Creep-rupture of service-exposed base metal and weldments of alloy 800H

摘要

An alloy 800H outlet manifold with weldments made using welding Electrode 112 was removed from service after normal operation at approximately 870 deg C for 64,000 hours, because nondestructive testin gindicated cracks in the circumferential butt welds. The objective of the research was to evaluate th remaining creep-life of the manifold, based on creep-rupture testin gof base metal and weld metal specimens. This information was then used to evaluate similar manifolds that had been repaired and left in service. Creep-rupture tests were performed at stress levels comparable to the service stress and temperatures above the design temperature were selected to accelerate the testing. The results showe dthat the base metal did not suffer significant creep damage from the prior service exposure and that the weld metal had a very low resistance to creep damage. Metallographic analysis of a weld sample taken from a comparable in-service manifold supported this conclusion, and data for new material reported in the literature support the finding of low high-temperature creep strength for welds made using welding Electrode 112. It was recommended to replace or refurbish the welds using welding Electrode 117, which has a greater creep strength.