resistant alloy cra corrosion resistant alloys are well suited for service in extreme environments these alloys form a thick and stable oxide layer on their surface protecting the alloy from the corrosive environment however the metal body 50 may be comprised of a metal other than a cra examples of corrosion resistant alloys that may be used for the metal body 50 are nickel and cobalt alloys such as uns n07718 uns n07725 uns n09925 uns r30006 and uns r31233 uns n07718 uns n07716 uns n07725 and uns n09925 are generally classified as precipitation hardenable nickel alloys uns r30006 and uns r31233 are generally categorized as cobalt based alloys these nickel and cobalt alloys and others not listed are intentionally alloyed and heat treated to provide the corrosion resistance and strength the combination of elements makes the alloy resistant to hydrogen embrittlement and stress corrosion cracking these alloys are resistance to general corrosion pitting crevice corrosion and stress corrosion cracking in many aqueous environments including sulfides and chlorides however an alloy other than the aforementioned alloys may be used alloys uns n07718 uns n07716 uns n07725 uns n09925 and uns r31233 are listed in annex a of part 3 of nace mr 0175 as cras part 3 of nace mr 0175 is entitled u201c cracking resistant cras corrosion resistant alloys and other alloys u201d annex a is entitled u201c environmental cracking resistant cras and other alloys u201d precipitation hardened nickel based alloys that are cras and their.