Pipe Clamp Coefficient of Friction

[pipestresser08]

Hi everyone,

Running a piping model in CAESAR II which utilizes these cushion clamps as restraints in the 3-inch headers. Currently the Mu is defined as 0.3 but I am wondering if anyone has a resource for a cushion clamp coefficient of friction for piping models.

I can imagine this would be dependent on the clamping force used. The model axial force during seismic overcomes the 0.3 friction so I am wondering if the clamp actually tends to act more so as an anchor than a vertical/transverse support with 0.3 friction.

Hydra-Zorb: Cushion Clamp Product Guide

 

[LittleInch]

CoF will be a lot higher than 0.3. It's. It's basically a set of anchors/line stops 5 feet apart if you follow the recommendations.

How you work out the clamp force though I have no idea.

 

[pipestresser08]

Hey thanks for the reply. I agree with you it'll act more as a line stop than a friction support. My problem is I can't find the data to back this up. Of course the cushion clamp provider doesn't reply..

I've seen calcs for the clamp force acting on the pipe is essentially bolt tension * 2pi. I am sure that's over simplified but somewhere to start.

 

[LittleInch]

Your problem is essentially that these things are not supposed to be analysed using Ceasar.

Three inch pipe is pretty big for something really designed for one inch tubing.

Is really only the end fittings which are an issue as Ali the others the thermal forces cancel each other out.

The clamp force in reality is going to be highly variable depending on the pipe fitter.... And any lubricant and any deterioration of the clamp flex material.

These things are basically similar to U clamps which are notoriously difficult to model.

Why are you doing this for 3" pipe? I wouldn't bother.

 

[Snickster]

I would not use that in process piping. It looks like it is more for plumbing and HVAC piping. The attachment you posted provides a link to a document which provides allowable loads in all three directions. For 3" it lists F vertical = 800#, F axial and F lateral = 125#. However, I don't see how it provides much restriction to loads except for the vertical direction.

In the horizontal direction the clamp is slotted in the unistrut so it appears it will move if there is a horizontal lateral force. In the axial direction the only thing providing a restriction is the clamping force developed by tightening the bolt. This force cannot be that much as by tightening the bolt a force is developed by the clamp due to a cantilever beam type deflection of each side of the clamp. With thin metal like that I don't see how the force could be that significant. Then the perpendicular normal force developed needs to multiplied by the friction coefficient of the plastic to get the resisting axial force which can't be that much.