This was a new pressure vessel that failed during its hydro test following its fabrication. The vessel’s Post Weld Heat Treatment was not properly conducted, when some parts of it did not reach the required temperature. Coupled with a small hydrogen crack, the failed post weld heat treatment was sufficient to cause catastrophic failure while it was undergoing it hydro test.
To understand more about PWHT and specifically its impact on Ammonia Refrigeration Systems, visit Gartner Refrigeration’s well written article on the effects of PWHT. CLICK HERE (pdf) for the Gartner Refrigeration article.
Above is a pciture of a High Pressure Receiver (HPR) in an ammonia refrigeration system showing a pinhole leak stemming from propagation of SCC from the interior of the vessel (Bansch 2005)