Pressure vessel failures

Failures of pressure vessels are veiy rare. Many of those that have been reported occurred during pressure test or were cracks detected during routine examination. Major failures leading to serious leaks are hard to find. 

Low-pressure storage tanks are much more fragile than pressure vessels. They are therefore more easily damaged. Some failures are described in Chapter 5. 

A few vessel failures and near-failures are described next—to show that they can occur. Failures of vessels as a result of exposure to fire are described in Section 8.1. 

1 Failures (and Near-Failures) Preventable by Better Design or Construction 

The multiwall vessel was made from an inner shell and 11 layers of wrapping, each drilled with a weep hole. The disintegration was attributed to excessive stresses near a nozzle. These had not been recognized when the vessel was designed. 

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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. 

Pressure Vessel Failure Statistics and Probabilities Nuclear 4 tables containing failure data for vessels Primarily concerned with boiler failures 113. 

This report summarizes data on non-nuclear pressure vessel failures in order to develop data which could be applied to the nuclear power industry. Tables 3 through 6 present summaries of vessel failures and failure rates. 

Transmission and Gathering Lines—1970 through June 1984. Pressure Vessel Failure Statistics and Probabilities. 4.7-21... 

A physical explosion, for example, a boiler explosion, a pressure vessel failure, or a BLEVE (Boiling Liquid Expanding Vapor Explosion), is not necessarily caused by a chemical reaction. Chemical explosions are characterized as detonations, deflagrations, and thermal explosions. In the case of a detonation or deflagration (e.g., explosive burning), a reaction front is present that proceeds through the material. A detonation proceeds by a shock wave with a velocity exceeding the speed of sound in the unreacted material. A... 

Arulanantham and Lees (1981) have studied pressure vessel failures in process plants such as olefins plants. They define failure as a condition in which a crack, leak or other defect has developed in the equipment to the extent that repair or replacement is required, a definition which includes some of the potentially dangerous as well as all catastrophic failures. In olefins plants fired heaters have failure rates of about 0.4 failures/year, while process pressure vessels have 0.0025 failures/year and heat exchangers 0.0015 failures/year. It is noticed that fired heaters are much unsafer than process pressure vessels, which are a little unsafer than heat exchangers. 

Accumulation of water, certain vapors, and other materials can damage paint and promote corrosion. Undetected corrosion has led to building collapse, pressure vessel failure, mechanical linkage separation, and electrical breakdown. 

It was fairly evident from a study of the service failures that these steels were abnormally sensitive to stress-raising geometries, but a quantitative assessment of this characteristic was lacking. So long as this condition prevailed, any incentive to use the higher strength Q T steels was overshadowed by the possibility of a major pressure vessel failure in refinery service. 

The foregoing supplemental requirements are not of an anticipatory nature. Each is based on a significant number of actual pressure vessel failures. 

Certain other supplementary requirements, of which there are many, are anticipatory in that they are aimed at eliminating foreseeable causes for pressure vessel failures. Others are directed at such things as keeping maintenance costs and service factors within reasonable ranges. 

Schleyer GK. Predicting the effects of blast loading arising from a pressure vessel failure a review. Proc Inst Mech Eng Part E J Process Mech Eng 2004 218(4) 181—90. 

Pressure vessel failure in particles with defective or missing coating layers. 

Pressure vessel failure in standard particles, i.e., particles without manufacturing defects. 

At each reload, the fuel failure fraction in the core decreases due to the replacement of the oldest one half of the fuel in the core with fresh fuel. The results indicated that the predicted fuel particle failure due to temperature effects was very small even at the high temperature points (at the outer boundary of the active core in the proximity of the control rods) since such high fuel temperatures are maintained for only short periods of time. The predicted pressure vessel failure was negligible. Thus, the overall particle failure was predicted to be caused by manufacturing defects, primarily by particles with missing buffer layers. 

Control power produced per particle. Control pressure vessel failure. 

Many items are inherently very reliable, so it is difficult to develop a large database for events such as pressure vessel failure. 

An analysis should also be carried out to determine how the containment basemat might fail as a result of the molten core-concrete interaction which would occur after pressure vessel failure. Estimates should be made of the conditional probability of basemat failure as a function of the residual heat level and the coohng available to the molten material. Special care should be taken when the basemat of the containment has additional compartments above so that penetration of the basemat could lead to a radioactive release via unfiltered pathways. 

Table 7.9. Element inventory of the structural and control rod materials of a BOOM We PWR and fractions vaporized prior to reactor pressure vessel failure (linear extrapolation of measured Sascha results)...

Engineers and scientists may now understand the mechanisms of pressure vessel failures, and have the tools and techniques for monitoring for cracks and preventing corrosion, but it still requires a great deal of vigilance to ensure that their integrity is maintained. 

Two major hazards may occur from high pressure vessel failures. The vessel itself may rupture and the formation of vapor cloud as a result of the rupture is possible. If the vessel ruptures, it will produce flying projectiles and usually release large quantities of vapors, and in the case of most hydrocarbons are combustible.The projectiles could harm individuals or damage the process facility, possibly increasing the incident proportions. Secondly, the release of a combustible gas from a pressurized vessel may cause the formation of combustible vapor cloud, which if a suitable amount of congestion is present or some turbulence of the cloud occurs, an explosive blast may result once the cloud contacts an ignition source. 

The main causes of large fires and explosions in oil industries are release or overflow of flammable liquid or gas, overheating or hot surfaces, fitting or pipe failure, electrical breakdown, and overpressure or pressure vessel failure, explosion in equpment chemical reaction, and inappropriate operation (Khan Abbasi, 1999). 

In the Seventies huge efforts have been made to provide the nuclear and chemical engineers with a credible set of data on pressure vessels failure frequencies and modes. In an article by Bush (1988), the historical studies, conducted in previous decades at three major industrial countries, USA, UK and Germany, are reviewed and compared in a critical way. In the review eight national studies on pressure vessels are reported in detail. In each study, 10.000 to 100.000 pieces of equipment were observed for ten years and more. Those studies consider, as a whole, 3 million years-vessel (both fired and unfired) with some 8.600 minor faults and 155 major events. In following decades the world of pressure equipment changed dramatically, because the new steels alloys introduced in the years, the new certification rules introduced by the PED Directive in 1998, the new design and production techniques, the new inspection and maintenance... 

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