Sweet Corrosion

Definition - What does Sweet Corrosion mean?

Sweet corrosion is the deterioration of metal due to contact with carbon dioxide or similar corrosive agents, but excluding hydrogen sulfide (H2S). Sweet corrosion typically results in pitting or material loss and occurs where steel is exposed to carbon dioxide and moisture. It is the corrosion of carbon and low-alloy steel by carbonic acid and its derivatives.

Sweet corrosion is a major problem in the oil and gas industry, costing billions of dollars every year. In gas condensate wells, sweet corrosion takes the form of deep pitting inside the tubing walls. The pitting is produced only at depths where the acidic gas contacts condensed water droplets.

Sweet corrosion is also known as CO2 corrosion.

Corrosionpedia explains Sweet Corrosion

Sweet corrosion is generally characterized first by simple metal dissolution followed by pitting. The corrodant is H+, derived from carbonic acid (H2CO3) and the dissolution of CO2 in the produced brine. The pitting leaves distinctive patterns (e.g., "mesa" corrosion), attributable to the metallurgical processing used in manufacturing the tubing.

Sweet corrosion is caused by the presence of carbon dioxide (CO2) dissolved in water to form carbonic acid (H2CO3). Corrosion increases as the concentration of CO2, system pressure, and temperature increase. This corrosion is typically slow, localized and results in pitting attack. Pits are very difficult to detect because of their tiny size and the corrosion products that cover them.

In oil and gas production and processing industries, corrosion inhibitors have always been considered the first line of defense against internal corrosion. Inorganic inhibitors, such as sodium arsenite (Na2HAsO3) and sodium ferrocyanide, were used in early days to inhibit carbon dioxide (CO2) corrosion in oil wells, but the treatment frequency and effectiveness were not satisfactory. This led to the development of many organic chemical formulations that frequently incorporated film-forming amines and their salts.

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