Issues with the diaphragm material of pressure transmitters and self-acting control valves
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I have two questions for everyone: 1. In coal chemical plants, the gas contains about 50% hydrogen, the temperature is at room temperature, and the pressure is around 4 Mpa. Can a diaphragm made of 316L be used for the pressure transmitter? Under what levels of pressure, temperature, and hydrogen concentration must the issue of pressure-sensitive diaphragm materials be considered? 2. Is a self-acting control valve suitable for reducing the pressure of the aforementioned gases? (Primarily for safety reasons: in the event of a failure, the pressure-regulating stand-alone control valve located downstream of the valve remains in the fully open position, allowing high-pressure gas to flow into the low-pressure area.) Also, in the event that the diaphragm ages and gets damaged, hydrogen and gas will leak out of the diaphragm chamber – is this safe? Can self-acting control valves be used in environments with flammable and toxic gases? ）
1. Suitability of 316L material for pressure transmitter diaphragms in hydrogen: 316L possesses good corrosion resistance and mechanical properties, as well as a relatively strong resistance to hydrogen embrittlement; it can be used under conditions of 50% hydrogen concentration, room temperature, and a pressure of 4 MPa. However, when the hydrogen concentration is higher, the pressure exceeds 5 MPa, or the temperature rises significantly, it may be necessary to consider using higher-grade hydrogen-resistant materials such as Hastelloy or titanium alloys. 2. Safety issues associated with using self-acting control valves for pressure reduction: Self-acting control valves generally do not require an external power source and are suitable for automatically regulating system pressure. However, in a high-pressure gas environment, there is a safety risk once the diaphragm of the control valve ages or gets damaged, as such damage can lead to high-pressure gas leaking into low-pressure areas. Given that gases are flammable and toxic, it is recommended to consider using safer control solutions in such applications, such as electric or pneumatic control valves, along with appropriate safety devices like pressure relief valves or emergency shut-off valves, to ensure the safe operation of the system. In short, when selecting materials and equipment, it is essential to fully consider the safety requirements and durability under specific operating conditions. In situations involving flammable and toxic gases, safety must always come first. .
1. The factors affecting hydrogen permeation are numerous; the main considerations include temperature, pressure, hydrogen concentration, and whether the medium is humid. If the medium is relatively dry and the temperature is normal, 316L should not present any problems. Plating the diaphragm with gold simply serves to extend the lifespan of the instrument and improve its reliability; if this instrument is important, considering gold-plated diaphragms is a good option. The reliability of self-acting valves is lower than that of control valves; if there are safety concerns, it is recommended to replace them with control valves.