WELDMENT EVALUATION OF HIGH-PRESSURE STEAM ROTORS

Life extension of high pressure and intermediate pressure rotors by we ld repair is a viable alternative considering the latest developments. Our objective is to select a filler wire that will produce a weld wit h mechanical properties compatible with those of the rotor material. T hree filler metals, (CrMoV, 12 percent Cr and 5 percent Cr) were used in the investigation. Multipass submerged are groove welds were produc ed, post weld heat treated at 677-degrees-C (1250-degrees-F), and subm itted to a series of mechanical tests at room and elevated temperature s. The tests samples were machined parallel to the weld direction (lon gitudinal), which included only weld metal, and perpendicular to the w eld metal (crossweld) so that the test sample includes portions of the weld metal, heat-affected zone (HAZ) and base metal. A limited metall urgical evaluation was also performed. The room temperature tensile pr operties of the CrMoV and 12 percent Cr crossweld samples exceeded tho se of the rotor metal, but the tensile properties of the 5 percent Cr crosswelds did not match those of the rotor metal. The 12 percent Cr c rossweld samples failed in the weld metal during hot tensile and stres s rupture testing, and these failures were attributed to slag entrapme nt; yet the yield and tensile strengths of these weldments just exceed ed those of the rotor base metal. The CrMoV crossweld specimens perfor med the best at the high temperature testing; the failure for the hot tensile specimens occurred in the weld metal and the values matched th ose of the all weld metal (longitudinal) specimens which greatly excee ded the rotor base metal strengths. The crossweld stress rupture sampl es failed outside the weld metal at the heat affected zone (HAZ) near the unaffected base metal with rupture lives lower than the rotor base metal. Microhardness evaluations in the CrMoV and 12 percent Cr cross weldments about the HAZ/base metal boundary identify a soft region at this location. The mechanical properties of the 5 percent weldment we re in general inferior to the rotor base metal. The weld metal's hardn ess was lower than the rotor base metal given its superior Charpy ener gy values; however, the creep rupture strength was inferior.