Crack Susceptibility in 347H SS Welds and Potential Mitigation Solutions

347H SS has a combination of good creep strength and sensitization resistance compared to other 3XX SS grades for mildly corrosive, elevated temperature applications. Weldments of 347H stainless steel are susceptible to stress relaxation cracking at elevated service temperatures and potentially during post weld heat treatment in highly restrained welds. Mitigation of stress relaxation cracking susceptibility within a multipass thick weld requires a good understanding of welding practices and manufacturing techniques to control high tensile residual stresses and quantification of the critical stresses/strains for stress relaxation cracking to occur. In this study, the dependence of residual stress distribution in 347H stainless steel on the baseplate thickness, joint geometry design, and preheating condition was systematically investigated by using three-dimensional finite element models. The finite element models were validated through good agreement between neutron diffraction measurements and calculated elastic strains. Critical stresses as a function of temperature were also identified for the heat affected zone and weld metal, respectively. Such information is critical for determination of allowable PWHT temperature range as a function of maximum residual stress

Keywords: stress relaxation cracking, stainless steel, residual stress, post weld heat treatment