Advanced material of nickel-based alloy for Oil Country Tubular Goods (OCTG ) has been developed in order to be usefully applied to sour condition and seawater injection well. At oil and gas services, injection of medium such as seawater, carbon dioxide and wet gas to well makes oil and gas be retrieved. These medium, however, causes deterioration of the corrosion environment. Hence, these conditions may require the usage of superior corrosion resistant alloy. The UNS No. of the material is N06845. The chemical composition of the one is 22wt.%Cr-45wt.%Ni-6wt.%Mo with tungsten, copper and nitrogen. The material type of the alloy complies with the condition for type 4d of nickel based alloy in ISO15156-3. The strength of the material is enhanced by alloying nitrogen and cold working so that it can be achieved to 125ksi of yield strength.
The developed alloy has exhibited equivalent stress corrosion cracking resistance in severe sour condition to conventional UNS N06255 (25wt.%Cr-50wt.%Ni-6wt.%Mo) with 125ksi grade. The alloying tungsten and copper advances the corrosion resistance of the material because effective corrosion products form at the surface of the metal under the sour condition. In addition to that, alloying tungsten and nitrogen as well as chromium and molybdenum improves the pitting and crevice corrosion resistance. The PREW (Pitting Resistance Equivalent number with tungsten (W); %Cr +3.3*(%Mo +0.5*%W ) +16*%N ) of this alloy achieves more than 50.
Key words: CRA, Stress corrosion cracking, Hydrogen sulfide, Seawater, Hydrogen Embrittlement, Cold Work, Chromium, Nickel, Molybdenum, Copper, Tungsten, Nitrogen.