Assessing the Strength of Casing Pipes that Contain Corrosion Pit Defects

doi:10.11885/j.issn.1674-5086.2017.06.21.01

Abstract

Abstract: The corrosion of oilfield casing pipes has become increasingly severe in recent years. According to statistical data, the corrosion of the casing pipes in each block of the Dagang Oilfield has reached 34.4%, leading to problems such as severe casing damage and leakage. To address this problem, this study constructed three-dimensional finite element models for casing pipe-concrete sheath-ground strata systems with casings that contain either one or two corrosion pit defects based on elasticity theory and mechanical models of casing pipes with spherical corrosion pits. By studying the patterns of stress distribution in casing pipes using the model with two corrosion pit defects, it was found that the model with a single corrosion pit defect could be used to evaluate the casing strength if the gap between the corrosion pits exceeds 0.65 mm. The effects of the corrosion pit radius and depth on the strength of the casing pipes and the variational patterns of a casing pipe's stress concentration factors were studied herein using the single-corrosion pit defect model. The effects of steel grade on the loading of casing pipes with corrosion pitting in hydrated strata were also investigated. Consequently, the maximum stress and stress concentration factors in the casing pipes with corrosion pitting both increased with the increasing corrosion pit depth. The stress concentration factor also increased as the radius of the corrosion pit decreased. The stress concentration factor may exceed 2.0 in certain cases. Furthermore, the strata hydration accelerated the damage of casing pipes that contained corrosion pits.

Key words: corrosion pit defects, stress concentration factor, maximum stress, finite element, casing damage

CLC Number:

TE983

LIAN Zhanghua, LUO Zeli, YU Hao, LIU Yang, HE Yong. Assessing the Strength of Casing Pipes that Contain Corrosion Pit Defects[J]. 西南石油大学学报(自然科学版), 2018, 40(2): 159-168.

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URL: http://journal15.magtechjournal.com/Jwk_xnzk/EN/10.11885/j.issn.1674-5086.2017.06.21.01

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