Pressurized vessels, rupture

As the previous ehapter discussed nuelear power reactor operation and how to perform a PSA on it, this chapter attempts to apply a similar framework to chemical processing. The problem is the diversity of chemical processing that blurs the focus. This chapter begins by showing that accidents in the chemical process industry cost lives and dollars. Descriptions of deadly chemical accidents arc presented to show the chain of sequences that were involved to suggest how their PSA may be structured. Background on selected hazardous chemical process is presented followed by descriptions of how their PSA have structured. The chapter concludes by applying FTAPSUIT to a pressure vessel rupture analysis. 

Another simple hazard is a pressure vessel rupture due lo over pressure. A steam vessel rupture may scald vorkers and injure them viih shrapnel. Many people died in the last century from boiler explosions. The ves-... 

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. 

At the instant a pressure vessel ruptures, pressure at the contact surface is given by Eq. (6.3.22). The further development of pressure at the contact surface can only be evaluated numerically. However, the actual p-V process can be adequately approximated by the dashed curve in Figure 6.12. In this process, the constant-pressure segment represents irreversible expansion against an equilibrium counterpressure P3 until the gas reaches a volume V3. This is followed by an isentropic expansion to the end-state pressure Pq. For this process, the point (p, V3) is not on the isentrope which emanates from point (p, V,), since the first phase of the expansion process is irreversible. Adamczyk calculates point (p, V3) from the conservation of energy law and finds... 

The ASME pressure vessel rupture stress formula is applied to calculate a vessel stress is S = P(R+0.6t)Et Where ... 

McIntyre, D. Assessment of Fire and Explosion Damage to Chemical Plant Equip-ment/Analyzing Explosions and Pressure Vessel Ruptures. Materials Technology Institute of the Chemical Process Industries, Publication 30, National Association of Corrosion Engineers. 

This means "Boiling Liquid Expanding Vapor Explosion" and characterizes the physical explosion of a liquefied gas/supercritical fluid that is brutally decompressed to atmospheric pressure, in case of pressure vessel rupture or opening. Catastrophic BLEVE occurred when liquefied petroleum gases vessels burst (Mexico, Feyzin,...), followed by the "chemical" explosion due to gas cloud inflammation. In fact, this hazard is directly linked to metal weakening in case of fire around the vessel(s). It is the reason why it is recommended to install fire detectors that could order immediate depressurization of the whole plant in case of fire. 

Most accident sequences lead eventually to Loss of Containment, which usually means either that a pressure vessel ruptures or that a tank overflows. Therefore, Figure 15.29 can be expanded into Figure 15.30. 

During the past 45 years of peaceful use of nuclear energy, no case of a nuclear reactor pressure vessel rupture has occurred. This hypothetical event is not included in the design basis accidents (DBAs) nor, according to the most recent trends, among the severe accidents to be reasonably considered. This is not, as it will be discussed more extensively later, the only possible choice it, however, has been considered acceptable and practicable. 

Pressure vessel ruptured by forklift (external damage forklift not part of system). 

Pressure vessel ruptures because of overpressure from runaway pump (pump part of system). 

This reactor, named LEADIR-PS, (an acronym for LEAD-cooled Integral Reactor, Passively Safe) incorporates the inherent safety features of the Modular High Temperature Gas Cooled Reactor (MHTGR), while avoiding the cost of reactor and steam generator pressure vessels, and the safety concerns regarding pressure vessel rupture. 

Eliminate Severe Accident Scenarios Eliminate real and perceived beyond design basis events for which there are not transparent, inherent or passive solutions. For example, pressure vessel rupture, graphite bum, sodium water/iur reaction. 

Reactor pressure vessel rupture Elimination of longitudinal welds, and reduction of number of other welds, reduce initiating frequency for severe RCPB leaks and ruptures ... 

Remember that the HAZOP guide word and the process condition (flow, pressure, temperature, pH level, etc.) is the process deviation. And the process deviations that most interest us are the ones with hazardous consequences. For example, a node with MORE PRESSURE can lead to pressure vessel rupture, killing plant operators, spilling toxic wastes to the environment, and forcing the rest of the plant to shut down due to losing a critical process. 

Except for a few unusual initiators, such as pressure vessel rupture or an extremely large earthquake, an initiating event must be followed by multiple, additional failures in order for core damage to occur. An important part of current design requirements for U.S. nuclear power plants is the single failure criterion ... 

The MELCOR code has been used within the Chair of Nuclear Technology (Polytechnical University of Madrid) to analyze three accident sequences in a typical W-PWR 900 Mwe 3 loop plant. The study includes (1) An AB sequence initiated by the rupture of the loop including the pressurizer in the cold leg close to the vessel. (2) A V sequence initiated by the rupture, within the auxiliary building, of a low pressure injection pipe connected to the hot leg of the primary circuit. (3) A SGTR sequence initiated by the simultaneous rupture of ten inlet tubes close to the plate. In this presentation emphasis is put on release, transport and revaporization of FP s during the in-vessel phase of the accident up to pressure vessel rupture. 

P. M. Wood, A Study of the Possible Blast Effects from HRT Pressure Vessel Rupture, USAEC Report CF-54-12-100, Oak Ridge National Laboratory, Dec. 14, 1954. 

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