Tensile and Bending Capacity of Threaded Pipe Coupling 1

[BowSoe]

This one has me stumped. Client is insisting on using a threaded pipe cap (similar to below) as a way to attach field-installed pipe/tray supports that will be hung under a structure. The idea is weld this cap to the structure in the fab yard and then screw in a threaded pipe in the field that will be used for hanging L-type supports.

Does anyone have a jumping off point that I could use to figure out how to determine the tension and bending capacity of this connection? Welding the pipe to the pipe cap is not an option.

I checked ASME B16.11 which was no help for the structural capacity of these things. I'd like to tell the client that these are meant for pressured pipes, not structural members and propose a more typical solution for this application. But they have used these for other structural applications over the years, so I would prefer to come up with further justification as to why they won't work (or if they do work, great).

Thanks!

 

[GBTorpenhow]

For tension, you could convert the internal pressure that the cap is rated for into an end force. That would give a starting idea of how much shear force the threads are capable of supporting in typical pressure piping use. 3M fittings are rated for whatever a Sch 160 pipe can take, which varies by size and material.

Bending is trickier but with the extra meat on the coupling vs a pipe, I would start by checking the pipe right at the end of the coupling, with an assumed full thread cut out of it, I would guess this is probably the limiting factor in bending.

Seems a little janky, a generous safety factor is recommended.

 

[HTURKAK]

I do not know if the threaded length will justify standard threaded coupler length or not. However , that could be checked with minimum necessary threaded length of bolts or half the length of threaded reinf. coupler

My approach would be ,

- Check the circular weldment btw cap and the steel structure ,

- calculate the tension str. of threaded joint ( divide the str. to perimeter )then check for bending and tension the thread ring ,

- check the threaded pipe for bending , tension and for shear if necessary

- Proof testing of the subject set-up is also acceptable engineering methods..



A sketch could be useful to get better responds ..















Not to know is bad;
not to wish to know is worse.

NIGERIAN PROVERB

 

[MotorCity]

Even if you can prove that it works by calculation, I would not allow it.

If your client insists, simply point to the code.

You would be sticking your neck out to allow a piece of hardware to be used for an application for which it was not intended.

There are structural rod couplers out there (typically used for sag rods, tension rods, hangers, etc.)

 

[EdStainless]

My problem with this the use of tapered pipe threads.
Unless the thread engagement is well controlled (ha ha) you don't know what the capacity will be.
I am sure that if you GBT's approach and convert rated pressure into tensile load you will find a fairly low number.
These caps come in different ratings, some are limited to sch40 pressures.
And using burst/failure stress I would divide by 5 or more to get a use limit since this in not the designed loading.
Take MotorCity's advice.

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P.E. Metallurgy, consulting work welcomed

 

[phamENG]

MotorCity nailed it. If this is hanging over occupied space, or holding anything of any weight or consequence, don't do it. If they want to insist, walk away and let them take the risk themselves. Hopefully, you can guide them to a safe alternative.

When my son was born, I made sure everything I used to hang the mobile over his crib had a certified rating. Didn't need to be much, obviously, but I still made sure somebody was willing to stand by the product because they had tested it. Unless you're planning to do a comprehensive series of destructive tests to verify the reliability of this design, don't do it.