WATER TANK CORROSION

WATER TANK CORROSION

APPARATUS:THE SHOPS

I have a question pertaining to metal water tank corrosion. Our specialty pieces don’t get used very much; however, we keep the tanks full of water to ensure the best response times. Over the past several years, we hare noticed increasing iron in the tank water. Do you recommend any type of water-based synthetic corrosion inhibitor to reduce the corrosion rates in metal water tanks?

Chief Scott A. Graboyes

Washington Tup. l ire Dist.. Station J

Seu ell. Sen Jersey

First, let’s understand what is taking place in your tanks. Corrosion is the natural deterioration or destruction of a material as a result of its interaction with its environment. The term is applied mostly to metals —particularly to their reaction with oxygen, which causes rust.

Another form of deterioration, known as electrolysis, is the decomposition of a chemical system by passing a direct electric current through it. This includes the decomposition of water into hydrogen and oxygen. Pure water is a poor conductor of electricity; however, the many impurities found in natural water transform it into a relatively good conductor.

To combat corrosion and electrolysis in modern steel water tanks, two steps usually are taken. First, the inside of the tank is either coated with an epoxy coating or treated by hot-dip galvanizing. Both methods prevent the water from acting directly on the metal. Second, sacrificial anodes— rods of exotic metal (sometimes magnesium) suspended in the tank water through the tank lid —can be installed in the tank to reduce the electrolysis process. The anodes deteriorate and must be replaced periodically.

With this basic understanding in mind, you can try one of the following solutions to the problem of water tank corrosion.

  • The most difficult solution is to remove the tank lid, clean the inside of the tank, and coat it with a cold galvanizing compound. This process is involved, could be expensive, and requires the apparatus to be out of service for a period of time; its success could depend on how well the tank is cleaned and the present corrosion is removed.
  • Inspect the tank for the presence of anodes that may have been installed by the original manufacturer and have since deteriorated. Check with the original equipment manufacturer (OEM) to determine if anodes were used. Also ask about the feasibility of adding a sacrificial anode to the tank at this time to cut down on corrosion.
  • Although I have not personally tried it. a chemical treatment to prevent rust in booster tanks is commercially available. 1 contacted Paul Darley, vice president of W.S. Darley Equipment & Apparatus Co., who indicated that his company sells a product called Tank Saver. The advertising material for the product indicates that it prevents rust in booster tanks and also lubricates valves and gates. One-half gallon treats 500 gallons of tank water. It is relatively inexpensive and can be ordered from W.S. Darley at 1-800-323-0244 (Stock #H694).
  • If and when the tank requires replacement, investigate some of the newer fiberglass or plastic tanks. They will not rust or corrode, but they may require that additional mounting supports be installed on an older apparatus. Good luck!

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