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.

0091-22-66157017

info@torqbolt.com

Home

Super Duplex Stainless Steel

Home

API 17D: Super Duplex 2507 for Subsea Wellhead and Tree Equipment

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

API 17D (also published as ISO 13628-4) is the API specification for subsea wellhead and Christmas tree equipment. It is the subsea counterpart of API 6A and inherits 6A's PSL framework while adding subsea-specific requirements: external hydrostatic pressure, ROV intervention interfaces, cathodic protection compatibility, and extended design life under seawater immersion. Super duplex 2507 (UNS S32750 / Werkstoff 1.4410) is the dominant CRA for subsea bolting, valve trim, and exposed pressure-containing parts under API 17D.

TorqBolt supplies subsea super duplex 2507 fasteners, forged components, and valve trim to API 17D with mill test certificates that record all PSL, NACE MR0175, and seawater-relevant qualification.

API 17D Scope

API 17D applies to subsea wellhead equipment, mudline suspension equipment, drill-through equipment, subsea Christmas trees, tubing hangers, and associated valves, controls, and connectors used at the seabed. The standard covers material selection, mechanical design, fatigue and fracture mechanics, manufacture, testing, qualification, marking, and traceability.

Material Class HH for Subsea Sour Service

API 17D inherits API 6A material classes. Material class HH-NL is the typical class for subsea super duplex 2507 components in sour service, where:

Body and bonnet are CRA (super duplex 2507 forging per ASTM A182 F53)
Trim is CRA (super duplex 2507 or upgrade Inconel 625)
NL suffix denotes NACE MR0175 / ISO 15156 compliant
Bolting is CRA per NACE MR0175 with 28 HRC max

External Pressure and Seawater Exposure

Subsea components see external hydrostatic pressure equal to seabed depth (about 100 bar at 1,000 m). Super duplex 2507 has yield strength (550 MPa min) and toughness sufficient to handle external pressure on standard 6A wall sections. Seawater exposure introduces a chloride pitting and crevice corrosion challenge; 2507 PREN above 41 keeps the alloy above the seawater pitting threshold for long-term immersion at temperatures up to about 20 degrees Celsius (typical seabed). Cathodic protection compatibility is verified per project specification.

Subsea Bolting in 2507

Subsea bolting is the most common 2507 application under API 17D. Hot-headed and solution-annealed stud bolts per ASTM A479 with NACE MR0175 compliance are the standard supply. The 2507 grade replaces B7 / B7M where sour service or seawater exposure exceeds the carbon-steel bolting envelope. Coatings are specified per project; PTFE-based dry-film lubricants and Xylan are typical. Galvanic coupling with surrounding cathodic protection systems is checked per project material selection diagram.

Hydrogen Embrittlement Risk under Cathodic Protection

Subsea components under cathodic protection (impressed current or sacrificial anode) are exposed to atomic hydrogen generated at the steel surface. Super duplex stainless steels including 2507 are susceptible to hydrogen-induced stress cracking (HISC) at high stress ratios. API 17D and DNV-RP-F112 set design and stress limits to manage HISC risk. TorqBolt supplies are accompanied by hardness records and ferrite measurements that fall within the conservative window required by HISC management.

Subsea Components Made in 2507

Subsea wellhead bodies and bonnets (per A182 F53)
Subsea Christmas tree valve bodies and trim
Production master valves and wing valves
Choke bodies and trim for subsea production chokes
Subsea bolting (stud bolts and heavy hex nuts)
Tubing hanger and casing hanger seals and seats
ROV interface tooling components
Connector locking systems

Subsea Qualification Testing

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)
Ferrite content	35 to 65 percent per ASTM E562
Charpy V-notch	At minus 46 degrees Celsius, 45 J average / 35 J individual
Hydrostatic body test	1.5 x rated working pressure (PSL 3 / 3G)
Gas test	Required for PSL 3G
NDE	Full body MT or PT plus volumetric per PSL
HISC stress check	Per DNV-RP-F112 (cathodic protection regime)
Fatigue qualification	Per project SN curve

API 6A: surface wellhead and tree (parent standard)
API 17A: design and operation of subsea production systems (general)
API 17H: ROV intervention interfaces
DNV-RP-F112: design of duplex SS subject to HISC
NACE MR0175 / ISO 15156-3: sour service materials
ISO 21457: petroleum gas materials selection
NORSOK M-630: Norwegian MDS (D55, D57)

API 17D Frequently Asked Questions

What is the difference between API 6A and API 17D?

API 6A covers surface wellhead and Christmas tree equipment. API 17D covers subsea wellhead and Christmas tree equipment. API 17D inherits 6A's PSL framework and adds subsea-specific requirements: external hydrostatic pressure, ROV interfaces, cathodic protection compatibility, and extended design life under seawater immersion.

What material class fits super duplex 2507 in subsea sour service?

HH-NL. CRA body and bonnet, CRA trim, NACE MR0175 / ISO 15156 compliant. HH-NL covers severe sour service where carbon steel bodies and B7M bolting are excluded.

Is 2507 susceptible to HISC under cathodic protection?

Yes. Super duplex 2507 is susceptible to hydrogen-induced stress cracking (HISC) at high stress ratios under cathodic protection. API 17D and DNV-RP-F112 set design stress limits and ferrite content controls to manage HISC risk. Hardness within 28 HRC and ferrite within 35 to 65 percent reduce susceptibility.

What coatings are typical on 2507 subsea bolting?

PTFE-based dry-film lubricants (Xylan, Magni 565, Whitford coatings) are typical. The coating provides anti-galling, friction control for accurate preload, and a barrier against marine growth. Cathodic protection compatibility is checked per project material selection.

Does seawater pitting affect 2507 at seabed temperatures?

Super duplex 2507 with PREN above 41 stays above the seawater pitting threshold at typical seabed temperatures (about 4 to 20 degrees Celsius). At elevated temperatures (above about 50 degrees Celsius in stagnant seawater) the alloy approaches its CPT envelope. Project material selection diagrams confirm the alloy fits the operating temperature.

Can 2507 substitute Inconel 625 in subsea trim?

Within the qualified MR0175 envelope, yes. 2507 is lower cost than Inconel 625 and offers higher strength. Inconel 625 is preferred when H2S partial pressure or chloride concentration exceeds the 2507 envelope, or when the operator standardises on a single high-end CRA across the asset.

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

About Us

Questions? Contact us.

Showcase of our Microsites.