Dezincification is an electrochemical reaction between zinc and water chemistry that results in the selective loss of zinc from the brass alloy.
Dezincification of brass is a critical concern with valves, fittings, taps etc. in contact with water and can develop in a variety of ways depending on the water composition and application.
“Two types of corrosive attack characterize dezincification:
Plug-type dezincification is localized within surrounding surfaces mostly unaffected by corrosion. 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 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.
The service conditions generally present where dezincification occurs include:
-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).”
This is why several governmental authorities recommend or prescribe the use of special alloys for valves handling water.
DZR or CR brass
Dezincification resistant (DZR or DR) brasses, sometimes referred to as CR (corrosion resistant) brasses, are used where there is a large corrosion risk and where normal brasses do not meet the standards. Applications with high water temperatures, chlorides present and water hardness in addition to water flow, alkalinity and air pollution all increase the potential of corrosion. The brass alloy must be produced with great care, with special attention placed on a balanced composition and proper production temperatures and parameters to avoid long-term failures.
In addition, regulations for drinking water have been released in many countries some focusing on lead content, others on dezincification effects.
In addition to its well established CW602N range, with specific drinking water approvals gained in Scandinavia, UK and Australia, BONOMI INDUSTRIES also offers products made with CW511L, CW625N and CW626N to comply with specific national approvals, as well as to UBA (DE) positive list which represents the main European guideline on this matter.
BONOMI INDUSTRIES enforces a strict material sourcing program and always purchases first quality Italian made raw material to guarantee quality and product reliability.
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