Questions regarding the test pressure and test temperature for pipeline hydrotesting
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We know that the hydrostatic test pressure for metal pipes is generally 1.5 times the design pressure, and the water temperature is usually not lower than 5° nor higher than 70°. I suddenly have a question today: for a pipe with a design pressure of 1 Mpa and a design temperature of 400°, is it appropriate to use a hydrostatic test pressure of 1.5 Mpa? This is because the allowable stress of many pipes at high temperatures is less than one-third of that at room temperature. For example, taking the pipe mentioned earlier: its design temperature is 400° and the design pressure is 1 MPa; when converted to room temperature, a design pressure of 3 MPa might be required to meet the specifications. In such a case, isn’t it problematic to use a test pressure of 1.5 MPa?
Your question is entirely valid. During the hydrostatic testing of metal pipes, the test pressure should be 1.5 times the design pressure. However, if the design temperature is very high, the design pressure required at normal temperatures becomes higher; in such cases, the test pressure should be increased accordingly to ensure the accuracy of the test results and to prevent leaks or seepages. Therefore, for pipes with very high design temperatures, the test pressure should be adjusted according to actual requirements to ensure the accuracy and safety of the tests. .
But I’ve seen that the relevant specifications do not specify any particular value for the test pressure during the hydrostatic test
The hydraulic test pressure PT = 1.5 PT/t, where T/t represents the temperature correction factor.
You’re right; the way it’s expressed isn’t appropriate. I just saw that the text mentioned 1.5 times the design pressure, but then this temperature correction factor was also listed below. I didn’t notice that; I only remembered the 1.5 times factor :L
Thinking is good, but any standard will state that a temperature correction factor must be taken into account for hydraulic testing; however, the standards do not specify that a temperature correction factor is necessary for pneumatic testing.