Quality Control In Surface Welding Repairing On Damaged Turbine Generator Rotors

The thesis is dedicated to the quality control of damaged rotor repairing via argon-arc welding,which occurs due to collision in manufacturing process or wear in running period of gas turbine generators.The research is focused on the control of crack initiation and propagation during repairing welding of rotors made of 25Cr2Ni4 MoV where heat treatment is not allowed.The main research work includes:1.The selection of welding wires in terms of the damage features is investigated first.An illustration model to feature the damage is established via the statistical analysis of damaged rotors.Four kinds of test samples are prepared on the 25Cr2Ni4 MoV steel plates with different depth of damage ranging from 2mm to 30 mm.Four types of welding wires are used for every typical damage to check the fitness by examine the repairing qualities via penetration test,ultrasonic inspection,mechanical properties test,and microstructures examination.It is revealed that the welding wire ER80S-Ni1 will result in the best repair properties for damages with a depth varying from 15 to 30 mm,while wire ER80S-Ni2 should be recommended for the damaged groove with a depth under 15 mm.2.The influences of welding layers and welding passes on the residual stress in the repaired 25Cr2Ni4 MoV rotors are examined subsequently.A finite element model is established to simulate the difference on temperature field and residual stress distribution for samples with different welding layers and passes.The simulation result shows that the residual stress can be decreased though multilayer welding with more passes for 25Cr2Ni4 MoV rotor repair,as compared with the welding repair finished in single pass.3.Experimental validation of the repairing effect is designed and conducted finally.A ring sample with pit and annular slot damages is designed to simulate the structure,the geometric and dynamic condition,and the process constrains of turbine generator rotors.The over speed test is conducted to check the argon-arc welding repair of 25Cr2Ni4 MoV turbine generator rotor,which is followed with the magnetic properties examination as an electrical generator.The two experiments together with the nondestructive testing of the welding repair area show the validation and feasibility of the repairing strategy proposed in this thesis for 25Cr2Ni4 MoV turbine generator rotor repair with argon-arc welding.