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Pex Tubing

Cross-section of corroded fitting

New brass fitting

Wall damage due to faulty valves.

Corroded brass fitting

Richard D. Malin & Associates: Technical Library


In the last 20 years or so, many new homes or homes with revamped plumbing systems have PEX tubing as a part of the plumbing system. PEX is made from crosslinked High Density Polyethylene (HDPE) polymer and looks similar to a garden hose when coiled up. (See below). Crosslinking is a chemical reaction that allows HDPE to become stronger, more flexible, and more resistant to cracking due to cold temperatures or upon impact. We want to make clear that PEX tubing on it's own is a good product and has several advantages over copper pipe and rigid plastic pipe such as PVC. It is flexible, resistant to scale and chlorine, doesn't corrode or develop pinholes, is faster to install, and has fewer connections and fittings.

The difficulty occurs with the brass fittings and valves commonly used with PEX. Brass is a copper alloy that may contain between 5 to 40% zinc. Zinc is added to brass to increase strength. Since the corrosion of brass increases as the percentage of zinc increases, it is generally recommended that the percentage of zinc in brass fittings be less than 15%, although some experts say that number can safely go to 19%. The dilemma is that many brass fittings and valves on the market have a zinc content of 35% or more. When water flows through the fittings and valves, it corrodes the metal. Zinc leaches from the brass and creates a powdery buildup inside the fittings. This corrosion process is known as dezincification, and it causes two main problems. First, the zinc builds up inside the walls of the fitting decreasing water flow and eventually causing a blockage. Second, the porous copper-rich structure that is left behind has little strength and is prone to seepage and breakage.

What are some telltale signs that dezincification is taking place? There may be a powdery white substance (zinc oxide) and/or mineral stains on the exterior surface of the brass fitting or valve. Water may also be weeping from the fitting body or the seal. When the situation is acute, there can be signs of water damage in the floors, ceilings, and walls surrounding the faulty plumbing.

Although there are a number of brands of brass fittings and valves on the market today that are susceptible to dezincification, some companies sell "dezincification-resistant" brass fittings. Check with the manufacturer that the percentage of zinc is 15% or less before installing them in your home. Your plumbing is only as good as the products used. Unfortunately, if you have failure-prone brass fittings and valves in your home, you may have a ticking time-bome behind your walls. If you discover flexible plumbing lines in your home and you are not sure if your situation merits concern, contact a licensed, professional contractor/plumber or ASHI® certified home inspector to evaluate the situation.

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