Dezincification has become a buzzword in the forensic engineering world and the plumbing product industry. Dezincification as a contributor to the failure of brass components has seemingly become more common. But what is dezincification?
To understand it, first let’s talk about brass. Brasses are a family of metal alloys whose main components are the elements copper and zinc. There are numerous brass formulations, with varying ratios of copper to zinc, as well as the inclusions of other elements. Altering the ratios of the elements creates brasses with differing mechanical and chemical performance characteristics, and changes the ease of manufacturing of the material. For instance, zinc is often added to aid in the machining, and provide strength to the brass. However, brasses with greater than 15% zinc can experience dezincification. Most brasses used in plumbing components contain a zinc percentage below 40%. At approximately 40%, the benefits of increased zinc are overwhelmed by the decrease in ductility and the higher chance for dezincification. Many of the brasses used in plumbing products are commonly called yellow brasses.
Dezincification is the selective leaching and removal of zinc from the brass, and into the water supply. This corrosion process decreases the strength of the brass and increases porosity in the now copper-rich material. For brasses with increased zinc, the zinc available for removal is greater, and the corroded brass product experiences a greater loss of material and strength. With the decreased strength and the water-pressurized working environments of plumbing products, brittle fracture failures of weakened brass plumbing products can occur.
A reddish discoloration at the fracture surface of a brass product is a common characteristic of dezincification. The loss of zinc creates copper-rich material that has a reddish hue. Some fractures will exhibit white deposits near the fracture surface. This may be a zinc oxide compound that is deposited after being leached from the brass.
A number of industry standards have been created in recent years to address the dezincification of brass. In 2009, NSF instituted Standard 14 which governs the physical and performance requirements for brass fittings and valves. In part, it states:
Fittings and valves made from copper alloys containing more than 15% zinc by weight intended for use in plastics piping systems shall be resistant to dezincification and stress corrosion cracking (SCC) and meet the following requirements…
To meet this standard, brass suppliers and plumbing component manufacturers may add small amounts of other elements, such as tin, arsenic, phosphorus, and antimony. These added elements offer increased resistance to the dezincification process, but do not completely prevent it from occurring.
Manufacturers also have the option of decreasing the zinc weight percentage to below 15%. These brasses are commonly called red brasses, and their lower zinc content eliminates dezincification from occurring entirely. It is probable that manufacturers do not produce red brasses as readily because of the increased manufacturing costs associated with the production of these more refined, and dezincification-resistant brasses.