Overpressure protection general

Selection of Pressure Relief Device - From the range of available pressure rehef valves and other devices, selection is made of the appropriate type for each item of equipment subject to overpressure. Instrumentation, check valves, and similar devices are generally not acceptable as means of overpressure protection. 

Looking beyond the incoming complaints about the valve itself, a lot of installations are just not protected at all. A statistical analysis shows that the pressure relief systems on nearly half of the equipment in the oil, gas and chemical industries lacks adequate overpressure protection as defined by recognized and generally accepted good engineering practices and by the codes, hence the law. 

The rules of Division 3 [3] describe the design, construction, inspection, and overpressure protection of metallic pressure vessels with design pressures generally above 68.95 MPa. 

Containment (Explosion-Pressure-Resistant Design for Maximum Explosion Overpressure) An explosion-resistant construction is understood to mean the possibihty of designing vessels and equipment for the full maximum explosion ove (pressure, which is generally of the order P = 9 bar. The explosion-resistant vessel can then be designed as explosion pressure resistant or explosion pressure shock resistant. This protective measure is generally employed when small vessel volumes need to be protected, such as small filter units, fluidized-bed dryers, cyclones, rotaiy valves, or mill housings. 

Explosion isolation can also be effected by rapid action barrier valves. At present, they can be arranged only in horizontal pipehnes and are suitable, in general, only for streams with a small amount of dust. Such valves are thus frequently used to protect ventilation lines. As a certain explosion overpressure is necessaiy to close such valves, a distinction is made between self-actuated and externally actuated barrier valves (Fig. 26-46). 

In some cases where the ASME Code woidd not require pressure relief protection, the 1.5 Times Design Pressure Rule is apphcable. This rule is stated as follows Equipment may be considered to be adequately protected against overpressure from certain low-probability situations if the pressure does not exceed 1.5 times design pressure. This criterion has been selected since it generally does not exceed yield stress, and most Ukety would not occur more frequently than a hydrostatic test. Thus, it will protect against the possibility of a catastrophic failure. This rule is applied in special situations which have a low probability of occurrence but which cannot be completely ruled out. 

First, we need to define generally what we are talking about A pressure relief device is any device that can purge a system from an overpressure condition. More particularly, an SRV is a pressure relief device that is self-actuated, and whose primary purpose is the protection of life and equipment. Through a controlled discharge of a required (rated) amount of fluid at a predetermined pressure, an SRV must prevent overpressure in pressurized vessels and systems, and it operates within limits which are determined by international codes. An SRV is often the final control device in the prevention of accidents or explosions caused by overpressure... 

The second level, i.e. the general protection stage provides the whole steam generator isolation and its drying out on the water side, as well as protection of the secondary circuit against overpressure. 

The United States Environmental Protection Agency (EPA) provides lookup tables and simple equations for some of the commoner chemicals to calculate the distance of the overpressure waves. These tables are generally conservative, i.e., they predict greater impact than would be likely to actually occur. Nevertheless, they do provide a useful starting point. 

Moreover, a specific study to generalize the protection of the primary circuit against overpressurization caused by inadvertent operation of the high pressure injection pumps (TQ n3) and high pressure boron injection pumps (TQ n4) is underway. 

Blocked-outlet pressure protection may be required because of overpressure by pumps or compressors. The following general guidelines should be used to establish the protection requirement and contingency ... 

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