Articles & Case Studies

A DIGESTER REFURBISHMENT THAT’S EASY TO SWALLOW

Posted: Wednesday 4th June 2014

A major utility company in the North of England recently refurbished one of its digesters to totally resist chemical attack in the future and prolong the life of this vital asset. The refurbishment also prepared the digester for the addition of a cover, which, without this treatment, would have caused even more aggressive corrosion to occur. Furthermore, the treatment was carried out so swiftly that the digester was available for other renovation works just four hours after the coating application.

The gas space within the digester was sprayed with the Ultracoat 100% solids epoxy coating system from Source One Environmental. Graham Howard, Source One Environmental’s Technical Sales Manager for Ultracoat, explained the issue, “The cement matrix of the concrete in the gas space had been attacked by Hydrogen Sulphide leaving exposed friable concrete and reinforcing bars. The planned addition of a cover was expected to increase the concentration of H2S from 500ppm to 1500ppm, thus exposing the already-damaged substrate to even more aggressive corrosion.”

Key to the selection of Ultracoat was its proven and independently tested high resistance to Hydrogen Sulphide and other chemicals routinely produced in municipal waste treatment. “Once applied, Ultracoat will provide a durable, long-lasting finish. The system is so well-tested and established that we gave the customer a 50 year warranty,” added Graham.

In addition, Ultracoat’s speed and ease of application and its ability to adhere to damp substrates were also useful. “This was a thorough and complex renovation project,” stated Graham. “The swift Ultracoat application offered time savings compared with other refurbishment methods. This freed up time for other necessary works to be carried out and expedited the whole project.”

Ultracoat is applied during a single spray, without a primer coat, and was applied in this instance to a 6mm thickness. Following spraying, it was left to cure and then spark tested to ensure its integrity. The only additional time required was during the initial preparation of the substrate, which was achieved using common techniques. The initial process was to high pressure water blast the chambers to SSPC-SP7, leaving a good key to the substrate. Following the pressure blasting, a termination chase was formed 2m down the wall. The final part of the preparation was a mild bleach wash to kill off any bacteriological growth, followed by a wash down, and a light (Muriatic) acid etch to remove any sulphates, with a final wash down to complete the procedure.

The Ultracoat system has been available for over 25 years and has been used to renovate in excess of 50,000 structures worldwide, with no failures. It is chemical resistant from pH 2-14 and offers complete resistance to high levels of hydrogen sulphide, up to 40% concentration of nitric acid, acetic acid, calcium chloride and others. It can be applied safely in confined spaces, as it contains no harmful VOCs (Volatile Organic Compounds). Ultracoat leaves an exceptionally hard wearing, permanent and waterproof coating, suitable for the refurbishment of manholes, bunds, culverts and other structures.




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