Stress corrosion cracking and electrochemistry of C−Mn steels in CO−CO₂−H₂O environments

To discover if stress corrosion cracking (SCC) of C−Mn steel is possible at ambient pressure and temperature in a CO−CO₂−H₂O environment.

Approach involved electrochemical testing, slow strain rate testing (SSRT) and fractography. The chemistry within a crack or crevice during SCC differs from that of the bulk environment. To simulate this condition, a specimen was designed containing a steel plate, microelectrodes and artificial crevice. Electrochemical tests were performed to discover if conditions likely to cause SCC could be achieved. Slow strain rate tests and fractography was also carried out to support the electrochemical data.

Results indicated that CO can adsorb onto the metal and that localized corrosion occurred at defects in the adsorbed CO layer due to CO₂, which led to the onset of SCC. Consequently, larger anodic and cathodic currents were measured with or without a crevice, when CO₂ was in solution. Similar behaviour was observed on the microelectrodes. Regions of brittle fracture were discovered on the specimen surface after SSRT were conducted in a vapour phase environment. After such tests, the ductility of the steel was found to be impaired.

Practically the results could help to predict the potential range in which SCC may occur.

Paper is new because previous results were at high pressures. However, results indicate that SCC is a danger at atmospheric pressure. The paper is of value to people in the oil and gas industry.