Monel Scrap: 400 vs K-500, How to Identify It and How to Sell It

Which Monel Grades Are Traded as Scrap?

Two grades turn up most often as Monel scrap: Monel 400 and Monel K-500. A third, the free-machining grade R-405, turns up in bar ends and turnings from screw-machine shops and needs to be identified separately.

Trade lists use several names for the same alloy. “Monel 500”, “Monel K500” and “Alloy K-500” all mean K-500; “Alloy 400” means Monel 400. Writing the UNS number next to the name removes any doubt, which is the whole point of the system described in how UNS numbers work.

Monel 400 vs K-500: Why Does the Difference Matter to a Buyer?

Monel 400 and K-500 differ only in aluminium and titanium, but that difference decides which melts each one can go into. K-500 is Monel 400 with those two elements added so it can be age-hardened for strength. A melter producing a heat of 400 does not want aluminium and titanium arriving unannounced, and a melter producing K-500 needs to know how much is coming in.

Nickel and copper are almost the same in both grades, so a standard handheld XRF will often call either one “Monel 400”. Aluminium is a light element that ordinary XRF measures poorly. To prove K-500 you need an analyser with a light-element setup or a spark OES burn, as explained in choosing XRF, OES or laboratory analysis. The Monel 400 vs K-500 comparison lists both grades side by side.

In practice, the source of the material is a strong clue. Shafts, drill collars, high-strength bolting and doctor blades are usually K-500; seawater piping, valve bodies and exchanger tube are usually 400. Use that clue to sort, then confirm with the right instrument before you describe the lot.

Is Monel Scrap Magnetic?

Monel 400 can be weakly magnetic around room temperature, and K-500 is non-magnetic, so a magnet gives inconsistent answers on Monel and should never be used to identify it. The reason is that the Curie point of Monel 400, the temperature where it stops being magnetic, sits close to room temperature. The same pipe can feel slightly magnetic on a cold morning and not at all in afternoon sun.

That causes two kinds of loss. Pieces of Monel 400 get pulled out with the steel and sold as ferrous scrap, and pieces of K-500 are assumed to be stainless because they do not respond. The magnet test article explains where a magnet does help, which on a Monel lot is mainly finding carbon steel fittings and supports.

How Do You Tell Monel from Cupronickel, Brass and Stainless?

Read the ratio of nickel to copper: Monel is about two-thirds nickel, while 70/30 cupronickel is the other way round, roughly 70% copper and 30% nickel, and 90/10 cupronickel has only about 10% nickel. All three are used in seawater systems, often in the same ship, and their colours are close once weathered.

Stainless steel is easier: it reads mostly iron with chromium, and neither Monel grade contains chromium. Brass and bronze read copper with zinc or tin and little or no nickel. A single XRF reading on a cleaned spot settles each of these.

The chart also explains why Monel must be kept out of other nickel alloy lots. Inconel and Hastelloy melts have tight limits on copper, and a few Monel offcuts in a bin of Inconel 625 can push a heat out of specification. Copper is listed among the contaminants in tramp elements and remelting for that reason.

Where Does Monel Scrap Come from?

Monel scrap comes mainly from the sea and from refineries, with a steady stream of bar and turnings from machine shops.

• Ship recycling and marine refits. Seawater valves, pump casings, strainers, piping and propeller shafts. Expect bronze trim, steel flanges and marine growth. See marine scrap.
• Refinery hydrofluoric acid alkylation units. Monel 400 piping, valves and vessel internals from turnarounds. Material from acid service needs cleaning and a decontamination declaration before any buyer will handle it. See oil and gas scrap.
• Feedwater heaters and exchangers. Monel 400 tube bundles, usually with carbon steel tube sheets and shells.
• Oilfield and machine shops. K-500 bar ends, drill collar offcuts and turnings; R-405 bar ends and chips from fastener and fitting production.

How Should a Monel Lot Be Prepared?

Prepare Monel so that each lot is one grade, one form and free of the copper alloys and steel it was assembled with. Monel equipment is rarely all Monel: valves have bronze or stainless trim, shafts carry sleeves and couplings, and tube bundles sit in steel.

• Pipe and tube. Cut free of steel tube sheets and flanges; bundle by grade. See Monel 400 pipe scrap.
• Bar ends. Keep 400, K-500 and R-405 apart at the saw. Stencils or paint codes on bar stock are often still readable on offcuts. See Monel K-500 bar scrap.
• Shafts and solids. Remove bronze sleeves, keys and couplings. See Monel K-500 solids.
• Turnings. One grade per bin, dry and oil-free. R-405 chips need to be declared because of their sulfur, which some melts must control. The general rules are in solids vs turnings.

What Decides the Value of a Monel Lot?

Nickel content sets the base of a Monel offer, with copper as a secondary credit, and the rest of the offer depends on how certain, clean and uniform the lot is.

For how these adjustments add up across nickel alloys generally, see what decides the value of nickel alloy scrap.

Which Mistakes Cost Monel Sellers the Most?

Most of the value lost on Monel lots comes from mislabelling and mixing, and nearly all of it is avoidable with a few minutes of reading and sorting.

1. Selling Monel 400 as ferrous. Because 400 can be weakly magnetic, pieces get pulled out with the steel on a cold day. Read anything grey and heavy that came out of seawater service before it leaves your yard.
2. Calling cupronickel “Monel”. Condenser tube and seawater pipe in 70/30 or 90/10 cupronickel look much like Monel once weathered. A buyer who finds copper-base tube in a Monel delivery will re-read every piece and treat the rest of the lot with suspicion.
3. Labelling shafts and bolting as 400. High-strength parts are often K-500. If you have not checked aluminium, say so: “nickel-copper, grade not confirmed between 400 and K-500” is honest and still sells.
4. Ignoring R-405 bar. Screw-machine bar ends look exactly like 400. Check bar stock tags and invoices from the shop that produced them.
5. Leaving trim and plating on. Bronze seats, soldered joints and plated fasteners bring lead, tin and zinc into a nickel melt, and the buyer will deduct for the risk.

A short note listing what you removed and what you could not confirm builds more trust than a confident label that turns out to be wrong.

Which Standards and Markings Appear on Monel Scrap?

Monel 400 plate and sheet is made to ASTM B127, bar to B164 and pipe and tube to B165, usually dual-marked with the matching ASME SB number. K-500 bar, rod, wire and forgings are made to ASTM B865. A stencil showing one of these specifications with N04400, N05500 or N04405 and a heat number is good evidence of grade, and better still when a matching mill certificate is available. The full list is in ASTM B specifications for nickel alloys, and European designations are covered under EN and W.Nr. numbers.

Older marine material may carry naval or federal specification numbers rather than ASTM marks. Record them anyway and back them with readings.

What Should You Send to Get an Offer?

Send the grade, form, approximate weight and location, photographs of the lot and of any markings, and readings that show nickel and copper values, plus aluminium and titanium for anything you describe as K-500. Say where the material came from, because a buyer reads “refinery HF unit” or “propeller shafts” very differently from “mixed marine”. The Monel scrap overview links every grade and form page if you need detail on a particular piece.

A clear line such as “Monel 400 pipe, 2 to 6 inch, cut free of steel flanges, about 1.5 tonnes, readings on 10 pieces” gets a firmer first offer than “Monel scrap, mixed”. Send the details and we’ll review your enquiry.

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