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The development of consistent residual stress estimates for various welded components that may be used in a Fitness-For-Service (FFS) service assessment and the development of recommended procedures for performing local post-weld heat treatment (L-PWHT) are covered in this Bulletin. A large number of residual stress and local PWHT analyses using the finite element method were carried out. The major findings are summarized as follows.

The through-thickness residual stress distributions can be decomposed into three basic parts: through-thickness membrane; through-thickness bending; and through-thickness self-equilibrating. The combined peak residual stress value may be scaled by the yield strength of material. The membrane and bending components are dominated by joint restraint conditions in terms of translational restraint and rotation restraint conditions. The pipe wall thickness and thickness to pipe radius ratio serve as two important parameters determining the actual amount of sectional bending moment under a given net shrinkage force of a girth weld in the hoop direction. The self-equilibrating part is dominated by welding procedure related parameters such as the total layers of weld passes to complete weld, joint configuration, and the number of weld pass deposition sequences. Although the self-equilibrating part of the residual stress distributions can exhibit a complex variation over plate or pipe wall thickness, the fracture mechanics treatment used in an FFS assessment indicates that only the lowest order approximation of such variations is important. Temper bead, HAZ phase change, and other small scale level phenomena mostly contributes to a higher order variations. The residual stress decomposition technique is shown proven to be equally applicable for different weld configurations such as seam welds, nozzle to vessel welds, repair welds. Through-thickness residual stress distributions (also referred as profiles in literature) have been generated for girth welds, seam welds, repair welds, lap fillet attachment welds and nozzle welds. The transverse residual stress (perpendicular to weld) distributions, which are of particular interest to fitness for service assessment, may also be uniquely related to some of the through-thickness distribution characteristics of the longitudinal residual stresses (parallel to weld). Parametric equations have been developed that can be used in an FFS assessment to generate a through-thickness axial residual stress distribution with the magnitude scaled by yield strength of the material. If a component is subjected to hydro proof test before service, additional benefits in the form of an overall magnitude reduction in the residual stresses may be realized. The residual stress distribution characteristics remain essentially the same both before and after hydro proof tests. This suggests the same functional form used for the as-welded condition may be used to approximate the through-thickness distribution after hydro proof test, except the magnitude in residual stress is reduced depending up joint geometry and hydro proof test conditions.

Detailed observations and recommendations are provided for L-PWHT in in terms of both thermal stress and residual stress reductions. For FFS purposes, the same functional form of the through-thickness residual stress profile as that under as-welded conditions can be used to approximate the residual stress profile after local PWHT within the weld area for most of cases investigated, as long as the requirements proposed in Section 5.3 are satisfied. However, considerations must be given to the additional residual stress generated at some distance away from the weld.

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Published: 2016 Number of Pages: 270 File Size: 1 file , 6.6 MB