Polyurea Coating for Digester Tank
THE CHALLENGE
The client’s digester tank was showing signs of water and gas leakage, as well as chemical damage that was threatening the integrity of the tank. In addition, there were also signs of corrosion caused by carbonation on the exterior walls of the tank.
To return the tank to working order the existing coating had to be completely removed from the interior and exterior walls and replaced with a new chemical-resistant, gas-tight coating system.
OUR SOLUTION
Surface Preparation
If you fail to prepare, you’re preparing to fail. This is why we always take thorough care when preparing the surfaces of substrates before applying any coating. In this case, the surface preparation was completed per NACE Standard SSPC-SP13. This standard ensures that the surface is completely free of contaminants, which is essential to the success of coating adhesion.
Firstly, the inside of the tank was high pressure jetted (18,000+ psi) to remove the majority of surface laitance and debris from the tank internals. Then we inspected the tank for any remaining contaminants or residue of the previous coating, which were then abrasive blasted off. Once the blasting was completed, we applied a water-based degreaser followed by one final high-pressure wash to completely rid the tank of residue.
The exterior walls of the tank were high pressure jetted (5000 psi) to clean off any contaminants and provide a suitable surface for applying the anti-carbonation coating system.
Recently the concrete tank had been fitted with some new concrete casting, leaving voids and an uneven surface, which can negatively impact the coating performance. To amend this, we used a rotary diamond wheel to grind down the structures, creating an even surface. We then spray-applied a polymer modifying resurfacing material to the required areas to create a smooth finish and fill the voids. Now the tank was ready to coat.
Coating Application
We spray-applied a monolithic pure polyurea coating system. This coating was chosen due to being a flexible, tough, resilient monolithic membrane with water and chemical resistance which protects the integrity of the tank and prolongs its service life.
The exterior walls of the tank received a 3-layer anti-carbonation coating system, which consisted of a primer and two heavy coats. This provided a waterproof and anti-carbonation covering over the tank that will prevent any long-term degradation to the coating structure. This coating also had a degree of elongation, which allows it to stretch and flex with the tank without a risk of failure.
The client was extremely happy with the end result.
