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International Journal of Corrosion
Volume 2016, Article ID 6930234, 6 pages
http://dx.doi.org/10.1155/2016/6930234
Research Article

Investigation of Stress Concentration and Casing Strength Degradation Caused by Corrosion Pits

State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing, China

Received 21 July 2016; Accepted 15 September 2016

Academic Editor: Ksenija Babic

Copyright © 2016 Wei Yan et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Downhole casing and tubing are subjected to corrosion in many cases because of the exposure to corrosive environment. A more serious problem is that pitting corrosion occurs in the casing inner surface. Meanwhile, downhole strings are subjected to various forms of mechanical loads, for example, internal pressure load, external collapse load, or both. These loads acting on the corrosion pits will cause stress concentration and degrade the casing strength. Thus, it is essential to evaluate the stress concentration degree reasonably. The SCF (stress concentration factor) is usually used to characterize the degree of stress concentration induced by corrosion pits. This paper presented a comparison on the SCFs regarding the analytical method for a single pit and experimental method for double pits. The results show that the SCF of a single pit depends mainly on the depth of the corrosion pit; however, the SCF of the double pits strongly depends on the pits distance. A correction factor of 1.3 was recommended in the double pits SCF prediction model.