ASME SA789 UNS S31260 Duplex Stainless Steel Tube

ASME SA-789 / SA-789M sits in Section II Part A of the Boiler and Pressure Vessel Code as the adopted product standard for seamless and welded ferritic/austenitic stainless steel tubing for general service. In the 2023 BPVC text the grade sheet is identical with ASTM A789/A789M-18, but the governing name on a Code purchase remains SA-789. Grade UNS S31260 is the tungsten- and copper-bearing 25Cr duplex listed in Table 1 with chromium 24.0–26.0%, nickel 5.5–7.5%, molybdenum 2.5–3.5%, nitrogen 0.10–0.30%, copper 0.20–0.80%, and tungsten 0.10–0.50%, at carbon ≤0.030%.

SHH STEEL can produce and supply ASME SA789 UNS S31260 duplex stainless steel tube as seamless product and as welded product with no filler metal in the seam, in the OD × wall sizes heat-exchanger and process buyers usually enquire, with EN 10204 3.1 certificates that carry ladle chemistry, tensile and hardness results, and the Table 2 heat-treatment record. We manufacture this grade under the SA-789 acceptance tables rather than trading an unverified “25Cr duplex” label. Dual SA-789/A789 stencil marking is available when the purchase order asks for both names; this page stays ASME-first for Code work.

S31260 is titled Duplex on this series (not Super Duplex), even though tungsten and the higher molybdenum push PREN toward the upper edge of the standard-duplex window. Buyers who need a simpler 25Cr row without W/Cu often look at SA789 S31200; the mainstream 22Cr reference is SA789 S32205; for PREN ≥40 offshore duty the usual step-ups are SA789 S32750 or SA789 S32760. Related plate is ordered under A240 / SA240. Full grade set: SA789/SA789M.

Table 1 of ASME SA-789 fixes the heat analysis for S31260. Product analysis, when Section 8 or the purchase order invokes it through A1016/A1016M, uses the A480/A480M product-analysis tolerance annex; those tolerances are not reprinted inside SA-789. Copper and tungsten are intentional alloying additions on this grade — not residuals — and both appear with ranges rather than ellipses, so the MTC must report them.

Reading the row: molybdenum at 2.5–3.5% plus tungsten and copper distinguish S31260 from the leaner 25Cr row of S31200. Using PREN = %Cr + 3.3×%Mo + 16×%N on mid-range aims (Cr ≈25, Mo ≈3.0, N ≈0.20) gives PREN ≈ 25 + 9.9 + 3.2 ≈ 38. Some industry practice also credits tungsten with a partial PREN contribution (often 0.5×%W in mill literature); SA-789 itself does not define that term for this grade, so the W-adjusted figure is a trade estimate only. Either way, S31260 sits at the high end of standard duplex pitting resistance without meeting the footnote PREN ≥40/41 rules written for S32760/S32750.

Table 4 of ASME SA-789 sets S31260 tensile and hardness floors after final heat treatment. Lot sampling follows Section 9 (and Notes 1–2 for lot definition). Mechanical properties do not apply below 1/8 in. [3.2 mm] OD or 0.015 in. [0.4 mm] wall.

The 100/65 ksi pair matches S31200 on tensile and yield, while the hardness ceiling is one Rockwell point higher (30 HRC / 290 HBW versus 29 HRC / 280 HBW). Design allowables remain in Section II Part D and are not quoted here. Source: ASME BPVC.II.A-2023 SA-789/SA-789M Table 4.

Section 5 of ASME SA-789 requires tubes to be made by the seamless or welded process with no filler metal added. Welded S31260 therefore carries an autogenous longitudinal seam that is heat-treated with the tube, not a filler-welded pipe joint under SA-312 rules. Marking must state seamless or welded and whether wall is average or minimum.

Seamless lots take a flaring test (10% minimum ID expansion). Welded lots take a flange test plus reverse flattening on each 1500 ft [450 m] of finished tubing. Tension and hardness apply to both routes. SHH STEEL produces seamless and welded SA789 S31260 under those clauses and records the route on the stencil and MTC.

Order SA789 S31260 by OD × wall (average wall unless minimum wall is specified) and length — tube language, not B36.19 pipe schedules first. Table 5 of SA-789 sets OD, average-wall, minimum-wall, and cut-length tolerances by OD group; thin-wall ovality follows 12.2.

State average versus minimum wall on the PO — the percentage bands differ. Source: ASME BPVC.II.A-2023 SA-789 Table 5. SHH STEEL quotes OD × wall or BWG explicitly for every S31260 enquiry.

UNS S31260 under ASME SA-789 is the governing tubing designation here. Approximate wrought cousins and EN numbers are chemistry-family hints, not drop-in Code substitutes. Confirm the product standard, tensile table, and heat-treatment clause before accepting an “equivalent” offer.

S31260 is less commonly nicknamed than 2205 or 2507, so spell the UNS number and SA789 on the purchase order. Do not treat tungsten-bearing S31260 as interchangeable with S31200 without checking Mo, Cu, W, and hardness ceilings.

Table 2 requires S31260 solution treatment at 1870–2010 °F [1020–1100 °C] with rapid cooling in air or water. That air-or-water option is broader than the water-only quench listed for S31200, but rapid cooling remains mandatory to limit intermetallic precipitation.

Seamless tubes may be quenched directly after hot forming when the forming temperature is not below the minimum solution-treatment temperature. Slow cooling through the sigma nose after hot work or welding is especially unwelcome on Mo- and W-bearing duplex: those elements stabilize intermetallics. SHH STEEL ships SA789 S31260 only heat-treated per Table 2, with the record on the MTC.

SA-789 scopes duplex tubing for general corrosion resistance with emphasis on stress-corrosion cracking. S31260’s higher molybdenum, plus copper and tungsten, push estimated PREN near ≈38 from the Cr+Mo+N formula on mid-range aims — higher than S31200’s mid-30s estimate, still short of the footnote PREN ≥40 class written for S32760.

For seawater, sour, or high-chloride exchanger duty that needs super-duplex margins, step up to SA789 S32750 or SA789 S32760 rather than stretching S31260. Prolonged service near 475 °C can embrittle duplex ferrite; SA-789 warns that these steels are susceptible to embrittlement after prolonged elevated-temperature exposure. Keep design temperature and post-weld practice inside the qualified window.

S31260 tube is specified where a 25Cr duplex with molybdenum, copper, and tungsten is written into the datasheet — often process exchangers and corrosive general service that want more pitting margin than basic 22Cr without a full super-duplex jump. Choose it by the UNS row and SA-789 tables, not by a vague “duplex” BOM line.

If the datasheet already names 2205, quote SA789 S32205. If it names 2507 / Zeron-type chemistry, quote the matching super duplex rather than forcing S31260 into a PREN ≥40 slot.

Fabrication welds on S31260 tube (tube-to-tubesheet, attachments) typically use matching duplex filler under a qualified WPS; the SA-789 welded tube product itself remains autogenous with no filler in the mill seam. Heat input, interpass limits, and rapid cooling after welding are the fabricator’s Code responsibility.

Molybdenum and tungsten raise intermetallic risk if the HAZ cools slowly. Control ferrite balance, avoid prolonged soaks in the sigma range, and clean thoroughly after welding. SHH STEEL can discuss common filler families used with S31260 tube work; the fabricator owns the WPS/PQR.

Default mill delivery is heat-treated and descaled/pickled, suitable for inspection per Section 13. Slight oxidation is not scale; excessive mill scale is rejectable. Bright anneal, bore polish, or specified Ra are agreement items and must appear on the order.

Fouling-sensitive exchanger specs that quote Ra maxima are commercial finish overlays on SA-789 product, not automatic with the grade stamp. SHH STEEL quotes special finishes against the written enquiry.

Required testing covers Table 1 heat analysis, Table 4 tension and hardness, flare or flange tests by route, reverse flattening for welded tube, and hydro or NDE electric test on every length. Hydrostatic calculation uses the duplex factor 64000 (441.2) in place of the A1016 default. Manufacturer chooses hydro versus NDE unless the PO locks the method.

Section 14 marking adds seamless-or-welded and average-or-minimum wall to the A1016 marking set. SHH STEEL EN 10204 3.1 MTCs tie heat, chemistry, mechanicals, heat treatment, and test method to each length.

S31260 tube ships from SHH STEEL in tagged bundles with end protection matched to the length mix. Tags repeat ASME SA789, grade, seamless or welded, OD × wall, heat number, and PO reference for receiving checks.

Export options include wrapped bundles or wooden cases for bright or small-bore material. Incoterms and document flow follow the order acknowledgment.

SHH STEEL produces and supplies ASME SA789 UNS S31260 as a manufactured Code Book tubing product — seamless and welded (no filler metal) — with full Table 1 chemistry including Cu and W, Table 4 tensile/hardness, and Table 2 heat treatment on the EN 10204 3.1 MTC. We do not treat S31260 as a trader alias for generic 25Cr duplex.

If the service truly needs PREN ≥40, we redirect toward SA789 S32750 or SA789 S32760. If Cu/W are not required, we discuss whether SA789 S31200 or SA789 S32205 is the cleaner fit. Dual SA-789/A789 marking is available on request. That production-plus-selection honesty is how we support export buyers on this grade.

SHH STEEL can produce and supply ASME SA789 UNS S31260 duplex stainless steel tube to the edition, route, and finish on your enquiry. Capability summary and Stock / Available sizes follow.

Stock / Available sizes — SHH STEEL regularly enquires and produces SA789 S31260 in heat-exchanger bands such as OD about 12.7–50.8 mm with common BWG / metric walls, and can extend into larger Table 5 OD groups on agreement. Cut lengths and end prep are quoted against the PO. We do not invent warehouse tonnages; send OD × wall, length, route, and quantity for a production and near-stock reply.

List ASME SA789 UNS S31260, seamless or welded, OD × wall, wall basis, length, quantity, and test preferences on the enquiry.

ASME SA789 UNS S31260 is the tungsten- and copper-bearing 25Cr duplex tubing grade for Code and general service when the datasheet wants more molybdenum than basic S31200 without a full super-duplex jump. SHH STEEL produces and supplies seamless and welded (no filler metal) SA789 S31260, heat-treated per Table 2, tested per Section 9, and certified on EN 10204 3.1 MTCs. Lock OD × wall, wall basis, manufacture route, and dual-marking needs on the purchase order. For technical follow-up, contact admin@steelspecs.com.