Weekly Topic: Selection of operating conditions during valve pressure testing (Pressure testing of high-temperature valves?) ）

1. Test pressure: The strength test pressure specified in almost all codes is 1.5 times the nominal pressure. However, in most specifications (of the SH JB category), the pressure for the high-pressure sealing test is 1.1 times the nominal pressure, whereas in GB50235 it is 1.0 times the nominal pressure. 2. Holding time: Some standards (GB50235) require a holding time of 5 minutes, while others (SH) specify a holding time of 60 to 120 seconds. Generally, a pressure holding time of 5 minutes is adopted, and most petrochemical plants require compliance with SH-class specifications. 3. Test items: In our construction work, for any type of valve, strength and high-pressure sealing tests are usually carried out (since most valves do not have a sealing structure). The tests that must be performed are the strength test and the low-pressure sealing test; high-pressure sealing testing is optional.

Reply to 1# Chuan Nao Liao Kun: It is best not to conduct random inspections on high-temperature valves; instead, each one should be tested for pressure resistance. A medium with strong permeability, such as kerosene, is suitable for these pressure tests. Installation can only take place after the valves pass the tests； The strength test pressure for valves is 1.5 times the valve’s nominal pressure, while the tightness test pressure is equal to the valve’s nominal pressure. The test duration is less than 5 minutes; the valve is considered qualified if there is no leakage from the housing or packing.

Reply to 1# Chuan Nao Liao Kun: 1. Test pressure: The strength test pressure specified in almost all standards is 1.5 times the nominal pressure. However, for high-pressure sealing tests, the test pressure specified in most codes (of the SH and JB categories) is 1.1 times the nominal pressure; but GB50235 (I’m not sure if any other codes specify the same value?) ) is 1.0 times the nominal pressure. 2. Holding time: Some specifications (GB50235) require a holding time of 5 minutes, while others (SH) specify a holding time of 60 to 120 seconds. 3. Test items: During construction, for any type of valve, strength and high-pressure sealing tests are generally carried out (most valves do not have a sealing structure). However, petrochemical standards specify different requirements for various types of valves. For example, for gate valves with DN25PN150 specifications, the tests required according to petrochemical standards (SH3064, JB/T9092) include a strength test and a low-pressure sealing test; high-pressure sealing testing is optional.

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I think in terms of pressure testing, there isn’t much difference between high-temperature valves and ordinary valves, as the pressures specified in our designs are generally converted from high-temperature values to normal-temperature values; therefore, following the design parameters for normal temperatures will not pose any problems

May I ask how to convert the design pressure from high-temperature pressure to normal-temperature value?

Upstairs, the relationship between temperature and pressure for valves can be found in ASME B16.34 and GB 12224, which specify the temperature-pressure ratings; there are rules stating the maximum pressure that can be applied at each temperature level, with higher temperatures corresponding to lower allowable pressures

API598 specifies several types of tests depending on the valve type: a) Valve body test, b) Check valve seat test, c) Low-pressure shut-off test, d) High-pressure shut-off test, e) Double block and bleed high-pressure shut-off test, f) Visual inspection of the casting by the manufacturer, g) High-pressure air valve body test