Failure analysis of a dissimilar weld joint in a steam generator

Dissimilar metal joints between pipes of ferritic steel and austenitic steel are widely used in steam generators of power plants. Literature survey indicated that significant number of premature failures occurred in the ferritic steel side of the dissimilar weld joint. This paper highlights the failure analysis carried out on a failed dissimilar joint of a thermo-well boss used in the steam generator of a Fast Breeder Test Reactor (FBTR). The failure analysis revealed that the failure of the weld joint could be attributed to the combined effect of the presence of residual stress in the absence of post weld heat treatment and possible carbon migration from the low alloy steel to the stainless steel.