Bursting pressure vessel described

The bursting of a large pressure vessel at Feyzin, France, in 1966 was at the time one of the worst incidents involving LFG that had ever occuired but has since been overshadowed by the events at Mexico City (see Section 8.1.4). It caused many companies to revise their standards for the storage and handling of these materials. Because no detailed account has been published, it is described here. The information is based on References 3 through 6 and on a discussion with someone who visited the site soon after the fire. 

Many operators find it hard to grasp the power of compressed air. Section 2.2 (a) describes how the end was blown off a pressure vessel, killing two men, because the vent was choked. Compressed air was being blown into the vessel, to prove that the inlet line was clear. It was estimated that the gauge pressure reached 20 psi (1.3 bar) when the burst occurred. The operators found it hard to believe that a pressure of only twenty pounds could do so much damage. Explosion experts had to be brought in to convince them that a chemical explosion had not occurred. 

This subject has received little attention in the context of pressure vessel bursts. Pittman (1976) studied it using a two-dimensional numerical code. However, his results are inconclusive, because the number of cases he studied was small and because the grid he used was coarse. Baker et al. (1975) recommend, on the basis of experimental results with high explosives, the use of a method described in detail in Section 6.3.3. That is, multiply the volume of the explosion by 2, read the overpressure and impulse from graphs for firee-air bursts, and multiply them by a factor depending on the range. 

In the preceding subsections, bursting vessels were assumed to be filled with ideal gases. In fact, most pressure vessels are filled with fluids whose behavior cannot be described, or even approximated, by the ideal-gas law. Furthermore, many vessels are filled with superheated liquids which may vaporize rapidly, or even explosively, when depressurized. 

In this section, three examples of blast calculations of BLEVEs and pressure vessel bursts will be given. The first example is designed to illustrate the use of all three methods described in Section 6.3.2. The second is a continuation of sample problem 9.1.5, the BLEVE of a tank truck. A variation in the calculation method is presented instead of determination of the blast parameters at a given distance from the explosion, the distance is calculated at which a given overpressure is reached. The third example is a case study of a BLEVE in San Juan Ixhuatepec (Mexico City). 

The long-term burst strength of plastic pressure vessels is determined by subjecting the pressure vessels to constant internal pressure and observing time-to-failure. This test is a static pressure test, as opposed to the dynamic quick-burst test described earlier. 

The tube diameter is L and the inner diameter - dp. The tube outlet flange has an exit diameter ofd< dp. Experiments described in [40,46] have shown that there are optimum didp andLjdp ratios at which a minimum pressure level Fc 4 MPa in the high-pressure vessel is reached and the outflow hydrogen jet exhibits spontaneous ignition. Spontaneous ignition of methane and propane has not been observed. The air pressure downstream of the bursting membrane was 0.1 MPa. When the... 

Note that the recommended value for p is not always conservative. In some cases, heat input may be so high that the safety valve cannot vent all the generated vapor. In such cases, the internal pressure will rise until the bursting overpressure is reached, which may be much higher than the vessel s design pressure. For example, Droste and Schoen (1988) describe an experiment in which an LPG tank failed at 39 bar, or 2.5 times the opening pressure of its safety valve. Note also that this method assumes that the fluid is in thermodynamic equilibrium yet, in practice, stratification of liquid and vapor will occur (Moodie et al. 1988). 

BLEVE (Boiling Liquid Expanding Vapor Explosion) See Boilover the same phenomenon may occur in a pressurized container, resulting in an explosion or bursting of the tank or vessel in which a fire is occurring. The term is almost exclusively used to describe a disastrous effect from a crude oil fire. 

The liquid sulfur dioxide solutions described in the preparations have a vapor pressure of about 3.3 atm at 21 °C. Therefore, well-constructed glass vessels and a glass (or metal) vacuum line must be employed to prevent pressure bursts. Thick leather gloves, safety goggles, a face shield, and a rubber apron should be worn and the experiments have to be conducted behind a safety shield or explosion-proof glass in a fume hood to prevent possible contact with the reaction mixtures as well as with AsF5 and SbFs. 

AIChE (1994) describes a procedure developed by Baker et al. (1975) and Tang et al. (1996) for determining both the peak overpressure and impulse due to vessels bursting from pressurized gas. This procedure is too detailed to be described in detail here. The method results in an estimate of the overpressure and impulse due to blast waves from the rupture of spherical or cylindrical vessels located at groimd level. The method depends on the phase of the vessel s contents, its boiling point at ambient pressure, its critical temperature, and its actual temperature. An approach is also presented to determine blast pressures in the near-field, based on the results of numerical simulations. These methods are only for the prediction of pressure effects. 

---