Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
Monel 400 Marine Applications - Seawater Hardware, Shafts, Fasteners
Monel 400 marine applications cover seawater valve trim, propeller shafts, marine pump impellers, tidal-zone marine fasteners and offshore topside piping. Monel 400 (UNS N04400, ASTM B164) is a nickel-copper alloy at 63 to 70 percent Ni and 28 to 34 percent Cu that resists flowing seawater at rates below 0.025 mm per year up to 6 m/s, against chloride pitting that defeats SS 304 and crevice attack that defeats SS 316L above 30 degrees Celsius. Monel 400 seawater behaviour is set by a nickel-copper oxide film that holds in chloride and biofouled conditions. Monel® is a registered trademark of Special Metals Corporation; TorqBolt is not authorized by, affiliated with or endorsed by Special Metals. Numbers cited are from ASTM B164, B165, B564, F468 and NACE TM0169.
Why Monel 400 in Seawater
Three failure mechanisms drive marine alloy selection: chloride pitting, crevice corrosion under fouling deposits, and galvanic mismatch at dissimilar joints. Monel 400 resists all three. The nickel-copper film does not pit under chloride up to saturated brine and holds against biofouling-driven oxygen depletion. General corrosion stays below 0.025 mm per year in flowing seawater up to 6 m/s. SS 304 pits within months above 30 degrees Celsius; SS 316L crevice-corrodes under gasket seats and barnacle fouling. Detail on the seawater corrosion and corrosion resistance pages.
Marine Fasteners - Stud Bolts and Heavy Hex Nuts in Tidal-Zone Flanges
Monel 400 marine fasteners are specified for tidal-zone flanges, splash-zone topside connections, seawater pump and valve bolting, and seawater-cooled heat-exchanger channel covers. ASTM F468 governs the bolt grade; ASTM F467 governs the nut grade. Standard size range is M6 to M76 (1/4 in. to 3 in.) for stud bolts to ASME B16.5 and B16.47 flange ratings up to Class 2500. The galling-resistant nickel-copper film holds against carbon-steel mating and against stainless studs in mixed-metal joints.
Typical assemblies: stud bolts with heavy hex nuts on seawater pump suction flanges; hex bolts on valve bonnets; anchor bolts on tidal-zone skids; U-bolts on topside seawater piping. Washers to ASTM F467 Class B. Full bolt reference on the bolts page.
| Marine product form | Monel 400 spec | Typical service |
|---|---|---|
| Bolts, screws, studs | ASTM F468 | tidal-zone flange bolting, valve bolting |
| Nuts | ASTM F467 | seawater pump and valve assemblies |
| Rod and bar | ASTM B164 | propeller shafts, pump shafts, valve stems |
| Seamless pipe and tube | ASTM B165 | seawater piping, brackish cooling-water |
| Forgings and flanges | ASTM B564 | pump impellers, flanges, valve bodies |
| Plate and sheet | ASTM B127 | tank work, offshore brackets, hull plate |
Propeller Shafts and Marine Pump Shafts
Monel 400 bar to ASTM B164 is supplied as hot-worked annealed (25 ksi / 170 MPa yield) and cold-worked (85 ksi / 585 MPa yield) for shafting. Annealed bar covers low-stress seawater pump shafts, valve stems and minor propeller shafts on tugs and workboats. Cold-worked bar covers medium-load pump shafts and stern-tube liners. For propeller shafts above 200 mm diameter and high-cycle pump service, the age-hardened Monel K-500 at 90 ksi yield is the design choice. Bar reference on round bar. Marine pump impellers are machined from forging stock to ASTM B564 for seawater lift, fire-water and ballast pumps. Stern-tube sleeves, rudder pintles and tiller hardware on warships use the same nickel-copper grade for non-magnetic compliance.
Offshore Platform Topside Piping
Offshore topside piping uses Monel 400 for two service classes: HF gas separation downstream of the alkylation reactor in floating refining and LPG processing, and brackish cooling-water lines on coastal platforms where chlorination and biofouling rule out SS 316L. Seamless pipe to ASTM B165 covers 1/2 in. NPS to 24 in. NPS; seamless pipe is the supply reference. Condenser tube to ASTM B163 covers seawater-cooled tubing on produced-water coolers and amine reboilers. Flanges to B564, fittings on the fittings page, plate on the plate page. HF service detail on HF resistance and HF alkylation; sour-service on NACE MR0175.
Naval Applications - Non-Magnetic Bulkhead Hardware and Minesweepers
Monel 400 is weakly ferromagnetic below its Curie point near 35 to 50 degrees Celsius and effectively non-magnetic above it. For minesweeper hulls and topside fittings the design temperature exceeds the Curie point and the alloy reads as non-magnetic. Naval applications: non-magnetic bulkhead fastening, hatch and door dogging hardware, antenna mast bolting, sonar dome attachment, submarine periscope hardware. Detail on the magnetic permeability page. Minesweeper bolting uses studs to F468 and nuts to F467; round bar for pintles; forging for valve bodies; wire for lock-wire.
Companion Alloys - Monel K-500 for Harder-Service Shafts
Monel K-500 (UNS N05500) is age-hardened by aluminium (2.30 to 3.15 percent) and titanium (0.35 to 0.85 percent) additions to the same nickel-copper base. Mechanical envelope: 90 ksi (620 MPa) yield, 130 ksi (895 MPa) tensile, 250 to 350 HBW after age hardening. Seawater corrosion matches Monel 400. K-500 replaces Monel 400 wherever shaft, stem or thread stress exceeds the 25 ksi annealed yield. Typical landings: large propeller shafts, deepwater pump shafts, high-load valve stems, submarine fastening above NACE limits. Selection detail on the vs Monel K-500 comparison page.
Galvanic Compatibility - Monel 400 with Carbon Steel, SS 316 and Bronze
The seawater galvanic series ranks alloys by open-circuit potential against a silver / silver-chloride reference in clean seawater at 10 to 25 degrees Celsius. Compatibility is set by the potential gap and the area ratio of the two coupled metals.
| Coupling alloy | Potential vs Ag/AgCl, V | Coupled to Monel 400 | Design action |
|---|---|---|---|
| Monel 400 (UNS N04400) | 0.10 | self-couple, no risk | baseline reference |
| Carbon steel (A36, A105) | -0.65 | carbon steel corrodes accelerated | isolate with non-conductive gasket; keep large steel area |
| SS 316 / 316L (passive) | 0.05 | compatible, mild couple | acceptable in flowing seawater |
| Naval brass / aluminium bronze | 0.20 to 0.30 | bronze slightly anodic, low rate | compatible for pump-casing to Monel impeller |
| 90/10 cupronickel (UNS C70600) | 0.15 | compatible, near-iso couple | standard pairing on condenser tube + Monel waterbox |
| Super-duplex 2507 (UNS S32750) | 0.10 | compatible, near-iso couple | acceptable for offshore topside mixed-metal piping |
| Titanium (Grade 2, Grade 5) | 0.10 | compatible, near-iso couple | acceptable for heat-exchanger plates |
| Aluminium alloys (5083, 6061) | -0.80 | aluminium severely corrodes | full isolation mandatory; avoid couple |
| Zinc and galvanised steel | -1.00 | zinc sacrifices, intended for CP | used as sacrificial anode for the joint |
Source: NACE seawater galvanic series at ambient. Design rule: keep the anode area large relative to the cathode. A small carbon-steel saddle against Monel 400 piping corrodes rapidly; a large hull plate against a Monel 400 fastener stays in margin. Isolate dissimilar joints with phenolic gaskets where the area ratio inverts.
FAQ - Monel 400 Marine Service
Why Monel 400 marine? The nickel-copper film resists chloride pitting, crevice corrosion and biofouling-driven oxygen-depletion attack that defeats stainless. ASTM F468 covers bolts; B164 bar; B564 forgings; B165 pipe and tube.
Galvanic risk? Monel 400 at 0.10 V is cathodic to carbon steel and aluminium. Isolate with phenolic gaskets or keep the carbon-steel anode area large. Against SS 316, naval bronze, 90/10 cupronickel, super-duplex 2507 and titanium the couple is mild.
Crevice corrosion? Monel 400 is rated good in stagnant seawater versus poor for SS 304 and SS 316L. Design rules: full-face gaskets, no dead-leg piping, Monel K-500 for high-stress crevice locations like propeller-shaft sleeves.
Related Pages and Request a Quote
Related: seawater corrosion, bolts, stud bolts, round bar, vs Monel K-500, corrosion resistance, NACE MR0175, ASTM B164, ASTM F468, ASTM B564, nickel-copper alloy.
For Monel 400 marine fasteners, shafting bar, seamless pipe, flanges and forgings: pricing, lead time and certification documentation contact info@torqbolt.com or WhatsApp +91-22-66157017. Mumbai stock plus worldwide export through JNPT. Mill test certificates to EN 10204 3.1 (and 3.2 by arrangement), PMI on every heat, ultrasonic on shafting above 100 mm. Full reference on the main page.
Satisfaction Survey
