CRACKING IN STABILIZED AUSTENITIC STAINLESS-STEEL PIPING OF GERMAN BOILING WATER-REACTORS - CHARACTERISTIC FEATURES AND ROOT CAUSE

Cracks have been found in the welds of piping systems made from stabil ized austenitic stainless steels in German boiling water reactors (BWR ). In the course of the intensive failure analysis metallographic exam inations, microstructural investigations by electron microscopy, corro sion experiments and welding tests have been performed. The results sh ow that cracking under the given medium conditions is due to intergran ular stress corrosion cracking (IGSCC) in those parts of the heat affe cted zone (HAZ) which are overheated during welding and where solution of titanium carbides and subsequent precipitation of chromium carbide s and depletion of chromium along the affected grain boundaries could occur. (C) 1997 Elsevier Science S.A.