Abstract
Objective: To explore the failure cause of buried pipelines in an oil and gas station. Method: The chemical elements and metallographic structure of the failed pipes were analyzed to evaluate whether the pipe body meets the requirements of relevant standards; the morphology and composition of the corrosion products were analyzed to discover the cause of corrosion. Result: The metal surface was rough and full of pitting pits with severe localized corrosion, and no crack of the metallic matrix was found. The corrosion products mainly contain Fe3O4 and a small amount of FeCO3, wherein Fe3O4 is the secondary corrosion product formed in the air, and FeCO3 is the corrosion product of CO2 in an oil and gas environment. The surface of the corroded product is loose in structure and easy to peel off, leading to further corrosion of the metallic matrix. Conclusion: The pipeline corrosion failure was caused by CO2-induced corrosion failure in the medium.
Highlights
Oil and gas pipeline corrosion is concerned with the safe operation of oil and gas production
CO2, H2S and high Cl- are more likely to lead to localized corrosion, and along with higher temperatures of some pipelines, the localized corrosion rate is accelerated, resulting in corrosion failure and bringing hidden hazards to the safe operation of pipelines
By analyzing the pipelines’ macro morphology, we found obvious localized corrosion on the inner wall of the pipelines, and the most serious corrosion occurs in the liquid deposition area at the bottom of the pipelines, mainly localized platform-shaped pitting corrosion
Summary
Oil and gas pipeline corrosion is concerned with the safe operation of oil and gas production. The corrosion is characterized by multi-phase flow corrosion mediums where the oil, gas and water coexist; CO2, H2S and acidic water are the main corrosion media. CO2, H2S and high Cl- are more likely to lead to localized corrosion, and along with higher temperatures of some pipelines, the localized corrosion rate is accelerated, resulting in corrosion failure and bringing hidden hazards to the safe operation of pipelines. It is necessary to carry out sampling analysis on the failed pipelines, explore the cause of corrosion failure, and take control measures to ensure their safe operation
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