Copper Tubing Mashing Load Calculation? 1

[ArubaBob]

I need to calculate the maximum load that I can apply to copper tubing without permanetly deforming it (making it go oval). The application is that I have coils of copper tubing of different diameters and wall thicknesses and lengths. I would like to be able to calculate the yeild point deforming load on the tube. This is to be sure that I do not stack too many coils of copper on top of each other so that the coil on the bottom of the stack is overloaded, deformed, and damaged.

I find many references fior calculating axial applied loads, external pressure collaspe and burried pipe collaspe loading, but unfortunately not this type of loading.

I would appreciate any help or references to this type of calculation.

One size of copper tube that I am wanting to check would be 1/2" Type L fully annealed tube. This is .625" O.D x .049" wall thickness. The Yeild Strength is approximately 6,700 PSI, the Modulus of Elastisity is 17,000,000 PSI, Poisson's Ratio is .33, Tensile Strength is 31,300 PSI.

Thanks again,

Bob

 

[SteelPE]

I seem to remember a similar problem I had during my time at University. I think you will find at least some help on page 4 of the attached. Using these equations it's just a matter of knowing material properties and geometrical properties to solve your problem. I would be the moment of inertial of the tube wall per unit length.... basically bt^3/12 where b is unit length and t is the tube thickness.

 

[ztengguy]

How high are you thinking of going with your stack? I would think it would be reasonable not to worry about this until you get over about 25.25' stack.

 

[rb1957]

you've got a coil of tuding ... do you know the length of the tubing or the weight ?

whatever, convert length to weight (L*A*p).

i think the diameter of the coil matters, the weight is distributed along pi*D ...
W/(pi*D) = w (lbs/in)

the maximum moment in the tube is m = w/2*R (in.lbs/in)

the bending stress = 6m/t^2

 

[racookpe1978]

Crushing the tube from round to oval will be worse case at the bottom tube of the bottom coil --- assuming (big assumption!) that the copper weight actually compresses the coil.

See, lots of the weight will go into squishing the coils against each other - compressing the loose space between the individual coils of each copper pipe. Imagine, if you will, a bunch of springs in a bin: the point load at the bottom will be the weight of the whole mass from the top down, but averaged over the whole area that is being touched by the load. It is concentrated at just one point.

 

[1gibson]

Turn up both ends of a coil, fill with water. Load until it do drips (indicating reduced tube volume, which indicates reduced tube cross section.

To be conservative (and a lot simpler than stacking a bunch of tubes) you could add weights to a flat plate on top of one coil, and then calculate the amount of tubing allowable based on the weight that causes it to drip. When it is stacked coils rather than a flat plate, you will have some slippage to help distribute the load (as already mentioned.)

Oh, and to answer your question, you then generate an equation that fits the data. Model the equation after others for similar loading. I'd think 4 sizes (2 of same nominal diameter, 2 of same wall thickness) would be enough.

P.S. are there OSHA guidelines for max stack height of... things? I believe there are for stacking pallets, at least I've seen a clearly marked height limit in every indoor manufacturing/industrial environment I've been exposed to.

 

[ArubaBob]

My thanks to everyone who replied for taking the time and providing me some good information and ideas to use.

Best regards,

Bob

Ps: I am not aware of a specific OSHA guideline for the stack height.

 

[TXStructural]

I think your computation will be confounded by how the tubes stack, that is, do they stack tube on tube, or will they nest, where a tube on top is supported by two tubes below. The computation would be analogous to bending of a curved beam, with the load applied as appropriate.

Try this, found with a Google for "curved beam bending":
courses.washington.edu/me354a/Curved%20Beams.pdf