This report is limited to the 22% Cr and 25% Cr grades of DSS - the grades most commonly used within refineries. The UNS numbers of these grades include S31803, S32205, S31260, S32520, S32550, S32750, S32760, S39274 and S39277. Another grade, S32304 with about 23% Cr and very low Mo, has been used for storage tanks primarily for its higher strength compared to CS, but has lower corrosion resistance than the other DSS grades and is less-commonly used in refineries. Hence, it is not included in the scope, but is included in some tables and figures for comparison purposes. It is observed that new DSS are being introduced and are likely to continue to be introduced. These new grades can be reasonably placed in the context of this discussion based on their composition.
The product forms within the scope are tubing, plate, sheet, forgings, pipe, and fittings for piping, vessel and exchanger applications. Later revisions of this report may consider expanding the scope to include castings and other product forms for pumps, valves, and other applications.
The majority of refinery services where DSS are currently being used or being considered contain:
a. A wet, sour (H2S) environment which may also contain hydrogen, ammonia, carbon dioxide, chlorides and/or hydrocarbons,
b. Water, containing chlorides, with or without hydrocarbons, or
c. Hydrocarbons with naphthenic acids at greater than 200°C (400°F) (but below the maximum allowable temperature in the ASME Code for DSS [260°C - 343°C] [500°F - 650°F] depending on the grade).
The specific plant locations containing these services are described in a later section and the report scope will be limited to these environments. Appendix E is a form on which DSS applications, and especially corrosion experience can be reported, which will help expand the scope and improve the content of this document in future revisions. Completed reports can be sent to API at firstname.lastname@example.org or faxed to 202-962-4797.