Guides / Materials

Dezincification and the Brass Grades That Resist It

September 21, 2026

Ordinary yellow brass has a failure mode that catches buyers out because the part looks intact right up until it leaks. It is called dezincification, and it is the main reason alloy choice on a water part is not just about lead.

What actually happens

Brass is a copper zinc alloy. Zinc is the less noble of the two. Under the right conditions the zinc leaves the alloy and goes into the water, and what remains behind is a porous copper sponge occupying the same space the solid brass used to.

The part keeps its shape. The dimensions do not change. But what is left has almost no strength, so the failure presents as a sudden leak, a stripped thread or a fitting that shears when somebody touches it.

Two visual signs are worth knowing. The affected area turns pink or copper coloured against the surrounding yellow. And a probe pushed into it crumbles the material rather than scratching it.

What accelerates it

Temperature. Hot water lines fail far sooner than cold.
Low flow or stagnation. Dead legs and recirculating loops are worse than running lines.
Chlorides. Seawater is the extreme case, but softened or treated municipal water can be enough.
Soft or slightly acidic water. Some regions are simply harder on brass than others.
High zinc content in the alloy. Alpha-beta brasses with more zinc are more vulnerable than single phase alpha brasses.

That last point is the lever engineers actually have.

The grades that resist it

C69300 silicon brass. The silicon addition and the resulting structure make this highly dezincification resistant. It is also lead-free at under 0.09 percent, roughly twice as strong as C360, and rated near 80 for machinability. When a part is both a drinking water part and a hot water part, this is usually the alloy that solves both problems at once. See NSF/ANSI 61 and 372 for brass fittings.

DZR brass, CW602N and CZ132. A leaded brass with a small arsenic addition and a controlled heat treatment that stabilises the structure. Developed specifically for water fittings, widely used in the UK and Europe, and easy to hot forge and machine. It is still a leaded alloy, so it answers corrosion but not the lead question.

C464 naval brass. About 1 percent tin, which is the traditional marine answer. Rated 30 for machinability, so it is slow and expensive to cut. Specify it because the environment demands it, never because it sounds stronger. See which brass alloy to specify.

Low zinc brasses and the red brasses. Below roughly 15 percent zinc the problem largely disappears, but so does the machinability that made you pick brass.

What does not resist it: C360, C385, C377 and the ordinary yellow brasses. They are excellent alloys in dry, industrial and electrical service, and they are the wrong choice sitting in hot water.

How resistance is proven

ISO 6509 is the standard test. A prepared sample sits in a copper chloride solution at a controlled temperature for 24 hours, then it is sectioned and the depth of the dezincified layer is measured under a microscope.

A grade passes when that depth stays below the limit in the relevant product standard, commonly 100 or 200 micrometres.

Two things buyers should know about this.

It is a material test, not a part test. A DZR certificate proves the bar met the standard. It does not prove your finished part will, because machining and any subsequent heat treatment can change the structure near the surface.

It is usually done by the mill, and the result appears on the material certificate. Ask for it explicitly if the part is going into water, because a standard 3.1 certificate will give you composition without necessarily giving you the ISO 6509 result.

Writing it on the drawing

As with the lead rule, write the requirement rather than only the alloy.

Hot water service, up to 90 C, recirculating.
Material shall be dezincification resistant,
tested to ISO 6509, max depth 200 micrometres.
Suggested alloy: C69300 or CW602N DZR brass.
Mill certificate with ISO 6509 result required.

That lets a shop offer whichever qualifying bar it can source, which matters because DZR and silicon brass stock is thinner on the ground than C360.

Dezincification is not the only way brass fails in service. Stress corrosion cracking is the other, it has different causes, and a grade that resists one does not automatically resist the other. If your part is cold worked, heavily machined or ends up anywhere near ammonia or an amine, read stress corrosion cracking in brass parts as well.

Got a water or marine part to quote? Send the drawing and describe the service environment in the part description. It changes which shops we match it to.

Frequently asked questions

What does dezincification look like on a failed part?

A pink or copper coloured patch where the brass should be yellow, often with a plug of porous material that crumbles under a probe. The part usually keeps its shape until it is disturbed, which is why failures tend to appear as a sudden leak rather than a gradual one. The remaining material is close to pure copper and has almost no strength.

Is C464 naval brass the same as DZR brass?

They solve the same problem differently. C464 adds about 1 percent tin, which is the traditional seawater answer. DZR grades such as CW602N are leaded brasses with a small arsenic addition and a controlled heat treatment, developed for water fittings. C69300 silicon brass resists dezincification without either addition and is also lead-free.

How is dezincification resistance tested?

ISO 6509 is the usual method. A prepared sample is held in a copper chloride solution at a controlled temperature for 24 hours, then sectioned and examined under a microscope to measure how deep the dezincified layer went. A grade passes when the depth stays under the specified limit, commonly 100 or 200 micrometres depending on the product standard.

Does hot water make dezincification worse?

Yes. Temperature, low flow, high chloride and slightly acidic or soft water all accelerate it, and hot water systems tend to combine several of those. That is why a fitting that lasts for decades on a cold line can fail in a few years on a hot recirculating loop made from the same alloy.

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