ASTM A790 DUPLEX / SUPERDUPLEX PIPE

WHAT IS DUPLEX?

Duplex steel UNS 2205 (UNS 31803 / UNS 32205) is a nitrogen-enhanced stainless steel developed to overcome the issues of the 300 series stainless steels as 316L and 317L (chloride stress corrosion cracking, under tensile stress in cases where the metal is exposed to fluids containing chlorides or by steel exposure to high temperatures). The term "duplex" refers to a family of stainless steels that have double structure - i.e. they are neither a fully austenitic SS structure, as 304 stainless, nor a standard ferritic, such as the 430 series. The microstructure of duplex steels consists of austenite pools surrounded by a continuous ferrite phase (approx 40-50% ferrite). The benefits of duplex steel is that it combines the qualities of a ferritic structure (high resistance to corrosion cracking and high tensile strength) with the qualities of a austenitic steels (easy manufacturing and good resistance to corrosion and erosion).The 2205 grade of the duplex family is the most widely used type for temperatures below 600 degrees F. UNS 2205 duplex steel finds application in marine projects, oil & gas exploration, closed loops water systems, desalinization plants, hydrocarbons storage and transportation, downstream refining, pulp and paper.

Duplex pipes match the following fittings materials: ASTM A815 (butt weld fittings) and ASTM A182 F51 / F60 (flanges / forged socket weld - threaded fittings ).

DUPLEX PIPES ASTM A790/A928

The ASTM A790 / ASME SA790 specification covers seamless duplex steel pipes (source ASTM):

The specification covers seamless and straight-seam welded ferritic/austenitic steel pipe for general corrosive service, with particular emphasis on resistance to stress corrosion cracking. The pipe shall be made by the seamless or an automatic welding process, with no addition of filler metal in the welding operation. Heat analysis shall be made to determine the percentages of the elements specified. Tension tests, hardening tests, flattening tests, hydrostatic tests and nondestructive electric tests shall be made to conform to the specified requirements. This abstract is a brief summary of the referenced standard. It is informational only and not an official part of the standard; the full text of the standard itself must be referred to for its use and application. ASTM does not give any warranty express or implied or make any representation that the contents of this abstract are accurate, complete or up to date.

1. Scope

1.1 This specification2 covers seamless and straight-seam welded ferritic/austenitic steel pipe intended for general corrosive service, with particular emphasis on resistance to stress corrosion cracking. These steels are susceptible to embrittlement if used for prolonged periods at elevated temperatures.

1.2 Optional supplementary requirements are provided for pipe when a greater degree of testing is desired. These supplementary requirements call for additional tests to be made and, when desired, one or more of these may be specified in the order.

1.3 Appendix X1 of this specification lists the dimensions of welded and seamless stainless steel pipe as shown in ANSI B36.19. Pipe having other dimensions may be furnished provided such pipe complies with all other requirements of this specification.

1.4 The values stated in either SI units or inch-pound units are to be regarded separately as standard. Within the text, the SI units are shown in brackets. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard. The inch-pound units shall apply unless the M designation of this specification is specified in the order. NOTE 1: The dimensionless designator NPS (nominal pipe size) has been substituted in this standard for such traditional terms as nominal diameter, size, and nominal size.

The ASTM A928 / ASME SA928 specification covers welded EFW duplex steel pipes (source ASTM):

This specification covers standard requirements for ferritic/austenitic (duplex) stainless steel pipe that is electric fusion welded with addition of filler metal suitable for corrosive service. Heat treatment shall be performed after welding and in accordance with specified temperature and quench conditions. Several grades of ferritic/austenitic steel shall conform to the requirements of the applicable specification and grade designation. Heat and product analyses shall be conducted and shall conform to the requirements for the particular grade. The plate used in making the pipe shall conform to the required tensile properties. The steel pipe shall undergo several mechanical tests including transverse tension test, transverse guided-bend test, nondestructive test, hydrostatic test, and nondestructive electric test. This abstract is a brief summary of the referenced standard. It is informational only and not an official part of the standard; the full text of the standard itself must be referred to for its use and application. ASTM does not give any warranty express or implied or make any representation that the contents of this abstract are accurate, complete or up to date.

1. Scope

1.1 This specification covers electric-fusion-welded steel pipe suitable for corrosive service. NOTE 1: The dimensionless designator NPS (nominal pipe size) has been substituted in this specification for traditional terms such as nominal diameter, size, and nominal size.

1.2 This specification covers grades of ferritic/austenitic steel as indicated in Table 1. The selection of the proper alloy and requirements for heat treatment shall be at the discretion of the purchaser, dependent on the service conditions to be encountered. (A) Except as indicated, common name, not a trademark, widely used, not associated with any one producer. (B) An AWS standard filler metal is not yet available for inclusion in this table. (C) A grade designation originally assigned by the American Iron and Steel Institute (AISI). 

1.3 Five classes of pipe are covered as follows:

1.3.1 Class 1—Pipe shall be double welded by processes using filler metal in all passes and shall be radiographed completely.

1.3.2 Class 2—Pipe shall be double welded by processes using filler metal in all passes. No radiograph is required.

1.3.3 Class 3—Pipe shall be single welded by processes using filler metal in all passes and shall be radiographed completely.

1.3.4 Class 4—Same as Class 3, except that the weld pass exposed to the inside pipe surface is permitted to be made without the addition of filler metal (see 6.2.2.1 and 6.2.2.2).

1.3.5 Class 5—Pipe shall be double welded by processes using filler metal in all passes and shall be spot radiographed.

1.4 Supplementary requirements covering provisions ranging from additional testing to formalized procedures for manufacturing practice are provided. Supplementary Requirements S1 through S4 are included as options to be specified in the purchase order when desired.

1.5 The values stated in either SI units or inch-pound units are to be regarded separately as standard. Within the text, the SI units are shown in brackets. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard. The inch-pound units shall apply unless the M designation of the specification is specified in the order.

CHEMICAL COMPOSITION

Cr
Ni Mo C N
22.0-23.0 4.50-6.50 3.00-3.50 .030 Max 0.14-0.20
Mn Si P S Fe
2.00 Max 1.00 Max .030 Max .020 Max Balance

 

 

 

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