Vessel Rupture and Blast Wave

Understanding vessel rupture

A vessel rupture is a catastrophic failure of process equipment, typically involving a loss of containment. Specific examples of vessel rupture include Boiling Liquid Expanding Vapor Explosion (BLEVE) Blasts and Gas Blasts. These events occur when vessels containing pressurised liquefied gas or compressed gas fail.

Fireballs and Blasts are discussed separately in the Fire and Explosion chapters due to their distinct effects. While a blast results from the sudden release of pressure causing a shock wave, a fireball involves rapid combustion of flammable materials, combining both explosive and thermal impacts. However, vessel ruptures do not always involve a thermal component, as seen in explosions of compressed air tanks or steam boilers.

When a vessel contains flammable substances, the resulting explosion is followed by rapid combustion, giving rise to a Fireball immediately after the explosion which combines both the mechanical effects of an explosion and the thermal effects of a fire. The accompanying video showcases a BLEVE Fireball as provided by Gexcon’s Fire and Explosion department, illustrating the combined damage effects.

Types of damage resulted by a vessel rupture

Thermal effect: Intense heat generated by the combustion of flammable materials.

Blast wave: High-pressure shock wave causing structural damage.

Propelling debris: Fragments of the vessel becoming projectiles.

Dispersion of toxic combustion products: Hazardous materials released into the environment.

Causes of vessel rupture

Vessel ruptures can occur due to various reasons:

• Temperature and pressure increase: Internal runaway reactions or external heating raise pressure beyond the vessel’s burst pressure.

• Mechanical stress: Repeated stress or mechanical damage such as corrosion or erosion weakens the vessel.

• Material and manufacturing defects: Welding defects, material degradation, or inadequate pressure relief systems can lead to failure.

• External impacts: Collisions during transport of LPG, industrial accidents, natural disasters such as earthquakes or extreme weather conditions.

Mechanical energy released by the explosion

The rupture of a pressurised vessel results in the release of mechanical energy. BLEVE Fireballs and Gas Fireballs are detailed in the Fire chapter. Further, we will explore the effect of the explosion from the mechanical energy point of view.

Upon rupture, the vessel’s stored energy is released, causing:

• Fragmentation: The vessel breaks into pieces.

• Overpressure Wave: A shock wave propagates through the air.

• Propelled fragments: Vessel fragments can be thrown at significant distances.

If the involved substance is flammable, then a third pressure peak can be observed resulting from the combustion process of the fuel contained in the vessel. If the substance is not flammable, the pressure wave and the projectiles will be the only effects of the explosion.

BLEVE Blast

Once the vessel bursts, depressurisation causes the flashing of a two-phased liquid/vapour mixture. The quickly increasing volume of the released material generates an overpressure which exhibits 2 peaks:

• The expansion of pre-existing vapour: Immediate release of pressure.

• Flashing: Instantaneous vaporisation of the liquid.

Although a short pressure drop occurs between these two Blast Waves, they are typically combined into a single conservative estimate for safety assessments.

Gas Blast

When a vessel contains only gas, the Overpressure Wave is solely due to the expansion of pre-existing vapour without the additional flash vaporisation phase seen in BLEVEs.

References

Bosch, C. v. (2005). Methods for the calculation of physical effects 'Yellow book' CPR 14E. The Hague: Ministerie van Verkeer en Waterstaat.