Effects of Weld Surface Finish and Counterbore on Piping Performance

摘要

The objectives of the program were to evaluate the effect of counterbore on the fatigue behavior of butt-welded, consumable-insert joints in 4-inch-diameter, Schedule 40, carbon-steel and copper-nickel piping and the effect of as-welded surface, with and without nominal 1/64-inch external undercut, on the fatigue behavior of butt welds with consumable inserts and with backing rings in 4-inch-diameter, Schedule 40 carbon-steel and copper-nickel pipe and with consumable inserts in nickel-copper pipe. The tests of the copper-nickel and nickel-copper consumable-insert joints with external undercut were not made when the fatigue lives of these joints without undercut were found to be severely degraded. The specimens were welded without undercut and used instead to determine the effect of limited weld finishing. The pipe specimens were fatigue tested as cantilever beams in resonance induced by a rotating deflection at the free end. The test weld was located about 5 inches from the fixed end. The pipes were pressurized internally with fresh water for the carbon steel and salt water for the copper-nickel and nickel-copper specimens. By rotating the free end of the specimen, each area of the test weld around the circumference experienced the same tensile and compressive stresses. After fatigue testing, the specimens were carefully examined to determine the origin of failure.