoPhillips, Houston, TX

W. D. Dover, R. F. Karé, N. Stone

TSC Inspection Systems, Milton Keynes, UK

Paper No. OMAE2007-29185, pp. 45-56; 12 pages
doi:10.1115/OMAE2007-29185
From:
  • ASME 2007 26th International Conference on Offshore Mechanics and Arctic Engineering
  • Volume 4: Materials Technology; Ocean Engineering
  • San Diego, California, USA, June 10–15, 2007
  • Conference Sponsors: Ocean, Offshore and Arctic Engineering Division
  • ISBN: 0-7918-4270-3 | eISBN: 0-7918-3799-8
  • Copyright © 2007 by ASME

abstract

The estimation stress concentration factor (SCF) of weld details of floating structures is critical parameter for fatigue life predictions. The common practice for predicting the SCF value is the use of code-specified empirical equations and through detailed finite element analysis (FEA) for critical joints. Under certain conditions, it becomes necessary to reassess the SCF value while the structure is in service. The most accurate approach is to measure the SCF value on the real joint since variations in FEA results always exist due to variation on modeling techniques by different analysts. While the use of strain gauges is the standard approach, applying strain gauges in service can be extremely complicated. Therefore, an alternative approach for direct measurement that does not require removal of coating and bonding to the surface is attractive. The StressProbe that takes advantage of the change in the magnetic permeability of steel due to the presence of a mechanical stress offers the required alternative as a non-contacting strain measurement method. The paper presents the results of a study to assess that capability of the StressProbe in measuring SCF value by measuring variations in strain in a high strain gradient region of a hopper corner detail that is typical in floating structures and compare the results with those obtained using both strain gauges and finite element analysis. The results show that the StressProbe can be used for the determination of the SCF at a weld under various scenarios and it can also be used to monitor cyclic stresses during periods when there is wave loading. While there is some variability in the StressProbe results but given the variability found with strain gauges it is considered that the StressProbe could be used to replace strain gauges.

Copyright © 2007 by ASME
Topics: Measurement , Stress

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