Structural failures precipitated by weld discontinuities

A literature review was conducted to assess the effects of weld defects upon the failure of welded structures. This effort was focussed on storage tank failures with emphasis on those fabricated for cryogenic liquid containment in order to assess the significance of past storage tank failures relative to the 9% nickel steel storage tanks currently in service. Consideration of past failures can be instructive for insuring the integrity of these vessels. Along with other documented failures, three cryogenic storage tank failures are documented herein. One of these was a liquefied natural gas (LNG) tank, the other two were designed to store liquid ethylene. Although details of design differed slightly, the overall design was the ‘tank within a tank’ concept. In each of the three failures detailed in this review, a breach of the outer tank integrity resulted when cryogenic liquid came in contact with the outer tank wall. This can be attributed to the fact that the outer steel wall was brittle at service temperatures. In addition to the above failures, this review has revealed a pattern of failures in pressure vessels resulting from faulty welds (usually fillet welds) associated with nozzle attachments and branch connections. These are undoubtedly areas of concern in cryogenic storage tanks along with the ones delineated more fully in this review.