In-situ Weld Repair of Cracked Shrouds of Turbine and Characterization of The Weld Joint

Abstract

Cracked shrouds of the 3^rd stage of a Low Pressure turbine was in-situ repaired by removing the cracked pieces of the shroud and welding new shroud pieces to the existing shroud. The shroud material was made of AISI414 martensitic stainless steel (SS), and the repair welding was carried out using ER 410NiMo filler wire. The tenon heads of the blades, which were removed for carrying out the in-situ repair, were also built-up by weld deposition. The repair welds were subjected to in-situ two-stage post weld heat treatment (PWHT) as required for the 414 SS material and the 410NiMo weld metal. For prior to simulation of the constraints of actual in-situ repair, a mock-up piece was made using the same blade material, welding consumable, welding procedure and PWHT as were to be used for the actual repair. After successful completion of the repair, the mock-up piece as well as separate weld pads prepared using the shroud material and ER 410NiMo consumable were subjected to detailed microstructural characterization and mechanical properties testing to generate data on the properties of the repair weld now in service. The paper discusses the details of the in-situ repair and results of the characterization of the weld joints. Results confirm the repair weld has adequate strength and ductility. The turbine with repair welded shrouds has been performing satisfactorily since 2008.