Specification reference for seamless and welded ferritic-austenitic stainless pipe in pressure-containing service
ASTM A790 / A790M is the controlling spec for seamless and welded ferritic-austenitic (duplex and super duplex) stainless steel pipe in pressure-containing service: ASME B31.3 process piping, ASME Section VIII pressure-vessel internals, and NORSOK L-005 hydrocarbon piping. Ferralium 255 (UNS S32550) enters the standard alongside standard duplex S31803 / S32205, super duplex 2507 (S32750), and Zeron 100 (S32760). Pipe is supplied solution-annealed at 1040 to 1120 °C with rapid water quench, hardness ≤ 32 HRC for NACE MR0175 sour-service, ferrite content within 35 to 55%. Wall-thickness schedules SCH 5S, 10S, 40S, 80S, 160, and XXS per ASME B36.19, sizes NPS 1/8 through 24, with larger NPS available by piecing or by hot-rolled-and-welded route.
| Test | Method | Frequency |
|---|---|---|
| Chemistry (heat + product) | 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 | A790 paragraph 14, 1.5 × MAWP or 0.6 × yield | Each pipe length |
| Flattening test (welded only) | A790 paragraph 15 | Per finishing lot |
| NDE on weld (welded only) | EC or UT or RT, 100% of weld | Each pipe length |
| Microstructure / ferrite content | ASTM E562 point count, 35 to 55% | Per heat |
| S2 intergranular corrosion (supplementary) | ASTM A262 method E | Per heat where specified |
| S5 Charpy V-notch (supplementary) | ASTM E23 (typical 45 J at -46 °C) | Per heat where specified |
Seamless A790 pipe is produced by extrusion or by mandrel-pierce-and-elongate from solid billet, with no longitudinal weld seam. Welded A790 pipe is produced by roll-forming plate or strip and longitudinal-seam welding (TIG, plasma, or laser), then 100% NDE on the weld plus an internal weld bead removal pass for sizes ≥ NPS 4. For sour-service ASME B31.3 piping the seamless route is the conservative default; welded A790 is acceptable where the project specification permits and the welder qualification follows ASME IX with ferrite-content acceptance on the weld metal per AWS D10.18 or NORSOK M-630 supplementary requirements.
