Residual Stress Assessment in API X65 Pipeline Welds by Non-destructive Instrumented Indentation

摘要

Conventional residual stress-measurement methods are difficult to use in industrial structures largely because of their complexity and destructive nature. In particular, the rapid microstructural gradients across welds impede a quantitative assessment of residual stress. An instrumented indentation technique has been developed to overcome the current problems in measuring the residual stress. Here this instrumented indentation technique was used to characterize the residual stress in API X65 steel welds in a natural gas transmission pipeline. The difference in indentation load between the stressed and unstressed regions at a fixed penetration depth was converted to a quantitative residual stress value through an analytical procedure. The stress distribution assessed across the welds agreed roughly with that from destructive saw-cutting tests. The discrepancy in absolute stress values from the two methods was considered to arise from the effects of microstructural difference and stress directionality in the welds.