The Client

Each tank, 80% of which was standing above ground level, was of vertical cylindrical design with funnel-shaped floors sloping at 45°. Built from reinforced concrete some forty-five years ago, the tanks had been lined with acid-proof tiles.

Challenges

• The tannery was unable to fill the vessels by more than 50-60% because the additional pressure caused the tanks to move and crack.
• The grouting between the tiles had been damaged by the chemicals. 
• The walls were approximately 30cm thick and worn with age.
• The scaffolding had to be free-standing within the tank/s to allow us access to all treatment surface areas.

Solution

We chose to treat all the upper areas of the tank initially and the tannery erected the scaffold, which was supported on the centre roof and floor. Once that was removed, we were able to treat the conical floor.

For this project, we used a chemical and abrasion-resistant elastomeric polyurethane-based lining material. It had excellent resistance to the chemicals in use, offered excellent abrasion resistance and could tolerate the stretching and flexing of vessels.

The tanks were initially steam-cleaned and degreased before being abrasive grit blast-cleaned to loosen any unsound substrate and produce a mechanical profile. After careful vacuum cleaning and the application of a primer coat, the new lining was sprayed on the surface at a thickness of 1.5 – 2mm using plural feed airless hot paint spray.

Cracks on the external surfaces were filled and sealed using a liquid epoxy resin and a pressurised injection system. Using an electronic testing device, known as a holiday detector, we tested the newly applied lining for the absence of holes or micro-porosity in the new lining. Any areas found were repaired and re-tested. 

The Results

The gaps between the tiles and bricks were filled and bridged with the spray-applied flexible resin coat. The tanks now have a smooth and flexible lining that can move with the tank and be easily cleaned. The lining ought to last several years.