Determination of the initial thickness of tubes subjected to bending. Part I, Derivation of the basic expressions and relationships

Part one of the paper presents the derived equations for calculations of the initial wall thickness g0 of tubes to be bent for elbows, and a proper bending angle αb. The expressions for calculating g0 were presented for a suitable measure of the big actual radius Ri in the bending zone for an exact (general) solution and for three formal simplifications of the 1st, 2nd, and 3rd order. In any case, a value of g0 depends on the radius and angle of bending, external diameter of the tube, and permissible elbow thickness according to the European-Polish Standards and recommendations of the European-Polish Technical Inspection Office, on the coordinates of the point where the thickness g1all was determined, and the coefficient of the bending zone range k (defined during tests). In this paper, the external or internal diameter of the tube subjected to bending is applied as a parameter.