【Haichuan Chemical Valve Knowledge】What is the purpose of valve fire resistance testing?

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What is the purpose of valve fire resistance testing? In high-risk industrial sectors such as petrochemicals, natural gas transmission, and offshore platforms, valves serve as critical equipment for medium control. Their reliability in fire environments directly affects the escalation of accidents and the effectiveness of system isolation. In the event of a fire, if the valves experience through-leakage or become stuck due to high temperatures, they can serve as pathways for the continuous release of fueling substances, leading to an out-of-control fire situation. Therefore, fire testing based on standardized procedures is the key method to verify whether a valve can maintain basic sealing and operational capabilities in a fire scenario. The engineering logic behind fire resistance testing is to simulate the extreme conditions that occur when valves lose their non-metallic seals in typical industrial fires. Existing mainstream standards such as ISO 10497, API 607, and API 6FA differ slightly in terms of specific loading conditions, but their testing frameworks are highly similar: water or nitrogen at rated pressure is used as the medium, the valve is placed in a controllably burning environment, and it undergoes five stages – heating, holding, extinguishing, cooling, and operational verification. During the heating phase, it is required that the flame cover the valve body, valve cover, and end-face connection areas, so that the wall temperature of the valve body reaches a range of approximately 650–980°C within a specified time period, and this temperature is maintained for at least 30 minutes. This process is intended to cause soft sealing materials such as polytetrafluoroethylene and nylon to carbonize and become ineffective, relying solely on the metal-to-metal secondary seal to maintain the system airtight. The technical challenges are mainly reflected in two aspects. The first is the maintenance of high-temperature sealing. During a fire, due to differences in thermal expansion coefficients and reduced material strength between the valve seat and the valve core, as well as between the packing and the valve stem, the original clearance between these components undergoes significant changes. The design must incorporate structures such as surfacing with Stellite alloy or a nickel-based hard layer, or the use of wavy spring washers, to ensure that after the soft seal is burned out, the metal sealing surface can still provide sufficient specific pressure. The second is structural integrity under cooling water impact. After the flame heating is completed, test standards typically require immediate spray cooling of the valve to simulate the thermal stress cycles generated by the activation of a fire suppression system. The casing, connecting bolts, and welds must not exhibit peeling, cracking, or a sudden drop in pressure. Leakage determination is the core output indicator of the test. During heating, a limited amount of flame or steam emission from the packing area or flange gasket due to the combustion of organic components is permitted; however, the rate thereof must be kept within strict thresholds, which typically range from 10–200 mL/min, depending on the valve size and pressure rating. After the spraying is complete, wait until the valve has cooled to room temperature, and then conduct an internal leakage test in accordance with the procedures; the leakage rate at the valve seat seal must not exceed the allowable value for soft-sealed valves at room temperature as specified in the standards. Additionally, operational performance tests are equally crucial: before heating, during heating (if operation is required), and after cooling, the valve must be able to complete a full opening-to-closing cycle via manual or power actuation. The operating torque must not significantly exceed the rated value at normal temperature, and there should be no seizing or stem breakage. From an engineering perspective, fire resistance testing is not merely a simple \"burning test\"; it represents a comprehensive evaluation of the suitability of valve materials, the design of thermal gaps, the redundancy of sealing mechanisms, and the valve’s resistance to jamming. Common failure modes of valves that fail the test include: thermal seizure between the valve stem and the stuffing box, excessive leakage caused by ovalization of the metal sealing surface of the valve seat, and the inability of bolt preload to resist internal pressure during the cooling phase after relaxation at high temperatures. Therefore, successful fireproof test valves are often specially optimized in terms of hard-seal structure, valve stem guidance clearance control, and high-temperature lubrication treatment. It is important to note that passing fire tests and obtaining type certification does not mean that the valve is suitable for all high-temperature operating conditions. The test represents a typical short-lived, extreme, and fixed fire scenario, whereas real fires may be accompanied by mechanical shocks, uneven heating, or prolonged thermal radiation. Therefore, when selecting a valve, in addition to checking the fire test certificates, it is also necessary to evaluate its long-term creep and thermal cycling fatigue behavior within the operating temperature range. Overall, fire testing provides a final controllable barrier for valves in the rare but deadly scenario of a fire, and it is an essential equipment verification step that cannot be omitted in the safety management of high-risk processes.