Stress state and strength of welded joints in large-diameter pipes

Abstract

In 1995, the losses from failures of oil pipelines in the Russian Federation were approximately 280 billion rubles. Consequently, examination of the strength properties of welded joints in large diameter pipes is an urgent and important problem. In this work, we propose a new method of examining the stress state and strength of dissimilar welded joints with the H -S -H (hard -soft-hard) hardness schema for welded joints in large-diameter pipes. The cross section of the longitudinal welded joint in a large diameter pipe can be regarded as a region with two orthogonal axes of symmetry on which the components of the stress tensor are determined. The longitudinal welded joint, interpreted as a ductile layer, is sufficiently large and, consequently, its stressed state can be examined by the methods of solving a statistically determinate planar problem of plasticity theory.We shall examine the threshold state of a mechanically heterogeneous welded joint under tensile loading which determines the load-carrying capacity of the weld under ductile fracture conditions. Usual assumptions [1] and simplifying conditions will be accepted. The medium of the examined section is regarded as ideally rigid-plastic. In the resultant solutions, the parameters of such medium are replaced by the parameters of the strengthened medium, in particular, the shear yield limit kr was replaced by ultimate strength Ice.According to the static definability of the problem, we solved the system of equations of plastic equilibrium in relation to the unknown components of the stress tensor ax (x; y), % (x; y), 7",~ (x; y), given on the cross section of the welded joint by the plane normal to the plane of the pipe. As a result of the large diameter of the pipe, this cross section is assumed to be a rectangle with width L (thickness of the pipe) and height h (thickness of the welded joint). Let it be that k = L/h is the relative thickness of the welded joint.Usually, the available values of the stress tensor at the boundary of the region are insufficient for obtaining an unambiguous solution of the boundary-value problem. In addition to the zero values of the components at the free boundary, only the value of the tangential stress at the line of contact of the plastic layer and the parent metal in the vicinity of the free boundary -the extreme value r~ at the contact line -is usually known (from physical considerations and is included in the problem as a boundary-value condition). In this section, the tangential stress is stabilized in many cases (compression in pressure working of metals [2], tensile loading of the welded joint in the pipe [1]), reaching the highest value

Stress-Strain State of a Plastic Layer under Compression by Two Rigid Parallel Rough Plates

“…Nevertheless, there are meaningful papers [7][8][9][10][11], using, together with numerical methods, the condition (1). Hypotheses of a deformation character is the hypothesis of plane sections (HPS) [12][13][14][15][16] ( ) ( )…”