99 Diseases of Pressure Equipment: Repair Welds

Repair welds can be another undetected and insidious "fabrication defect" that eventually results in equipment failure. Any experienced metallurgist that has completed numerous failure analyses over the years will tell you that periodically they see failures that initiated at the site of a repair weld. Sometimes those repair welds are field repairs, but not infrequently they occurred during original fabrication and were unknown to the purchaser. Typically our standards and specifications do not cover repairs completed by the fabricator, so they believe they are free to do whatever they want to repair a manufacturing or fabrication defect, then grind it flush, finish the fabrication and ship the product. Again, "buyer beware". These repair welds may well end up being the site of an in-service through-wall crack 5 years later because of a hardness problem, dissimilar weld chemistry, stress raiser, or other hidden defect. The least we can do is to require in our purchase specifications that the fabricator inform us of any defects that they have repaired, or better yet, before they repair them, so we can get involved in the QA/QC required for the repair. Field repairs are another matter. We typically know about field repairs, usually because we specify them to occur. But as we all know, field repair conditions are normally not as good or as controlled as conditions for shop repairs. Hence they require extra careful specification and QA/ QC, with input from knowledgeable specialists for alloys or non-ferrous materials or where other special circumstances require design, materials and corrosion prevention knowledge.

Do you give repair welds the attention and QA/QC required to make sure they don't end up being worse than the flaw you are trying to repair?