Surface Treatments
Certifications
- ISO 9001:2015
- NORSOK M-650
- NACE MR0175
- ISO 15156-3
- PED 2014/68/EC
- EN 10204 type 3.2
- AD 2000 W2/W7/W10
Ferralium 255 Seawater Service, Pumps, Valves, Heat Exchangers
Ferralium 255 (UNS S32550) is selected for seawater service because its PREN ≥ 40 chloride pitting resistance handles ambient seawater (3.5% NaCl, ~30 °C) with substantial margin, while its 2% Cu addition gives reducing-acid resistance for downstream chemical-injection service. Standard duplex (Duplex 2205, PREN ~35) is generally limited to seawater ≤ 30 °C; austenitic 316L (PREN ~25) is unsuitable for warm seawater. Super duplex grades like Ferralium 255 extend service to warmer seawater (40+ °C), high-velocity flow regimes, and crevice-prone geometries.
Q: Why is super duplex stainless steel preferred for seawater service over 316L?
Why Super Duplex for Seawater
Seawater corrosion attack on stainless steels is dominated by chloride-driven pitting and crevice corrosion. Resistance is predicted by Critical Pitting Temperature (CPT) per ASTM G48 method A: 316L CPT ≈ 5 °C, Duplex 2205 CPT ≈ 25 °C, Ferralium 255 CPT ≥ 35 °C, Super Duplex 2507 / Zeron 100 CPT ≈ 40 °C. PREN correlates closely with CPT, both metrics confirm super duplex grades extend the service envelope ~10–15 °C above standard duplex.
Q: Why use Ferralium 255 specifically in seawater applications?
Why Ferralium 255 Specifically
Among super duplex grades, Ferralium 255 is preferred when seawater service involves additional reducing-acid exposure, e.g., chlorination injection (creating reduced HOCl species), sulphate-reducing-bacteria (SRB) microbially influenced corrosion, or chemical injection systems carrying H2SO4, HCl, or organic acids. The 2% Cu in Ferralium 255 forms a stable Cu-rich passive film that improves performance in these reducing environments compared to Cu-free grades like Super Duplex 2507. For pure seawater service without reducing-acid exposure, all three super duplex grades (Ferralium 255, 2507, Zeron 100) perform comparably.
Q: Which seawater components are typically made from Ferralium 255?
Typical Seawater Components in Ferralium 255
- Seawater pumps, impellers, casings, shafts, wear rings (high-velocity erosion-corrosion service)
- Seawater valves, ball valves, gate valves, check valves, butterfly valves (often with Inconel-overlay seats)
- Heat exchangers, tube-and-shell, plate-and-frame for seawater cooling, condensers
- Firewater systems, deluge ringmains, sprinkler nozzles, high-pressure firewater pumps on offshore platforms
- Manifolds & piping, seawater intake / outfall, ballast water systems, hypochlorite generation
- Fasteners & bolting, Ferralium 255 hex bolts, stud bolts, hex nuts for flange connections in seawater service
Q: What design considerations apply to Ferralium 255 in seawater service?
Design Considerations for Seawater Service
- Avoid crevice geometries where possible; if unavoidable, specify min CPT 35 °C per ASTM G48 method A on heat MTC
- Galvanic corrosion: do not couple Ferralium 255 directly to copper-alloy or carbon-steel components in seawater, specify isolation or compatible bolting (super duplex)
- Welding: maintain ferrite content 35–65% in weld zone per NORSOK M-630; use 25.10.4.L matching filler; heat input 0.5–2.5 kJ/mm
- Surface finish: avoid roughness pockets that promote crevice corrosion; passivation per ASTM A967 after fabrication
- NACE MR0175 sour service: hardness ≤ 32 HRC enforced; combined seawater + sour-gas service requires both NORSOK M-650 QTR + NACE MR0175 documentation
Q: Which standards apply to Ferralium 255 in marine and offshore seawater service?
Spec & Compliance for Marine / Offshore Seawater
NORSOK M-650 QTR is typically required for North Sea and Norwegian offshore seawater service per material data sheet MDS D55. NACE MR0175 / ISO 15156-3 compliance is required when seawater combines with sour-gas exposure (downhole, wellhead, X-mas tree internals). TorqBolt provides per-heat MTC (EN 10204 type 3.2) certifying both NORSOK M-630 chemistry / ferrite-content compliance and NACE MR0175 hardness limits.
Need Ferralium 255 for seawater service? Email info@torqbolt.com or WhatsApp +91-22-66157017 with form, dimensions, quantity, ASTM/EN spec, MTC level (3.1 / 3.2). NACE MR0175 sour-service stamp on every heat. NORSOK M-650 QTR on request. Per-heat EN 10204 type 3.2 MTC included with every consignment.
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