This paper presents two case histories from oil wells in the Middle East in which hardened and tempered alloy steel completion equipment underwent severe corrosion from CO2. The fact that in one case the API J-55 tubing string did not exhibit corrosion but did in another case indicates that corrosion in CO2 service can be influenced by several factors: the steel composition, its strength, or its heat treatment. A study was initiated to determine which properties or combination of properties should be altered to remedy the problem. Consideration was given to the use of different steels and/or heat treatments for completion equipment in order to achieve corrosion performance in CO2 environments similar to that of J-55 tubing.

It was determined that the alloy steel normally used for this equipment could not be reprocessed with heat treating to provide the needed corrosion resistance without a compromise of its metallurgical properties. This indicated a need to investigate alternative materials. The subsequent investigation of 9Cr-1Mo and 410 stainless steels found them to have superior corrosion resistance and good metallurgical properties. Therefore, these will be the materials of choice for completion equipment used to replace existing alloy steel equipment in these wells.

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