Water tank project reveals corrosion

‘Super high’ structure will need replacing at next maintenance

A contractor for the Altoona Water Authority recently recoated and completed other maintenance on the authority's "super high" water distribution tank above the former Keith Athletic Field for less than the amount budgeted.

But the discovery of corrosion around a previously welded area ensures that when the recoating wears out, the authority will need to replace the tank, rather than recoat it again, according to staff engineer Michael Sinisi.

The recently completed recoating and maintenance contract was for $188,500, plus a $73,000 addition to deal with the corrosion, but replacing the tank could cost from $750,000 to $2 million, authority officials said.

Still, the recoating work, with special attention paid to the corroded area, "might have bought us 15 years," Sinisi said.

The last time the 66-year-old tank was recoated, which was "before our time," workers simply painted over the problem, which was identified this time by robotic inspection, Sinisi said.

That inspection showed that pitting had penetrated halfway through the thickness of the steel, Sinisi said.

Welding can make steel vulnerable to corrosion, according to Sinisi and board member Jack Speece.

Contractor M&A Coatings applied zinc primer, then an epoxy paint, and also added "cathode protection," Sinisi said.

Those efforts should stop further corrosion, he said.

"This holds it in place," he stated.

Corrosion of steel tends to occur when steel is "stressed," and welding can cause that stress, according to an article on the American Water Works Association website, "Cathodic protection for steel water storage tanks."

In such cases, stressed areas are "anodic" to unstressed areas, losing electrons to the unstressed areas through electrical current activity, according to the article.

Cathodic protection, using a source of charge in the tank, reverses the process, adding electrons back for the stressed areas, according to the article.

"(T)ank owners view cathodic protection as a low-cost way to safeguard investments in their storage tanks and protective coating systems," the article states.

The authority "super-chlorinated" the super high tank to disinfect it before putting it back in service, Sinisi said.

Mirror Staff Writer William Kibler is at 814-949-7038.