Residual Strength of the Overhead Section of a Main Pipeline with Annular Cracks
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RESIDUAL STRENGTH OF THE OVERHEAD SECTION OF A MAIN PIPELINE WITH ANNULAR CRACKS А. R. Dzyubyk,1, 2 L. V. Dzyubyk,1 G. V. Pokhmurs’ka,1 and І. А. Prokopyshyn1, 3
UDC 622.692.4
We propose a procedure for the evaluation the parameters of brittle and ductile fractures of multisupport overhead sections of pipelines weakened by annular semielliptic cracks, which takes into account the membrane, global couple, and residual welding stresses. To describe the process of bending of pipeline, we use the model of a beam with piecewise variable stiffness with regard for the elasticity and possible displacements of the supports, and soil masses. Keywords: overhead crossings of pipelines, annular cracks, brittle fracture, ductile fracture.
Pointed transverse defects in the zone of welds are among the most widespread types of defects of the main pipelines. As a rule, they are simulated by annular semielliptic cracks. For the underground sections of pipeline, the static strength in the zone of these defects depends on the levels of membrane and residual stresses. At the same time, the sections of overhead crossings placed on the supports are characterized by the presence of global bending, which leads to the appearance of additional axial couple stresses. The stress intensity factor (SIF) for the first mode of deformation K I is the determining parameter of brittle fracture for this type of cracks and loading of this kind. For cylindrical shells with annular cracks, this coefficient is computed additively via the axisymmetric axial variables across the thickness of the shell and the global couple stresses. It is now well-studied and described in handbooks, guides, and standards [1–3]. The last achievements and prospects of the analysis of strength and local fracture based on the concept of SIF can be found in [4, 5].
The ratio of a parameter to its critical value corresponding to the onset of ductile fracture serves as the index of ductile fracture in the case of a single type of loading. However, under combined loading, the cumulative index of ductile fracture is not additively determined via the marginal parameters [1, 3, 6]. A survey of the methods intended for the evaluation of the parameters of ductile fracture for cylindrical shells with annular cracks and their comparison can be found in [7, 8].
The static strength of the underground sections of pipelines with annular semielliptic cracks under the action of axial stresses caused by the internal pressure, temperature drops, and residual welding stresses was analyzed in [9]. In [10], the influence of residual stresses on the limiting equilibrium of a cylindrical shell weakened by an internal crack of any configuration located in the zone of the weld was investigated according to the criterion of critical crack-opening displacement. However, the influence of stresses of global bending on the static strength of pipelines with annular cracks is studied quite poorly. 1 2 3
“L’vivs’ka Politekhnika” National University, Lviv, Ukraine. Corresponding author; e-mail: dar.lviv@gmail
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