Advances in Measurement and Treatment of Residual Stresses

Many techniques have been applied and copious measurements of weld residual stress have been made on relatively simple shapes, such as welded plates and pipes.  This reflected in the information provided in current compendia of weld residual stress distributions specified in standards and codes.  Are these compendia becoming obsolete and unrelated to more complex and practical welded components relevant to industry?  This paper will illustrate those recent advances and trends, in both measurement and treatment of residual stresses, which would allow significant changes to be made.

While the basic techniques and principles of residual stress measurement have changed little, it is wholly evident that advances in measurement methods now permit complex shapes to be studied, together with increases in the depth of measurement and the level of resolution.  Validation studies and refinements in measurement methods have improved the degree of repeatability and reduced the level of error.  There have also been several studies that demonstrate the advantages of using combinations of techniques.  The application of complementary techniques provides enhanced confidence in the results.  Notably, advances in measurement methods demonstrate that refinements to various numerical tools are often necessary.

The foundations for the treatment of residual stresses in assessing the integrity of a structure remain unchanged, principally because the assessments are intended to ensure conservative outcomes.  Nevertheless, there is growing pressure to reduce the degrees of conservatism.  Recent work has sought to examine the mechanics and boundary conditions for including residual stresses in integrity assessments.  For example, it remains ambiguous whether residual stresses can be treated as primary or secondary stresses.  Alternatively, a solution to this ambiguity can be sought by treating the residual stress as a misfit in the structure and exploring the conditions under which the misfit is accommodated.