Water losses can be overwhelming for property owners and residents, and the cost of repairs can be very high. Many times dezincification of plumbing components is indicated as the cause of the loss. This leaves non-metallurgists wondering “what is dezincification?”
Brass is an alloy, a mixture of copper and zinc with some other elements added. Copper usually makes up the majority of the elements in brass, and zinc is added to the copper. The amount of zinc added can vary from 5% to 45%, depending on the alloy. Note that pure zinc is bluish-white in color, while copper is red. Thus, the addition of zinc changes the color of copper from red to yellow. When the amount of zinc is high, some say greater than 15%, the zinc can be leached out of the brass by certain types of water. The zinc is removed, therefore the brass is “dezincified.”
As you can imagine, dezincification, or removal of the zinc from brass, is not good for the brass. The addition of zinc to copper strengthens the copper, making it stronger. When the zinc is removed, it leaves behind holes, or voids, in the brass that act a lot like perforations in the metal, making it weaker than pure copper. See image* below, which shows dezincification that had 42% zinc. After a time, the brass easily tears apart along the perforations.
It is sometimes hard to detect dezincification with the naked eye. One easy method is to simply look at the color of the component in and around the failure. If the failure area is copper-colored, or red, and the rest of the component is yellow, dezincification is likely. In the image above it can be seen that the dezincified zone is reddish and the base brass material is yellow. (The black areas in the dezincified region are voids.) However, to conclude with a reasonable degree of engineering certainty that the material dezincified, a destructive metallurgical examination of the failure is needed, which includes cutting the sample, polishing and etching the cross section and viewing it with a metallurgical microscope. (That’s how the image above was prepared.)
When you experience a loss due to water damage, ARCCA’s metallurgical experts will perform the necessary inspections/examinations to determine how the failure occurred and how it can be corrected.
JAMES J. MASON, PhD, P.E. is a Senior Engineer at ARCCA specializing in the mechanical failure of consumer and industrial products/equipment and machinery design/failure, as well as metallurgical laboratory analyses. He is also experienced in failed consumer medical devices, such as orthopedic implants and plastics.
*Image from http://www.diehl.com/en/diehl-metall/company/brands/diehl-metall-messing/cuphin/material.html