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Due to the fact that pipe flanges rely on bolts, and bolts rely on friction, it seems obvious to me, as a manufacturer of piping, to recommend that bolt torques need to be checked every so often, to ensure piping doesn't leak. I've got a few questions about this, but here is the first one:

How often do you normally check torques on bolts at a plant? In other words, what is a good industry standard preventative maintenance schedule when it comes to threaded fasteners that are loaded below yield? I would prefer that answers provide a reputable source for reference.

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    $\begingroup$ Bolts tend to stay in a long time if they are not vibrated loose and even then you have options to fix it into place using pins $\endgroup$ – ratchet freak Jul 2 '15 at 15:59
  • $\begingroup$ Repeated checking can cause its own problems. There have been issues with aircraft where people over-enthusiastic about "safety" regularly stripped the threads on fuel tank drain plugs etc, by checking they were tight every day using with a torque wrench. For some things, visual inspection (and in that particular example, the smell of leaking fuel!) is all you need. $\endgroup$ – alephzero Aug 9 '17 at 19:29
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There is no answer because there are too many variables, amount of vibration and thread geometry being just two of them. A joint could last for 10,000 years or work loose tomorrow. There is no way to know.

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  • $\begingroup$ If the person who designed the flange "didn't know if it will last 10,000 years or less than a day", and didn't design in any features to show which is the case, then fire him as quickly as possible before he kills somebody ;) $\endgroup$ – alephzero Aug 9 '17 at 19:26

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