(41y) Comparison of BLEVE Models on TTF Basis

The siting of hydrocarbon processing and storage facilities requires several types of hazards to be quantified so the impact to onsite and offsite personnel and structures can be properly assessed. Among these hazards, the potential for Boiling Liquid Expanding Vapor Explosions (BLEVEs) is often a primary concern. Since BLEVEs, with rare exceptions, represent an escalation of an initial event (i.e., a fire), evaluating the risk of BLEVEs requires two steps: 1) assessing whether, and when, a given vessel may fail due to high heat exposure, and 2) quantifying the potential consequences of such BLEVE.

This paper will focus on the first step in a BLEVE risk assessment, that is, the thermal response of a vessel exposed to elevated heat fluxes. This analysis can be very complex, as it generally involves non-uniform heat fluxes to the exterior surface of a cylindrical vessel with multiple penetrations (e.g., fill and discharge pipes, relief lines, etc.); the vessel may be single- or double-walled and will generally have one or more pressure relief systems; finally, heat entering the vessel is transferred to a stratified two-phase fluid.

A number of models have been developed over the years and are available in the published literature, which aim to calculate the behavior of a vessel exposed to external heat and to predict its time to failure (TTF); each model has different assumptions, particularly as it relates to the two-phase fluid inside the vessel; therefore, different results are expected depending on the model used, and limited data is available to assess the accuracy of each model.

The purpose of this paper is to evaluate BLEVE models and compare them to one another, by using TTF as the criterion for comparison. TTF is a metric that represents the time elapsed from the onset of the heat exposure to the point of vessel failure and, when compared with the time to initiate emergency response, it represents a practical quantity that can inform the potential for a BLEVE to occur in a given scenario. The paper will also compare these thermal response models to published TTF probit functions for pressure vessels (e.g., Ustolin, F. et al. “Time to Failure Estimation of Cryogenic Liquefied Tanks Exposed to a Fire.” In Proceedings of the 31st European Safety and Reliability Conference (ESREL 2021), 935–42).