Monel 400 Sheet & Plate (UNS N04400): Seawater Corrosion, Sizes and Buying Guide

Quick answer: Monel 400 (UNS N04400) is a nickel–copper alloy with outstanding resistance to seawater and caustic, it stays non-magnetic when annealed, and it keeps useful strength from cryogenic temperatures up to about 450 °C. The bundle in our yard is marked "400 2.0×1220×3000 27张" — Monel 400, 2.0 mm thick, 1220 mm wide, 3000 mm long, 27 sheets. As sheet and plate it is supplied to ASTM B127 / AMS 4544; specify grade, thickness × width × length, temper and any leveling or surface film.

What Monel 400 is

Monel 400 is a solid-solution nickel–copper alloy — roughly two-thirds nickel, one-third copper — with small iron and manganese. It is one of the oldest and most proven corrosion-resistant alloys for marine and chemical service.

Reading the mark "400 2.0×1220×3000 27张"

That is a standard metric plate call-out: grade, then thickness × width × length, then the piece count.

Why Monel 400 (and when not)

Monel 400's headline trait is seawater — it resists flowing seawater, brackish water and marine biofouling far better than stainless, and it stays non-magnetic after annealing (a plus for instrument and sensor housings).

Sheet and plate: sizes and condition

The 2.0 × 1220 × 3000 mm sheet in the photo is a typical thin plate size, supplied flat-stacked on wooden runners.

Mechanical properties (annealed, ASTM B127)

Note the wide yield range — cold-worked tempers push yield up at the expense of ductility.

Where Monel 400 sheet and plate are used

• Marine: hull fittings, propeller shafts, seawater valve and pump bodies.
• Chemical: caustic (NaOH) handling, salt-production, alkylation.
• Oil & gas: sour-service trim, offshore platforms.
• Heat exchangers and condensers (especially with flowing seawater).
• Musical and architectural where a non-magnetic, corrosion-proof sheet is wanted.

For thin coiled titanium alternatives in corrosion service, see our TC4 strip guide.

Machining and welding notes

• Monel work-hardens quickly — use rigid setups, sharp tools, positive rake, and keep cutting to avoid dwell that hardens the surface.
• Weld with matching Monel 60 (ERNiCu-7) filler; it is readily weldable by GTAW/SMAW.
• Annealing (about 700–900 °C followed by rapid cool) restores ductility and non-magnetic behaviour after cold work.

Monel 400 sheet/plate RFQ checklist

1. Grade: Monel 400 / UNS N04400.
2. Size: thickness × width × length (mm), and sheet count.
3. Temper: annealed (O) or cold-worked.
4. Standard: ASTM B127 / AMS 4544, with MTC.
5. Flatness / leveling and any protective film.
6. Weight planning via the alloy weight calculator (density 8.8).

FAQ

Q: Is "400" on the bundle Monel 400? A: Yes. On nickel-alloy plate, "400" is the Monel 400 grade (UNS N04400); the rest of the mark gives thickness × width × length and sheet count.

Q: Is Monel 400 magnetic? A: Annealed Monel 400 is essentially non-magnetic. Cold working can induce slight magnetism; annealing restores the non-magnetic state.

Q: Monel 400 or 316L for seawater? A: For flowing or stagnant seawater and long life, Monel 400 is the stronger choice; 316L pits and crevice-corrodes faster in chlorides.

Q: Can Monel 400 sheet be welded? A: Yes, with ERNiCu-7 (Monel 60) filler; it welds well by GTAW/SMAW. Keep it clean and avoid contamination.

Q: How heavy is a 2.0×1220×3000 mm sheet? A: 1.22 × 3.0 × 0.002 m³ × 8.8 g/cm³ ≈ 64.5 kg per sheet; 27 sheets ≈ 1.74 t — verify with the weight calculator.