The four process tanks were leaking as a result of chemical attack from the aggressive caustic chemicals contained within them. The worst corrosion was occurring on the internal welds which was allowing aggressive chemicals to leak on to the production area floor.
We proposed the application of an extremely chemical and temperature resistant lining from Chemco International.
Preparing the tanks for relining
Initially following drain down of the tanks we conducted a soluble salt test to ensure that the tank internals were free from chloride contaminants which would be detrimental to the new tank lining. This is an essential part of the tank relining process as if soluble salts are present and left in place they will draw moisture through the lining resulting in premature lining failure.
Fortunately the soluble salts were found to be below the level permitted by Chemco as this would have introduced further works into an already tight tank relining program.
All surfaces were prepared to SA2.5 by method of abrasive blasting which was particularly challenging given the extremely restricted working environment. A minimum surface profile of 75 microns was achieved to ensure excellent adhesion of the new tank lining.
Applying the stripe coats
As per good coatings practice separate stripe coats were applied to all angles, edges and welds as tank linings pull thin in these areas due to surface tension and gravity.
A unique feature of this tank lining project was the presence of the heating tubes which reach temperatures in excess of 140 degrees centigrade. To protect the lining from this Chemco developed a special insulating grade of their epoxy novalac tank lining using hollow micro spheres to reduce the temperature of the lining at this interface.
Applying the tank lining
Chemco RW500 was applied in two coats of contrasting colour to a dry film thickness of 800 microns. Each coat was tested during application using wet film thickness combs and after using dry film thickness gauges.
Testing the tank lining
As part of our standard quality assurance and the final stage of the tank relining process the linings were tested using DC holiday spark testers to check for pin holing and porosity. Where found these were marked with chalk prior to touching in using the same material.
All four tanks were relined simultaneously which was a considerable commitment in the week before Christmas. To ensure the linings were sufficiently cured and ready for return to service heating was left in place in the tanks over the Christmas shutdown when there would be not heating in the factory.