Photo Gallery B10: Brass Dezincification
Dezincification is more of a chemical transformation than a corrosion event. It occurs to brass pipe after a long period of service, typically at or about 80 years, and is greatly dependent upon the type of brass pipe installed in combination with the composition and aggressiveness of the local water supply. The problem arises from the natural affinity of water for zinc, a chemical element from which brass pipe is made. Red brass has a lower percentage of zinc and is far less impacted by dezincification, whereas more commonly used yellow brass has a much higher percentage of zinc and therefore is far more vulnerable.
Common signs of dezincification are round chalk like deposits on the pipe surface, which represent areas where the zinc has been leached out or been removed to produce a more porous form of copper. If removed or cut open for visual inspection, similar chalk like deposits are also viewed inside. Where no such markings are present, a metallurgical lab analysis is required to identify the condition. As certain photos in our gallery illustrate, removing the external deposits produces a condition where the brass pipe has seemingly been inlaid with copper. This is a very weak and more porous form of copper, however, and will be the future site of a leak. The most common mode of failure is for pinholes to develop, although long splits and fractures along the pipe are also possible when operating under higher pressures. Hot water brass pipe typically exhibits the first sign of this occurrence given that heat accelerates most chemical reactions.
Although dezincification has been a problem mainly to old properties having soft water supplies, we are now seeing extremely advanced failures of newly installed brass fittings. Brass pipe is very rarely installed for domestic water service any longer in lieu of copper, but brass valves, strainers, flow control valves, and other fixtures are common to every such system. With many of today’s brass products being manufactured overseas and having a much higher concentration of zinc, as well as thinner wall thickness dimensions, resulting service life expectations have plummeted. Add to that fundamental product weakness the common installation of water softeners and even reverse osmosis equipment to remove virtually every trace of hardness from the water, and such ultra-soft water’s attack against new brass valves and fittings skyrockets.
In contrast to older buildings finally realizing the need to replace their 85 year old yellow brass domestic water pipe due to dezincification, new properties in operation for less than 6 years have suffered the same result.
