(189d) Atmospheric Tank Failures:  Mechanisms and an Unexpected Case Study

Most of the literature on catastrophic failures of low pressure tanks focuses on the ignition of explosive mixtures in the vapor space of those tanks. Rightly so, because most catastrophic failures of atmospheric tanks involve explosions of such mixtures.  Moreover, there is a general sense in the industry that the only other hazard associated with low pressure tanks is the occasional dramatic implosion of a vessel that is inadequately protected against vacuum.

In fact there are a number of mechanisms that can lead to the catastrophic failure of a low pressure tank that have nothing to do with combustion or vacuum.  Under certain circumstances, even a tank equipped with an atmospheric vent and containing nothing other than salt water can explode, with disastrous impacts.

This paper reviews the mechanisms for catastrophic failure of low pressure tanks, both implosion and explosion, and serves as a reminder of what to look for during a hazard review.  It also includes a recent case study of an atmospheric caustic tank explosion that resulted from a previously unreported mechanism involving neither combustion nor vacuum.