Can flange bolts be tightened under pressure during a hydrostatic test?
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After pipeline welding, a hydrostatic test was conducted at a pressure of 5.6 MPa (for pipelines of 8\" diameter). Once the test pressure was reached, leakage was detected at the blind flange. Question: Can the leak point be tightened under pressure? If not, are there any relevant standards to refer to?
This post was last edited by ylb913 on 2015-9-17 07:43. In any case, it’s not allowed according to the standards; pressure testing is supposed to be the responsibility of the construction unit, so I hadn’t paid attention to it before, but this practice is common when applying pressure to the equipment. Raising and lowering the pressure during hydrotesting isn’t that complicated either; why take such a risk?
Sure, but be careful. It is best to do this after releasing pressure; the water pressure test allows for rapid pressure release, and pressure can be increased again once everything is in order.
Personal opinion: It’s not easy to achieve a leak-free tightness at 5.6 MPa either; that’s 56 kilograms of force per square centimeter.
It is acceptable during a hydrostatic test, but not during a gas test.
“Many people tighten flange bolts while the system is under pressure; however, for safety reasons, it is better to relieve the pressure before tightening, as standards do not approve of tightening under pressure.
It’s best not to do this. Once water pressure leaks, it’s better than air pressure ； When I first graduated, I heard about someone who was cutting a blind flange by himself; during the pressure test, he used a hammer to strike the nut, and the piece shattered and hit him in the head.
Tightening under pressure is not allowed; it is extremely dangerous to do so at a pressure of 5.6 MPa. As for pneumatic pressure, there’s no way you should even think about tightening under such conditions.
Whether it is hydraulic or pneumatic, operating under pressure is generally not allowed, as it poses certain safety risks! ! ! ! !
Actually, everyone is aware of the safety risks, but some people find it troublesome and rely on luck. Moreover, the provisions prohibited by the standards are all derived from accident cases; do not take risks just to save time.
It seems that if there’s a leak in the flange area, it’s very likely that the workers didn’t tighten the bolts properly – not level enough. If a leak occurs at that point, it becomes more difficult to fix by simply tightening the bolts again. If the process is carried out without applying pressure, releasing pressure once isn’t enough to resolve the issue; multiple releases and tightenings may be required, which is why workers are reluctant to do this.