Should threaded pipe be torqued to spec?


Torquing a bolted joint serves a very specific purpose - to set the clamping force exerted by the bolt on the joint. By applying some specific torque to a bolt with a certain thread pitch, the effect is to stretch the bolt by a specific amount. The bolt then acts like a spring, clamping the joint together. Overtightening the bolt applies too much clamping force and can actually deform the joint. Undertightening means the joint can't take as much force before it "floats" and fails.

Threaded piping is completely different. In this case, the threads aren't used to apply force to a joint, the threads are the joint. Their primary purposes are to keep the pipes from separating under pressure, and to seal the cavity inside from the outside. For strength, tightness is of little importance. For sealing, tightness matters, but no matter how tight, the pipes will never seal without a soft interface material like dope or tape. Therefore, thread pipes need to be tightened until they seal...

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All the piping is PL in the catalogs. The joint connection define what components can be put onto the pipe. So, when you put a threaded elbow on PL end pipe, the program understands that it requires a threaded connection. Likewise, when you put a buttweld or socketweld elbow, the program understands that a buttweld or socketweld is required. Rather than forcing the end connection in the pipe, the program chose to use the fittings to define how the pipe joins, since this is one method that pipe works IRL it is a valid method (eg you can by piping and prep the ends however you want).

I agree there should be threaded piping in the catalog, but it's not a big deal. Copy the family, and set the ends to THDM. It takes about 10 seconds. I recommend using your own catalog for components that you copy and modify. Remember that changing catalog names ends up being a big pain, so use a scalable naming scheme (component type or material). For example, you could break custom catalogs...

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