Repair Severely Damaged Rotors By Submerged Arc Welding.
Severely damaged rotors often can be rebuilt even when damage has occurred to the shaft/rotor forging. Such shop repair returns what would have been a scrapped or degraded rotor to original equipment standards. The repair procedure is to: • Remove damaged areas of the rotor by machining. • Build up metal with metallurgically compatible weld wire and fluxes, using submerged arc welding in sequences as dictated by repair design. • Thoroughly inspect the welded/machined area by magnetic particle, ultrasonic, and dye check procedures after each sequence. • Stress relieve the welded area after each sequence, using computer controlled heating of the desired area so as to control hardness in the heat affected zone (HAZ) and assure adequate metallurgical properties in the weld metal. • Repeat these sequences until the repaired area conforms to the design required by welding engineering, mechanical engineering, insurance specialists, and/or consulting metallurgical laboratories. These procedures can often provide metallurgical properties superior to those of the original material, move the heat affected zone (HAZ) out of the steam path, strengthen the repaired area, compensate for anticipated problems, and/or improve the original design of the rotor. Such repairs involve use of special jigs, equipment, techniques, and procedures. A detailed description of the turbine rim weld repair is given, including use of supplementary pictures, drawings and techniques. Cracks were discovered in the body of a nominal22 in diameter, first stage Curtis wheel of a forged turbine rotor. Laboratory analysis indicated the cracks were due to stress corrosion, believed to have been caused by caustic introduced accidentally with inlet steam. The damaged portion of the wheel was removed by machining at a point well into the unaffected portion of the wheel. The remaining rim was welded to build up, heat treated, finish machined to accept blades, and rebladed. The finished rotor was dynamically balanced at operating speed, installed in its casing, and returned to service. The reinstalled rotor has operated without trouble at up to design conditions for a number of months. These welding procedures were evolved and improved through experience gained over the past eight years in the repair of about 80 damaged turbine rims. Similar repairs have also been performed on centrifugal compressor rotor wheels and shafting. Monitoring and periodic shop inspection of these welded rotors has shown no degradation in the repaired areas. Repair costs have been well below those that would have been incurred by replacement with original vendor equipment and, most often, in significantly less time than it would have taken if a new rotor was provided from the original equipment manufacturer.
Heeter, Jim (1991). Repair Severely Damaged Rotors By Submerged Arc Welding.. Texas A&M University. Turbomachinery Laboratories. Available electronically from