Development of Weld Strength Reduction Factors and Weld Joint Influence Factors for Service in the Creep Regime and Application to ASME Codes
standard by ASME International, 06/26/2017
ASME STP-PT-077, 2017 Edition – Development of Weld Strength Reduction Factors and Weld Joint Influence Factors for Service in the Creep Regime and Application to ASME Codes
The purpose of the ASME-EPRI research project is to develop the methodology and data to help establishweld strength reduction factors (WSRF) for service in the creep regime for a wide range of materials withapplicability to various sections of ASME Boiler & Pressure Vessel Codes. A review of how various codesaddress creep behavior of welded structures and pressure vessels in the Task 1a literature review  showedthat no clear consensus exists between or even within various sections of codes around the world. The rangeof approaches include: no rules, requirements to follow `good engineering practice,? simple factors ondesign irrespective of material, and factors on design which may depend on material, class/group ofmaterial, time, or combination of material and weld metal (based primarily on assessments of weld metalonly data). ASME Section III-NH contains the most extensive set of rules for welded components based ondesign life, material and weld metal combination, and temperature. The origins of the strength factorsapplied in Section III-NH are primarily based, for stainless and nickel-based alloys, on the ratio of weldmetal strength to base metal strength, the source for the chromium-molybdenum steels is not known, andthe grade 91 values are biased on some cross-weld data with more recent data showing the assessment tobe non-conservative at higher-temperatures and/or longer-times . The applicability of these rules hasbeen assessed for a few of the material-weld metal combinations by Corum  for a large body of structural`feature? tests, and the results are provided in Figure 1. The figure shows that in all cases, the applicationof the Section III-NH rules to welds produced conservative lifetimes relative to measured life in the test,suggesting a material/material class grouping approach is appropriate for design purposes.
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