First, the importance of regulating valve fire In the chemical, petroleum and other automation systems, in the event of a fire, if some of the equipment in the system can be promptly cut off the flow of flammable fluid to the fire environment, then you can avoid fire directly from the fire The area spread to the plant area caused by a significant loss. Control valves are an important part of an automation system that is installed on-site to control the flow path so that it is the primary device that cuts off the flow path to prevent the flammable fluid from reaching the fire when it is ignited. It is crucial that it is on or off in the event of a fire. Since the regulator is controlled by the regulator in the control room and is not manually operated, the main features of the fire damper should be: to withstand short-term operation when tempered, or to minimize leakage when it is time to close. Valve fire resistance should be seen as a very desirable performance to consider, hoping to arouse the attention of the personnel concerned. Second, the standard valve fire What kind of valve is the fire valve? Foreign referred to the fire-resistant valve (fire-safe valve), the definition of foreign fire on the valve a lot of non-uniform, this definition is still lacking in the industry clearly defined. To date, there is still no single test or definition that clearly identifies whether a valve is fire proof. Many industrial societies, oil companies, insurance companies, valve manufacturers, and relevant agencies in the United Kingdom and the United States already have various test methods. However, the type of test valve and the main test specifications vary with the test method. The debate over combustion valve tests continues, with some trying to combine two or more methods into one complete method, but still not conclusive. How to accurately define the fire protection valve? This is exactly the problem we are going to study. First, we should study the problem of valve seat standard. Some people think that in the fire will not melt the metal gate valve and globe valve (globe valve) is a fire damper. These valves are designed and constructed to ensure that they are metal-to-metal contact both before and after the fire, thus preventing flammable fluids from entering the fire. However, when the metal seat is operated before the fire, the sealing property is not good. Due to the small amount of leakage, it is also permitted in most fire protection standards that have been developed. Users require the valve in normal operation both good sealing, but also has fire resistance. Many valve manufacturers tried to solve this complex problem as early as 15 to 20 years ago and they have developed a wide variety of "soft" "hard" sealing elements, all of which can hold metal surfaces Seal of contact. Hard seat is made of metal or alloy, itself can withstand high temperatures. The soft seat is made of rubber, plastic or elastic material with a melting point of less than 700 ° C (approx. 370 ° C). The soft seat can be burnt down after a large fire and then relied on system pressure, rotation of the valve plate, spring force or own gravity Keep the metal surface in contact. However, many soft valve seat valve after the fire safety is not satisfactory. If these flexible seat can not be completely burned in the fire, you can not form a metal surface contact. The following table summarizes several combustion tests, including soft valve seat. From the table, it seems that various test standards have different valve test specifications for analysis and comparison, so as to understand which five standards are more stringent. It must be noted that the American Petroleum Institute standard API607 "soft seal ball valve combustion test (1977)" is a tentative standard, it applies to all ball valves under 16 inches. Later, the second version of the standard API RP6F was modified to require more stringent. Valves supplied by different manufacturers may only comply with one or two of the fire safety standards described in the table below. For example, Rockwell's Flameproof Ball Valves and Ball Valves meet only API607 and API RP6F standards Other companies offer valves that meet other standards. Third, the specific measures for regulating valve fire 1, the valve body fire Although some of the valve has a different view of fire resistance, the development of different specifications, test methods are different, but the valve on how to fire should have a more consistent view. For the valve body, it should have the following three points of performance, and to ensure that these three points should take various concrete measures. (1) the smallest internal leakage. In order to ensure this performance, the valve body should first be considered with metal surface contact with the valve seat, in the fire or after the fire, the valve body at high temperatures, regardless of the sealing structure, how the spring force and applied pressure changes, are This should be guaranteed, and should be considered as the key to ensuring its precision closure. (2) the smallest amount of external leakage. In order to minimize external leakage, consider ways to: Use a fire-resistant stem seal material, to avoid the use of larger gasket-type valve body connection. (3) continuous operation. After burning the valve can still work properly, naturally has the ability to resist deformation, a resistance to damage. In order to ensure the body has fire performance, many manufacturers have conducted various attempts. For example, they put a multi-layered felt cover on the valve, made of refractory material and made it separate from the outside. However, these methods are not satisfactory, because the valve should be opened for each maintenance, build on. Same, due to the valve installation location restrictions, this method may not be able to use. Currently, a more satisfactory method is to use a fireproof bag, which can be put in a few minutes, easy to uncover when repaired. The pouch's material contains multiple layers of eramic or fiberglass bundled with nylon and fastened to the unit with vinyl-coated stainless steel wire. In general question, does not need to change the pipe position, the installation space is small, through the experiment in the 2000? Flames combustion 30 minutes, the valve is still not damaged, the performance is satisfactory. 2, the implementing agencies of the fire as the implementing agencies directly control the valve position, so need more careful study. In order to keep the valve closed in time, so easy to fire occasions often choose spring pneumatic diaphragm steel (iron) actuator, the main advantage is the use of low melting point membrane characteristics. In the event of a fire, the spring moves to put the valve in the closed position due to the low melting point of the diaphragm which is rapidly damaged. The use of heat-sensitive fusible hole plugs reduce the pressure in pneumatic systems and are especially suitable for piston-type reciprocating spring actuators. A serious fire can change the characteristics of a metal part, causing the metal to soften and lose its tempering properties, and some of the metal actually melts. The size of the spring force and the tempering characteristics have a direct relationship, the remaining spring force after combustion can maintain the valve position enough, the need for implementing agencies to prove that the combustion test. For butterfly valves, the remaining spring moment is often required after combustion to maintain the closed position of the valve, and the force required to close it seems to be much less than the original output force of the actuator. On ball valve actuators, the residual spring force is important. Under the same pipe pressure, balanced ball valves require less spring force than unbalanced ball valves, so they are used in ballistic applications where a balanced ball valve is preferred. To operate the actuator after it has been burned, the spring must be protected from flame annealing. There are three ways to protect the spring: with insulation, with a sprinkler or with a fire-resistant coating. Including the multi-layer insulation, the use of heat shields or fire bags, so that the normal operation of the actuator half an hour after the fire. However, this trick and sealing method is more cumbersome and inconvenient, taking up a lot of space. The installation of sprinklers on the top of the actuator increased installation and maintenance costs and prevented the water from being supplied to the sprinklers due to frequent water breaks in the event of a fire. The actuator can be coated with a thin layer of epoxy-based material that allows the actuator to function properly. In a combustion test, the actuator survived for 42 minutes due to paint protection despite a fire temperature of 1400-1700 ° C. The test was performed on a 1,600-pound spring-loaded cast iron actuator about 7 feet long with a cylinder bore of 12 inches and was burned with nine propane injection torches. During the entire combustion process, the spring of the actuator reciprocates every minute. The output torque of the spring decreases only 6% after combustion, and is mainly caused by the decrease of bearing accuracy and the increase of friction. Experiments show that the spring is not affected by the combustion flame, the piston and connecting rod seal is still as old, well sealed. After completing the test, immerse the actuator in cold water. Simulation of high temperature shell sudden cooling effect. Tests show that the actuator housing and internal parts are not adversely affected by sudden cooling. The intumescent coating is smeared onto it, just like wiping the cement. When wiping it, it can be done in the field. Take care not to wipe the sealing part, which will make the maintenance inconvenient. When the coating is dry, a hard, impermeable seal is formed. Jamesbury also made plates and boxes in the main parts, which were applied separately so that the plates could be removed during maintenance. If the actuator is an aluminum housing it is difficult to fire even with paint because aluminum has a low melting point (1033 to 1150 ° C) and the part will fail and the valve will not close in hydrocarbon-mixed flames above this melting point. Finally, we will introduce a method of connecting rod protection. Reciprocating spring units are supplied by individual control valve manufacturers. These spring units are in a "stand-by" position, which fires only when caught in a fire and when the valve is fired, moves the valve to a self-contained position. There will also be holding elements that can be used with fusible links, brittle links or electric links. Electric link and fusible link function, can be heated start. In the dangerous moment of fire, these connecting rods are immediately disconnected by the flue gas follower, so that the valve is in a safe position.
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