Open Access

ARTICLE

A Model for the Determination of Semi-Circular Spot Corrosion Damage and Residual Strength in Oil Pipes

Hongtao Liu¹, Maoxian Xiong¹, Bo Zhang^2,*, Junfeng Xie¹, Jinrui Deng¹, MifengZhao², Ruijing Jiang¹, Yushan Zheng¹

1 Research Institute of Oil and Gas Engineering Tarim Oilfield Company, PetroChina, Korla, 841000, China
2 CNPC Research Institute of Safety and Environment Technology, Beijing, 102206, China

* Corresponding Author: Bo Zhang. Email:

(This article belongs to the Special Issue: Fluid Flow and Materials Strength related to the Wellbore Safety)

Fluid Dynamics & Materials Processing 2023, 19(6), 1709-1720. https://doi.org/10.32604/fdmp.2023.025513

Received 18 July 2022; Accepted 25 October 2022; Issue published 30 January 2023

Abstract

Pitting corrosion often occurs due to the presence of various corrosive substances, such as CO₂ and H₂S, in the pipe service environment. As a result of this process, the residual strength of oil pipes is reduced and this can compromise the integrity of the entire pipe string. In the present work, a model is introduced on the basis of the API579 standard to determine the so-called stress concentration coefficient. The model accounts for pitting corrosion shapes such as shallow semi-circles, semi-circles, and deep semi-circles. The relationship between the corrosion pit depth and opening diameter and the residual strength of the oil casing is obtained. The results show that the influence of the pit opening diameter on the stress concentration coefficient is smaller than that of the pit depth. For a constant pit opening diameter, the coefficient increases gradually with increasing the pit depth. The compressive strength and internal pressure strength of the carbon steel oil casing decrease accordingly. When the depth of the corrosion pit is relatively small, the growth of the coefficient is slower; when the depth of the corrosion pit increases to a certain value, the increase in stress concentration coefficient becomes obvious.

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Keywords

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