Bursting pressure vessel

Figure 6.33 can be used to calculate the initial velocity Vj for bursting pressurized vessels filled with ideal gas. The quantities to be substituted, in addition to those already defined (p, po, and V), are... 

Kinetic energy Noncontainment of moving components (e.g. RAT, Fans, APU Engine, burst pressure vessel). Wheels (e.g. tyre burst, flaiUng tread, lim release, etc). FlaUing shafts. Need to consider issues such debris trajectory (e.g. see ARP4761, p. 304) and resulting vibration, loss of function, etc. 

Figure 7.43 Comparison between measured pressure waves from a burst pressure vessel and advance computations according to the TNT equivalent method (7-61).

Little error is introduced using the idealized stress—strain diagram (Eig. 4a) to estimate the stresses and strains in partiady plastic cylinders since many steels used in the constmction of pressure vessels have a flat top to their stress—strain curve in the region where the plastic strain is relatively smad. However, this is not tme for large deformations, particularly if the material work hardens, when the pressure can usuady be increased above that corresponding to the codapse pressure before the cylinder bursts. 

A difference between tank cars and most pressure vessels is that tank cars are designed in terms of the theoretical ultimate or bursting strength of the tank. The test pressure is usually 40 percent of the bursting pressure (sometimes less). The safety valves are set at 75 percent of the test pressure. Thus, the maximum operating pressure is usually 30 percent of the bursting pressure. This gives a nominal factor of safety of 3.3, compared with 4.0 for Division 1 of the ASME Pressure Vessel Code. 

Brittle fracture is probably the most insidious type of pressure-vessel failure. Without brittle fracture, a pressure vessel could be pressurized approximately to its ultimate strength before failure. With brittle behavior some vessels have failed well below their design pressures (which are about 25 percent of the theoretical bursting pressures). In order to reduce the possibility of brittle behavior. Division 2 and Sec. Ill require impac t tests. 

Pb as the vessel burst pressure in bars. Other sources are Baker Explosion Hazards and Evaluation, Elsevier, 1983, p. 492) and Chemical Propulsion Information Agency Hazards of Chemical Rockets and Propellants Handbook, voT. 1 NTIS, Virginia, May 1972, pp. 2-56, 2-60). 

The precious metals are many times the cost of the base metals and, therefore, are limited to specialized applications or to those in which process conditions are highly demanding (e.g., where conditions are too corrosive for base metals and temperatures too high for plastics where base metal contamination must be avoided, as in the food and pharmaceutical industries or where plastics cannot be used because of heat transfer requirements and for special applications such as bursting discs in pressure vessels). The physical and mechanical properties of precious metals and their alloys used in process plants are given in Table 3.38. 

The blast pressure, P, at the surface of an exploding pressure vessel is estimated by Prugh (I tSS) with equation 9.1-26 where P, is the pressure at surface of vessel (bara), Pb is the burst... 

Line 1 clears the screen and requests the input of the burst pressure of the vessel. Line 2 sets gamma to 1.4 and the absolute temperature to 300. If your pressure or temperature is different, edit the program Line 3 requests the molecular weight of the gas in the vessel. Lines 5-10 loop to perform the iteration. Line 6 iterates I ... 

These are thin diaphragms held between flanges and calibrated to burst at a specified static inlet pressure. Unlike relief valves, rupture discs cannot reseal when the pressure declines. Once the disc ruptures, any flow into the vessel will exit through the disc, and the disc must be replaced before the pressure vessel can be placed back in service. Rupture discs are manufactured in a variety of materials and with various coatings for concision resistance. 

An old 100-m pressure vessel, a vertical cylinder, designed for a gauge pressure of 5 psi (0.3 bar), was being used to store, at atmospheric pressure, a liquid of flash point 40°C. The fire heated the vessel to above 40°C and ignited the vapor coming out of the vent the fire flashed back into the tank, where an explosion occurred. The vessel burst at the bottom seam, and the entire vessel, except for the base, and contents went into orbit like a rocket [4]. 

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. 

Ninety minutes after the fire started, the sphere burst. Ten out of 12 firemen within 50 m were killed. Men 140 m away were badly burned by a wave of propane that came over the eompound wall. Altogether, 15-18 men were killed (reports differ), and about 80 were injured. The area was abandoned. Flying debris broke tbe legs of an adjacent sphere, w hich fell over. Its relief valve discharged liquid, which added to the fire, and 45 minutes later this sphere burst. Altogether, five spheres and two other pressure vessels burst, and three were damaged. The fire spread to gasoline and fuel oil tanks. 

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. 

If a vessel ruptures as a result of excessive internal pressure, its bursting pressure may be several times greater than its design pressure. However, if the rupture is due to corrosion or mechanical impact, bursting pressure may be lower... 

BLAST EFFECTS OF BLEVEs AND PRESSURE-VESSEL BURSTS... 

This section addresses the effects of BLEVE blasts and pressure vessel bursts. Actually, the blast effect of a BLEVE results not only from rapid evaporation (flashing) of liquid, but also from the expansion of vapor in the vessel s vapor (head) space. In many accidents, head-space vapor expansion probably produces most of the blast effects. Rapid expansion of vapor produces a blast identical to that of other pressure vessel ruptures, and so does flashing liquid. Therefore, it is necessary to calculate blast from pressure vessel mpture in order to calculate a BLEVE blast effect. 

This section first presents literature review on pressure vessel bursts and BLEVEs. Evaluation of energy from BLEVE explosions and pressure vessel bursts is emphasized because this value is the most important parameter in determining blast strength. Next, practical methods for estimating blast strength and duration are presented, followed by a discussion of the accuracy of each method. Example calculations are given in Chapter 9. 

In the following subsections, a selection of the theoretical and experimental work on pressure vessel bursts and BLEVEs will be reviewed. Attention will first be focused on an idealized situation a spherical, massless vessel filled with ideal... 

Free-Air Bursts of Gas-Filled, Massless, Spherical Pressure Vessels... 

Experimental Work. Few experiments measuring the blast from exploding, gas-filled pressure vessels have been reported in the open literature. One was performed by Boyer et al. (1958). They measured the overpressure produced by the burst of a small, glass sphere which was pressurized with gas. 

Pittman (1972) performed five experiments with titanium-alloy pressure vessels which were pressurized with nitrogen until they burst. Two cylindrical tanks burst at approximately 4 MPa, and three spherical tanks burst at approximately 55 MPa. The volume of the tanks ranged from 0.0067 m to 0.170 m. A few years later, Pittman (1976) reported on seven experiments with 0.028-m steel spheres that were pressurized to extremely high pressures with argon until they burst. Nominal burst pressures ranged from 100 MPa to 345 MPa. Experiments were performed just above ground surface. 

The peak overpressure developed immediately after a burst is an important parameter for evaluating pressure vessel explosions. At that instant, waves are generated at the edge of the sphere. The wave system consists of a shock, a contact surface, and rarefaction waves. As this wave system is established, pressure at the contact surface drops from the pressure within the sphere to a pressure within the shock wave. 

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. 

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