Determination of the criterion for the use of a toroidal mandrel during the mechanical bending of pipes with varying wall thicknesses

This paper presents the results of model tests related to the process of forming a pipeline arch by mechanical mandrel bending.The problems that occur during the pipeline manufacturing process and the methods and instrumentation used in forming the bent section of a pipeline, in particular the so-called mandrel bending, are presented.The main part of the paper consists of the results of model tests of stresses and deformations arising from the process of forming the arc of a mechanically bent pipeline using the proposed version of the mandrel with a torus-shaped forming part.These studies included an analysis of the effect of the pre-positioning of the mandrel on the values of deformations and stresses occurring in the cross-section of the bent pipe arch as a function of changes in the wall thickness and external diameter of the pipe and the bending radius.Based on the test results obtained, criteria were established enabling the selected pipe bending method to be used so that the resulting stresses and dimensions in the cross-sections of the bent pipe section are within the limits imposed by the normative recommendations.It was also shown that the criterion determining the efficiency of the bending process is the allowable recommended value of the ovalisation of the pipe cross-section.