Philosophy of weld repair of steam turbine rotors

Weld repair of a cracked rotor should never be limited to simply grinding out cracks and filling up with weld metal. It is essential to know where and why a crack appeared. In several instances in the past weld repairs have been made of fatigue cracked rotors which have been placed successfully into service. Prolonged further operation can be assured only if the cause of cracking is known and if the design weakness demonstrated in this way is eliminated. However, in cases where creep cracking is encountered or where the creep life is approaching exhaustion, a local repair even if achieved crack-free, cannot ensure successful long-term further operation. The decision must be made to replace a major section of the rotor. The paper describes weld repair trials performed on an HP rotor after 100,000 hours of operation. The results demonstrate the feasibility of making weld repairs of low-toughness CrMoV rotors according to this philosophy