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Stress Analysis and Loop Spacing for Roped or Bent Pipeline

Stress Analysis and Loop Spacing for Roped or Bent Pipeline

Stress Analysis and Loop Spacing for Roped or Bent Pipeline

(OP)
Hi guys.  Calling out you pipeliners for a question (you know who you are...).  For an above-ground pipeline, if the line is roped or bent, at what bend angle can I assume that I don't need to re-run my stress calcs to space the expansion loops?  In other words, there is probably some angle of roping or field/shop bending below which I can assume the pipe behaves like a straight pipe.  But, if the bend/roping exceeds that angle, then the reaction moments at the anchors due to the eccentricity get 'large enough' to the point where I need to re-run the calcs.  

If it matters, the lines in question are 8" XH and 12" sch 60, both A106B, 25,000' OAL, with quite a few angle points and some up-down elevation relief change betwen some stations.  I anticipate using roping or field bending to negotiate the up-down elevation changesrelief.  Where I have to miter fittings I will re-run my stress calcs.

What say ye grizzled pipeliners?

Thanks!!!  Pete

RE: Stress Analysis and Loop Spacing for Roped or Bent Pipeline

An answer would be dependent on a lot of things, line temperature and length between virtual anchors, sum of friction forces on supports, lengths and runs of loop legs, pipe wall thickness and allowable stress.  With all those variables, of course there is no chance for a simple answer.  

When bending due to axial compression load occurs with eccentricity, M = P * e, the axial compressive load is rapidly reduced as bending occurs, as long as the ends stop moving closer together and the maximum eccentricity is thereby limited.  That would probably happen, if the maximum pipe temperature is limited.  Does that suggest something to you.

Look at the axial and bending stresses in a very slightly curved arc as one support is moved a small distance closer to the other.  The lost axial resistance is balanced by moment and bending resistance.  If your bending lengths are long, deflections are increased, but bending stresses can be limited, and axial stresses are reduced.   

Let your acquaintances be many, but your advisors one in a thousand'  ...  Book of Ecclesiasticus

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