RFQ Today
Certifications available: EN 10204 3.1 / 3.2 MTRs, NACE MR0175 compliance, passivation per ASTM A967, Third-Party Inspection (SGS / BV / DNV / Lloyds), and complete offshore and marine export documentation packages.
Marine Grade
Stainless Fasteners
A world-class technical reference for EPC contractors, structural and mechanical engineers, procurement heads, TPI inspection agencies, and global project buyers specifying marine grade stainless steel fasteners — bolts, studs, nuts, screws, and washers — for offshore platforms, ship structures, marine process equipment, seawater systems, coastal infrastructure, desalination plants, and all applications requiring proven corrosion resistance in marine and chloride-bearing environments.
Corrosion Mechanisms
& Selection Principles
Marine grade stainless fasteners are bolts, studs, nuts, screws, and washers manufactured from austenitic, duplex, or super duplex stainless steel grades selected for their resistance to the specific corrosion mechanisms present in marine and seawater environments — primarily chloride-induced pitting, crevice corrosion, and stress corrosion cracking.
1.1 — Technical Definition and Marine Environment Context
The marine environment presents four distinct corrosion threats to stainless steel fasteners that do not exist, or are far less severe, in non-marine environments: (1) chloride pitting — seawater chloride ions (Cl⁻ at 19,000–20,000 ppm) penetrate the chromium oxide passive film at surface heterogeneities (inclusions, grain boundaries, surface defects), initiating a localised deep pit that propagates rapidly under the self-acidifying chemistry of the pit cavity; (2) crevice corrosion — the geometry of a bolt head or nut bearing face against a structural surface creates an occluded cell where oxygen is depleted and chloride ions concentrate, destroying the passive film locally; (3) stress corrosion cracking (SCC) — austenitic SS under sustained tensile stress in hot chloride environments (above 50–60°C) is susceptible to transgranular SCC — a brittle failure mode with no visual warning; and (4) galvanic corrosion — when SS fasteners are coupled to less noble metals (aluminium, zinc, carbon steel) in seawater electrolyte.
The correct marine grade selection — SS 316L for mild marine, Duplex 2205 for offshore seawater, Super Duplex 2507 for hot concentrated seawater — is the primary engineering decision for marine fastener specification. Selecting SS 304 (A2) instead of SS 316 (A4) in a marine application is a systematic error that results in widespread pitting within 2–5 years of service. RR Hydraulic manufactures marine grade stainless fasteners under all applicable international standards with full EN 10204 3.1 / 3.2 material traceability.
1.2 — Marine Stainless Grade Classification
A2 / SS 304 — Not Marine Grade
ISO 3506 Property Class A2 — SS 304 (18% Cr, 8–10% Ni, no molybdenum). The most widely used stainless steel globally, often incorrectly specified as “stainless” in marine applications. Without the molybdenum addition (which is 2–3% in SS 316), SS 304 has insufficient pitting resistance in seawater and marine atmospheric environments — it will pit within 1–5 years in direct seawater exposure. A2 is acceptable for mild atmospheric marine service (sheltered locations, low salt deposition) but must NOT be specified for submerged, splash zone, or direct seawater-wetted applications. Pitting Resistance Equivalent Number (PREN) ≈ 18 — far below the marine threshold of PREN ≥ 25.
A4 / SS 316L — Standard Marine Grade
ISO 3506 Property Class A4 — SS 316L (16–18% Cr, 10–14% Ni, 2–3% Mo, low carbon ≤0.03%). The “L” designates low carbon — prevents sensitisation at weld heat-affected zones. The 2–3% molybdenum addition provides PREN ≈ 26 — adequate for ambient-temperature seawater, marine atmospheric exposure (all zones including splash zone), and mild chloride industrial environments. The universal marine fastener grade for EPC offshore, coastal, and marine applications below 60°C seawater temperature. A4-70 (700 MPa UTS) is standard; A4-80 (800 MPa UTS) for higher-strength connections. Cold-drawn and strain-hardened condition for A4-80.
316Ti / 316H — Stabilised and High-Temperature Variants
SS 316Ti (titanium-stabilised) and SS 316H (high carbon) are variants for elevated temperature service. 316Ti prevents sensitisation during service at 400–900°C by fixing carbon as titanium carbide rather than chromium carbide. 316H (0.04–0.10% C) provides higher creep strength at elevated temperature. Both maintain the PREN ≈ 26 pitting resistance of standard 316 in marine environments while providing elevated temperature performance not available from 316L. Used for marine steam piping fasteners, exhaust system bolting, and marine boiler connections where both corrosion resistance and elevated temperature strength are required.
904L — High-Alloy Austenitic
SS 904L (20% Cr, 25% Ni, 4.5% Mo, 1.5% Cu) — PREN ≈ 36. High-alloy austenitic SS with superior pitting and crevice corrosion resistance compared to SS 316L. The copper addition improves resistance to sulphuric acid and reducing acid environments. Used in: severe marine chemical environments (seawater plus acid or alkali contamination); concentrated chloride process equipment; offshore produced water treatment systems. More resistant than 316L but less so than Duplex 2205 in seawater. An intermediate grade for applications where 316L is inadequate but Duplex is overspecified. Not common in standard offshore structural fastener applications.
Duplex 2205 (S31803) — Offshore Seawater Standard
UNS S31803 / S32205 Duplex (22% Cr, 5% Ni, 3% Mo, 0.17% N) — PREN ≈ 34–36. The offshore industry standard for seawater-immersed and splash zone structural fasteners. Duplex microstructure (50% austenite / 50% ferrite) provides: higher yield strength than austenitic SS (≥ 450 MPa vs 170 MPa for 316L) enabling smaller diameter fasteners; superior chloride pitting and crevice corrosion resistance vs 316L; and resistance to stress corrosion cracking that austenitic SS 316L lacks above 60°C. NACE MR0175-compliant. Limited service above 315°C due to 475°C embrittlement risk in the ferrite phase.
Super Duplex 2507 (S32750) — Extreme Marine Service
UNS S32750 Super Duplex (25% Cr, 7% Ni, 4% Mo, 0.28% N) — PREN ≥ 42. Highest chloride pitting resistance of all standard stainless steel grades — significantly superior to Duplex 2205 in hot concentrated seawater and combined sour+chloride environments. Used for: seawater injection pump and manifold fasteners; subsea production equipment in high-chloride formation water; offshore heat exchanger tube-and-sheet bolting in hot seawater above 50°C; and any application where Duplex 2205 pitting resistance is insufficient. Higher cost than Duplex 2205 — specify only where the PREN ≥ 40 threshold is required by the corrosion engineer’s assessment.
1.3 — Pitting Resistance Equivalent Number (PREN)
%Mo = Molybdenum content (weight %) — strengthens passive film in chloride environments; weight factor 3.3×
%N = Nitrogen content (weight %) — further strengthens passive film; weight factor 16× (highly effective)
PREN thresholds for marine environments:
PREN < 18 → Not stainless in seawater — pit immediately; CS with coating preferred
PREN 18–25 → SS 304 range — atmospheric marine only; NOT for seawater immersion
PREN 25–30 → SS 316L range — standard marine; seawater at ambient temperature
PREN 30–36 → Duplex 2205 / 904L range — offshore seawater immersion and splash zone
PREN > 40 → Super Duplex 2507 range — hot concentrated seawater; severe combined sour+Cl⁻
SS 304 (A2): PREN = 18.5 + 3.3×0 + 16×0 = 18.5 → atmospheric marine only
SS 316L (A4): PREN = 17.0 + 3.3×2.5 + 16×0 = 25.3 → standard marine fastener
Duplex 2205: PREN = 22.0 + 3.3×3.0 + 16×0.17 = 34.6 → offshore seawater
Super Duplex 2507: PREN = 25.0 + 3.3×4.0 + 16×0.28 = 42.7 → extreme marine
1.4 — Marine Corrosion Mechanisms and Mitigation
Chloride Pitting — Mechanism and Prevention
Chloride pitting initiates at surface defects where the Cl⁻ ion penetrates the passive film and dissolves the metal beneath, creating an increasingly acidic pit chemistry (pH can drop to 0–1 inside an active pit) that prevents passive film re-formation — the pit propagates autocatalytically. Prevention: select SS grade with PREN adequate for the chloride concentration and temperature (use the PREN formula above); maintain passivation; avoid chloride contamination of the SS surface from iron tools or carbon steel contact; specify surface finish Ra ≤ 0.8 µm — smoother surfaces have fewer pit initiation sites. Critical pitting temperature (CPT) for 316L ≈ 20°C in seawater; Duplex 2205 CPT ≈ 45°C; Super Duplex 2507 CPT ≈ 75°C.
Crevice Corrosion — Marine Fastener Hot Spot
The geometry of bolted connections — the annular crevice under the bolt head, under the nut, in the threaded engagement zone, and between the washer and mating surface — creates ideal crevice corrosion conditions: restricted oxygen access, chloride concentration, and acidification. For marine SS fasteners: (1) use PREN ≥ 34 (Duplex 2205) for splash zone and immersed applications — critical crevice temperature (CCT) for 316L is below ambient seawater in many locations; (2) use non-metallic (PTFE or neoprene) washers to eliminate the metal-to-metal crevice under the head; (3) apply sealant (epoxy or PTFE paste) in the crevice zone before assembly; (4) use oversized washers to move the crevice boundary further from the thread zone.
Stress Corrosion Cracking (SCC) — Temperature Dependence
Austenitic SS (304, 316) is susceptible to chloride SCC at sustained tensile stresses above approximately 50% of yield strength in hot chloride environments (typically above 50–60°C). SCC failure is brittle and catastrophic — no plastic deformation, no visual warning. Duplex and Super Duplex stainless steels are substantially more resistant to SCC than austenitic grades. For marine fasteners above 60°C seawater or process temperature: specify Duplex 2205 or Super Duplex 2507 instead of SS 316L — the duplex microstructure provides SCC resistance that austenitic SS lacks. Cold-worked high-strength SS (A4-80) has higher residual stress and is more SCC-susceptible than annealed A4-70.
Galvanic Corrosion in Marine Assemblies
SS 316L (A4) sits at approximately +0.05 V vs SCE in seawater — relatively noble. When coupled to less noble metals: aluminium (−0.75 V) loses metal at the contact zone; zinc-coated steel (−1.0 V) loses zinc rapidly; carbon steel (−0.50 V) corrodes at the contact point. The galvanic attack is concentrated at the area immediately adjacent to the SS fastener contact. For SS fasteners in aluminium structures: specify isolating sleeves (PTFE) and isolating washers (PTFE/nylon) to prevent direct SS-Al contact; or specify aluminium alloy 5083 bolts to eliminate the galvanic couple. For SS fasteners in carbon steel structures: the galvanic couple is less severe — carbon steel corrodes locally but the large cathode-to-anode area ratio limits the attack rate.
Marine Atmospheric Zones and Fastener Selection
Offshore structures experience different corrosion severity by zone: (1) Immersion zone (below lowest tide) — continuous seawater exposure; specify Duplex 2205 or Super Duplex; CP system if steel structure; (2) Tidal zone (between tide levels) — alternating wet/dry; highest biological fouling; Duplex 2205 minimum; (3) Splash zone (above highest tide to approximately 5m) — most aggressive atmospheric zone; highest salt deposition, UV, and mechanical wave action; Duplex 2205 minimum; (4) Atmospheric zone (above splash) — salt aerosol exposure reducing with height; SS 316L (A4) generally adequate above 10m elevation from splash zone; SS 304 (A2) only acceptable in sheltered locations above 30m+ from sea level.
Iron Contamination — The Hidden Corrosion Trigger
Free iron particles on the surface of stainless steel fasteners — from carbon steel tools, carbon steel swarf in the machining shop, or carbon steel packaging hardware — cause galvanic pitting at the iron particle site in marine atmospheres. The iron particle forms a galvanic couple with the SS surface (iron is anodic to SS) and corrodes, leaving a rust stain and a pit in the underlying SS. Prevention: use dedicated SS-only tools and fixtures for handling SS fasteners; segregate SS fasteners from carbon steel hardware in all packaging; passivate per ASTM A967 after final machining to remove any iron contamination from the manufacturing process. Passivation is a mandatory manufacturing step for all marine grade SS fasteners — not optional.
Submit your grade, thread size, length, head type, property class, and quantity for a documented RFQ within 24 hours.
Mechanical Properties
& Standards Compliance
Marine grade stainless fastener mechanical properties are governed by ISO 3506 (property classes A2-70, A2-80, A4-70, A4-80), ASTM F593 (SS bolts), ASTM F594 (SS nuts), and ISO 898-1 equivalent class system. All applicable standards are supported at RR Hydraulic with full certification.
Submit grade, diameter, length, thread, head type, property class, and quantity to sales@rrhydraulics.com for a certified offer.
2.1 — ISO 3506 Marine Stainless Fastener Property Classes
| Property Class | SS Grade | UTS (MPa min) | Yield 0.2% (MPa min) | Elongation (% min) | Hardness Max | Condition | Marine Application |
|---|---|---|---|---|---|---|---|
| A2-50 | SS 304 | 500 | 210 | 0.6d | 220 HV | Annealed | Non-marine; atmospheric only |
| A2-70 | SS 304 | 700 | 450 | 0.4d | 220 HV | Cold-drawn | Non-marine; atmospheric only |
| A4-50 | SS 316 / 316L | 500 | 210 | 0.6d | 220 HV | Annealed | Light marine; non-structural |
| A4-70 | SS 316 / 316L | 700 | 450 | 0.4d | 220 HV | Cold-drawn | Standard offshore marine grade |
| A4-80 | SS 316 / 316L | 800 | 640 | 0.3d | 250 HV | High cold-drawn | Higher-strength marine; structural |
| Duplex (F51) | Duplex 2205 | 620 | 450 | 25% | 293 HB | Solution annealed | Offshore seawater; splash zone |
| Super Duplex (F53) | Super Duplex 2507 | 750 | 550 | 15% | 310 HB | Solution annealed | Hot seawater; extreme marine |
2.2 — Marine SS Grade vs Corrosion Environment Selection Guide
| Environment / Zone | Cl⁻ Conc. | Temp | Min PREN Required | Recommended Grade | Why |
|---|---|---|---|---|---|
| Inland / non-marine | <200 ppm | Ambient | 18+ | A2-70 (SS 304) | No chloride pitting risk; lowest cost SS |
| Coastal atmospheric (>10 km offshore) | 200–1000 ppm | Ambient | 25+ | A4-70 (SS 316L) | Mo addition essential for coastal Cl⁻ aerosol |
| Offshore atmospheric zone (>5 m above splash) | 1000–5000 ppm | Ambient | 25+ | A4-70 (SS 316L) | Standard offshore atmospheric fastener |
| Offshore splash zone (tidal to +5 m) | 19,000 ppm | Ambient | 32+ | Duplex 2205 | 316L pits in sustained seawater splash exposure |
| Seawater immersion — ambient | 19,000 ppm | <30°C | 32+ | Duplex 2205 | 316L CCT below ambient seawater in many locations |
| Seawater immersion — warm | 19,000 ppm | 30–60°C | 36+ | Duplex 2205 / 2507 | Higher temperature requires higher PREN |
| Seawater immersion — hot (>60°C) | 19,000 ppm | >60°C | 40+ | Super Duplex 2507 | 316L and 2205 CCT exceeded; SCC risk for austenitic |
| Desalination brine (>60,000 ppm) | 60,000+ ppm | 60–120°C | 40+ | Super Duplex 2507 | Concentrated brine at elevated temp; 2205 borderline |
| Combined sour + seawater (offshore) | 19,000 ppm | Ambient–80°C | 36+ | Duplex 2205 / 2507 | NACE + PREN combined requirement; austenitic SS unsuitable |
2.3 — Applicable Standards and Compliance Framework
ISO 3506 Parts 1–4
The primary international standard for stainless steel fastener mechanical properties. Part 1: Bolts, screws and studs; Part 2: Nuts; Part 3: Set screws and similar; Part 4: Tapping screws. Defines property classes (A2-50, A2-70, A2-80, A4-50, A4-70, A4-80, C1-70, F1-45, etc.) with UTS, yield (proof stress), elongation (expressed as fraction of diameter — 0.6d, 0.4d), and hardness requirements. A4-70 is the specified minimum property class for all marine and offshore structural SS fasteners — A4-50 is only for non-structural applications. All marine grade SS fasteners supplied by RR Hydraulic are marked with the property class designation on the head or shank.
ASTM F593 / F594
ASTM F593: Stainless Steel Bolts, Hex Cap Screws, and Studs. ASTM F594: Stainless Steel Nuts. Cover alloy groups 1 (304/305), 2 (316/316L), 6 (Duplex) with condition designations CW (cold-worked), SH (strain-hardened), and HE (hot-worked and equalized). F593 / F594 are the US code equivalents of ISO 3506. Used on ASME B31.3 process piping projects and AISC structural projects where ASTM material designations are required. F593 Alloy Group 2 / Condition SH (316 cold-worked) corresponds approximately to ISO 3506 A4-70 for marine fastener specification.
ASTM A276 / A479
Raw material standards for stainless steel bar stock used to manufacture marine SS fasteners. ASTM A276: Stainless Steel Bars and Shapes — covers hot-finished and cold-finished rounds, squares, hexagons in Types 304, 316, 316L, and other grades. ASTM A479: Stainless Steel Bars and Shapes for Use in Boilers and Other Pressure Vessels — same grades but with additional mechanical test and heat treatment requirements for pressure service. For marine EPC fasteners: specify ASTM A479 Grade 316L bar stock (pressure quality) for all process-wetted and pressure-containing marine fasteners; ASTM A276 Type 316L for structural and non-pressure marine fasteners.
ASTM A815 / A182
ASTM A815: Wrought Ferritic, Ferritic/Austenitic, and Martensitic Stainless Steel Piping Fittings. ASTM A182: Forged or Rolled Alloy-Steel Pipe Flanges and Fittings. Both cover Duplex (F51/S31803) and Super Duplex (F53/S32750) material — the governing material standards for bar stock used to manufacture Duplex and Super Duplex marine fasteners. A182 F51 bar is the standard material specification for Duplex 2205 stud bolts for offshore flanged connections; A182 F53 for Super Duplex. EN 10204 3.1 on the A182 bar stock is the starting point for Duplex marine fastener material traceability.
NACE MR0175 / ISO 15156
For marine fasteners in combined sour (H₂S) + chloride environments — offshore production equipment, subsea production trees, sour crude separator flanges in marine locations: SS 316L (A4-70, annealed) is NACE-compliant at ≤ 220 HV; cold-drawn A4-80 may exceed the NACE hardness limit and must be verified individually. Duplex 2205 (≤ 293 HB) and Super Duplex 2507 (≤ 310 HB) are NACE-compliant. For offshore sour+marine combined service: Duplex 2205 is the preferred grade — NACE-compliant AND adequate PREN for seawater service. Individual hardness verification per lot for all NACE marine fastener supply.
ASTM A967 — Passivation
Standard Specification for Chemical Passivation Treatments for Stainless Steel Parts. Defines passivation methods: Nitric Acid (Method 1 — 20–45% HNO₃ at 21–49°C for 20–30 minutes); Nitric Acid with Dichromate (Method 2); Citric Acid (Methods C1–C4 — preferred for environmental reasons). Acceptance tests: water immersion test (no rust or staining within 24 hours); copper sulphate test (surface does not copper-plate in 6 minutes); high-humidity test; salt spray test. All marine grade SS fasteners from RR Hydraulic are passivated per ASTM A967 before dispatch — passivation certificate on lot documentation.
ISO 9227 / ASTM B117
Salt spray (fog) testing standards. ISO 9227: Corrosion Tests in Artificial Atmospheres — Salt Spray Tests. ASTM B117: Standard Practice for Operating Salt Spray (Fog) Apparatus. Used to validate the corrosion performance of passivated marine SS fasteners and coated SS fasteners. A4-70 (SS 316L) passivated fasteners should withstand ≥ 1000 hours in neutral salt spray test (5% NaCl fog at 35°C) without red rust per ISO 9227. Duplex 2205 fasteners: ≥ 2000 hours. These test durations are used as lot acceptance criteria for marine grade fasteners destined for offshore and coastal EPC projects requiring corrosion performance documentation.
DNV-OS-C401 / Lloyd’s Register
DNV-OS-C401 (Fabrication and Testing of Offshore Structures) and Lloyd’s Register Ship and Offshore Structure Rules govern the material and testing requirements for fasteners used in DNV-classed and Lloyd’s-classed offshore structures and vessels. Both classification societies require EN 10204 3.1 minimum certification on all structural fasteners; EN 10204 3.2 with third-party countersign for safety-critical structural connections (primary structural joints in load-bearing frames, lifting appliance connections, pressure-boundary flanges). The classification society approval authority must be confirmed for each project at the procurement stage.
Anti-Galling Treatment
& Passivation
Marine grade stainless fasteners require controlled manufacturing to maintain the passivated surface condition, prevent iron contamination, and ensure consistent mechanical properties through the cold-drawing or solution-annealing process. RR Hydraulic manufactures marine SS fasteners from certified ASTM A276 / A479 / A182 bar stock with full EN 10204 3.1 / 3.2 traceability from raw bar to finished fastener.
3.1 — Marine SS Grade Corrosion Performance vs Key Environments
| Material | PREN | Seawater Immersion | Splash Zone | Hot Seawater >60°C | H₂S Sour | HCl / H₂SO₄ | Bleach / Cl₂ |
|---|---|---|---|---|---|---|---|
| SS 304 (A2) | 18 | Poor — pits | Poor | Very Poor | Fair | Poor | Poor |
| SS 316L (A4) | 26 | Fair (ambient) | Good | Poor — SCC risk | Good | Fair | Fair |
| SS 904L | 36 | Good | Very Good | Fair | Very Good | Good | Good |
| Duplex 2205 | 35 | Very Good | Excellent | Good (≤60°C) | Very Good (NACE) | Very Good | Very Good |
| Super Duplex 2507 | 43 | Excellent | Excellent | Excellent | Excellent (NACE) | Excellent | Excellent |
3.2 — Manufacturing Process
3.2.1 — Cold Heading vs Bar Turning
Marine grade SS fasteners in the M3–M24 range are manufactured by cold heading from SS wire or bar stock — the work-hardening during cold heading raises the mechanical properties from annealed condition (A4-50) to the cold-drawn condition (A4-70) without heat treatment. The cold heading process for SS 316L requires approximately 30% higher forming force than for carbon steel due to SS’s higher work-hardening rate — proper tool steel die selection and lubrication are essential to achieve the required head geometry without cracking. For M30 and above, bar turning on CNC lathe is the manufacturing method — cold heading tooling for large SS diameters is impractical.
3.2.2 — Duplex and Super Duplex Fastener Manufacture
- Solution annealing mandatory: Duplex 2205 and Super Duplex 2507 fasteners are manufactured from bar stock in the solution-annealed condition (1020–1100°C quench for 2205; 1025–1125°C quench for 2507) — the annealing controls the ferrite/austenite ratio to 40–60% / 40–50% respectively
- No cold working after annealing: Unlike austenitic SS (A4-70/A4-80 achieved by cold drawing), Duplex and Super Duplex fasteners are NOT cold-worked after annealing — cold work destabilises the ferrite/austenite balance and can promote sigma phase formation, reducing both toughness and corrosion resistance
- Ferrite content verification: Metallographic examination of cross-section from each production lot — ferrite 40–60% (Duplex 2205) or 40–50% (Super Duplex 2507) per ASTM E562; deviation from this range indicates incorrect annealing and is a rejection criterion
- No heat input during threading: Threading of Duplex and Super Duplex fasteners must be performed at ambient temperature with flood coolant — any heat input above 300°C risks sigma phase or chi phase precipitation that causes embrittlement without visual indication
3.2.3 — Anti-Galling Treatment for SS Marine Fasteners
- Galling mechanism in SS: SS-to-SS thread assembly causes galling (cold welding) at the asperity contact zones on the thread surfaces — austenitic SS is more susceptible than carbon steel due to its lower work-hardening rate and higher surface energy; Duplex SS has lower galling tendency than austenitic due to the ferritic phase providing a harder surface
- Anti-galling compounds for marine SS: PTFE-based thread lubricant (Jet-Lube SS-30 or equivalent) — most common for marine SS fasteners; MoS₂ paste (Molykote G-Rapid Plus) — for higher load applications; copper-based anti-galling paste (Never-Seez NSN-8) — for extreme load Duplex/Super Duplex fasteners; Nickel-based paste (Never-Seez Pure Nickel) — for elevated temperature and sour service SS fasteners
- Application protocol: Apply anti-galling compound to male thread and under-head bearing face before nut run-down; do NOT apply to female thread; never use petroleum-based grease on marine SS threads — petroleum greases wash off in seawater and leave threads dry after immersion
- Nut run-down speed: Manual run-down recommended for Duplex and Super Duplex nuts — power impact wrench run-down without anti-galling compound is a primary cause of Duplex fastener galling and fracture during installation
Industry Applications
& Documentation
RR Hydraulic maintains full traceability from certified bar stock to final passivated and packed marine SS fastener shipment. PMI on every SS lot, mechanical testing, thread gauging, ferrite content verification (Duplex/Super Duplex), passivation certification, and complete EN 10204 3.1 / 3.2 documentation are standard on all project-grade marine stainless fastener supply.
4.1 — Inspection & QC Protocol
4.2 — EN 10204 Material Test Certificate Requirements
| Certificate | Content | Signatory | Marine / Offshore Requirement | When Mandatory |
|---|---|---|---|---|
| 2.1 / 2.2 | Declaration / non-specific | Manufacturer | Not acceptable for offshore structural | Never for DNV/Lloyd’s-classed marine fasteners |
| 3.1 | Bar heat-traceable mech + chem | Manufacturer’s authorised QC | Minimum for all marine SS fasteners | All offshore, coastal, and marine structural SS fasteners |
| 3.2 | 3.1 + TPI countersign | Manufacturer + SGS / BV / DNV / Lloyds | Subsea; offshore safety-critical; NACE+marine | DNV/Lloyd’s-classed structures; subsea; NACE sour+marine |
4.3 — Applications by Industry
Offshore Platform Structural and Process Bolting
A4-70 (SS 316L) stud bolts and hex bolts for all offshore topside general structural connections, piping flange connections, equipment base plates, and firewater system bolting. Duplex 2205 for splash zone and immersed structural connections — jacket leg clamps, J-tube fixings, conductor guide bolting, and any connection in sustained seawater contact. All with EN 10204 3.1; EN 10204 3.2 with DNV or Lloyds TPI for safety-critical primary structural connections. PMI on 100% of lots; passivation per ASTM A967; anti-galling compound applied before dispatch.
Seawater System Pump and Valve Bolting
Duplex 2205 stud bolts for seawater lift pumps, seawater injection pump casings, and seawater intake and discharge valve flanges. Super Duplex 2507 for hot seawater injection and high-temperature seawater heat exchanger flange bolting (above 60°C). The pump casing-to-cover flanged joint uses Duplex 2205 studs with Duplex 2205 heavy hex nuts — matching grade ensures no galvanic couple within the joint. Full passivation post-manufacture; anti-galling compound mandatory for nut assembly; torque values calculated for lubricated Duplex threads (lower friction coefficient than unlubricated).
Offshore Wind and Tidal Energy Structures
Duplex 2205 or Super Duplex 2507 anchor bolt arrays for offshore wind turbine monopile transition piece bolted connections — the flanged connection between the steel monopile and the turbine tower transition piece uses 60–160 large-diameter (M52–M80) Duplex fasteners per connection, torqued to specification by hydraulic bolt tensioner. All bolted connections in the intertidal and splash zone: Duplex 2205 as minimum grade. Subsea monopile grouted connection alternative — no fasteners required. Tower flange bolting above splash zone: A4-70 SS 316L is adequate. EN 10204 3.2 with TPI for all offshore wind primary structural fastener supply.
Desalination and Water Treatment Plants
Super Duplex 2507 for multi-stage flash (MSF) and multi-effect distillation (MED) desalination plant evaporator and brine heater section bolting — brine concentrations 45,000–70,000 ppm Cl⁻ at 60–120°C. Duplex 2205 for seawater reverse osmosis (SWRO) pressure vessel end cap bolts at 55–70 bar and ambient-temperature seawater. SS 316L (A4-70) for fresh water product piping and distribution system bolting. The desalination plant spans all three marine SS grade levels — verify design temperature and chloride concentration at each bolting location before specifying the grade. Wrong grade selection in desalination plant bolting causes systematic fastener failure within 1–2 years.
Marine and Naval Vessel Structural Fasteners
A4-70 (SS 316L) bolts, studs, and machine screws for naval and commercial vessel deck fittings, hatch cover clamps, port and starboard light brackets, deck machinery foundations, and accommodation module connections. Duplex 2205 for below-waterline hull penetration fasteners, sea chest cover bolts, and propeller shaft stern tube bolting. Full passivation per ASTM A967; salt spray testing per ISO 9227 ≥ 1000 hours for naval vessel fasteners. EN 10204 3.1 minimum; 3.2 with class society (Lloyd’s, DNV, BV, CCS) countersign for classification-required hull and machinery fasteners.
Coastal and Port Infrastructure Fasteners
A4-70 (SS 316L) structural bolts for coastal bridge structural connections within 2 km of seawater; Duplex 2205 for tidal zone and splash zone exposed structural connections (pier bearings, fender panel fixings, mooring bollard base plates). Floating dock and pontoon hardware: A4-80 for high-strength connections; A4-70 for standard structural. Port crane runway girder splice bolts: Duplex 2205 minimum for harbour locations — crane runway girder fatigue-critical connections in salt spray environment require both the higher strength (450 MPa yield) and the corrosion resistance of Duplex over A4-70. Anti-galling compound mandatory for all Duplex and Super Duplex bolted connections.
4.4 — Export Packaging Specification
- Marine SS fasteners packed in dedicated stainless-only polybags — strictly segregated from carbon steel hardware; carbon steel swarf or contact leaves iron deposits on SS surfaces causing marine corrosion pitting at the contamination site
- Grade clearly labelled on every polybag and inner carton: “SS 316L A4-70”, “Duplex 2205”, or “Super Duplex 2507” — property class included; visible without opening packaging; different grades in separate polybags even if same diameter and length
- VCI poly packaging for all marine SS lots — prevents moisture condensation during ocean freight; VCI film chemically inhibits any residual surface activation without coating or film deposit on the passivated SS surface
- Passivated SS fasteners packed immediately after passivation inspection — avoid re-contamination from iron-containing packaging hardware; all packaging clips, staples, and bands must be SS or plastic for marine grade fastener packages
- Anti-galling compound application: for Duplex and Super Duplex marine fasteners where bonded anti-galling film is specified — fasteners packed with individual thread sleeves to protect the MoS₂ or PTFE coating from abrasion during transit; paste-type compounds applied separately at site per installation procedure
- Duplex and Super Duplex fasteners individually segregated by grade — 2205 and 2507 appear visually identical; separate packaging labels; colour-coded polybags (red = Duplex 2205; blue = Super Duplex 2507) per project colour convention
- ISPM-15 heat-treated timber crates for all international export; inner moisture barrier sealed bags with desiccant sachets for ocean freight to tropical and high-humidity destinations
- Documentation: EN 10204 3.1/3.2 MTC, mechanical test certificate, PMI report (lot), ferrite count report (Duplex/Super Duplex), hardness certificate (NACE lots), passivation certificate (ASTM A967), salt spray certificate (where specified), thread gauge report (100%), anti-galling treatment certificate, and FAI report in waterproof document pocket
4.5 — Complete Project Documentation Package
| # | Document | Standard / Format | Mandatory / Conditional | Notes |
|---|---|---|---|---|
| 01 | Material Test Certificate (MTC) | EN 10204 3.1 / 3.2 | Mandatory — all marine SS fasteners | Bar heat-traceable; ASTM A276/A479/A182 per grade |
| 02 | Chemical Composition Report | Certified lab analysis per ASTM / ISO | Mandatory | Cr, Ni, Mo, N, C, Mn, Si, P, S limits per grade |
| 03 | Mechanical Properties Report | UTS, yield (proof), elongation, hardness | Mandatory | Per ISO 3506 / ASTM F593 for grade and property class |
| 04 | Hardness Test Report | ISO 6507 Vickers / ASTM E10 Brinell | Mandatory — NACE lots; Duplex; S.Duplex | A4-70 ≤ 220 HV; Duplex 2205 ≤ 293 HB; 2507 ≤ 310 HB |
| 05 | PMI Report (XRF) | Per lot — all marine SS grades | Mandatory — all lots (100% lot basis) | 316L vs 304; 2205 vs 2507; 904L vs 316L differentiation |
| 06 | Ferrite Content Report | ASTM E562 metallographic | Mandatory — Duplex and Super Duplex lots | 40–60% (2205); 40–50% (2507); cross-section photograph |
| 07 | Dimensional Inspection Report | Per ISO 4014 / ASME B18.2.1 / drawing | Mandatory | All critical dimensions per applicable standard |
| 08 | Thread Gauge Report | ISO 965 / ASME B1.1 Go/No-Go — 100% | Mandatory — 100% all threads | Post-passivation verification; metric 6g or UNC 2A |
| 09 | Passivation Certificate | ASTM A967 — method and acceptance test | Mandatory — all marine SS fasteners | Method (nitric/citric); water immersion or Cu-sulphate test |
| 10 | Salt Spray Test Certificate | ISO 9227 / ASTM B117 | Conditional — offshore critical; DNV/Lloyd’s | A4-70 ≥ 1000 hrs; Duplex ≥ 2000 hrs without red rust |
| 11 | Anti-Galling Treatment Certificate | Compound type + application method | Conditional — Duplex; Super Duplex; elevated torque | PTFE paste / MoS₂ film; application confirmation |
| 12 | NACE Compliance Statement | Hardness + heat treatment declaration | Conditional — sour + marine combined service | Grade + hardness limit; heat number reference |
| 13 | First Article Inspection (FAI) Report | Project-specific format | Mandatory — new project line items | All parameters including ferrite count; before batch production |
| 14 | TPI Witness Certificate | SGS / BV / DNV / Lloyds | Conditional — EN 10204 3.2; DNV/Lloyd’s classed | Co-witness at manufacturer; dimensional + PMI + ferrite |
| 15 | ISO 9001:2015 Certificate | Third-party QMS certification | Mandatory — EPC / offshore projects | Scope covers marine SS fastener manufacture |
| 16 | Country of Origin + Packing List | Chamber of Commerce / item-level | Mandatory | HS tariff code; grade-separated lot packing list |
| 17 | Commercial Invoice + Bill of Lading | Per INCOTERMS 2020 | Mandatory | Freight forwarder issued; HS tariff code |
4.6 — ISO and Quality System Compliance
ISO 9001:2015
Quality Management System covering ASTM A276/A479/A182 bar procurement and heat traceability, cold heading and bar turning process qualification for SS grades, Duplex solution annealing process control (temperature and time records), ferrite count inspection procedure qualification, passivation process qualification (acid concentration, time, temperature records), salt spray test procedure per ISO 9227, 100% PMI procedure, thread gauge protocol, and full material traceability from bar heat to finished marine fastener. Mandatory for all offshore, marine, and EPC marine SS fastener procurement qualification.
NORSOK M-630
NORSOK Standard M-630 (Material Data Sheets for Piping) is the Norwegian offshore standard governing materials for piping components including fasteners on Norwegian Continental Shelf (NCS) offshore projects. NORSOK M-630 includes material data sheets (MDS) defining SS grade, heat treatment condition, mechanical properties, and inspection requirements for offshore bolting — including specific Duplex 2205 requirements for seawater-wetted connections. All offshore EPC projects for Norwegian operators (Equinor, Aker BP, Vår Energi) reference NORSOK M-630 for marine fastener material specification alongside ISO 3506 and ASTM F593.
DNV-OS-B101 / GL Rules
DNV-OS-B101 (Metallic Materials) and Germanischer Lloyd (GL) Rules for Classification of Ships and Offshore Installations govern SS fastener material approval for DNV- and GL-classed structures and vessels. Both classification societies maintain approval lists for fastener grades and require EN 10204 3.2 countersign for safety-critical structural fasteners. The classification society material approval scheme confirms that the fastener manufacturer’s quality system produces material consistently within the approved grade specification — a separate qualification process from ISO 9001:2015 that addresses the specific requirements of marine classification.
ISO 3506 / EN 3535 (Aerospace)
ISO 3506 is the global marine SS fastener standard. For SS 316L (A4-70) fasteners in European PED-compliant pressure equipment (pressure vessels and piping in marine or offshore locations): EN 1515-1 flange bolting material requirements reference the ISO 3506 A4-70 property class as the CE-marking-compatible SS bolting material. For aerospace-grade SS fasteners on marine patrol aircraft and naval aviation support equipment: EN 3535 (Aerospace series — SS bolts) specifies the equivalent aerospace SS fastener requirements with additional testing for fatigue, corrosion, and dimensional accuracy beyond ISO 3506.
Submit your grade, diameter, length, head type, property class, and quantity to RR Hydraulic for a complete, certified commercial offer.