UNS N04400 Monel Pipe

UNS N04400 Monel Pipe is the workhorse of the nickel-copper alloy family. It has been in continuous industrial service for over a century because it does one thing exceptionally well: it stands up to seawater, hydrofluoric acid, and strong alkalis at a cost far below nickel alloys like Inconel 625 or Hastelloy C276. If your project involves salt water, HF acid, or caustic service, this is usually the first alloy a materials engineer asks about.

Product Forms

Bar & Rod

Plate & Sheet

Coil & Strip

Pipe & Tube

Fitting: Flange, Tee, Elbow, Reducer etc.

Forging: Ring, Shaft, Circle, Block etc.

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What Is Monel 400?

Monel 400 is a nickel-copper alloy with a nominal composition of 63% nickel and 28–34% copper, plus small amounts of iron, manganese, carbon, and silicon. It is identified by:

• UNS N04400
• Werkstoff 2.4360 (European designation)
• ASTM B165 - seamless pipe and tube
• ASTM B725 - welded pipe and tube
• ASME SB165 / SB725 - the pressure-vessel code equivalents

The alloy is single-phase and stays austenitic at all temperatures up to its melting point, which means it cannot be hardened by heat treatment. It is magnetic at room temperature - something that surprises many buyers - and it can be strengthened only by cold working. Monel K-500 takes the age-hardening route instead, which is why it is the higher-strength member of the family.

Chemical Composition (ASTM B165)

The nickel-copper balance is what gives the alloy its identity. If the MTR shows nickel below 63%, or copper outside the 28–34% window, the material does not meet the standard regardless of what the certificate says.

Mechanical Properties (ASTM B165 / B725)

Pipe supplied in the annealed condition must meet these minimums:

Cold-drawn or stress-relieved product can be supplied at higher strength, but the annealed values above are what most project specifications reference. If your design needs a higher minimum yield, state it on the purchase order - it changes the mill's production route and the price.

Physical Properties

Corrosion Resistance: What It Handles - and What It Does Not

This is where Monel 400 earns its keep, and where buyers most often misapply it.

Product Forms and Available Sizes

Monel 400 pipe is produced as:

• Seamless (ASTM B165) - NPS 1/8" to 12", schedules 10S through 160S, random or cut lengths
• Welded (ASTM B725) - larger diameters and lighter walls, cost-effective for non-critical circuits
• Cut-to-length - custom lengths for prefab spooling and site installation

Stock availability changes with the heat lot, so the fastest way to check NPS, schedule, and quantity is to send the size list directly. Most inquiries we see are for NPS 1/2" to 6", Sch 40S and 80S. As a rule, seamless is the default for pressure service above 150 psi; welded with full radiography is an acceptable alternative for lower-pressure lines.

Typical Applications

Monel 400 vs Monel K-500 vs 316L: Quick Comparison

If you need Monel 400 chemistry but higher strength, K-500 is the answer. If you need seawater resistance in warm stagnant conditions, neither Monel grade is the right call - that is where super duplex 2507 or Inconel 625 belongs.

What to Check When You Receive the Pipe

Before releasing payment, verify against the purchase order:

MTR (EN 10204 3.1) - confirm the heat number matches the pipe stencil, and check Ni/Cu percentages against the table above.

PMI - positive material identification on a sample of the lot confirms the nickel-copper balance.

Dimensions - OD, wall thickness, and length tolerances per B165 / B725.

Surface - no deep scratches, pits, or corrosion stains; ends properly protected.

Pressure test and hardness records - when specified on the PO.

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