Super duplex 2507 stainless steel

Identity and supplied product

Alleima's solution-annealed SAF 2507 seamless tube and pipe has 550 MPa minimum 0.2% proof strength at 20°C through 20 mm wall. The same supplier lists 42.5 minimum PRE for seamless tube and 41 for bar. PRE compares pitting resistance from composition. Use the applicable product and test requirements for the purchase. Alleima tube data, Alleima bar data

2507 denotes a super-duplex, austenitic-ferritic stainless steel associated with UNS S32750 / EN 1.4410. SAF 2507 is Alleima's producer designation; generic 2507 stock does not establish that provenance. Alleima seamless tube and pipe data

Outokumpu describes its 2507 and 4501 as super-duplex grades and lists desalination, seawater systems, flue-gas cleaning and pressure vessels among applications. These identify candidate service areas, not unrestricted compatibility with every chloride solution or fabrication route. Outokumpu duplex grade overview

Form-specific mechanical properties

Alleima's seamless tube/pipe sheet gives the following values for solution-annealed material at 20°C with wall thickness ≤20 mm:

A uses the sheet's proportional gauge length; preserve that specimen basis when comparing results. Alleima tube mechanical properties

The separate bar sheet lists Rm 760–930 MPa in the solution-annealed and quenched condition, with a special minimum of 800 MPa below 50 mm diameter. For its >200–250 mm bar impact entry, longitudinal Charpy V results at −50°C are 45 J average/35 J single. This is a specific producer/bar/test-direction statement, not a universal impact guarantee for plate, tube or a welded assembly. Alleima bar data

Keep measured certificate results, specified minima and typical catalogue values in separate fields. Proof strength is not an allowable design stress, and a Charpy result alone does not establish a component's minimum design temperature. Select the governing design method and include fatigue, buckling, joint geometry and the required fracture assessment where applicable.

PRE is a comparison index, not a service rating

Alleima defines PRE as %Cr + 3.3 × %Mo + 16 × %N. Its seamless-tube sheet gives a minimum PRE of 42.5; the separate bar sheet gives 41. Do not impose either producer-form value on every generic S32750 product. Alleima tube PRE, Alleima bar PRE

As an original arithmetic example, assumed mass percentages Cr 25, Mo 4 and N 0.30 produce PRE = 25 + 3.3 × 4 + 16 × 0.30 = 43.0. This calculation is not a heat analysis, a test result or proof of compliance with either minimum. It does not characterize surface condition, phase balance, weld quality or actual service chemistry.

Alleima's bar sheet describes comparative pitting/crevice tests using 6% ferric chloride and a 24-hour exposure, with temperatures stepped by 5°C when its failure criterion is not reached. Its figure is described as similar to ASTM G48. The resulting critical temperatures belong to that test setup; they are not maximum seawater operating temperatures. Alleima bar corrosion-test description

For a corrosion assessment, record temperature, chloride concentration, pH, oxidants, dissolved gases, deposits, crevices and cleaning conditions. Include shutdown and upset exposure. Qualify the final fabrication and surface state rather than assuming that an acceptable bulk chemistry makes every welded joint equivalent to the parent product.

Welding and thermal history

For SAF 2507, Alleima recommends heat input 0.2–1.5 kJ/mm and interpass temperature <150°C, without preheating. Its GTAW filler recommendation includes AWS ER2594. These are producer procedure-development recommendations, not a qualified welding procedure for every joint. Alleima tube welding guidance

IMOA's fabrication guide explains the need to manage duplex microstructure during hot forming and thermal processing, including the risk of intermetallic-phase formation. It also discusses higher forming forces and springback relative to austenitic stainless steels. A process transferred from 316L therefore needs review rather than automatic acceptance. IMOA fabrication guidelines

Specify joint preparation, filler, shielding/backing, pass sequence and thermal controls in the procedure. Establish which qualification tests demonstrate the required strength, toughness and corrosion performance. Include repair welds and attachments: they introduce thermal cycles even if they carry little structural load.

Alleima warns that prolonged exposure above 250°C changes microstructure and reduces impact strength. Treat elevated-temperature service as a specific engineering question; this warning is neither a universal instantaneous failure temperature nor permission for unlimited exposure below it. Alleima thermal-exposure note

Finished surface and inspection

IMOA identifies weld heat tint and related fabrication defects as detrimental to corrosion performance and discusses post-weld removal, including removal of the chromium-depleted layer. Its guidance does not make a generic passivation statement equivalent to complete weld cleanup. IMOA post-weld cleaning guidance

Specify the final surface and cleanliness criteria, inspect inaccessible roots before assembly closes them off, and define acceptance for machining damage and contamination. Select cleaning and pickling through a qualified process with the relevant chemical handling controls. Do not turn an example acid treatment for another duplex grade into a universal 2507 cleaning recipe.

For procurement review, resolve three separate questions: whether the delivered product meets the order; whether fabrication preserves the required condition; and whether the completed assembly meets service requirements. Retain the evidence for each rather than treating one certificate as proof of all three.

Source versions and related reference

Alleima's tube sheet is updated 2026-02-16, and its bar sheet 2026-02-23, each superseding previous editions. IMOA's PDF explicitly identifies Third edition, 2014, ISBN 978-1-907470-09-7. The Outokumpu overview has no verified technical revision date here. These source dates are distinct from this draft's review date and from the editions required by a purchase order or construction code.

Grades, tempers and conditions