Pipeline pressure testing
Thread Content
1. Why is a pressure testing blind plate used instead of simply closing the valve when testing pipes? 2. For pressure testing of pipes under high pressure, should a pressure testing blind plate be used or is there another method? Under high stress conditions, the pressure testing blind plate may need to be thicker
1 I’m not sure what pressure is used for testing; it doesn’t seem like there’s any specific requirement stating that blind flanges must be used during testing. Blind flanges might be needed in order to isolate certain systems. What I mean is that there might be reasons for using blind flanges, but it doesn’t mean that valves cannot be used for testing. Think about it: if there is water pressure, and once that pressure reaches a certain level, it still needs to be controlled by valves. If the pressure is still high, I guess the pressure rating of the valves won’t be very low either. It would be great to conduct pressure tests simultaneously – is it really necessary to use blind flanges? Haven’t heard of it; there’s no such requirement
1. Valves can only be used to regulate flow rate; they cannot serve as blind flanges, and closing a valve does not guarantee a 100% seal； 2. I’m not sure what the pressure level is for the high-pressure pipelines you’re referring to; generally, installing blind flanges is sufficient for medium-pressure pipelines, and lens gaskets can be used for pressure testing in ammonia synthesis system pipelines
1. When pressure is applied to a pipeline, no valves should be involved under any circumstances. There are two reasons for this: first, to prevent impurities in the pipeline from entering the valves and getting trapped there; this could lead to improper sealing or wear during valve operation, especially affecting automatic valves significantly. Second, pressure application is intended for the pipeline itself, not the valves. It constitutes a strength test, and if valves were involved, their sealing surfaces would come into direct contact with high-pressure gas. The valve sealing surface cannot withstand it (refer to the standards regarding pressure applied to valves). 2. For pressure testing of pipes under high pressure, pressure test blind plates are used; the thicker the blind plate, the higher the pressure it can handle.
The main reason why pressure testing blind flanges cannot be used in place of valve gates is that the gate will deform as a result of the pressure testing, and thus will be unable to provide a seal – this is strictly prohibited
1) When closing the valve for pressure testing, the high pressure can easily deform the valve blind plate, making it impossible to create a support and thrust device. Moreover, 2), which is strictly prohibited by GB50268, allows for the use of elliptical end caps that can be connected to pipelines.
May I ask which standard and which article it is? Thank you!
Reply to 7# rain666, GB 50268, etc. – this is definitely the case
Regarding the first point, the moderator has already answered it clearly. I would like to add that I have worked on many pipelines where, due to high temperatures, the pressure used for testing was very high – usually twice the normal operating pressure – which makes it easy for the valves to get damaged. So consider this.
Due to the high pressure during compression, it is easy to damage the valve, thereby compromising its sealing properties
Based on my own experience, I believe that manual valves also need to be pressure-tested. However, during such testing the valve must be in the open position, as it is also part of the sealing inspection process. This is why a blind plate is needed; the pressure required to penetrate this blind plate – well, at that pressure level, will the pipe not explode?