Specification reference for seamless and welded ferritic-austenitic stainless tubing in general service
ASTM A789 / A789M is the controlling spec for seamless and welded ferritic-austenitic (duplex and super duplex) stainless steel tubing for general service. The standard accepts standard duplex S31803 / S32205 (PREN ~35), Ferralium 255 (UNS S32550, PREN ≥ 40), super duplex 2507 (UNS S32750, PREN ≥ 41), Zeron 100 (UNS S32760, PREN ≥ 40), and the 25Cr lean duplex grades. The tube is supplied solution-annealed at 1040 to 1120 °C with rapid quench, hardness ≤ 32 HRC for NACE MR0175 sour-service compliance, ferrite content within 35 to 55% per ASTM E562 point count. Each piece is hydrostatic-tested per A789 paragraph 13 to 1.5 times the maximum allowable pressure or to a maximum stress of 0.6 of the specified minimum yield strength.
| Test | Method | Frequency |
|---|---|---|
| Chemistry | Heat analysis + product analysis on request | Per heat |
| Tensile | ASTM A370 / E8 | Per heat per finishing lot |
| Hardness | ASTM E18 (HRC) | Per heat per finishing lot |
| Hydrostatic test | A789 paragraph 13 | Each tube length |
| Flattening test (welded only) | A789 paragraph 14 | Per finishing lot |
| Reverse-flattening test (welded only) | A789 paragraph 15 | Per finishing lot |
| NDE (welded only) | EC or UT, 100% of weld | Each tube length |
| Microstructure / ferrite content | ASTM E562 point count | Per heat |
| Intergranular corrosion (supplementary S2) | ASTM A262 method E | Per heat where specified |
| Charpy V-notch (supplementary S5) | ASTM E23 | Per heat where specified |
A789 covers tubing for general service: heat-exchanger tube, instrumentation tube, hydraulic tubing, and condenser tube. A790 covers piping for ASME B31 service: process piping, NORSOK L-005 hydrocarbon piping, and pressure-vessel internal piping. The chemistry and heat-treat requirements are identical between the two standards; the dimensional / wall-thickness conventions and supplementary test requirements differ. For tube-OD products specify A789; for NPS-pipe products specify A790.
