Do pipeline pneumatic tests have advantages over hydraulic tests?
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It is suitable for both pneumatic and hydraulic testing of ordinary pipes, but since hydraulic testing is safer than pneumatic testing, pneumatic testing is generally preferred. However, in accordance with the requirements of GB/T20801, \"a piping system that has passed the pneumatic test and has not been disassembled after the test does not need to undergo a leakage test.\" It seems that pressure testing is the preferred option in this case. As for the issue of safety, it is up to the testing agency to ensure it, and it has nothing to do with the designers.
Pneumatic testing has pressure limits, and most should be subjected to hydraulic testing.
Are there any regulations specifying restrictions? Please provide the basis
Safety concerns everyone; use water pressure whenever possible, and if that’s not feasible, use air pressure. Whoever carries out the task must prioritize safety first.
What are the advantages? During pressure testing, instruments must be removed, such as safety valves, check valves, instruments, flow meters, etc.; these items cannot be used in the pressure testing process. After the pressure testing is complete, as long as there are removal ports and reinstallation ports, a leak test must be carried out, regardless of whether it is under air pressure or water pressure. However, it is true that after the water pressure is applied, compressed air is used for drying.
If you are a designer, you should first study the standard specifications thoroughly and understand them well, as this will be useful for your work; otherwise... 20801 is not a design standard, nor a design manual, nor a construction procedure standard – it is rather a technical standard for pipeline safety (the regulations on the safety supervision of pressure pipelines – the industrial pipelines section). The \"9. Testing\" section of 20801.5 makes it clear: hydraulic testing is the preferred method, while pneumatic/mixed testing are alternative options; they are not presented as equal choices ； 9.2 The leakage test section also places what you mentioned in e) at the end. The standards and regulations are revised in this way to meet practical needs; otherwise, if everything were fixed rigidly, there would be no room for flexibility. But that’s not a reason for taking advantage of loopholes
Which process system are you looking at? For systems where water is prohibited, a pneumatic test can be used as a substitute for a hydraulic test; or in winter, when hydraulic testing is not feasible, a pneumatic test can be used instead.
Both pneumatic testing and hydraulic testing are acceptable; in general, the choice depends on the medium flowing through the pipeline, with hydraulic testing being more commonly used in practice.
Pressure testing still carries risks; generally, it is necessary to evacuate most of the people present at the site. This is similar to speeding on a highway – not every car that speeds will cause an accident. When working on projects, one must never rely on luck; it’s better to be cautious.
I have a question: after the pressure testing is completed and a leak test is carried out, if one system is separated from another by a blind flange and the connection is reestablished after the leak test, are there still access points for disassembly at that point?
You can use the port for venting/bleeding; if none is available, simply remove the valve at one of the pressure gauges.