Repair welding of cracked shrouds in steam turbines

The procedure for repair welding of cracked shrouds in steam turbines has been developed using the gas tungsten are welding process and ER 316L filler wires. The procedure development included selection of welding consumable, optimisation of post weld heat treatment parameters, determination of mechanical properties of weldments in as-welded and PWHT conditions, and selection of suitable method for local PWHT of repair welds. Three different filler wires (ER 309L, ER 316L, and ER NiCr-3) were evaluated during procedure qualification. All these filler wires were of austenitic type and were preferred over matching composition filler wires to avoid preheating of the job and hydrogen induced cold cracking. This procedure has been applied for repair welding of 8 cracked shrouds in 4 steam turbines of 3 Indian nuclear power plants. The details of the procedure development and the experience of in-plant repair welding are presented in this paper.