June 11, 2009

HERMANN LUYKEN

Sacrificial anodes, above, have been welded to Port Hope’s cast iron watermains to deter corrosion.

Cathodic protection prolonging life of iron watermains

PETER KENTER

corrrespondent

The Municipality of Port Hope, Ont. is slowly replacing its cast iron water main system. Some of the town’s pipes go back almost a century and are showing the signs of age.

The original lines are starting to demonstrate symptoms of microbial tuberculation — commonly known as red water. They’re also suffering from pitting and leaks largely caused by the acidity of the surrounding soil. The municipality is targeting the worst pipes first, replacing them with both polyvinyl chloride (PVC) and ductile iron, while extending the life of the existing cast iron pipes by embarking on a $100,000 cathodic protection program.

“Anything put out and installed in the last 15 years is better protected or poly-wrapped,” says Ed Simmons, Water Distribution Supervisor for Port Hope. “We’ve found out through professional articles and by our own experience, that cathodic protection helps the cast iron pipes to last longer.”

The technology is employed by welding magnesium tubes — known as sacrificial anodes — to the water mains. Because magnesium corrodes more quickly than cast iron, it takes the worst that the acidic soil can throw at it, sparing the cast iron from degradation.

“We tender the work out,” says Simmons. “The contractor just uses a truck and an augur and cores a hole to the water main, then uses an arc welder to attach the anode, which is about a metre long and weighs about 32 pounds (15 kilograms).” The anode is often set on a bed of sand or limestone before being buried.

The municipality has been using cathodic protection since the mid-1990s and the system has proved effective in protecting its iron pipes.

“We’ve seen water main breaks drop drastically where the system has been used,” says Simmons. When we dig up the sites where we placed the anodes, sometimes there’s nothing left of them—they’ve been completely used up, depending on the rate of corrosion in the area and the pH of the soil.”

The city estimates it could take up to 50 years to fully replace the existing water lines, so assistance from cathodic protection in stretching their service life is welcome.

“Every little bit helps,” says Simmons.

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