Keywords: TIG welding, nuclear reactors, in situ repair, weld repair, blade tenon, steam turbines, nuclear power plants, nuclear energy, turbine blades, tensile load, martensitic stainless steel, inspection, testing, tungsten inert gas welding
In situ weld repair of blade tenon of steam turbine in a power plant
During one of the routine inspections in a nuclear power plant, it was found that a tenon of one of the third-stage blades of the Low-Pressure (LP) turbine had been worn/broken off the turbine blade, leaving only the remaining tenon riveted to the shroud piece. With only one of the two tenons remaining, the blade was at risk of getting freed from the shroud piece. Hence, it was necessary to repair the damaged tenon before the turbine was put back into service. This repair was carried out by rebuilding the damaged tenon in situ by weld build-up, using a procedure that would ensure that no welding occurred between the blade and the shroud. The rebuilt tenon is required to hold a minimum design tensile load of 3 tonnes. The blade that was repaired is made of a martensitic stainless steel and the repair was carried out by the Tungsten Inert Gas (TIG) welding process using ERNiCr-3 filler wires. This paper describes the welding procedures, mock-up studies and the inspection and testing conducted on both the actual job and the mock-up piece.