FITNESS FOR SERVICE ASSESSMENT UTILIZING FIELD RESIDUAL STRESS MEASUREMENTS

摘要

Welding residual stress is defined as the stress which remains in a welded joint as a result of thermo-mechanical interaction after welding has been completed. The presence of tensile residual stresses are a large factor in stress corrosion cracking and stress oriented hydrogen induced cracking (SOHIC). Unknownresidual stress distributions can also result in overly conservative fitness for service assessment in pressure vessels and piping. An enhanced blind hole drilling technique with depth monitoring using continuous recording and calculation instrumentation, was developed to obtain reliable residual stresses of pressure vessels and piping in the field. The newly developed technique was successfully applied to several pressure vessels during a plant turnaround. The technique can be applied to on-site residual stress measurement reliably and more importantly, without affecting the integrity of the subject vessel. The measured results revealed the quality of the postweld heat treatment, and the measured residual stresses were then used as an input for fitness for service assessment. This paper illustrates the depth monitoring residual stress measurement technique and its application to a fitness for service assessment during the plant turnaround.