Cementitious Coatings for Tanks In Special Applications

cementitious-Coatings

Credit: AMTECH TANK LINING SYSTEMS
The HydraStone cement lining

Editor’s note: This article first appeared in the July-August-2016 issue of Water Efficiency.

Non-potable hot water and cold water storage can present different challenges due to the temperature of the stored water itself.

AmTech developed its HydraStone cement lining for use on steel hot water tanks after the tanks’ original cementitious or thin mil epoxy linings have failed. The manufacturer points out that if the owner fails to reline the tank, further erosion will occur that will eventually permeate the outer steel wall, ultimately resulting in tank failure. Rob Pearlman, senior containment systems engineer and managing director at AmTech, recalls several instances similar to that involving the laundry operation at a large hotel convention center in the New York City area that experienced firsthand the result of compromised tank integrity. A facilities manager who was responsible for physical plant operations had received a call from the housekeeping manager, who reported that newly laundered sheets and pillowcases were tinged orange.

“The temperature in a pressurized tank may get up to 600 degrees and traditional linings aren’t going to be able to take that type of elevated heat, so a cementitious coating system is ideal for that,” says Pearlman. “For an OEM cementitious coating product for new tanks, some ask, ‘Why can’t I just go to Home Depot, buy some Quikrete, and put it on there—won’t it do the same thing?’ The main difference is the coefficient of expansion—how heat affects the expansion and contraction of something. If you’re putting a cementitious coating on a steel tank and you’re heating up that tank to hundreds of degrees, the tank is going to expand and contract at a different coefficient of expansion from that of the cement product.” AmTech’s cement lining is designed to mimic the coefficient of expansion of the metal tank, he adds.

Linings have also been engineered to suit steel cold water tanks, according to AmTech. Many buildings need large volumes of water for air-conditioning system chillers. The sheer volume of water can stress these tanks, so they require periodic inspections to ensure that their structural integrity is holding up. When the existing internal coatings reveal signs of ultimate failure, these tanks can be efficiently relined and quickly returned to service using AmTech’s DuraChem 580 polylining system, or a HydraStone Alkrete cement lining. According to themanufacturer, these linings suit cold-water storage tanks from 1,000- to 2-million-gallon capacity and above.

Pearlman describes the DuraChem lining, which is applied at high temperature and high pressure and sets up immediately, serving as “Tupperware for a tank,” a flexible material that doesn’t break down or deteriorate. Some thin-mil tank coatings reveal corrosion issues not unlike blistering on the paint on a car’s rocker panels, Pearlman adds. Oxidation causes a bubble to form, and the condition spreads until the coating is rendered ineffective and the condition threatens the tank’s structural integrity. The AmTech lining does not allow blistering to spread beyond its membrane because the curing process establishes a monolithic integrity of the lining’s membrane.

The HydraStone lining works differently, Pearlman explains. In contrast to the DuraChem lining, which forms a waterproof membrane, HydraStone hydrates. However, sacrificial anodes installed on the tank surface prevent the hydration from promoting corrosion. WE_bug_web

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