Abstract
The slow strain rate (SSR) test is a quick and simple method that is used to gauge the susceptibility of metals to stress corrosion cracking (SCC). This research uses the SSR method to study the effect of prior cold-work of API 5CT P110 martensitic casing and tubing steel on stress corrosion cracking (SCC). Two cold-work processes were used, namely, cold-rolling and tubular expansion. The steels were cold-worked to 10% and 20% levels of strain. Longitudinal tensile specimens were extracted from the rolled plates and the expanded tubes. In an solution test, the specimens were exposed to an environment of synthetic formation water, CO2 pressure of 200 psi (1.4MPa) and stretched to failure at a constant strain rate of 10-6 /sec at laboratory temperature. Two baseline tests were performed in air and under the same conditions of temperature and strain rate used for the environment test. The values of the yield strength, ultimate tensile strength (UTS), time to failure, elongation, and reduction in area were obtained using the data from the environment and baseline tests. The surface morphology was characterized using field emission scanning electron microscopy (FE-SEM) coupled with EDS and with X-ray diffraction. It was observed that an iron carbide film is formed on the surface of all specimens. The time to failure decreased for the cold-worked specimens in the solution from that of the cold-worked specimens in air except in the case of 20% expansion. The time to fracture in air and solution was identical. For the cold-rolled steels, the 10% cold-work shows the highest ductility and time to failure ratios, and the lowest stress corrosion index. The expanded steels did not show a significant change in the UTS between the 10% and 20% deformation in the solution environment. On the other hand the ductility of the 10% expanded specimens showed a dramatic loss in ductility.
