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2.3.4 Use of Expansion Loops in Piping Design & Stress Analysis

In the event that model refinement is not sufficient to solve the problem (i.e., there is a real problem, and not just one on paper), something must be done. Re-examining the equation for the guided cantilever model:

expansion stress in piping expansion loop by meena rezkallah, p.eng. for piping design& stress analysis and structural engineering services across canada

It is evident that the stress analyst cannot easily change the terms 6, E, R, or delta. This leaves only 1, the length of the leg absorbing the thermal growth. This can be done through the addition of an expansion loop. In this case, the thermal growth is partially absorbed by each of the legs running orthogonally to the thermal growth:

the thermal growth, partially absorbed by each of the legs of the expansion loop running orthogonally to the thermal growth by Meena Rezkallah, p.eng.

The stress range calculated in the longer leg is only 3937 psi (note that the maximum expansion stress is found in the longest leg resisting the displacement), compared to 17,700 psi without the loop. Generically, the stress range in a leg j, due to thermal expansion in a direction perpendicular to that of leg j, is:

the expansion stress range in expansion loop leg by meena rezkallah, p.eng. for piping engineering services across canada

Therefore, the calculated stress range should always decrease if expansion loops are added in any direction perpendicular to a direction of thermal growth, since the denominator in the expression for the expansion stress will increase.


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