Applicable scope. Such as: ball valve, butterfly valve, plug valve. The following valve units are not covered by this standard:. In addition to the manual transmission box or other similar mechanism when they become part of the usual valve device outside the transmission such as: electric, pneumatic, hydraulic fire test requirements. Specification for Fire Test for Valves. Such as: ball valve, gate valve, plug valve.
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Because so many of the applications where valves are used are sensitive to the danger of fire and explosion, fire testing is a critical part of the process of designing the right valves.
Much has occurred in the world of fire testing standards over the last years. Fire test standards for valves date back to the s, but many important standards developments have occurred since the s.
For that reason, this article begins with that decade, and takes us to the present day—the latest published and in-committee revisions of the American Petroleum Institute API fire test standards.
Exxon has always been an industry leader in developing and requiring fire testing of valves. The company had one of the earliest fire test standards—an infamous process that required a valve to be pressurized with kerosene and burned for 30 minutes.
The requirement was that flames from an external leak could not exceed a certain distance from the valve body. Needless to say, the test itself was hazardous to those who performed it. Fueled no pun intended by safety and insurance requirements, fire-tested valve designs became mandatory. When the fourth edition of API was released in , Exxon dropped its requirement for its own standard and accepted valves qualified to API All the API test standards specify a minute burn period, which was determined early on to be the maximum amount of time that a facility on fire might possibly be saved.
The innovation of this edition was that it was the first to require that soft-seated valves be tested at lower pressures. The low pressure causes difficulty during a fire test through leakage, since there is less pressure on the ball to force it into the remaining softened downstream seat or create a sufficient metal-to-metal sealing contact.
After cooldown, the valve is cycled open and closed with an additional low pressure through-leakage test performed. This proved to be a difficult test for soft-seated ball valves. Charred or melted polymer material left on the sealing surfaces could create a leak path. Experience also has shown that for ball valves, those that are intermediate sizes 3—4 inches often have the most difficulty in this regard. For 2-inch and smaller valves, sufficient heat during the test will completely burn the polymer seat material.
For 6-inch and larger valves, enough seat material remains to maintain a good seal. The 3—4-inch valves, however, often burn their seats partially, with what is closest to the burners removed the most and those on the opposite side the least. Because of this, bits of the remaining seat material can lodge between the ball and body during the operational test. Exxon also used the fourth edition in as a basis for a gasket fire test. Three changes occurred with the fifth edition of API , which was released in The second, fairly significant technical change was that the through-leakage measurement after the cooldown period occurred before cycling the valve.
This made the test a little easier to pass since the primary sealing member was not moved from its seated position. The sixth and seventh editions went through mostly editorial changes. An emphasis was added that cavity pressure in dual-seated valves should be measured, and that the tests ended if the maximum allowable cavity pressures specified by the manufacturer were exceeded during the test.
Specifying the maximum allowable cavity pressure became the burden of the valve manufacturer. Another difficulty in designing a self-relieving seat for this circumstance is that the 30 psig test pressure has little influence on moving the ball downstream. As a result, when cavity pressure builds and both seats are almost equally loaded, the direction the pressure will go is unpredictable.
Cavity pressure relieving downstream will often create a leak path that cannot be remedied. While cavity pressures greater than 10 times the valve pressure rating have been observed during fire tests, the seventh edition limits the allowable pressure to one-and-a-half times the valve rating or a pressure obtained from the manufacturer from hydrostatic testing.
Cavity taps need to be installed by the valve manufacturer before the valve is tested. API 6FA is currently in committee for its fourth edition.
The third edition has been in place since The test parameters are similar to API for non-soft-seated valves, with the major difference in the operational test procedure after the cooldown period. API 6FA is most commonly used for metal-seated products, including ball, gate and globe valves.
While the majority of these valves do pass this test, some designs fail miserably. Leakage can slow as the temperatures equalize, but not after failure in most circumstances. Actuator qualifications are not part of API 6FA or , although when the actuator is part of the valve assembly, it is engulfed in flames during the burn.
Actuators are required to sufficiently activate the valve during the operation test. The latest edition of API states that removal of the grease from inside the gearbox is allowed, which reduces some hazard of flaming grease dripping or spraying out of gearboxes during a test. The fourth edition is due out in the current year.
Some of the changes under consideration involve adding cavity pressure requirements, specifying a cool-down period and expanding on the qualification criteria for various body and seal materials. After the cooldown period, a valve in 6FA is operated open and closed. For a check valve, the flow is reversed at this stage to verify the operation of the check valve. Figure 1.
API 6FB states that it is the test standard for end connections, so a variety of products can be tested to this standard. The standard has the option for on-shore and off-shore tests both with a bending moment applied and without. The bending moment option is not a common request, however. The temperature differences of each option are shown in Table 1. Figure 2. Besides flange gaskets, API 6FB is also the primary fire test standard for various end connections and fittings. The off-shore option is specifically vital for drilling rig and platform equipment Figure 3.
Figure 3. API 6FB is the dominant test standard for testing flange gaskets used in upstream, midstream and downstream applications. Before this existed, the Exxon-modified API fourth edition test was the leading standard for testing flange gaskets Figure 4. The test setup required millions of BTUs per hour to achieve those temperatures. Figure 4. Exxon-modified API gasket fire test. Changes to the scaling of qualifications for gasket sizes and pressure ratings will be addressed.
API was first released in , with the second edition released in The more common test standard for packing at this time is a modified version of API The test can be run on a gate valve, typically 4- or 6-inch Class carbon steel wedge, with the valve partially open during the burn and the downstream pipe closed. Allowable external leakage requirements are used. With recent attention on stem packing for fugitive emissions, it may be in the best interest of the industry to reactivate API Fugitive emission performance of graphite stem packing is often enhanced with the addition of lower melting point materials.
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API SPEC 6FD
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API 6FD - Specification for Fire Test for Check Valves - 95
Specification for Fire Test for Check Valves. Envimnmentdl Partnership. Licensed by Information Handling Services. American Petroleum Institute. Washington, D.
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