Expansion joints for chemical processing units
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It was found at the site that the expansion joints were leaking after they were put into use. Some people said that pressure testing should be carried out before installing expansion joints; it’s the first time I’ve heard of this in my 20 years of experience in construction work. Most of the expansion joints used are bell-type, as well as those with hinges or universal joints, but pressure testing has never been done on them. That’s why I’m seeking advice from experts: is pressure testing necessary before installing expansion joints, and for which types of expansion joints is such testing required? What are the requirements for installing each type? Thank you! !
Is it the expansion joint itself that is leaking, or is it the connection surface? Expansion joints need to be pressure-tested together with the pipes, and proper restraint must be provided. I’ve never seen pressure testing done before installation; it must be difficult to carry out.
It’s not the flange surface; it’s the joint between the flange and the expansion joint that is leaking. Previously, a construction company tried to pressure-test the pipes together with expansion joints, and the expansion joints broke. The owner ordered that no pressure testing be carried out. As a result, water got in------it leaked out from the expansion joint itself. Moreover, in my company, there have been cases where pressure testing was carried out together with the expansion joint, which resulted in problems with that expansion joint; therefore, when conducting pressure tests in our company, we generally do not use expansion joints.
Before leaving the factory, manufacturers conduct strength and sealing performance tests on expansion joints based on the pressure and the medium involved. After the expansion joint is installed, it can be pressure-tested along with the system, unless the expansion joint was not manufactured to the designed pressure.
Everything has been done before leaving the factory; it’s unclear on-site. . .
There’s no problem doing it on-site; this is something that needs to be done before the product leaves the factory. As for any issues that arise during pressurization on-site, it will likely be necessary to consider factors such as the type of expansion joint and whether the screws surrounding it are fully loose, etc., in order to determine the cause
Is the leakage caused by the deformation of the expansion joint due to stress?
There is likely an issue with the welding quality of the circumferential weld between the bellows and the flange. Expansion joints should undergo strength tests and airtightness tests before leaving the factory. It doesn’t need to be done before on-site installation. After all the equipment and fixed supports are in place, the transportation fixtures of the expansion joint are removed, and then a pressure test is conducted on the entire piping system. This ensures that there are no issues when the system is running. When pressure testing is carried out on the expansion joint together with the system and problems arise with the expansion joint, it is usually not a problem with the expansion joint itself, but rather an issue with the supporting system, particularly insufficient strength of the fixing brackets. It’s better to have problems at this stage than after work has started. To ensure the safety of expansion joints, attention must be paid from system design and selection, expansion joint manufacturing, on-site installation, to the end users.
After investigating, it turned out to be a shoddy product; it was installed in September 2014, and by now the sealing around it has completely broken down.
Domestic metal bellows have truly been ruined by low prices. If manufacturers can’t raise prices, they cut corners; and the actual costs for factories aren’t necessarily lower either. There’s nothing to do; just wait