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Research Papers: Pipeline Systems

Analytical Assessment of the Remaining Strength of Corroded Pipelines and Comparison With Experimental Criteria

[+] Author and Article Information
Sérgio B. Cunha

Professor
Mechanical Engineering Department,
State University of Rio de Janeiro,
R. São Francisco Xavier 524,
Rio de Janeiro, RJ 20550-900, Brazil
e-mail: sergio.cunha@uerj.br

Theodoro A. Netto

Professor,
Ocean Engineering Department, COPPE,
Federal University of Rio de Janeiro,
Av. Athos da Silveira Ramos,
149, Prédio do CT, Bloco I,
sala 108, Cidade Universitária,
Rio de Janeiro, RJ, 21941-909, Brazil

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received November 11, 2015; final manuscript received July 29, 2016; published online November 4, 2016. Assoc. Editor: Haofeng Chen.

J. Pressure Vessel Technol 139(3), 031701 (Nov 04, 2016) (11 pages) Paper No: PVT-15-1251; doi: 10.1115/1.4034409 History: Received November 11, 2015; Revised July 29, 2016

Recently published analytical solutions for the remaining strength of a pipeline with narrow axial and axisymmetric volumetric flaws are described in this paper, and their experimental and numerical validation are reviewed. Next, the domains of applicability of each solution are studied, some simplifications suitable to steel pipelines are introduced, and an analytical model for the remaining strength of corroded steel pipelines is presented. This analytical solution is compared with the standards most widely used in the industry for assessment of corroded pipelines: ASME B31G, modified ASME, and DNV RP-F101. The empirical and analytical solutions are compared with respect to their most relevant parameters: critical (or flow) stress, flaw geometry parameterization, and Folias or bulging factor formulation. Finally, two common pipeline steels, API 5L grades X42 and X100, are selected to compare the different corrosion assessment methodologies. Corrosion defects of 75%, 50%, and 25% thickness reduction are evaluated. None of the experimental equations take into account the strain-hardening behavior of the pipe material, and therefore, they cannot properly model materials with very dissimilar plastic behavior. The comparison indicates that the empirical methods underestimate the remaining strength of shallow defects, which might lead to unnecessary repair recommendations. Furthermore, it was found that the use of a parameter employed by some of the empirical equations to model the assumed flaw shape leads to excessively optimistic and nonconservative results of remaining strength for long and deep flaws. Finally, the flaw width is not considered in the experimental criteria, and the comparative results suggest that the empirical solutions are somewhat imprecise to model the burst of wide flaws.

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References

Figures

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Fig. 3

Axisymmetric model comparison with experiments and FEM simulations—SAE 1020 carbon steel

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Fig. 4

Axisymmetric model comparison with experiments and FEM simulations—ANSI 304 stainless steel

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Fig. 5

Narrow flaw model comparison with experiments and FEM simulations—SAE 1020 carbon steel

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Fig. 6

Narrow flaw model comparison with experiments and FEM simulations—ANSI 304 stainless steel

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Fig. 7

Narrow flaw model comparison with full scale experiments [14]—API 5L X60

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Fig. 8

Circumferential strain components versus flaw width

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Fig. 9

Effect of flaw width—SAE 1020 carbon steel d/t2 = 50%

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Fig. 10

Effect of flaw width—ANSI 304 stainless steel d/t2 = 50%

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Fig. 11

Analytical versus empirical models—API 5L X42 steel

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Fig. 12

Analytical versus empirical models—API 5L X100 steel

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Fig. 13

Effect of the pipe slenderness—API 5L X100 steel, 75% wall loss

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