Before the advent of improved alloys like super duplex, companies could sometimes be forgiven for the accidents which happened at their plants. Often, these were a result of leaking, corroded or badly maintained pipe fittings. There’s no excuse for the events which happened at the Valero McKee Oil Refinery, Texas, in February 2007. Without warning, a massive fire ripped through the plant, injuring 4 workers and causing complete closure of the refinery for two months.

The report cited a leaky valve and escaped propane as the cause, but the real cause was far more insidious: one of the pipe fittings, an elbow joint which had been out-of-service since the early 1990s.

The fire broke out in the de-asphalting unit – an area that uses high-pressure liquid propane to separate gas oil from asphalt. The elbow-joint was part of a “dead-leg” formed when piping was taken out of service. It remained connected, but was no longer supposed to have any flow. However, unknown to personnel a piece of metal became wedged above the elbow, opening a valve and allowing propane to intermittently flow through from the high-pressure pipe above it.

Over time, water seepage collected in the crook of the elbow. During a period of cold weather the ice froze, fracturing the elbow joint. Later on, high-pressure propane flowed through the leaky valve and into the fractured pipe fitting.

We at Chemipetro always recommend pipe fittings and flanges are removed if not in use any more. Redundant pipe fittings have their uses (as a back-up route during maintenance, for example), but it is more often than not more practical to remove them.