Keywords: pipelines, corrosion defects, pit corrosion, residual strength, failure pressure, semi-empirical methods, finite element analysis.

Semi-empirical methods for isolated defects [1] are employed to compute the failure pressure of corroded pipes. Numerical models employing the finite element method with shell elements are constructed, and numerical results are compared to those obtained using semi-empirical methods. The pipe material chosen is the API-X65 steel, and a Von Mises plasticity model is adopted. Results for short defects are also compared with experimental results.

Results show that, in general, the semi-empirical methods are conservative. The DNV RP-F101 method appears to be less conservative than the B31 G and Rstreng 085 dl methods. Further, the Rstreng 085 dl method is not conservative for longer defects. The conclusion is that those methods should be used in actual practice for they provide reliable results.

Analytical methods are not available to estimate the residual strength of pipes containing corrosion pits. Thus, this task must be accomplished using a numerical procedure. Experimental investigation has demonstrated that cracks emanate from pits [2] and they will evolve. Thus, the present study aims at describing the stress distribution around pits present on a pipe. Internal pressure is applied incrementally in a plasticity analysis. Analyses are carried out for various depths, several pressure values and three different pipe diameters. Results consistently show an increase in stress with the increase in pit depth and also with diameter increase. Further, it is found that maximum stress is located at the bottom or, in some cases, slightly up on the wall.

1

A.C. Benjamin, E.Q. Andrade, "Modified method for the assessment of the remaining strength of corroded pipelines", IBP413-03, Rio Pipeline Conference & Exposition 2003, Rio de Janeiro, 2003.

2

A. Turnbull, L.N. McCartney, S. Zhou, "Modeling of the evolution of stress corrosion cracks from corrosion pits", Scripta Materialia, 54, 575-578, 2008. doi:10.1016/j.scriptamat.2005.10.053

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £145 +P&P)