THE PROBLEM
The glass fused steel sludge tank was leaking effluent into the surrounding environment after only 8 years in operation. Suspected damage to the glass enamel had led to perforations once exposed the hydrogen sulphide a biogenic sulphuric acid.
SOLUTION
We were provided this enquiry by Linex UK, so on their recommendation specified the application of their XS350 pure polyurea tank lining material.
Unusually the client was having difficulties using their existing tank cleaning company, so as part of our contract we were requested to provided sludge removal and cleaning of the tank, which were undertaken for ourselves by Clearway Environmental services.
Once clean all of the existing sealant was mechanically removed. This is essential in this type of tank as due to the edges of the panels not being coated with the same glass enamel this is where some of the worst corrosion can be found. Often other contractors will simply over coat this sealant, leaving a corrosion cell in place from which degradation of the tank structure will continue.
Preparing the tank internals by blasting
The tank internals were then prepared by method of abrasive blasting to both clean the glass enamel substrate and raise a mechanical profile for the new tank lining to adhere to. This blast profile was checked using a surface profile needle gauge as part of our standard quality assurance.
To ensure optimum adhesion of our polyurea tank lining, all surfaces were washed using fresh water, with the inclusion of an anti-corrosion inhibitor to prevent the flash rusting of the steel.
The tank internals were checked for soluble salts as part of our standard quality assurance. Following the first wash the soluble salt levels were still found to be high, so a second wash was instigated. This was an excellent example of why a thorough testing and inspection regime is imperative when undertaking tank lining projects. If these soluble salts had been left in place they could have led to premature tank lining failure as a result of osmotic blistering.
The cleanliness of the tank internal was checked using a dust tape test.
Glass fused steel is an extremely difficult surface to adhere to, even with abrasive blasting. The reason for this is that the surface profile created is not angular as per steel, meaning that many epoxy, polyurethane and polyester material struggle to gain sufficient adhesion. Fortunately we have developed our unique surface tolerant epoxy primer which has been specifically designed to adhere to difficult substrates such as glass fused steel – Corrolast DSP.
Applying the Corrolast DSP
Corrolast DSP was applied by method of airless spray to a thickness of 150 microns. To remove any risk of exceeding the re-coating window a pigmented quartz aggregate was dressed into the wet resin, to provide an excellent mechanical anchor for the polyurea tank lining to adhere to.
Linex XS350 pure polyurea was spray applied to a thickness of 2mm by method of heated plural component spray unit. Frequent dry film thickness readings were taken during application.
A DC holiday spark test was conducted to ensure a pin hole free finish. A single pin hole is a point of failure in a tank lining.
Finally termination points at the top and bottom of the polyurea lining were sealed using a polyurethane jointing compound to ensure a seamless finish.
