Tides and Coatings Don’t Mix:
Leaking Power Plant Tank

By  Jennifer Kramer

Photos courtesy of Tank Coating Technologies, LLC

With every high tide, salt water seeped in through hundreds of cracks in the de-ionized water concrete holding tank at a Somerset, Massachusetts power plant. Given that more than four teaspoons (59.15mL) of salt would damage the plant’s turbines and shut down operations, the 50-year-old, coal-fired power plant had a problem.

“The water from the nearby river poured from some of the cracks in a manner similar to a water fountain,” says Mitch Lewis of Tank Coating Technologies LLC. “And the concrete substrate itself had been poured in 1927 so it was extremely porous. Everyone said it was too wet to be coated. But we knew there had to be a solution.”

“If You Can Get In It We Can Fix It”

Lewis’ company motto is “If you can get in it we can fix it” and the crew from TCT had their work cut out for them with this project. The 100-foot-long by 22-foot-wide by 14-foot-high (30.48m x 6.71m x 4.27m) tank is located directly beneath the power plant, six feet (1.83m) below sea level, so all access had to be through a narrow 18-foot (5.49m) man way opening. This meant that not only would strict confined space protocols and PPE requirements be observed, but all equipment and gear would need to pass through the small “hole.”

Also, the plant couldn’t afford to keep the tank out of commission for long. Non-operational turbines – whether due to contamination or repair – represent a loss of money, so a strict 6-week deadline was specified.

But, in the end, it wasn’t access or time that would prove to be the biggest challenge. It was moisture. First, the crew set up sump pumps to help pump out the water. They also brought in dryers to dry and heat the concrete, as well as two fans capable of moving 12,000 cubic feet (339.8m3) of air per minute to both dry the substrate and circulate fresh air.

Strategic planning also helped, as Lewis reveals, “Our plan of attack was to work on the ceiling and walls first. Then, we used the spent blast media from those areas, which was non-toxic and lead-free, to create berms on the floor to hold back any water seepage.”

They blasted the tank with Black Beauty 1243 and a standard sandblast pot, using 10 to 12 tons (9,071.8kg – 10,886.2kg) of media. “Any spent media that wasn’t used as make-shift ‘sandbags’ had to be shoveled into five-gallon (8.93L) buckets and passed up through the man way,” says Lewis.

Once the concrete had been blasted it was easier to identify the cracks. “We did about 300 to 400 lineal feet of hydraulic injections with a proprietary polyurethane-based primer.” The sealant is pumped into the crack, where it expands upon contact with water. “Sealing the wall cracks alone stopped approximately 90 to 95% of the leaks,” Lewis recounts. “But we’d still have two inches (5.08cm) of salt water from the floor every morning.” Pumps would be a key to the success of the final install. But first, it was time to do what everyone said couldn’t be done -- coat the wet concrete.

Don’t Weep For Me

“All the water in the concrete creates a high hydrostatic (negative) pressure that will push any coating off,” Lewis explains. “So, our solution was to first fasten a system of steel ‘keepers’ similar to grating on the concrete to create a mechanical bond that would hold the coatings in place.”

Propane torch wands were used to draw moisture out of the concrete prior to the application of Rhino Primer 251. The crew then used Rhino system HVLP pumps and guns to spray-apply the primer to a thickness of approximately 12 mils (0.305mm) DFT. “It was a challenge to fit 70 feet (21.34m) of heated hose through the smaller man way,” says Lewis. “But our hole man was always monitoring the situation.”

After the primer had been applied, the crew attached the “keepers” using drills and lead anchors because the concrete was too porous for standard nail guns. Then, using the same HVLP equipment, they spray-applied Rhino’s Hi-Chem elastomeric polyurethane lining system directly over the keepers. The two-component, 100% solids coating was applied to a thickness of 250 mils (6.35mm) DFT.

Tyvek sheeting provided a floating base over the water so the Hi-Chem would not foam up. The sheets were transitioned from the floor onto the wall to make a seamless seal. This created a “floating floor” that flexes when it is walked upon. The crew then cut a hole in the Tyvek floor and installed a sump pump to remove any excess water, should it build up beneath the coating. Once the pump was put in place, it was then sprayed over with Hi-Chem, making the installation permanent.

Fast-forward several years. The power plant is still in operation. More importantly, thanks to Mitch Lewis and his crew from Tank Coating Technologies, the tank’s lining still separates the contaminated and damaged concrete from the de-ionized, distilled water. Although they may wait for no one, time and tides have not damaged these coatings.
 

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