|Description / Abstract
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|This report covers many of the "lean," "standard," and "super"
grades of duplex stainless steels (DSS) most commonly used within
refineries. The definitions of these terms have not been firmly
established by the industry, and vary between literature references
and materials suppliers. Table 1 shows how the various grades are
being classified into "families" for the purposes of this report.
The UNS numbers of the standard grades being used for corrosive
refining services include S31803 and S32205, while the super grades
include S31260, S32520, S32550, S32750, S32760, S39274, and S39277.
The grades which are labeled as "semi-lean" include S32304 and UNS
S32003, have either lower Cr or Mo than the standard grades, and
are used in some process services that are less aggressive. These
alloys and lean duplexes, such as S32101, have also been used for
storage tanks and structural applications primarily for their
higher strength compared to carbon steel (CS). It is observed that
new DSS alloys 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, exchanger, and
tank applications. The use of DSS for tanks is addressed by API
650, Appendix X. Later revisions of this report may consider
expanding the scope to include castings and other product forms for
pumps, valves, and other applications. Use of DSS as a cladding is
also not included within the scope of this document.
The majority of refinery services where DSS are currently being
used or being considered in the refining industry contain:
a) a wet, sour (H2S) environment which may also
contain hydrogen, ammonia, carbon dioxide, chlorides, and/or
b) water, containing chlorides, with or without hydrocarbons;
c) hydrocarbons with naphthenic acids at greater than 200 °C
(400 °F) but below the maximum allowable temperatures in the ASME
Code for DSS (260 °C to 343 °C [500 °F to 650 °F] depending on the
The specific plant locations containing these services are
described in a later section and the report scope will be limited
to these environments.
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