SUBMERGED ARC WELD RESTORATION OF STEAM TURBINE ROTORS USING SPECIALIZED WELDING TECHNIQUES

摘要

In the past 10 years, there have been significant gains made in the repair of steam turbine rotors by the use of welding. This has been the result of improvements in several areas dealing with materials, engineering analysis, nondestructive testing, and specialized welding techniques. Several papers have been written on the repair of LP rotors for central generating stations. A few have recently been written on repairs to HP rotors. There has been little written on the welded repair of mechanical drive steam turbine rotors. The specialized welding techniques needed to perform submerged arc welding restoration of mechanical drive steam turbine rotors are highlighted. The advantages of welded repair and the engineering analysis necessary to make a reliable repair to a rotor are also addressed. Basically, two categories of welded repair are studied. One is the welded journal repair. The other is the complete replacement of a stage disc on a monoblock rotor forging by the use of welding. Mock up test assemblies are used, along with sample weld test assemblies, in order to try to duplicate the actual welding situation as much as possible. Both destructive and nondestructive testing is performed on these test assemblies to determine occurrence of any flaws, mechanical and electrical runout, chemical composition variations, hardness distributions, tensile and yield strength in different directions at room and elevated temperatures, fracture toughness, fracture appearance transition temperatures, stress rupture strength, and fatigue endurance limits. The results from these tests are discussed along with the pertinent engineering requirements that pertain in order to give the limits of welded repair. Plans for further testing are outlined, along with the conclusion that supports continued acceptance of submerged arc weld restoration of steam turbine rotors ensuring reliability of the weld metal and the heat affected zone of the turbine base material.