Stress corrosion cracking (SCC) susceptibility of a tempered martensite downhole tubular steel were evaluated in CO2 partial pressures from 500-3000 kPa and different strain rates from 5×10-7 −2 ×10-6 S-1 at 175°C in carbonate-bicarbonate environments. Constant extension rate tests coupled with a high temperature/high pressure autoclave were used. Results revealed the occurrence of SCC at CO2 partial pressure from 500-1500 kPa. However, at CO2 partial pressures greater than 1500 kPa, SCC susceptibility decreased and uniform corrosion was observed without cracking. In addition, increasing strain rate decreased SCC susceptibility. Corrosion products and cracks distribution were analyzed by X-ray diffraction and scanning electron microscopy. The occurrence of SCC was attributed to the formation of protective corrosion products mainly iron carbonate layer on the surface. Moreover, delineation of the prior austenite grain boundaries indicated that the majority of SCCs propagated along the grain boundaries.

Subject
Strain rate, Steel surfaces, Materials, Intergranular stress corrosion cracking, Corrosion cracking, Partial pressures, Corrosion products, Steel, Carbonate stress corrosion cracking, Grain boundary, Stress corrosion cracking, Ductility, Martensite
Keywords:
Stress Corrosion Cracking, Carbonate-Bicarbonate, CO2 Corrosion, Tubular Steels, Downhole Environments
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2012
Association for Materials Protection and Performance (AMPP)
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