This series is intended to bring attention to failures in the “coded welding” practices. From not using certified welders, to failures in visual and NDE, and failures in Pressure/Leak testing. This first incident was caused by a decision NOT to perform Post-Weld Heat Treatment on a repaired pressure vessel.
A catastrophic pressure vessel rupture at the Union Oil refinery in Illinois resulted in a massive boiling liquid expanding vapor explosion (BLEVE), killing 17 people and causing millions of dollars in structural damage. The vessel (an amine absorber column handling a sour, hydrogen-sulfide-rich process stream) had undergone a major repair prior to the accident. The repair welding process introduced intense localized residual stresses and severe material embrittlement into the heat-affected zone (HAZ) of the steel (Puryear et al., 2017). Critically, post-weld heat treatment (PWHT) was omitted following the repair.
Operating in a sour environment made the embrittled repair zone highly susceptible to hydrogen-induced cracking. Micro-cracks formed adjacent to the repair weld and rapidly propagated under normal operating pressures until the vessel experienced a sudden, catastrophic brittle burst.