Corrosion Control Engineer Explains Fluoride Action

reprinted from National Fluoridation News, July-September, 1975

Willis T. Bachellor, Inc. sent a sample of a broken rusted pipe and a container of sludge from a Seattle apartment house to the Food, Chemical and Research Laboratories, Inc. for analyses on March 27, 1972. The sample of pipe showed 1,044 ppm and the sludge 475 ppm of fluoride.

Mrs. Elizabeth M. Boyd, an interested and concerned Seattle resident recently mailed a copy of the fluoride findings to Dr. Willard E. Edwards, a consulting corrosion control engineer of Honolulu asking for a reason for the high fluoride content of the pipe and sludge. Dr. Edwards replied:

Fluoride acts differently in the water of various cities, since the water chemical content is seldom the same, unless the water supply is from the same source. In general, fluoride has a great affinity for iron oxide. It often softens previously hard pipe scale or iron oxide in steel pipes and tanks. This softened scale is often loosened and carried away from its previous location, thus allowing new iron oxide to form and corrode and weaken pipes and tanks under pressure.

Fluoride increases the electrical conductivity of water. In general, the higher the electrical conductivity of water, the higher its ability to allow corrosion to occur to metals it contacts. Where steel pipes or fittings are connected to brass, bronze or copper fittings, pipes or tanks, an electrogenic (corrosive) action takes place in the presence of fluoridated water, between the steel and the other metals. The steel becomes anodic while the brass, bronze or copper is cathodic, and the steel corrodes. This is called bi-metallic corrosion, and it occurs whenever two different metals are electrically (mechanically) connected in the presence of an electrolyte like fluoridated water.

Excessive corrosion can often be reduced by adding various chemicals to a water supply that has been fluoridated, but of course this adds to the cost of the maintenance and operation of the water system, and it makes the water less pure. I can honestly say that trouble due to pipe and tank corrosion greatly increases within a year after fluoridation is introduced.