Tank Lining Project

In 2017, Conomos was contracted to fulfill tank lining work on an open top water clarifier tank that included removing and replacing the internal lining system. The tank was located at a power generation facility and the work was scheduled to be performed during a major facility outage. The outage allowed an adequate window of time to complete surface preparation, coating application, and cure.

PROJECT SPECIFICATIONS

The water clarifier tank in question was built with carbon-steel and had a height of 18 feet and a diameter of 85 feet. The tank bottom slanted downward toward the center for a deepest and longest point of 21 feet. The project’s outlined specifications included:

  • Removal of existing coatings from the center drum, carbon-steel walls, rake, weir, and concrete floor
  • Installation of a hinge joint at the juncture of the concrete floor and steel wall
  • Application of a primer and a finish of novalac epoxy on the walls at 10-15 mils DFT for each coat, or 20-30 mils of aggregate thickness
  • Application of a coat of epoxy sealer and two finish coats on the floor at 10-15 mils DFT each; and
  • Completion of the work during the plant’s scheduled outage

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Surface Preparation

Weather is always a major challenge for contractors and proactive steps must be taken to properly manage it. Conomos’ first step was to protect the area from the elements by installing a canopy tarp. In this situation, the canopy tarp installed was cone-shaped to ensure any rain water would run off the sides rather than pool in areas and cause problems.

After the tank was drained, a peculiar residue remained. Prior to blasting, debris that had accumulated had to be cleared away. The unforeseen debris build-up expanded the amount of surface preparation work. The material that was adhered to the water clarifier tank needed to be scraped out by hand.

Coating Removal

After initial cleaning was finished, the water clarifier tank internal surfaces had to be stripped down to concrete on the floor and carbon-steel on the walls.

An SSPC-SP 10/NACE No. 2, “Near-White Metal Blast Cleaning” standard was a requirement for the walls of the tank. Though it was relatively easy to achieve this standard of surface preparation on the walls, abrasive blasting proved to be more difficult on the floor. With the floor being concrete and the coating being an elastomeric system, abrasive blasting caused it to “roll like bubble gum.” The floor’s surface preparation proved to be much more tedious. The use of 40K-UHP water blasting was off the table because the concrete floor would absorb the water and there wasn’t ample time to let it dry sufficiently during the plant outage.

The elastomeric coating was eventually removed. A bulk blast set-up with four blast nozzles was used for production. Proper surface preparation and ideal profile results were achieved through the use of a medium-grade coal slag abrasive. It was necessary to have a confined space watch throughout the project. Equipment was used to collect dust and minimize humidity ensuring a clean area and an ideal environment. After blasting was completed, a chloride test was performed to check for the presence of chemical contaminates.

COATING APPLICATION AND HINGE JOINT INSTALLATION

Both reinforcement and flexibility are important for the tank, so a fiberglass-embedded hinge was installed. The hinge joint was installed prior to the first lining coat application. This joint was needed to be 12 inches across the floor and 12 inches up on the wall. To ensure there was a smooth transition from the floor to the wall, coatings were applied by trowel. After this, two layers of fiberglass were added followed by two coats of Novaguard 840 epoxy lining from PPG. This epoxy lining was applied to the tank’s interior walls, the tank drum, rake, weir, and floor. However, the floor was first primed with Amerlock, a sealer from PPG.

Weather Challenges

With the beginning of winter fast approaching, the weather proved to be a major obstacle. Over a period of several days, high winds and torrential rainfall plagued the project. Even with the coned tarp in place, the weather was so intense that pooling occurred, and a tear developed. With water continuing to pool in other sections of the tarp, additional tearing was a possibility.

Conomos acted quickly to minimize these issues and prevent any further weather-related problems. A sump pump helped rapidly drain water from where it was pooling on the tarp. However, there was too narrow of a space to get a man lift close to one side of the tank. Luckily, any additional tears were avoided, and the project continued as planned. The weather also brought lower temperatures which meant a longer cure time for the coatings was needed. Forced heat sped up the dry time effectively.

Project Completion and Feedback

After the coating cured, Conomos performed a final test to check the quality of the application. Even with several surface preparation and weather issues, the water clarifier tank lining was ready in time for the facility to resume operation. The power company was more than satisfied with the quality of work performed on this project.

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