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All About Fire Safety Valves temperature-resistant properties, further restrict leakage in conjunction with a blow-out-proof anti-static stem, so that the flammable fluid stays separate from the heat source that may ignite it.
A fire-safe valve may also be made up of four main mechanisms: a spring pack, a trigger assembly, mounting hardware, and a fusible link. The components work in unison to close the valve should a fire be detected within a facility. The fusible link is the key part of the assembly. It keeps the valve open by maintaining tension on a spring pack through the trigger assembly. When a fire breaks out, the fusible link separates once it is heated to a certain high temperature, which releases the spring pack and allows it to close the valve.
A fire-safety valve with fusible links has a primary drop-tight seat, usually made of TFE, along with a second seat made of metal for isolation in a fire. The secondary seat also has graphite seals for further protection. This means that the shut-off valves can be paired with any quarter-turn ball valve, butterfly valve, or fire ball valve.
Summary
This article presents an understanding of fire safety valves. For more information on related products, consult our other guides or visit the Thomas Supplier Discovery Platform to locate potential sources of supply or view details on specific products.
The definition of a fire-safe valve has more than one answer since different standards exist for such valves. The major standards are presented in this article and their criteria discussed as an aid in specifying these devices. Fire-safety standards for equipment used in the chemical process industries (CPI) are critical however no single test for fire-safe valves has been developed that covers all of CPI. Since all fires are not alike, safety precautions should not all be the same for all situations. This article attempts to answer such questions as whether the refining industry's standards cover fire hazards posed by media and processes specific to the rest of the CPI and which criteria come closest to providing proper guidelines for choosing a fire-safe valve for non-oilrefining service.
The effectiveness of fire air release valve has been investigated when offshore process equipment is exposed to a fire. Simulations of several typical offshore pressure vessels have been performed using the commercial software VessFire. The pressure vessels are exposed to a small jet fire, large jet fire, and a pool fire on both the wetted and unwetted part of the vessels. Rupture times of the vessels are calculated by comparing the pressure in the vessel with the tensile strength of the material. Rupture times are then compared for the vessels, with and without a PSV, in order to see the effect of the installed PSV. It is found that when a fire affects the unwetted part of a vessel, the PSV offers only minor or no additional protection. When a fire affects the wetted part of a vessel, the PSV relieve the inventory as designed. It is argued that PSVs provide insufficient fire protection for typical offshore fire scenarios and that Blowdown Valves and Passive Fire Protection should be considered as alternatives.
In order to protect process equipment from a possible overpressure scenario a PSV is installed as a mechanical barrier. Often, when other credible over-pressure scenarios such as process upsets are ruled out, either due to the vessel in question being protected from over-pressure by upstream or downstream equipment, and/or the design of the vessel is to full pressure spec, the remaining credible scenario is a fire case. This is according to normal industry practice and according to code (API Standard 521, 2014, API Standard 14C, 2007). It is the authors’ experience that many vessels are equipped with a fire PSV as the main/only relief case. The main concern is that a pressure vessel exposed to a fire may cause a Boiling Liquid Expanding Vapor Explosion (BLEVE) upon rupture, leading to a significant escalation in consequences. The BLEVE scenario is relevant for vessels carrying significant components of light volatile liquid hydrocarbons such as separators and not for vessels only containing gas or non-volatile liquids. Standards such as API 521 (API Standard 521, 2014) (ISO 23251) and API 14C (API Standard 14C, 2007) (ISO 10418) discuss the requirement for PSVs for fire protection and how to size such PSVs. The use of fire PSVs, in accordance with API 521, has been developed for pool fires on onshore refineries. However, on offshore oil and gas installation a more likely fire scenario will often be that of a jet fire. According to API 521 fire PSVs do not offer proper protection against jet fire, but other measures such as shutting down the jet fire source and depressurizing process inventories should be considered the primary protection against a jet fire. Pool fire heat loads applied in API 521 for offshore applications have also been questioned (VESSFIRE, 2003). Even in the case of pool fire a fire PSV may not provide adequate protection in accordance with API 521 if the pool fire exposes the unwetted part of the pressure vessel. Despite this, fire PSVs are often installed on offshore oil and gas installations to protect even completely gas filled pressure vessels.
Installing safety equipment such as a PSV that does not provide any or insignificant protections represent a significant lifecycle cost and it may also increase risk of operating the offshore installation as well as provide a false sense of security. The PSV will require testing, inspection and maintenance which will expose personnel to hazards, the PSV will be a source of potential leakage, and human errors in connection with the PSV can lead to increased risk of failure. In fact, there have been numerous examples in the offshore oil and gas industry wh
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