Regarding safety valves

General rules for selecting safety valves: 1) The \"nominal diameter\" of the safety valve shall be determined through calculations such that its discharge capacity is ≥ the safe relief capacity of the pressure vessel. 2) Determine the pressure rating of the safety valve based on the design pressure and design temperature of the pressure vessel. 3) Steam boilers or steam pipes generally use unenclosed, full-opening safety valves with wrenches. For safety valves used for steam with a starting pressure greater than 3 MPa, or for gases with a temperature exceeding 320°C, a model equipped with a radiator (fins) should be selected. 4) Hot water boilers generally use unclosed, wrench-operated slightly open safety valves. 5) For non-hazardous media such as air, hot water above 60°C, or steam, a safety valve equipped with a wrench should be used. 6) For incompressible media such as water and other liquids, closed, slightly-opening safety valves or safety relief valves are generally used. 7) For high-pressure feed water, closed full-opening safety valves are generally used, such as in high-pressure feed water heaters and heat exchangers. 8) Compressible media such as gases generally use closed full-opening safety valves, such as in gas storage tanks and gas pipelines. 9) Pulse-type safety valves are generally used in large-diameter, high-flow-rate, and high-pressure systems, such as desuperheaters and pressure reducers, power plant boilers, etc. 10) For flammable media with extremely or highly hazardous toxicity, closed safety valves must be used; if a valve equipped with a lifting mechanism is required, then a closed safety valve fitted with a wrench should be employed. 11) In cases where the safety valve may be subjected to a varying back pressure, with the variation exceeding 10% of the set pressure, or in toxic and flammable containers or piping systems, a safety valve equipped with a bellows should be selected. 12) For systems operating under negative pressure or that may generate negative pressure during operation, vacuum negative-pressure safety valves are generally used. 13) For systems with a low freezing point of the medium, insulated jacketed safety valves are generally used. 14) Tank cars, road tankers, and storage tanks used for transporting liquefied gas should be equipped with internal safety valves. 15) Hydraulic safety valves are generally used on the top of oil tanks, and they need to be used in conjunction with breather valves. 16) Pilot-operated safety valves are generally used for underground drainage or gas pipelines. 17) A safety return valve is generally used on the liquid-phase return pipeline at the outlet of the tank pump in LPG stations. 18) Select an appropriate safety valve material based on the medium properties. For media containing ammonia, copper or copper-containing safety valves must not be used ； Acetylene cannot use safety valves made of copper containing 70% copper or red copper. 19) For conditions with high discharge rates, a fully open type should be selected ； For operating conditions with stable working pressure and low discharge volume, a slightly open-type valve is recommended ； For conditions involving high pressure and large discharge volumes, a non-direct-acting type, such as a pulse safety valve, is recommended. For containers with a length of more than 6 meters, two or more safety valves should be installed. 20) For Class E steam boilers or fixed containers with a low operating pressure Pw, static weight-type (pressure cookers) or lever-weight type safety valves can be used. Mobile equipment should be equipped with spring-loaded safety valves. 21) For media that are viscous and prone to clogging, it is advisable to use a series combination of a safety valve and a rupture disc as the relief device. 22) The spring operating pressure rating is selected based on the nominal pressure of the safety valve. Relationship between the nominal pressure of a safety valve and the spring operating pressure.

The operating conditions are similar for those with and without a wrench; the handle is used for manual pressure release in emergency situations. There are no special requirements regarding hydrogen, and 2Cr13+PTFE is generally used for the valve disc

For the safety valves in hydrogen pipelines, it is necessary to consider the material of the valve’s internal components; for example, 416SST is not a suitable choice. Additionally, the flow rate must be taken into account, with the flow rate generally should not exceed 0.3 Mach

Hydrogen is considered a flammable and explosive medium; therefore, a closed-type safety valve should be used.

Great stuff, study hard*:lol

Fully open safety valves are generally used for gas and steam media； For liquids, fully open and slightly open types can be chosen ；

Should a burst disc be installed below the safety valve? And does the safety valve need to have a bypass circuit?

May I ask, regarding closed-type systems: in what situations should an open-type system be chosen? Is it true that open-type systems are used only for harmless gases, vapors, and steam? Is a harmless liquid okay?