Materials research and evaluation for geothermal corrosion environments. Progress report, December 15, 1975--December 15, 1976

Abstract

In terms of stress corrosion cracking resistance in sour brines, a recently developed modified 4135 steel has exhibited a design yield strength advantage of approximately 10,000 psi over the standard 4130 (Y.S. approx. = 110,000 psi) widely employed for casing, production tubing, etc. For a specified strength level, resistance to SCC is improved by higher tempering temperatures in heat treating, giving rise to an approach to new alloy design for constructional type steels. Preliminary results indicate that improvements over the modified 4135 can be achieved. Increasing test temperature reduces the susceptibility to SSC in the constructional steels thus moderately raising the useful strength level; but immunity cannot be achieved. On the other hand, susceptibility of the highly alloyed materials increases with increasing temperature, at least up to 425/sup 0/F. Increasing salt concentration from 5%-20% did not appear to increase susceptibility to SCC. Of the higher strength, corrosion resistant materials, MP35N has shown outstanding resistance to general corrosion and SCC. However, recent reports indicate that certain conditions related to anisotropy may cause SCC. An age hardenable austenitic alloy, A-286, is susceptible to SSC in the fully aged condition (190 KSI) at 325/sup 0/F and 425/sup 0/F. Susceptibility is greatly reduced by over-ageing to a still respectable strength level of 155 KSI.