Whichever the end-user's piping standards specify.
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"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Generally for sour gas applications NACE standards is referred and material is selected as per the guidelines of NACE standard hence depending upon your gas applications delect appropriate material grade.What are you designing? can you just brief me out??