Ross Mackay Forum Moderator 94 Posts
Re: Expansion pipe joints16 March 2007 at 1:29pmThe use of expansion (or flexible) pipe joints in a pump system that has no excessive temperature differential problems is only necessary when the pipe fitters installing the piping are unable or unwilling to install the piping without imposing any strain on the pump nozzles.
When they are used, it should be identified why theyre being used. The most common reason is to protect the pump against pipe strain that may be imposed by the movement of the piping during system operation. In such case, the side of the flexible pipe joint closest to the pump needs to be independently supported and secured against movement. This allows all the movement of the piping to be absorbed by the flexible joint, and none of it transferred to the pump.
Another thing to note is that an expansion joint will not necessary accommodate radial movement of the piping. Some of them are designed to accommodate only axial movement where the pipe and pump flanges are trying to get closer together or further apart. These are of no value against poor piping misalignment or thermal movement of the piping.
I have some doubts regarding expansion joint applications, before and after pump nozzles, mainly when the fluid being pumped is at normal or low temperature. There are designers that always consider installing expansion joints close to the pump nozzles because of potential piping misalignments, or maybe vibration matters, or something like that. Is that a right practice? On the other hand, IOM manuals of pump suppliers normally dont state anything regarding flexible joint requirements, except when the temperature is significant. In addition, checking technical brochures issued by expansion joint suppliers, they always recommend installing flexible joints between pumps and piping; but of course, maybe that is a matter of marketing. In fact, other questions are the following: Is it a good practice to always assemble expansion joint between pump and pipes? Which are the right necessities of assembling with expansion joint? Are there any pros and cons about expansion joint installation?
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