Determining the resistance to failure of pipes with axial surface cracks in plastic deformation

Abstract

Since in vessels and pipes of metals with significant ductility all the way to failure in the weakened cross section in front of a crack the stresses exceed the yield strength, the above approach may not be used in determining failure pressures. At the same time, as a result of difficulties in the elastoplastic analysis of the field of stresses in front of a crack, it is analytically impossible to obtain an expression for the failure pressure. Therefore only known empirical relationships are used [2]. They have been obtained in treatment of the results of failure tests of pipes of types of steel used abroad and may be used at present only for tests of materials in the investigated ranges of crack (notch) lengths and depths. This article proposes a general approach to calculating failure pressures in pipes with axial surface cracks based on an approximate analysis of the field of stresses in the plastic zone. Consideration is given to pipes of materials possessing an insignificant degree of work hardening, such as 12KhlMIF steel (Fig. i), which may be considered ideally plastic with an accuracy sufficient for engineering practice.