Achieving zero lead
The physical properties of lead-free alloys are important in material selection and installation.
For decades, lead has been used around the world as an essential element in the production of brass and bronze plumbing fittings and fixtures. In 1986, the U.S. Environmental Protection Agency amended the Safe Drinking Water Act under which any drinking water in contact with plumbing products such as pipe, solders and copper alloys (brass and bronze) used in fittings, faucets and lavatory fixtures with greater than 8% lead were no longer allowed. Products containing less than 8% were defined by the SDWA as “lead-free.”
The Reduction of Lead in Drinking Water Act, which was signed into law in January 2011, modifies the definition of “lead-free” in the SDWA, effective January 2014. The maximum lead content has been reduced to a weighted average of 0.25% for pipe, pipe fittings, plumbing fittings and fixtures.
Some states already have lead-free requirements in place equal to that of the federal mandate. California and Vermont were the front-runners in this category with legislation in effect in 2010. Maryland joined in 2012 and Louisiana in 2013. These states limit the amount of lead content to a weighted average of 0.25%.
To support manufacturers that offer products complying with these requirements, NSF’s joint committee on Standard 61 wrote and adopted an annex to Standard 61 known as Annex G, which is intended to provide manufacturers a means to certify product as meeting the prescriptive requirements of these new laws. Lead content evaluation and test methodologies can be found in NSF Standard 372, which is referenced by NSF 61 Annex G.
Since the inception of NSF 61 in the 1980s, most copper alloy plumbing products intended for drinking water distribution have been chemically washed or surface de-leaded to minimize the amount of lead that might dissolve into the drinking water.
To comply with the new law, suppliers developed and introduced several new low-lead or zero-lead copper alloys for the continued production of brass and bronze plumbing products. New lead-free copper alloys are widely known by their trade names — Envirobrass, Federalloy and EcoBrass.
These alloys are all unique in that they contain no purposeful introduction of lead and use small amounts of bismuth, bismuth-selenium or silicon in place of lead to allow the metals to be machined, forged or cast. Each of these replacement elements has its own pros and cons, but no matter the replacement element, all lead-free alloys will be more expensive to manufacture finished goods than leaded alloys.
Viega selected silicon as the key element to replace lead, based upon a number of factors such as corrosion, material strength and cost to produce. The lead-free alloys with silicon have excellent resistance to corrosion as demonstrated in laboratory and actual field testing.
Above the minimum
New copper alloys that are fully compliant with the upcoming legislation offer the best performance. The new lead-free fitting products made with Viega’s new alloy will contain less than 0.1% lead and are certified to NSF/ANSI Standard 61 Annex G.
Not all new alloys entering the market are truly lead-free, as some contain a purposeful amount of lead of just less than 0.25%, while others will introduce products that have a plating or coating applied to the wetted surface of the underlying lead-containing alloy, which may be subject to future legal action.
Material choice remains a critical consideration in selecting the right alloy for each application. Whether installing a copper or PEX system, it is important to understand the benefits of the various lead-free materials for the application and environment of the project. Bronze materials have historically been used for di-electric transitions and for aggressive soil and water conditions. The selection of brass vs. bronze will not change in the future.
In response to the lead-free mandates, Viega developed a bronze alloy specifically for mechanical cold-press fittings in order to meet state and federal requirements while maintaining a high level of quality. Many press ends are manufactured from a variety of lead-free brasses. While lead-free brass can be a very suitable material for lead-free plumbing fittings, its physical properties make it a more difficult material to press.
Depending on the alloy, lead-free brass has higher yield strength and tensile strength than zero-lead bronze. This means that press-force requirements may be higher for lead-free brass than zero-lead bronze, which can result in a fitting or valve that is not completely pressed at the completion of a pressing cycle.
Lead-free brass press ends that are properly pressed may have higher residual stresses at the completion of the press cycle as a result of their increased hardness. This is essentially a cold-working process. As residual stress increases, so does the potential for stress cracking. Often unnoticeable to the naked eye, the formation of microscopic cracks as a result of tensile stresses can occur when a material is deformed beyond its working limits.
The effect of stress cracking manifests itself in the form of stress corrosion in certain environments. Such a phenomenon can result in premature failure during the service life of a plumbing system. Zero-lead bronze is an example of a copper alloy designed specifically for press systems to minimize the risk of stress cracking and stress corrosion.
Many applications are well-suited to using lead-free brass alloys. Though they generally possess a higher heat capacity and may require specific practices, lead-free brass and bronze alloys can be used for soldering. Crimp-system fittings where crimp forces are exerted primarily on the crimp ring and tubing is another application where lead-free brass alloys are ideal.
The federal mandate for the use of lead-free materials in potable plumbing systems is effective Jan. 4, 2014. Physical properties of lead-free alloys remain an important consideration in material selection, and the design and installation of lead-free plumbing fittings, valves, components and overall systems.
About the authors: Paige Riddle is associate product manager for PEX products at Viega and Derek Bower is product manager at Viega. They work with Viega’s product lines in North America, maintaining existing PEX products and assisting in the development of new products.