THE PROBLEM
The glass fused steel tank was leaking after less than 5 years of service. Another tank lining contractor had applied an epoxy coating which was not suitable for the effluent contained within the tank and a new tank lining was required.
SOLUTION
We proposed that application of a flexible and chemical resistant polyurea lining in the form of SPI Corrolastic HT. This material can elongate in excess of 300%, meaning that it can comfortably cope with the both lateral and deflection forces that are present in these type of glass fused steel tanks.
Initially the existing epoxy tank lining was removed by method of abrasive blasting. This was followed by the removing of any sealant that the previous tank lining contractor had failed to remove.
Once the glass fused steel had been exposed all surfaces were thoroughly degreased and washed using a hot washer. This was essential as when we tested the surface for soluble metal salts as per best tank lining practice, the levels detected were found to be extremely high.
If soluble salts are left in place on the tanks surface, this can very quickly lead to osmotic blistering which brings moisture in contact with the tank surface, allowing corrosion to commence again.
Following cleaning the tank internals were re blasted, preparing exposed steel to Sa2.5 and raising a surface profile. Following this second blast the atmosphere in the tank was controlled using dehumidification in order to prevent corrosion from starting again.
All surfaces were vacuumed clean and a surface cleanliness test conducted in order to ensure optimum adhesion of the new tank lining.
Glass fused steel is an extremely difficult surface for coatings to adhere to as the material does not profile in the same way as steel. To overcome this we employed our specifically developed primer – Corrolast DSP.
As can be seen in the video below, this material adheres excellently even to unprepared glass fused steel.;
Corrolast DSP was applied to all exposed steel as this contains Corroless mined pigment that converts any corrosion present to stable iron oxides such as magnetite.
All seams and bolts were sealed using a flexible polyurethane jointing compound. This also serves to make the shapes easier to spray, given the quick gel time of the subsequent polyurea lining.
SPI Corrolastic HT pure polyurea was then spray applied to a thickness of 2mm by method of heated plural component spray unit. To enable the adhesion of this polyurea tank lining to the glass fused steel substate SPI’s AE4 adhesion promoter was added to the material. This is a cross linking agent which enables the material to bond tenaciously to substrates which contain silica such as glass.
As part of our standard quality assurance the new polyurea tank lining was checked for pin holing using a DC holiday spark tester. Because SPI Corrolastic HT contains SPI’s Ultrabond molecule this could be undertaken after all spraying had been completed, giving the time required for proper quality assurance. Unlike other lesser polyurea materials this product will bond to itself indefinitely.
Finally termination points were sealed using a polyurethane jointing compound. These works were warranted for 10 years from completion with an expected service life of the polyurea tank lining in excess of 30 years.
