The Flexibility of Short-Radius Pipe-Bends

Abstract
Experimental results are presented for the stresses and deflexions of typical pipe-bends of small bend radius and of thin wall section. The bends were subjected to external moments and, in one test, to a combination of an external moment and internal pressure. It is shown that the calculation methods based on Kármán's assumptions and analysis are inadequate for predicting the stresses and flexibility of bends of this type, but the modification of Kármán's analysis, described in the companion paper, is shown to be satisfactory down to values of the pipe factor of 2hR/r2 = 0.09, where 2h is the thickness of pipe, r the mean radius and R the radius of curvature, and to values of R/r = 2.2. The effect of superimposed internal pressure is to reduce the peak stresses arising from the externally applied moment, and, even when the pressure was raised to 2 1/2 times the maximum working pressure, the bend was subjected to no more severe stress combination than in the pressureless state. Consideration is given to the design of pipe-bends, and it is shown that a simple and reliable method of calculating safe working conditions can be derived.

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