Slender pressurized pipe buckling.

[leveles]

I have a slender pressurized plastic pipe (20' 6" 100psi) with variable compression endload. How do I estimate the number of (loose) clamps to prevent buckling?
Any formula or sites, sources?
thanks leveles

 

[Cockroach]

Nice problem, interesting application.

I would apply the Von Mises-Hencky equation for the triaxial state of stress governing Thick Wall Pressure Vessel (i.e. the general case) and set the factor of safety to unit, that is, allowable stress is the yield stress of the material at 2% offset. You can find the PVC material properties from duPont website or equivalent manufacturers or suppliers of pipe. With the pipe bore diameter understood, simply solve for stress.

With the stress calculated, use the Euler equation for slender columns, applied force equalling the normal load over wall area. This will give you buckling as a function of length. The solution is iterative, you will need to keep feeding in length until the desired stress equals that computed above.

This length is thereby the minimum allowable length of pressure vessel governed by material property and geometry. Put a clamp at every computed length, L.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[bvi]

Note that PVC creeps at room temperature, so if the duration is long, you may have a creep buckling problem.