By far the most comprehensive Blowdown simulation model to date accounting for most of the important processes taking place during blowdown was reported by Haque et al., (1992) and later extended by Mahgerefteh & Wong (1999). However, although extensively validated against experimental data, the simulation is ironically limited to blowdown under ambient surroundings only. The above is an important drawback as the most likely and catastrophic blowdown scenario would in fact involve a fire.

The combination of the external impinging heat load and the resulting fluid expansion induced internal temperature drop introduces severe temperature stress gradients across the vessel wall. Apart from the above, any such modelling must also take account of the accompanying triaxial pressure stresses due to the pressurised inventory as well as the thermal weakening of the vessel wall.

In this study, we have developed a robust numerical simulation, BLOWFIRE for predicting the risk of rupture during emergency depressurisation or blowdown of vessels containing high- pressure two-phase hydrocarbon mixtures under fire attack. Accounting for non-equilibrium effects between the constituent fluid phases, BLOWFIRE simulates the triaxial transient thermal and pressure stress profiles generated in both the wetted and unwetted wall sections of the vessel. A comparison of this information with the vessel material of construction temperature/yield stress data, allows the precise evaluation of the risk of failure and if applicable, the rupture mode during depressurisation.

The following diagram is a typical result from the BLOWFIRE simulation showing the longitudinal stress profiles resulting from the blowdown of a light hydrocarbon vessel under a 90 kW/m2 impinging heat flux.