Copper pipe corrosion is a significant source of copper in wastewater, a pollutant that is acutely toxic to plankton and upsets the natural balance of other species in San Francisco Bay.
According to a study conducted by the City of Palo Alto, much of the copper enter- ing San Francisco Bay (about 77 percent) passes through storm drains and goes into the Bay untreated. The rest comes from wastewater, which moves from sewers through wastewater treatment plants and is discharged to the Bay. Wastewater treatment plants must meet strict limits on the amount of copper they discharge into the Bay.
To ensure that our copper concentrations remain well below the maximum allowable limits, the District asks plumbers and plumbing designers to follow best practices that reduce corrosion of copper water pipes. The Palo Alto study showed that corrosion from newly installed copper pipes is five times higher than from older systems. Fortunately, the study also found that simple modifications in plumbing design and installation practices may reduce corrosion by as much as 50 to 75 percent.
Best Practices to Reduce Copper Corrosion
- Keep velocities low by using larger diameter piping when possible. For cold lines, velocities should be less than eight feet per second and for hot they should be less than four to five feet per second. Also, in circulating water systems, specify smaller capacity pumps.
- Avoid stagnant sections and minimize direction and size changes whenever possible.
- Use compatible materials wherever you can. When multiple materials do need to be joined, specify insulating unions. Also, specify copper or brass straps.
- Prevent electrical currents by specifying that electrical grounding connections be made directly to a copper rod driven into the earth. Do not attach a grounding wire to water pipes. Also, specify that electrical wires be routed away from water pipes and make sure installers know not to use galvanized nails that touch copper piping.
- Avoid induced stresses by providing enough support for pipes and allowing for thermal expansion in the design of the system.
- Consider non-copper pipe (e.g., stainless steel) where its use is permitted.
- If copper pipe must be used, specify cutting, joining, and clean-up procedures that minimize corrosion. Require that pipe installations be thoroughly inspected.
- Specify non- or low-lead faucets, valves, and appurtenances. Use low-flow fixtures and aerated faucets.
- Use stainless steel piping and components for industrial process water supplies, heat exchangers, chillers, and condensers when operating temperatures exceed 140 degrees Fahrenheit.
- Incorporate coupons or easily accessed inspection points into long stretches of pipe to make it more convenient to monitor corrosion.
- Provide flanged fittings or unions for pumps and other devices that must be removed for maintenance. This reduces the amount of soldering that will have to be done on aged pipe.
From What Plumbing Engineers and System Designers Need to Know, produced by Bay Area Clean Water Agencies
For more information, visit Baywise.org