NACE MR0175 / ISO 15156 governs material selection for oil and gas environments containing hydrogen sulfide. Understanding which clauses apply to your service conditions is the difference between a compliant - and a vastly over-engineered - material spec.
The standard breaks materials into three parts: carbon and low-alloy steels, CRAs (corrosion-resistant alloys), and other alloys. Each has environmental limits expressed in terms of partial pressure of H₂S, pH and chloride content.
The most common mistake we see: defaulting to Inconel 625 when 22Cr duplex would be more than sufficient - adding 5x material cost for service the cheaper grade can handle.