Pipeline pressure testing
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I would like to ask the experts: what standards should be followed for pressure testing nitrogen pipelines in the waste gas treatment systems used at petrochemical wastewater treatment plants? The function of nitrogen is to provide dry gas sealing for the water pump. The current operating pressure in the nitrogen pipeline is 0.6 MPa, while the design pressure is 0.78 MPa. The pipeline components and equipment installed on it are all selected according to PN10 standards. If the pressure in the nitrogen pipeline is set at 0.78 * 1.5 = 1.17 MPa, then this would exceed the current pressure rating of the pipeline, right? Do these nitrogen pipelines and associated equipment need to be upgraded to PN16?
Oh, really, it should indeed be selected according to PN16. Items of PN10 grade should be chosen with care. If it’s ordinary steam or water pipes, that will work; but for other applications, it’s better to choose ones with a higher pressure rating. Additionally, to avoid conflicts, consider using a pressure test; I think the factor is ×1.15. If it’s ×1.5, that would likely be the requirement for a hydrostatic test, for your reference.
Right. 1.5 times is based on hydraulic pressure; the value for pneumatic pressure is 1.15 times. Nitrogen at 0.6 MPA is commonly used in ordinary petrochemical plants. I’m not sure whether they use hydraulic or pneumatic pressure in such cases
For some medium and high-pressure containers, they must meet the requirements of hydrostatic testing, primarily for safety reasons. As for this pressure pipeline system, pneumatic testing is mostly used. However, for valve selection, it is better to choose those with PN16 grade for better durability.
It is preferable to choose a PN16 valve, but this has nothing to do with the test pressure; the pipeline pressure rating can be lower than the test pressure, and the pipes and fittings can be selected based on the design pressure.
The valves, fittings, and everything else have been purchased. If we conduct the liquid test at 1.5 times the pressure now, it will exceed the rating of our pipe fittings; I think the test pressure should not exceed the pressure rating of the pipes. May I ask which standard specifies the statement that follows: \"The pressure rating of the pipes can be lower than the test pressure, and the pipes and fittings can be selected based on the design pressure\"? I’d like to study it, thank you!
The wall thickness of the pipeline is calculated based on the design pressure (see GB20801), while the pressure class of the flange is selected according to the maximum operating pressure (see HG20592). The test pressure is independent of the selection of pipeline components.
The absence of the PN10 pressure rating option is a bit low
The pressure test is usually at 1.5, while the tightness test is generally in the range of 1.05 to 1.25
It’s hard to find PN10 fittings these days. It usually starts at 16.
Refer to Article 8.6.4(6) of the GB50235 Code for Construction and Acceptance of Industrial Metal Piping Systems: When the piping and equipment are tested as a single system, and the test pressure for the piping is equal to or less than that of the equipment, the testing shall be carried out at the pressure specified for the piping. When the test pressure for the pipeline is higher than that of the equipment, and it is not possible to separate the pipeline from the equipment, or when the test pressure of the equipment is greater than 77% of the pipeline’s test pressure calculated according to equation (8.6.4), testing may be carried out at the equipment’s test pressure, with the approval of the designer or the project owner. The test pressure for the pipes in this case is 1.17 MPa, while the design pressure of the equipment is 1.0 MPa. Therefore, the test pressure for the equipment should be 1.5 MPa. This means that the test pressure for the pipes is lower than that for the equipment, and testing should be carried out according to the test pressure of the pipes; there should be no problem with that