CARBON DIOXIDE STRESS CRACKING IN OIL PRODUCTION

Abstract

The article describes stress corrosion cracking (SCC) of pipe string elements associated with exposure to carbon dioxide. SCC can occur in solutions containing H2S, CO2, ammonia, nitrates, chlorides, acids, alkalis, etc. The article shows two typical examples of stress corrosion cracking of high-carbon steels of tubular string elements (grades 40X13, 40XH) after operation in field environments whose well products do not contain hydrogen sulfide. The possible mechanism of carbon dioxide stress cracking was analyzed in comparison with carbonate stress corrosion cracking (Carbonate Stress Corrosion Cracking) described in the API 571-2020 standard. It is shown that an integral part of the mechanism of carbon dioxide stress cracking is the growth and development of cracks during hydrogen evolution in the cathodic reaction. The general metallurgical and operational characteristics of steel elements of tubular strings subjected to carbon dioxide stress cracking are given, which are in good agreement with the available foreign literature data. Based on the results of operation, it was confirmed that in «conventional» oilfield systems with carbon dioxide, equipment failures by the mechanism of carbon dioxide stress cracking are possible. Examination of the described failures included the following assessment methods: analysis of the accompanying documentation, visual-measuring control, micro-examinations by light microscopy and scanning electron microscopy, tests to determine the mechanical properties of the metal.Carbon dioxide stress cracking was observed in the presence of the following factors: carbon dioxide environment (in the absence of hydrogen sulfide); high concentration of carbon in steel (0.4 % wt.); increased hardness of steel (from 30.3 to 33.9 HRC); the presence of constant and alternating mechanical loads.