ASME SA789 UNS S31803 Duplex Stainless Steel Tube

Inside ASME Section II Part A, SA-789 / SA-789M adopts the seamless and welded duplex stainless tubing product standard for general service. Grade UNS S31803 is the widely ordered 22Cr duplex chemistry with chromium 21.0–23.0%, nickel 4.5–6.5%, molybdenum 2.5–3.5%, and nitrogen 0.08–0.20% at carbon ≤0.030%. Buyers still meet S31803 on older drawings even though many modern 2205 purchases have migrated to the tighter nitrogen-controlled UNS S32205 row.

SHH STEEL can produce and supply ASME SA789 UNS S31803 duplex stainless steel tube as seamless product and as welded product without filler metal, in the OD × wall sizes exchanger and process buyers commonly request, with EN 10204 3.1 certificates covering ladle chemistry, tensile and hardness, and Table 2 heat treatment. We manufacture to the SA-789 acceptance tables for this UNS — not a vague “2205 equivalent” claim. Dual SA-789/A789 marking is offered when the purchase order asks for both; this page stays ASME-led for Code work.

When a datasheet already says 2205 / S32205, prefer SA789 S32205 because its nitrogen floor is higher (0.14–0.20% versus 0.08–0.20% on S31803) and its tensile floor is 95 ksi rather than 90 ksi. Lean duplex alternatives include SA789 S32304; for seawater PREN ≥40 duty step to SA789 S32750. Related plate: A240 / SA240. Hub: SA789/SA789M.

Table 1 fixes the heat analysis. Product analysis, when ordered, follows Section 8 via A1016/A1016M and A480/A480M tolerances. The nitrogen window 0.08–0.20% is the practical differentiator versus S32205: heats can land at the low end of nitrogen and still meet S31803, which is why many corrosion-critical buyers now specify S32205 explicitly.

Mid-range PREN estimate using %Cr + 3.3×%Mo + 16×%N with Cr ≈22, Mo ≈3.0, N ≈0.14 gives PREN ≈ 22 + 9.9 + 2.2 ≈ 34. That is an engineering figure from stated chemistry, not a Code minimum — SA-789 does not publish PREN for S31803. Sulfur is held to 0.020% max, tighter than some older duplex rows.

Table 4 sets the S31803 tensile and hardness floors after final heat treatment. Lot rules follow Section 9. Properties do not apply below 1/8 in. OD or 0.015 in. wall.

Note the 90 ksi tensile minimum — five ksi below SA789 S32205. Yield matches at 65 ksi on S31803 versus 70 ksi on S32205. Hardness ceiling is 290 HBW / 30 HRC for both. Source: ASME BPVC.II.A-2023 SA-789 Table 4. Design allowables live in Section II Part D.

Section 5 permits seamless or welded manufacture with no filler metal on the welded route. Autogenous seam plus full-tube heat treatment is the SA-789 welded product model, distinct from filler-welded SA-312 pipe, and the stencil must state which route was actually used for each length shipped.

Flaring to a minimum 10% inside-diameter expansion covers seamless lots under Section 9. Welded lots take a flange test on one end of one tube per lot plus reverse flattening on a specimen from each 1500 ft [450 m] of finished tubing. Tension and hardness tests apply to both manufacture routes on the lot basis defined in the notes to Section 9. SHH STEEL produces both SA789 S31803 routes and marks seamless or welded clearly on the tube and the EN 10204 3.1 MTC.

Specify OD × wall (average unless minimum wall is ordered) and length in tube language. Table 5 sets the OD-group tolerances; clause 12.2 covers thin-wall ovality.

Source: ASME BPVC.II.A-2023 SA-789 Table 5. SHH STEEL quotes average-versus-minimum wall explicitly on every S31803 enquiry.

UNS S31803 under ASME SA-789 is the governing designation here. “2205” in shop language sometimes means S31803 and sometimes S32205 — that ambiguity is exactly why Code POs should spell the UNS number.

Do not mark S31803 as S32205 (or the reverse) without meeting the tighter chemistry and tensile row.

Table 2 requires 1870–2010 °F [1020–1100 °C] with rapid cooling in air or water for S31803 — the same temperature band as S32205.

Direct quench after hot forming is allowed for seamless tubes when temperature stays at or above the minimum. Rapid cooling limits sigma-phase risk. SHH STEEL ships only Table 2 heat-treated SA789 S31803 with the treatment on the MTC.

S31803 delivers the classic duplex advantage — chloride SCC resistance well above 304/316 — with estimated PREN near the mid-30s when nitrogen sits mid-band. Heats at the low end of the 0.08–0.20% nitrogen window will land lower on PREN, which is the practical reason corrosion specifications often migrate to S32205.

Seawater and sour PREN ≥40 duty belong on SA789 S32750 or sister super duplex, not on stretched S31803. Respect 475 °C embrittlement and sigma risk on prolonged elevated-temperature exposure, as flagged in SA-789 scope language and duplex metallurgy practice.

S31803 tube still appears across process heat exchangers, coolers, and Code general-service duplex tubing where drawings have not yet been updated to S32205. Select it when the UNS is written; otherwise discuss whether S32205 is the better modern default.

New 2205-class designs usually specify SA789 S32205.

Fabrication welds commonly use 2209-type duplex filler under a qualified WPS; the SA-789 welded tube seam itself stays autogenous. Heat input, interpass limits, and cooling rate control ferrite balance in the HAZ.

Overheating promotes intermetallics; under-alloying the weld metal leaves excess ferrite. SHH STEEL can discuss typical filler practice; the fabricator owns WPS/PQR under the applicable Code.

Default finish for ASME SA789 S31803 is heat-treated and pickled or otherwise descaled so the tube is free of excessive mill scale and suitable for inspection under Section 13. A slight amount of oxidation is not treated as scale, while special bright-annealed or Ra-controlled finishes must be written into the purchase order as agreement items.

SHH STEEL quotes those special finishes against the written enquiry rather than assuming them with the grade stamp. Fouling-sensitive or hygienic exchanger specifications that quote an Ra maximum should treat that limit as a commercial overlay on top of SA-789 product requirements.

Heat analysis, tension, hardness, flare or flange tests, reverse flattening for welded tube, and hydro or NDE on every length form the base program. Hydrostatic factor 64000 (441.2) applies. Manufacturer selects hydro versus NDE unless the PO locks the method.

Marking shows seamless or welded and wall basis. SHH STEEL 3.1 MTCs tie heat, chemistry, mechanicals, heat treatment, and test method together.

Tagged bundles leave SHH STEEL with ASME SA789, UNS S31803, seamless or welded identity, OD × wall, heat number, and purchase-order reference on the labels, plus end protection suited to the length mix so receiving can check the shipment before opening every certificate packet.

Export packing options include wrapped bundles and wooden cases for bright-finished or small-bore material. Incoterms, packing lists, and document flow follow the order acknowledgment agreed at quotation.

SHH STEEL produces and supplies ASME SA789 UNS S31803 as manufactured Code Book tube — seamless and welded — with honest documentation of the nitrogen range that separates this grade from SA789 S32205. We do not silently upgrade or downgrade between the two UNS numbers.

If your corrosion spec really needs the S32205 nitrogen floor and 95/70 ksi tensile pair, we quote SA789 S32205. If the drawing locks S31803, we produce S31803. Dual marking and third-party inspection are available on request.

SHH STEEL can produce and supply ASME SA789 UNS S31803 tube to the edition, route, and finish on your enquiry. Capability and Stock / Available sizes follow.

Stock / Available sizes — Common enquiry bands include OD about 12.7–50.8 mm with usual BWG / metric walls; larger Table 5 groups by agreement. Cut lengths on request. Send OD × wall, route, and quantity — we confirm production and near-stock without invented tonnage claims.

List ASME SA789 UNS S31803, seamless or welded, OD × wall, wall basis, length, and quantity on the enquiry.

ASME SA789 UNS S31803 remains the legacy 22Cr duplex tubing designation still written on many Code and process drawings, sitting beside the tighter modern S32205 row. SHH STEEL produces and supplies seamless and welded (no filler metal) SA789 S31803, heat-treated per Table 2, tested per Section 9, and certified on EN 10204 3.1 MTCs. Spell the UNS clearly so S31803 is not confused with S32205 on the stencil. For technical follow-up, contact admin@steelspecs.com.