Failures in Pressure Vessels

Material—Improper selection of material defects in material. 

Design—Incorrect design data inaccurate or incorrect design methods inadequate shop testing. 

Fabrication—Poor quality control improper or insufficient fabrication procedures including welding heat treatment or forming methods. 

Service—Change of service condition by the user inexperienced operations or maintenance personnel upset conditions. Some types of service which require special attention both for selection of material, design details, and fabrication methods are as follows  

Elastic deformation—Elastic instability or elastic buckling, must be evaluated by considering vessel geometry, stiffness as well as properties of materials. 

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Figure 15.13 Cracking in weld deposit caused by lamination in steel base metal. (Reprinted with permission from Helmut Thielsch, Defects and Failures in Pressure Vessels and Piping, New York, Van Nostrand Reinhold, 1965.)...

Thielsch, H., Defects and Failures in Pressure Vessels and Piping, Reinhold Publishing Corp., New York, 1965. 

Design Philosopliy, 1 Stress Analysis, I Stress/Failure Theories, 2 Failures in Pressure Vessels, 5 lx)adings, 6 Stress, 7... 

Welded structures often have to be tested nondestructively, particularly for critical application where weld failure can he catastrophic, such as in pressure vessels, load-bearing structural members, and power plants. 

Baum, M. R. 1987. Disruptive failure of pressure vessels preliminary design guide lines for fragment velocity and the extent of the hazard zone. In Advances in Impact, Blast Ballistics, arui Dynamic Analysis of Structures. ASME PVP. 124. New York ASME. 

The maximum shear stress theory has been found to be suitable for predicting the failure of ductile materials under complex loading and is the criterion normally used in pressure vessel design. 

There has been a conspicuous number of in-service failures of pressure vessels built of certain steels having h her strengths obtained by quenching and tempering. Most of these failures originated in geometric details that had been used for decades w ith conventional steels without similar difficulties. 

In the design and evaluation of nuclear power plants, internally generated missiles arising from PIEs (such as the failure of pressure vessels and pipes, the failure of valves, the ejection of a control rod and the failure of high speed rotating equipment) should be considered. The potential for secondary missiles should also be evaluated. Measures to prevent the initiation of internally generated missiles should be undertaken if such measures are practicable. 

Fatigue has been recognized as a major failure mode in pressure vessels, and specific rules for its prevention appear in design codes. Stated simply, fatigue failure is caused by the cyclic action of loads and thermal conditions. In many design situations, the expected number of cycles is in millions and for all practical purposes can be considered as infinite. Accordingly, the concept of endurance limit has been employed in a number of design rules. 

The hazards related to the catastrophic failure of pressure vessels due to unsafe construction are recognized by the oil and gas industry (upstream and downstream) and by the petrochemical and refining industries. This hazard is the same whether the pressru-e vessel is used for exploration and production or is used in a refinery/chemical plant. To control the hazards related to the catastrophic failure of pressure vessels, employers must assure the mechanical integrity of their pressure vessels. One feasible means of abating this hazard would be to construct pressure vessels to Code requirements, [end of LOI]... 

To model the failure of pressure vessels, we must first differentiate between brittle fracture and ductile failure. The easiest way to do this is to think of the child s toy called Potty Putty or Silly Putty. If this material is pulled slowly, it will stretch to tens of times its original length before it breaks (ductile failure). However, if it is pulled sharply, it snaps with hardly any stretching (brittle fracture). In the right circumstances, metal components can also fail in either a plastic or brittle manner. 

For each scenario, possible release types for example pipe rupture, formation of holes in pressurized vessels, major or catastrophic failure etc. were identified which can cause in high loss of life in the surroundings. To ensure that the method remains workable, we propose that a select number of credible accident scenarios per industry, which may lead to potential offsite consequences, be considered. 

Very rare events include failure of pressure vessels (e.g. pressurizer and steam generator shell), failure of structural supports and turbine break-up. Pressure vessel and structural failures are precluded in the design by use ol)for example, the appropriate level of design and manufacturing codes and standards, quality assurance and in-service inspection. Again, safety analysis is not required. 

Cumulative Damage. Pressure vessels may be subjected to a variety of stress cycles during service some of these cycles have ampHtudes below the fatigue (endurance) limit of the material and some have ampHtudes various amounts above it. The simplest and most commonly used method for evaluating the cumulative effect of these various cycles is a linear damage relationship in which it is assumed that, if cycles would produce failure at a... 

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. 

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