Numerical prediction of the current and limiting states of pipelines with detected flaws of corrosion wall thinning

Authors

  • O.S. Milenin

Keywords:

3D discontinuity flaws, ductile fracture, failure probability, limiting state, mathematical modeling, the stress-strain state, welded pipeline.

Abstract

The main assumptions have been made for the physical and mathematical models of combined development of the stressstrain
state and voids of ductile fracture in welded pipeline elements and pressure vessels with the detected 3D metal
discontinuities (local corrosion losses of metal, macrovoids), including the ones located in the area of site welds for
determination of the characteristic features of defective structures’ limiting state. Analysis of the stress-strain state of the welded
pipeline section has been carried out based on finite element solution of the problem of non-stationary thermoplasticity by tracing
elastic-plastic deformations from the beginning of welding to the complete cooling of the structure and subsequent loading to the
limiting state. The continuum dilatation model of fracture is based on a stepwise prediction of micro- and macro-damage of
material both in welding and under loading with internal pressure and external force bending moment to the limiting state on the
basis of the Gurson–Tvergaard–Needleman theory. The criteria for macroscopic fracture of structure on a brittle-ductile
mechanism have been proposed.
Methods for probabilistic estimation of the stressed state of the pipeline structure from the point of view of fracture
susceptibility, which are based on the integration of the calculated field of principal stresses within the framework of the Weibull
statistics, have been developed. Functional dependences of Weibull coefficients on the properties of the metal, namely yield
stress and degree of strain hardening, were obtained for correct quantitative assessment of the state of critical structures based on
a complex analysis of the limiting state of steel pipelines under internal pressure.
Specific features of the limiting state under loading with internal pressure and bending moment have been investigated
based on an example of typical cases of operation damage of main pipeline elements such as local metal losses in the area of the
site weld. It was shown that nature of interaction of residual post-weld stress state of metal with operation stresses from the
geometry concentrator significantly affected the value of limiting pressure in the pipe. Besides, effect of the additional bending
moment on load-bearing capacity of the pipeline section with isolated flaw of local corrosion wall thinning has been determined.
The change of failure probability of the structure as a result of internal pressure and bending moment loading at various geometry
dimensions of thinning flaw has been investigated based on the results of integral analysis of the pipeline flawed section state.

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Published

2018-06-06

How to Cite

Milenin, O. (2018). Numerical prediction of the current and limiting states of pipelines with detected flaws of corrosion wall thinning. JOURNAL OF HYDROCARBON POWER ENGINEERING, 4(1), 26–37. Retrieved from https://ogpe.nung.edu.ua/index.php/jhpe/article/view/48