What Is Brass?
Brass is an alloy that mainly contains copper and zinc. It can also contain other elements, in smaller amounts, to improve mechanical properties, corrosion resistance or to ease its manufacturing. Moreover, brass is very ductile and flexible.
Brass is the most widely used copper alloy in the industry. Indeed, brass is less expensive than other copper alloys and has good mechanical properties. It is also easy to manufacture.
There are different types of brass. One of them is yellow brass, which is widely used in hardware and plumbing (valves, faucet cartridges, etc.). Yellow brass contains about 30 to 40% zinc.
Brass with a zinc content greater than 15% is vulnerable to certain types of corrosion, such as dezincification, in the presence of a corrosive environment.
What Is Dezincification?
Dezincification is one of the causes of failure in plumbing components. Dezincification can occur when brass containing more than 15% zinc is in contact with drinking water.
Dezincification is the process of selective corrosion of zinc. The dezincified area becomes a porous mass of copper, with significantly reduced mechanical properties. The dezincification will thus weaken the entire component until it will eventually break. The higher the percentage of zinc, the higher the risk of dezincification.
Some water parameters can promote dezincification:
- high chloride and sulphate levels,
- low water alkalinity, and
- a pH of about 8.
Since 2009, some Standards, such as NSF/ANSI 14 , require that brass used in plumbing be resistant to dezincification. To meet this requirement, a brass must contain less than 15% zinc or contain additive elements such as arsenic, antimony, phosphorus, or tin. However, both our experience and the published literature show that these additives limit the risk of dezincification without preventing it.
How to Identify Dezincification?
Visual and binocular examination can show dezincification. Photographs 1 and 2 show the fracture surface of a yellow brass faucet cartridge. The reddish areas correspond to the weakened areas. Indeed, it is the zinc that brings the yellow colour to the brass. To confirm the dezincification phenomenon, additional examinations are necessary: chemical analysis, SEM (Scanning Electron Microscope) examination, EDX (Energy Dispersive X-ray Spectroscopy) analysis, and optical microscopy.
Chemical analysis by spectrometry or ICP (Inductively Coupled Plasma) enable the determination of the exact chemical composition of the material. Since only brass with more than 15% zinc is susceptible to dezincification, it is important to determine the chemical composition of the brass.
SEM examination allows us to determine the failure mode of the component. When dezincification occurs, the fracture surface is associated with brittle fracture. Brittle fracture is not expected in brass, as it is a ductile material. Photograph 3, taken under the SEM, shows grain boundary decohesion and cracking, which are characteristic of brittle fracture.
Photograph 4, also taken under the SEM, shows porous areas. EDX analyses, which provide us with semi-quantitative estimates of the chemical composition of the fracture surface, indicate that the porous areas are depleted in zinc. Thus, the EDX analyses allow us to highlight variations in the percentage of zinc at different locations on the fracture surface.
The metallographic examination shows the areas affected by dezincification. Photograph 5, taken under the optical microscope, shows an area unaffected by dezincification (left) and an area affected by dezincification (right). The affected area is porous, as the zinc has been leached away. Only the copper remains intact.
Pour résumé
Dezincification is the selective corrosion of zinc in brass. It can occur when brass with more than 15% zinc is in contact with water. The higher the percentage of zinc, the more susceptible the brass is to this phenomenon. Some water parameters (alkalinity, pH, presence of chloride or sulphate) can cause dezincification of brass.
When dezincification builds up in the component, it considerably reduces its mechanical properties and may lead to its breakage.
Yellow brass, being very versatile, is widely used for plumbing fixtures. However, it is composed of more than 30% zinc, which makes it susceptible to dezincification. Despite the use of certain additives to make this brass more resistant to dezincification, dezincification failures are still common in plumbing.
