An engineer from a power plant in Florida contacted Corrocoat USA to look at two of their coal ash silos that had two different types of failed external wrapping systems. These were located at the base of the silo (which was 90 foot (27.4m) off the ground, causing a cavity that could have allowed valuable coal ash to weep from the bottom of the silo and into the atmosphere. Upon inspection, on Silo 1, the rubber liner was damaged in multiple locations and was leading to concrete deterioration and crevices. On Silo 2, there was a polymer liner that failed at the seam, thereby allowing an ingress of moisture and escape of coal ash. Each silo was 50 feet (15.24m) diameter. The repair included coating and sealing 16 inches (40.64cm) up onto the steel silo and 12 inches (30.48cm) onto the concrete base.
A plan was devised by Corrocoat USA, for the removal of each of the failed wraps, using pneumatic tools, working a portion of the surface from 125 foot (38.1m) using manlifts. The steel substrate was primed using Plasmet ZF, whilst Plasmet ECP was used for the concrete. A layer of multiaxial fibreglass followed and then finished off with an additional coat of Plasmet ZF and a polyurethane topcoat for UV protection. An unexpected problem occurred whilst filling holes with the Corrofill E; there were hundreds of holes ranging from the size of a pinhead to the diameter of a walnut.
Although the silo was said to be depressurised during the operation, the shape and size of the silo created a natural draft and therefore pressure on the silo. After filling about 80% of the holes, the pressure increased on the remaining cavities to the point that pinholes formed in the Corrofill E once placed. It took several passes and significant skill and patience to finally stop all of the air from escaping and fashion the filler to a shape that would allow for effective fiberglass application.
Corrocoat USA solved a difficult and potentially expensive problem. The work carried out by the team is predicted to protect the equipment for the foreseeable future – the life of the plant.
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