ASTM A790

Applies to: Seamless and welded ferritic/austenitic (duplex) stainless steel pipe; key grades S31803 (2205), S32205, S32750 (Super Duplex), S32760; corrosive service in oil & gas, offshore topside, chemical processing, and desalination.

Does NOT cover: Standard austenitic stainless pipe (ASTM A312); lean duplex or hyper duplex without verified grade listing; tubes for heat exchangers (use ASTM A789).

• Solution annealing heat treatment with rapid quench (mandatory for all grades)
• Ferrite/austenite phase balance verification (typically 40–60% ferrite by ASTM E562)
• Pitting resistance equivalent number (PREN ≥ 35 for S31803, ≥ 40 for super duplex)
• Corrosion test per ASTM G48 Method A (ferric chloride pitting test)
• Hydrostatic test or NDE per product specification
• Intermetallic phase check for super duplex grades

ASTM A790 covers duplex stainless steel pipe for service where austenitic grades lack adequate corrosion resistance or strength. The dual ferritic-austenitic microstructure provides approximately double the yield strength of 316L (≥65 ksi for S31803) and superior chloride stress-corrosion cracking resistance, making it the dominant material for offshore and desalination piping systems.

Engineering note: Duplex pipe must be supplied in the solution-annealed and quenched condition — improper heat treatment produces sigma phase or other intermetallics that severely degrade toughness and corrosion resistance. For sour service, verify PREN and specify the corrosion test batch on the material requisition.