Development of High-Strength Ni Alloy OCTG Material for Sour Environment

A new high-strength Ni alloy OCTG has been developed for use at high temperature and high pressure corrosive well. Corrosion resistance of the new alloy was evaluated using 4 point bend beam test method and slow strain rating test method in solution containing hydrogen sulfide gas and chloride ion. It was clarified from laboratory tests that the new alloy has equivalent stress corrosion cracking resistance to UNS N08535 of 110ksi grade. In addition to that, the influence of alloying nitrogen in austenitic alloy as soluble element for SCC susceptibility was investigated in this study. In the past studies, whether nitrogen was effective or detrimental on SCC susceptibility showed both results. Since alloying nitrogen can effect on not only corrosion resistance but also mechanical properties, nitrogen contents and the strength of cold-rolled material will be considered as the factors of SCC. The effect of nitrogen on localized corrosion resistance will be discussed by results of SCC test, surface film analysis, etc.