What is Super Duplex 2507?

Super Duplex 2507 (UNS S32750, Werkstoff 1.4410, X2CrNiMoN25-7-4) is a nitrogen-enhanced super duplex stainless steel with a balanced 50 to 50 austenite-ferrite microstructure. Nominal composition is 25Cr-7Ni-3.5Mo-0.3N with no intentional copper and no intentional tungsten. PREN above 41 qualifies the alloy as super duplex per NORSOK M-630. The alloy is solution annealed at 1040 to 1100 degrees Celsius and water quenched, with no precipitation hardening or aging step.

What is Super Duplex 2507 equivalent to?

Super Duplex 2507 is registered as UNS S32750 in the Unified Numbering System and as Werkstoff 1.4410 / X2CrNiMoN25-7-4 in EN 10088-3. Mill trademarks for the same UNS S32750 chemistry include SAF 2507 (Sandvik), UR 52N+ (Industeel ArcelorMittal) and Avesta 2507 (Outokumpu). It is covered by ASTM A479 (bar), A789 (tube), A790 (pipe), A815 (fittings, designation WP-S32750), A276 (shapes), and A182 grade F53 (forgings, flanges, forged fittings).

Is Super Duplex 2507 the same as Zeron 100?

No. Both are super duplex stainless steels with PREN above 40, but they are different alloys. Zeron 100 (UNS S32760) contains nominal 0.7 percent each of copper and tungsten. Super Duplex 2507 (UNS S32750) contains neither. The forging spec for 2507 is ASTM A182 F53; for Zeron 100 it is ASTM A182 F55. The two are not drop-in substitutes when a project specification names one or the other by UNS number.

What is the PREN of Super Duplex 2507?

Super Duplex 2507 has a PREN of approximately 41 to 43, calculated using the formula Cr + 3.3 times Mo + 16 times N. A typical mill heat with 25 percent chromium, 3.8 percent molybdenum, and 0.28 percent nitrogen yields PREN about 42. NORSOK M-630 requires PREN of 40 or above for super duplex classification.

What is the heat treatment of Super Duplex 2507?

Solution annealing at 1040 to 1100 degrees Celsius followed by rapid water quench. There is no precipitation hardening, no aging, no temper. The water quench must drive the material rapidly through the 600 to 1000 degrees Celsius band to avoid sigma-phase formation, which would cut Charpy toughness by 80 percent or more and compromise pitting resistance.

Is Super Duplex 2507 acceptable for sour service?

Yes, Super Duplex 2507 is qualified for sour service per NACE MR0175 and ISO 15156-3 with hardness restricted to 28 HRC maximum and ferrite content within 35 to 65 percent. Specific H2S partial pressure and chloride limits depend on the application zone classification. TorqBolt supplies 2507 fasteners and forgings with NACE compliance certification on request.

Why does Super Duplex 2507 have no copper or tungsten?

The defining chemistry of UNS S32750 is 25Cr-7Ni-3.5Mo-0.3N with no intentional copper or tungsten addition. Adding either changes the alloy. Zeron 100 (S32760) adds about 0.7 percent each. Ferralium 255 (S32550) adds copper. Mixing these chemistries on a 2507 page is incorrect and creates a chimeric specification that does not exist in any mill datasheet or ASTM standard.

Which welding filler is correct for Super Duplex 2507?

ER2594 (overmatching, slightly higher PREN than the base) is the most common choice per AWS A5.9. ER2553 (matching) is also acceptable for less aggressive service. Both are nitrogen-enhanced fillers. Heat input should remain between about 0.5 and 2.5 kJ per millimetre, with interpass temperature below 150 degrees Celsius to avoid sigma-phase precipitation in the heat-affected zone.

What is Super Duplex 2507 used for?

Super Duplex 2507 is used in seawater service (velocities up to 6 metres per second), oil and gas downhole and surface (NACE MR0175 sour service), desalination plants (MSF, MED, RO), marine and subsea hardware (manifolds, christmas trees, jumpers), chemical processing (dilute HCl, H2SO4, HF), pulp and paper bleach plants (chlorine dioxide service), and flue gas desulfurization (WFGD absorber, quencher, outlet duct). Service temperature range is approximately minus 50 to 250 degrees Celsius continuous; sigma-phase risk above 300 degrees Celsius limits long-term high-temperature service.

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API 6A: Super Duplex 2507 for Wellhead and Christmas Tree (PSL 3 / 3G)

Name: Super Duplex 2507 (UNS S32750 / EN 1.4410)
Brand: TorqBolt
SKU: TB-2507
Availability: InStock

API 6A (also published as ISO 10423) is the API specification for wellhead and Christmas tree equipment used in upstream oil and gas production. It governs material selection, design, manufacture, testing, and marking of bodies, bonnets, end and outlet connections, valve trim, ring joint gaskets, and bolting. Super duplex 2507 (UNS S32750 / Werkstoff 1.4410) is a qualified material for wellhead and Christmas tree pressure-containing parts and valve trim under API 6A.

TorqBolt supplies super duplex 2507 wellhead bolting, valve trim, and forged components to API 6A PSL 3 and PSL 3G with full traceability and material test certificates.

API 6A Scope

API 6A covers wellhead and Christmas tree components rated for working pressures from 2,000 to 20,000 psi at temperatures from minus 75 to 350 degrees Fahrenheit (minus 60 to 177 degrees Celsius), with specified product specification levels (PSL) and material classes. Super duplex 2507 is admissible across the body envelope and as valve trim, governed by the chemistry, mechanical, and qualification requirements of the spec.

Product Specification Levels (PSL)

PSL	Application	Inspection / Documentation
PSL 1	Onshore lower pressure conventional service	Basic; chemistry + mechanical + visual
PSL 2	Conventional service	Adds NDE on critical surfaces
PSL 3	Severe / sour service	Adds full body NDE, hardness mapping, full traceability
PSL 3G	Severe / sour service with gas testing	PSL 3 plus gas test of every assembly
PSL 4	Highest level (rare in field)	Adds enhanced NDE and elastomer qualification

Super duplex 2507 wellhead components are typically supplied to PSL 3 or PSL 3G. The PSL designation is set by the operator based on H2S partial pressure, design pressure, and field criticality.

API 6A Material Classes

API 6A categorises body and bonnet materials into classes from AA (general service) to HH (sour service with corrosive gas). Super duplex 2507 fits material classes DD-NL, EE-NL, FF-NL, and HH-NL depending on the trim metallurgy combination and PSL. The NL suffix denotes NACE-MR0175 / ISO 15156 compliant. For sour service the bolting and valve trim must independently meet 28 HRC maximum and the 35 to 65 percent ferrite window.

2507 Components in Wellhead and Tree

Body and bonnet forgings (per ASTM A182 F53 / API 6A class HH-NL) for severe sour service xmas trees
Valve trim (gate, seat, stem) for super duplex bodies or for upgrade trim in carbon-steel bodies
Stud bolts for studded wellhead and tree connections (typically replacing B7 / B7M when sour service forces an upgrade)
Heavy hex nuts matching the stud bolts
Tubing hanger and casing hanger components
Choke trim for production chokes
Ring joint gaskets in 2507 (when carbon steel R-groove material requires CRA gasket)

Wellhead Bolting in 2507

Wellhead and tree bolting is the most common 2507 application under API 6A. The bolting upgrade is forced when the field fluid contains H2S above the B7M envelope or when the operator standardises on a single sour-service bolt grade across the asset. 2507 stud bolts are supplied to ASTM A479 / NACE MR0175 with hot-headed and solution-annealed manufacture. Minimum yield 550 MPa allows higher preload than B7M (550 MPa yield typical at room temperature). For mating nuts, see heavy hex nuts.

Testing for API 6A PSL 3 / 3G with Super Duplex 2507

Test	Acceptance
Chemistry	Per ASTM A479 / A182 F53 within MR0175 envelope
Tensile	Yield 550 MPa min, UTS 795 MPa min, El 15 percent min
Hardness	28 HRC max (NACE MR0175 / ISO 15156 sour service)
Ferrite content	35 to 65 percent per ASTM E562
Charpy V-notch	At minus 46 degrees Celsius, per project requirement
Hydrostatic body test	1.5 x rated working pressure (PSL 3 / 3G)
Gas test	Required for PSL 3G (every assembly)
NDE	Full body MT or PT plus UT per PSL level

API 17D: subsea wellhead and tree (subsea equivalent of 6A)
API 6FA: fire test for valves
API 6DSS: subsea pipeline valves
NACE MR0175 / ISO 15156-3: sour-service materials
ASTM A182 F53: forging specification
ASTM A479: bar specification
API Q1: quality system for petroleum supply

API 6A Frequently Asked Questions

What PSL applies to super duplex 2507 wellhead bolting?

PSL 3 or PSL 3G. PSL 3 covers severe and sour service with full body NDE, hardness mapping, and traceability. PSL 3G adds a gas test of every assembly. Operators set the PSL based on H2S partial pressure, design pressure, and field criticality.

What API 6A material class fits super duplex 2507?

DD-NL, EE-NL, FF-NL, or HH-NL depending on the trim combination. The NL suffix denotes NACE MR0175 / ISO 15156 compliant. HH-NL is the highest sour-service envelope and is the typical class for super duplex bodies and bolting in severe sour wells.

Why upgrade from B7M to super duplex 2507 stud bolts?

B7M (ASTM A193 B7M with 22 HRC max) is admissible only within a limited NACE MR0175 envelope. Severe sour wells with high H2S partial pressure exceed the B7M envelope and force a CRA upgrade. 2507 has higher PREN (above 41), higher yield strength than B7M (550 MPa vs 550 MPa typical), and is qualified across the full duplex envelope of MR0175.

What is the hardness limit for 2507 wellhead components?

28 HRC maximum for sour service per NACE MR0175 / ISO 15156-3. The limit applies to bulk material, weld metal, and HAZ. Solution-annealed water-quenched 2507 typically lands at 22 to 26 HRC.

What hydrostatic test pressure applies to 2507 bodies under API 6A?

1.5 times rated working pressure for PSL 3 / 3G. PSL 3G adds a separate gas test on every assembly. The hydrostatic test verifies pressure containment; the gas test verifies bubble-tight sealing under gas service.

Does API 6A require Charpy testing for 2507?

Charpy V-notch impact testing at minus 46 degrees Celsius is required when project specifications invoke low-temperature service or NORSOK / Norwegian-style supplementary requirements. Acceptance is typically 45 J average / 35 J individual at minus 46 degrees Celsius.

Standards

Surface Treatments

Certifications

ISO 9001 - 2015 Certified
PED 2014/68/EC
NACE MR0175 / ISO 15156-2
NORSOK M-650 Qualified
API 6A Certified
DFAR
MERKBLATT AD 2000 W2/W7/W10

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