Cracking/delamination in thickener/clarifier tank

July 15, 2002
The maintenance crew at Pennsylvania Power Company’s Bruce Mansfield Plant in Shippingport, Penn., had a chronic problem with cracking and delamination in the power plant’s thickener/clarifier tank. The lining they were using kept breaking up where the tank’s concrete floor meets the circular steel walls. Consulting ITW Devcon Engineered Coatings, of Danvers, Mass., Penn Power learned there was another way to line its tank — a way that required neither frequent attention nor regular repair. ITW Devcon engineers designed a durable system that provides a flexible, long-lasting joint at the steel/concrete interface, lowering maintenance costs in the process. The solution was to use two different coatings — a glass flake formulation for the tank walls and a polyurea elastomer for the floor. VE 9300, a vinyl-ester-based glass flake system, provides exceptional chemical and permeation protection for the steel walls, while Iraseal 200, a sprayable polyurea, seals and protects the concrete floor from chemical attack and abrasion. Although either coating system may be used alone in a variety of applications, using them in combination takes maximum advantage of the characteristics of each. VE 9300, used on the walls, offers optimum resistance to acids, solvents, and other chemicals. Large-diameter glass flakes in the formulation produce a virtually impermeable barrier to water, yet the coating remains flexible and resistant to thermal shock or cycling. VE 9300 can withstand temperatures as high as 266° F wet and 350° F dry. A typical system consists of a primer, two mid or build coats, and a top coat. The base resin system may be modified to provide reinforcement or enhanced abrasion resistance. The Iraseal 200 polyurea system used on the floor offers resistance to mild acids and caustics, hydrocarbons, water, and wastewater. Its high elongation (up to 450%) makes it ideal for substrates prone to movement or cracking. It also demonstrates outstanding resiliency; physical strength (tensile strength 3000 psi); and resistance to punctures, abrasion, UV, and weathering on a variety of substrates. A 100% solids coating, Iraseal 200 has a gel time of 7 seconds, can be built up to any thickness in a single application, and can be put into light-duty service in as little time as 2 hours. For more information, contact Jeff Stewart, Technical Applications Manager, ITW Devcon Engineered Coatings, 30 Endicott Street, Danvers, MA 01923, Toll-Free: 800-933-8266, TEL: (978) 777-1100, FAX: (978) 774-0516, E-mail: [email protected], Web: