EVALUATION OF RESIDUAL STRESSES IN STEEL-TO-NICKEL DISSIMILAR JOINTS

Welds between ferritic and austenitic materials, commonly described as dissimilar metal welds (DMW's), are widely employed in various industrial applications. Failure of such joint can occur by a variety of failure mechanisms including creep, thermal fatigue and hydrogen embrittlement/corrosion While in some cases, the presence of long range stresses, due to design and fit-up, have been linked to failures, triaxial stress distribution across these types of joints have not adequately been investigated. In the present work, forged low alloy connectors were buttered with a nickel alloy and post-weld heat treated, before making closing welds to a pipeline steel. The DMW received no further post-weld heat treatment (PWHT). The residual strain profiles across dissimilar joints were measured in the axial, radial and hoop directions of a series of these joints containing multi-pin girth welds, using the neutron diffraction technique. Residual stresses were calculated from these measurements. Three dissimilar metal interface combinations were investigated: (1) ASTM A182 F22 steel to ERNiCrMo-3 (alloy 625) weld metal (PWHT'd joint), (2) AISI 8630M steel to ERNiCrMo-3 (alloy 625) weld metal (PWHT'd joint) and (3) ASTM A964-F65 low alloy steel to ERNiCrMo-3 (alloy 625) weld metal without PWHT. The current study attempts to create a better insight into the unique stress distributions across these joints.