What is Dezincification?
In this article, we are going to be discussing the dezincification process, and its relation to yellow brass fittings found in pex plumbing systems. Yellow brass was the primary product used in pex plumbing systems (at the fittings) from the mid 1990’s, till about 2010. These types of fittings are susceptible due to the molecular composition of the brass alloy itself. So, what is it is dezincification?
By definition, it is a process which selectively removes zinc from an alloy, leaving behind a porous, copper-rich structure that has little mechanical strength.
The process can show itself in a variety of ways depending on the water composition and service conditions. It may present itself as dull red spots on the surface of brass. It can also manifest as seepage of water through the walls of fittings or leakage at valves. Extreme dezincification can cause actual breakage, with a dull coppery appearance to the fracture surface.
How does the dezincification of yellow brass occur?
There are two types of corrosive attacks that characterize the dezincification of yellow brass fittings:
- Plug-type dezincification: This type of dezincification penetrates deeply into the sidewalls of valves and fittings. Common failures associated with plug-type attack include penetration through the sidewalls that causes water seepage or loss of mechanical strength in threaded sections to the point of fracture.
- Uniform-layer dezincification: This type of dezincification leaches zinc from a broad area of the surface. This type of dezincification uniformly reduces the wall thickness of the valve or fitting. A complex set of conditions must be present for dezincification to occur, and the occurrence is often related to region of the country.
Dezincification selectively removes zinc from the alloy, leaving behind a porous, copper-rich structure that has little mechanical strength. An in-service valve suffering from dezincification usually has a white powdery substance or mineral stains on its exterior surface. The valve may exhibit water weeping from the valve body or stem/bonnet seal.
What makes yellow brass fittings susceptible?
Brass Alloy (copper-zinc alloys) containing more than 15% zinc are susceptible to dezincification. Zinc is a highly reactive metal, as seen in its galvanic series ranking. This reactivity stems from the fact that zinc has a very weak atomic bond relative to other metals. Simply put, zinc atoms are easily given up to solutions with certain aggressive characteristics.
As previously mentioned, during dezincification, the more active zinc is selectively removed from the brass, leaving behind a weak deposit of the porous, more noble copper-rich metal; making them brittle.
Multiple products manufactures of pex plumbing systems have been the defendant in class action lawsuits due to the presence of yellow brass fittings, and their failures. Once such company, IPEX, had a recall issued for fitting and piping failure in 2005. The pex product described line was most commonly referred to as Kitec. For more information on Kitec Plumbing Systems, please click here: https://absoluteid.net/kitec-plumbing/
Over the past decade, an evolution in brass alloys has occurred, and yellow brass fittings that are dezincification-resistant do exist. However, specifiers who simply accept inexpensive yellow brass without regard to whether they are standard alloys, or even meet the performance requirements of standard alloys, are vulnerable to potential problems.
What are the service conditions generally present when dezincification occurs?
- Water with high levels of oxygen and carbon dioxide (uniform attack).
- Stagnant or slow moving waters (uniform attack).
- Slightly acidic water, low in salt content and at room temperature (uniform attack).
- Soft, low pH and low mineral water combined with oxygen, which forms zinc oxide (uniform attack).
- Waters with high chloride ion content (uniform attack).
- Neutral or alkaline waters, high in salt content and at or above room temperature (plug-type attack).
What’s the cure?
A tightly written valve specification that limits brass alloys to those containing no more than 15% zinc, or specification of proven dezincification-ant resist yellow brass alloys, say the experts. Further, manufacturers must be required to provide alloy design or chemistry for the materials used in their valves and fittings.
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