Experimental investigation of stresses in cold-bent pipes due to internal pressure and in-plane bending

Experimental measurements have been made of stresses in out-of-round pipe bends under internal pressure and in-plane bending. This paper describes the results of tests on one new and one ex-service pipe bend under the two loadings and compares these results with various theoretical predictions. For the pressure case the original formula due to Haigh² with modifications to take into account thickness variations and pipe bend radius, is reasonably accurate and for bending loads the recent formulation by Spence and Boyle¹² is a reasonable approximation. The code method of combining peak stresses by addition is confirmed in this case. The results of the tests have assisted designers in reviewing allowable limits on the ovality of manufactured pipes and in placing realistic limits on the cold springing of pipes to overcome erection tolerances.