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——Assessing the challenges of 'sweet' corrosion and protective strategies for high-performance materials
Understanding Sweet Corrosion (CO2) in Coiled Tubing:
Learn how CO2 causes pitting and fatigue failure in oil wells and why high-performance duplex steel and nickel alloys are the essential solution.
The widespread presence of carbon dioxide (CO2) in oil and gas wells is one of the main threats to the failure of coiled tubing. This phenomenon is known as "Sweet Corrosion" in the industry, which poses a serious challenge to the structural integrity and service life of continuous tubing.
The principle of carbon dioxide corrosion is that when CO2 dissolves in formation water, it forms corrosive carbonic acid (H2CO3). This weak acid will undergo electrochemical reactions with steel, leading to metal dissolution. Unlike other forms of corrosion, CO2 corrosion often manifests as highly destructive localized corrosion, such as rapid pitting, which can penetrate the pipe wall more quickly than uniform corrosion and lead to leakage.
Control line tubing needs to withstand repeated bending fatigue during operation, while also transporting high-pressure fluid internally. If there are pitting corrosion pits caused by CO2 corrosion in the pipe body, these small defects will become stress concentration points, greatly accelerating the propagation of fatigue cracks, and ultimately leading to sudden fracture of the pipe column under high pressure, causing major safety accidents.
High performance alloy materials, such as duplex stainless steel and nickel alloys, provide excellent solutions. MTSCO deeply understands this challenge. Siri Tubing, a self owned factory established in 2024, focuses on producing welded coiled tubing suitable for harsh environments. We use advanced materials such as 2205 and 2507 duplex steels, as well as Alloy 625 and Alloy 825 nickel alloys. These materials, with their high content of chromium, molybdenum, and nickel, can effectively resist CO2 corrosion and pitting corrosion caused by chlorides. Our coiled tubing can reach a single roll length of up to 50000 fts and have undergone 100% high-pressure testing, providing reliable protection against sweet corrosion for global oilfield service customers.
