DEFECT CHARACTERIZATION IN PIPE-TO-PIPE WELDS IN LARGE-DIAMETER STAINLESS-STEEL PIPING

Metallurgical evaluation of pipe-to-pipe welds in large-diameter, Type 304 stainless-steel piping used to construct the moderator/coolant wa ter systems for Savannah River Site reactors has demonstrated that sma ll weld defects found in this 1950-vintage system do not compromise th e integrity of the system. The weld defects were too small for detecti on by the preservice standard radiographic inspection, but were found through systematic ultrasonic testing and penetrant testing evaluation s of piping that had been removed during upgrades to the piping system . The defects include lack of weld penetration, slag inclusions, and o ther weld metal discontinuities. These discontinuities typically did n ot propagate during more than 35 years of service. The defects examine d were too small and isolated to degrade the mechanical properties of the pipe-to-pipe weldments and, therefore, did not compromise the inte grity of the piping system.