Does high temperature affect the setting pressure of a safety valve?

The ambient temperature only affects the pressure of the medium inside a sealed container, and the extent of this influence varies depending on the medium. Storage tanks for liquefied gas and similar substances often experience overpressure due to rising temperatures; therefore, water spray systems for cooling must be installed ； There have also been cases where oil leakage occurred due to increased pressure resulting from temperature changes, which caused damage to gaskets or smooth blind flanges; this requires special attention from chemical engineers and operators.

High temperatures cause materials to expand thermally, leading to leaks, which in turn affects the launch pressure! 1 I think it’s best to pay attention and check!

High temperatures can affect the setting pressure of safety valves. This requires considering how to select the safety valve. Safety valves are divided into ordinary spring-loaded safety valves and pilot-operated safety valves; I will share my understanding of spring-loaded safety valves. The opening pressure of a safety valve is set by the degree of compression of the spring (ignoring for now the effect of back pressure on this opening pressure). The elastic coefficient of the spring is one of its physical properties, and this coefficient is affected by temperature; higher temperatures reduce the elastic coefficient, which in turn lowers the opening pressure of the safety valve, leading to its premature activation. Therefore, in high-temperature operating conditions, safety valves need to be equipped with thermal isolation devices, such as insulating sleeves placed between the valve cap and the valve body, or heat sinks. Low-temperature operating conditions also need to be considered in this way, but there are certain differences.

Generally, for spring-loaded safety valves, the impact of high temperatures must be taken into account. Affected by heat conduction, the temperature of the safety valve body and spring during operation is generally much higher than the ambient temperature; this causes the elastic coefficient of the spring to change (decrease), resulting in a lower opening pressure. Generally, such safety valves have one parameter: the cold set tripping pressure. It is obtained by requiring parameters such as the starting pressure/operating temperature and those of the valve body itself. The cold-set start pressure is higher than the required start pressure.

When a safety valve operates at high temperatures, the spring stiffness decreases, resulting in a lower opening pressure. Therefore, when testing safety valves in a cold state, the effect of temperature on the set pressure must be taken into account, and necessary adjustments to the set pressure should be made.