Compressive Radial Load on Pipe 1

[Bree]

I am checking a 6" XS pipe in a crane lift configuration.

A 1.5" wire rope with a soft eye will be slung around each end of the pipe which is part of a skid holding a 50 000lb pump.

I'm trying to determine whether or not the pipe wall will buckle. The maximum sling tension is 38 350lbs.

A co-worker provided an unsubstantiated "Belt wrap formula" of Tension/Radius.

I have checked many formulas for a similar loading and have come up with differnet results.

If anyone can provide a definitive solution I will be eternally grateful.

Cheers!

 

[BigInch]

Then this is considering a failure by localized wall buckling from axial compression induced by the bending load. In otherwords, and if this was a skid beam, this would be like a 50000 point load at the center span causing bending stress (compression in top flange), but you want to know if it will fail due to local buckling of the compression flange, right?

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[BigInch]

As opposed to an indentation failure caused by the 50,000 load applied to the pipe wall.

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[Bree]

The skid is vertically oriented such that the pump load is eccentric from slings, not directly below.

There are I-beams, which make up the sides of the skid, near both ends of the pipe. The webs are welded to the pipe wall. Thus the load from the pump is transferred to the pipe via the beams. It is not a point load at the centre of the pipe span.

The slings wrap around a 5" section of pipe that extends beyond the beam webs. Also the pipe is capped with an end plate. I'm not aware of the details of the plate.

I have to provide proof that the tension in the slings will not buckle the pipe so DNV will certify the lift. However, I've not been able to do this so far. At least not with the formulas I've found.

The belt wrap formula is the radial load I've been applying to the pipe to determine if it will buckle.

 

[BigInch]

Maybe I still don't understand, but from what I picture it would be difficult to locally buckle a pipe wall (from axial compression load) that has a beam web welded 90º to it then followed by an end plate closing up the pipe end. The beam web would provide a lot of reinforcement and the end plate would tend to keep things from ovaling. And there is apparently no point load in the pipe span(?), so no bending stress in the pipe. Can you post a sketch or picture of this arrangement?

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[prex]

It depends very much on the distance of the sling to the pipe end plate. I concur with BigInch on the request for a sketch.
Anyway the problem of a rope eye wound around a pipe can be attacked more or less as follows:
-from geometry determine the angle of contact of rope to pipe; as this will probably be larger than 180 deg, take 180 deg as a maximum
-assume a constant pressure acts on the contact and determine this pressure (a linear load in fact) by equating the vertical component of the distribution to your load
-now imagine that the same pressure will act on the full circumference: go to the first site below, and to Pipes -> Axisymm.loads -> Free-free -> Radial load. Calculate a section of pipe sufficiently long so that end effects are minor
-you now have a maximum compressive circumferential stress in the pipe wall to compare to the allowable compressive stress in a vessel wall subject to external pressure
This procedure should be quite safe, but I imagine that your pipe will be far from buckling, so you only need a rough check.

prex

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[Bree]

I'm not sure if I posted this image correctly. Hope this clarifies the situation.

I checked the section of pipe against ASME B31.3 Pipe Wall Thickness Under External Pressure. For 5 inches between stiffeners (i.e. web and end plate) I got a Maximum Allowable Pressure of 1515psi. My applied pressure is around 7750psi if I've calculated that correctly.

Thanks!

 

[prex]

No luck with the image.
I would calculate the pressure as F/DL or 38350/6/5=1278 psi with your numbers.
With that formula the vertical resultant of pressure acting on the lower half of your pipe is equal to the load.

prex

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: Magnetic brakes for fun rides

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[Bree]

 

[BigInch]

I would only check for shear across the entire cross section of the pipe. Highly unlikely to buckle the wall with a web weld on half and an end plate at the other end only 5 inches away. I think you'd have more trouble with the fillet welds you probably used on the web to pipe connection.

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