CFD Modeling of Blast Loads From a Pressure Vessel Failure

Abstract

The downhole tool industry commonly conducts tests that require pressurization of a vessel. The most common failure mode is through the launching of end caps, plugs, and fittings as opposed to a catastrophic rupture of the vessel body. This type of vessel failure during high pressure gas testing can produce significant threats to nearby personnel in the form of high energy projectiles and blast waves that must be blocked or dissipated before reaching personnel. Adequately designing a structure to contain this energy depends on how well a worst case scenario event can be modeled. Blast waves ensue from a pneumatic pressure test failure. As a vessel fails, the volume of pressurized gas will expand into the surroundings. A computational fluid dynamics (CFD) model of the pressure vessel and its enclosure will provide an accurate assessment of the blast loads in the environment. This paper describes an experimental test program of a simulated pneumatic pressure vessel failure through the launching of a hypothetical end cap or plug inside an enclosure. The recorded blast loads from three tests at various pressures were compared to simplified two-dimensional CFD model results of the enclosure. Two CFD models were run for each test: the first accounts for the time required for the vessel to open during failure, and the second assumes an instantaneous release of pressurized gas. The CFD results for the first model matched the test results well and provided validation of the modeling approach. The second model indicates the level of conservatism of predicted blast loads when assuming an instantaneous vessel failure. A properly designed pressure testing enclosure can provide a high level of safety in the event of a failure; several types of enclosure designs have proven to be successful, which are discussed in this paper. Equally important is the need to have competent operators with an awareness of the risks involved with pressure testing combined with training and competency programs implemented throughout the industry.