Effects of Repair Weld Length on Residual Stress Distribution

This paper discusses residual stress distributions induced by repairing a stainless steel girth weld in a 19-mm thick pipe of outer diameter 541 mm. In particular, the effects of repair weld circumferential length are examined using finite element modeling. Results for three different repair lengths are presented having circumferential angular spans of 20 deg (short repair), 57 deg (medium repair), and 114 deg (long repair). A special 3-D shell element model is used which facilitates the simulation of multi-pass welds in 3-D piping components. The results shed light on a number of important 3-D residual stress features associated with repairs. Outer surface axial residual stresses in the weld and adjacent base material are tensile along the length of the repair, reach maxima values near the arc start/stop positions, and then drop into compression beyond the repair ends. The short repair develops the highest axial tensile stresses due to the overlay of start/stop effects. The circumferentially remote residual stresses are unaffected by the repairs. At midlength of the repair, profiles of axial stress along the pipe show tensile peaks at ≈40 mm away from the weld centerline; these peaks decrease in magnitude with increasing repair length. However, the medium repair axial stresses show the greatest range of influence along the pipe. The pre-existing original girth weld residual stresses have very little effect on the repair residual stress characteristics. Finally, residual stress measurements on mock-up components are discussed which confirm the validity of the finite element methods used.