Characterisation of Residual Stress Levels Retained in Fracture Mechanics Specimens Machined From Non-Stress Relieved Welds

Abstract

The structural integrity assessment of weldments in engineering components, including piping, is dependent upon the acquisition of valid fracture toughness data. Test standards provide guidance for the preparation of fracture mechanics specimens machined from welds, recognising that under some circumstances retained weld residual stress in the specimens may influence the test, for example, by impairing the ability to establish a valid fatigue pre-crack. To date, however, there are little experimental data quantifying the level and distribution of retained residual stress in fracture mechanics specimens. This paper describes an experimental study characterising the residual stresses retained in single-edge notched bend specimens machined from a non stress-relieved, narrow-gap Tungsten Inert Gas welded pipe, manufactured from 304L stainless steel. The original weld residual stress field was characterised using neutron diffraction and deep hole drilling. The residual stress levels retained in the test specimens were subsequently quantified using deep hole drilling. The results indicated that reasonable levels of residual stress are retained within specimens, although for high toughness, ductile steel, this is insufficient to influence the fracture toughness measurement. The results, however, have implications for testing non stress-relieved welds manufactured from low toughness materials, where retained residual stresses could unduly influence fracture toughness measurements.