Accelerated testing of three austenitic–ferritic superheater-tube transition welds under simulated ‘two-shift’ conditions

A test facility is described for testing boiler-tube samples under simulated ‘two-shift’ conditions involving cyclic pressure and temperature. The ‘overtemperature’ approach is used for test acceleration, and provision for realistic through-wall thermal stresses is made. These aspects are discussed in some detail. Three types of dissimilar metal-transition welds have been tested, two being fusion welds made with 309 stainless steel filler and Inconel, respectively, the third being a pressure weld. After 4062 cycles, the stainless steel and pressure welds showed damage similar to that observed in service welds, confirming the validity of the accelerated test. The Inconel weld was damage free, also in good agreement with service experience. The degree of damage in the test welds was less than that observed in service experience, supporting a belief that extraneous bending stresses had been involved in the latter cases.