UNUSUAL CASES OF WELD-ASSOCIATED CRACKING EXPERIENCED IN A HIGH-TEMPERATURE CATALYST REDUCTION REACTOR

Two case studies are described which concern instances of weld-associa ted cracking discovered in a high temperature Cr-Mo catalyst reduction reactor soon after commissioning. One of the defects was diagnosed as re-heat cracking at a heavy section nozzle-to-shell weld, which was a ttributed largely to the high stress concentration at the toe of the w eld in conjunction with tri-axial stress, resulting from the thick sec tion geometry. Cracking was believed to have initiated during post-wel d heat treatment which was only carried out 2 months after completion of welding. The other defect described is a classic case of HAZ cracki ng at the external support legs of the reactor, again attributed large ly to the delay in conducting post-weld heat treatment after fabricati on. In situ replication metallography was instrumental in establishing the failure modes in both instances, and was also able to demonstrate that the HAZ cracks were present before PWHT was carried out. (C) 199 8 Elsevier Science Ltd. All rights reserved.