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Application Guide

Valves for Marine & Offshore Service

Offshore oil and gas platforms, FPSOs, subsea wellheads, and marine vessels present the most aggressive corrosion environment in industry: high-chloride seawater, saline atmosphere, cyclic wave loading, and continuous hydrocarbon exposure. Valves in these applications demand Super Duplex (UNS S32750/F53) or Duplex (UNS S31803/F51) stainless steel, compliance with NORSOK M-710 qualification testing, DNV-OS-D101 marine system requirements, and full NACE MR0175 sour service documentation.

API 6DNORSOK M-710 (Elastomer qualification)DNV-OS-D101 (Marine systems)Lloyd's RegisterNACE MR0175 / ISO 15156API 607 (Fire test)ASME B16.34ISO 14313
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Recommended Valve Types for Marine & Offshore Service

Trunnion Ball Valve (Super Duplex)

Class 150 / 300 / 600 / 900 / 1500

Why: Full-bore isolation for seawater injection, produced water, and topside process — maximum corrosion resistance in high-chloride environments

Materials: Super Duplex UNS S32750 (F53), Duplex UNS S31803 (F51), Inconel 625 overlay for severe service

Standards: API 6D, API 6FA, NACE MR0175, NORSOK M-710

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Butterfly Valve (Duplex / Super Duplex)

PN 10 / PN 16 / Class 150 / 300

Why: Seawater cooling and ballast system isolation on FPSOs and offshore platforms — wafer or double-flanged, high-chloride resistant

Materials: Duplex UNS S31803 body, Super Duplex disc for seawater, EPDM or PTFE seat

Standards: API 609, EN 593, DNV-OS-D101

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Gate Valve (Slab / Expanding, Offshore Spec)

Class 600 / 900 / 1500 / 2500

Why: Through-conduit full-bore isolation for subsea wellhead and riser systems with pigging requirements

Materials: A182 F51 Duplex, A182 F53 Super Duplex, Inconel 625 overlay hard-facing

Standards: API 6D, NACE MR0175, ISO 14313

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Swing / Tilting Disc Check Valve (Marine Grade)

Class 150 / 300 / 600

Why: Non-return valve on seawater lift pumps, ballast systems, and produced water injection

Materials: Super Duplex UNS S32750, Duplex UNS S31803, bronze for low-pressure seawater service

Standards: API 6D, DNV-OS-D101, NACE MR0175

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Critical Requirements

Super Duplex (UNS S32750/S32760) or Duplex (UNS S31803) for all seawater-wetted surfaces — PREN ≥40 for super duplex
NORSOK M-710 elastomer qualification testing for FPSO and North Sea applications
NACE MR0175 / ISO 15156 compliance for sour (H₂S-containing) produced fluids
DNV-OS-D101 or Lloyd's Register certification for marine system valves
API 607 fire-safe design for hydrocarbon-carrying valves on offshore topsides
Cathodic protection compatibility — valves on submerged structures require galvanic compatibility
Impressed current cathodic protection (ICCP) isolation: electrically isolating flanges where required
Full documentation pack: EN 10204 3.2 material certs, PMI, charpy impact, hardness survey

Fluid & Service Challenges

⚠Seawater (high chloride, microbiologically influenced corrosion) — standard SS 316 is insufficient; duplex or super duplex required
⚠Produced water (oil + water + H₂S + CO₂ + chlorides) — combined NACE and duplex material requirement
⚠Sour crude with H₂S — sulphide stress cracking; hardness-controlled NACE materials mandatory
⚠Seawater injection for EOR — high-pressure, high-chloride; super duplex and NORSOK qualification
⚠Marine atmosphere (salt spray, humidity) — external coating system: zinc primer + epoxy + polyurethane topcoat (NORSOK M-501)

Material Selection Guidance

For offshore and marine applications, material selection is driven by chloride concentration and H₂S content. Standard SS 316 (CF8M) is inadequate for seawater service — pitting corrosion will occur within months. Minimum for seawater-wetted surfaces: Duplex UNS S31803 (F51), PREN ≥35. For seawater injection and severe FPSO service: Super Duplex UNS S32750 (F53) or UNS S32760, PREN ≥40. For sour service combined with seawater: Super Duplex with NACE MR0175 hardness compliance. Bronze (C83600/C95800) is acceptable for low-pressure marine seawater lines (ballast, bilge) only. All Super Duplex welds require controlled heat input and solution annealing to prevent sigma-phase precipitation.

Typical Service Points

Seawater injection for enhanced oil recovery (EOR)
FPSO produced water treatment and overboard discharge
Topside hydrocarbon process isolation
Subsea wellhead isolation and Christmas tree valves
Ballast and bilge systems on marine vessels
Offshore fire water and deluge systems
Riser and flowline isolation
Cooling water (open-loop seawater) on offshore platforms

FAQ — Valve Selection for Marine & Offshore Service

Why is standard SS 316 not suitable for offshore seawater service?
Stainless steel SS 316 (UNS S31600) has a PREN (Pitting Resistance Equivalent Number) of approximately 25, which is insufficient to resist pitting and crevice corrosion in seawater (chloride concentrations 18,000–35,000 ppm). Localised pitting can initiate within weeks in warm seawater. Duplex stainless (UNS S31803, PREN ~35) and Super Duplex (UNS S32750, PREN ~42) provide the corrosion resistance needed for continuous seawater service. For subsea and injection applications, Super Duplex is typically specified.
What is NORSOK M-710 and why does it matter for offshore valves?
NORSOK M-710 is a Norwegian offshore standard specifying qualification testing for non-metallic sealing materials (elastomers and thermoplastics) used in valves and other equipment on offshore installations, particularly on the Norwegian Continental Shelf. It tests resistance to high-pressure gas decompression, chemical resistance to hydrocarbons, and sour gas exposure. NORSOK M-710 qualification is required by most operators on the Norwegian Continental Shelf and is increasingly specified globally for FPSO and offshore topsides applications.
What documentation is required for offshore valve supply?
Offshore valve documentation typically includes: EN 10204 3.2 material test reports (third-party witnessed) for all pressure-containing components; PMI (Positive Material Identification) test results; charpy impact test results; hardness survey (weld and HAZ for duplex/super duplex); dimensional inspection report; pressure test certificate (shell, seat, and packing per API 598); fire-safe test certificate (API 607/API 6FA); NACE MR0175 compliance statement; NORSOK M-710 elastomer qualification certificates (for North Sea applications); and classification society (DNV/Lloyd's) certificate if required.
Can you supply valves for subsea Christmas tree and wellhead applications?
Vajra Industrial Solutions supplies API 6D and API 6A compliant valves for wellhead and Christmas tree applications including gate valves, ball valves, and check valves in Super Duplex and Inconel alloys. These are supplied with full documentation per API 6D / ISO 14313 requirements including fire-safe certificates, material qualification, and third-party inspection. For deepwater and subsea applications where ROV operability is required, we can source actuated and torque-tool-operated valve assemblies.

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Marine & Offshore Service

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Key Standards

API 6D
NORSOK M-710 (Elastomer qualification)
DNV-OS-D101 (Marine systems)
Lloyd's Register
NACE MR0175 / ISO 15156
API 607 (Fire test)
ASME B16.34
ISO 14313

Products for This Application

Ball ValvesGate ValvesButterfly ValvesCheck Valves

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