Have you ever wondered why copper alloys are used in products of importance such as water heater valves, backflow and metering devices?

The simple answer is that copper based products are renowned for their durability and predictable performance outcomes, even when exposed to extreme conditions, such as those that lead to dezincification.

The corrosion process, known as dezincification, was first recognized in the late 1950s. In its simplest form, dezincification was evident with brass nuts on tap washers. While in service, the affected nuts turned pink and disintegrated when the washer was being changed. More serious was the corrosion of fittings and valves, which exhibited a build up of visible white or blue/green deposits before they leaked.

It was discovered that the corrosion occurred due to the composition of some waters reacting with particular brass alloys (brass consists of the alloying of copper and zinc). It was determined that the brasses with high zinc content were the ones that suffered dezincification when exposed to aggressive water.

The affected metals consisted of two phases and it was the zinc rich phase that was attacked, with zinc being leached from the metal and the copper being re-deposited in a pink, spongy, brittle form. Whitish deposits, attached to failed valves, consisted of zinc-rich products.

Dezincification Resistant Brass (DR)

Industry was faced with the dilemma of how to make the popular, economical, brass products resistant to corrosion without having adverse impact on the unique properties of this metal (extrusion, forging, machining etc).

As a result of comprehensive research, laboratory tests and field trials, dezincification resistant (DR) brass was developed. Inhibition to dezincification was achieved, without affecting the intrinsic properties of brass, by adding small amounts of certain elements to the alloys. The metals were also processed in such a way as to reduce the size of the boundaries of the susceptible zinc-rich phase to minimise the potential for attack.

Australian Standard

In parallel with the research, Australian Standard AS 2345 “Dezincification resistance of copper alloys” was developed to provide a standardised method of testing copper alloys to assess their resistance to this form of corrosion.

In response, Water Authorities in localities where dezincification problems were apparent specified mandatory use of DR products. However, in areas where Water Authorities had not experienced significant dezincification problems, DR product was not mandated on the basis that there was a small, higher price for the product due to increased costs associated with the manufacturing process.

The disparity caused confusion in the industry. It wasn’t until the birth of the Plumbing and Drainage Standard AS 3500 that agreement was reached to make it mandatory for all copper alloy products be dezincification resistant and comply with the test requirements of AS 2345 and compliant product to be visibly and permanently marked DR.

When faced with challenges such as dezincification, the copper industry has responded and addressed issues within its control, resulting in satisfactory outcomes for all.