Tank Lining – Stainless Steel Digester Lining
The sectional stainless steel anaerobic digester tank had extensive perforations as a result of microbial induced corrosion, meaning that it was out of service and no longer gas tight.
We proposed the application of a highly chemical resistant polyurea tank lining from Specialty Products Incorporated as the best long term solution for this tank. This was supported with a 20 year material guarantee which gave the client peace of mind that they would not suffer a similar tank outage in the future.
Stainless steel tanks area difficult substrate to adhere tank linings to. Therefore to ensure an excellent mechanical profile for the tank lining to adhere to the stainless steel was prepared by method of abrasive blasting. The blast profile was tested by our in house ICORR accredited paint inspector to ensure that the required surface profile of 50 microns had been achieved.
The tank was then thoroughly vacuumed cleaned and a surface cleanliness test conducted to ensure that the substrate was clean enough for our tank lining to adhere to – something that is essential when relining tanks.
In the 600mm band where the perforations has occured a reinforcing bandage of glass fibre reinforced epoxy was applied using a material specifically designed to adhere to difficult substrates such as stainless steel. Remmers Epoxy Universal was then applied in three coats by brush and roller to the inverted U channel at the top of the tank, which would have been extremely difficult to achieve a seamless finish by spray application.
All nuts, bolts and cleats were detailed using a polyurethane mastic to simplify these difficult details for spray application. It is important when applying polyurea coatings to consider such areas, otherwise due to the fast set nature of the material cavities can form during application, creating penetrations in the tank lining.
SPI Corrolastic UB polyurea was then applied with the inclusion of AE4 adhesion promoter to a thickness of 2mm. AE4 is a coupling agent which allows the polyurea material to bond tenaciously to stainless steel.
The tank lining was then spark tested to ensure a pin hole free finish as part of our standard quality assurance, with any pin holes found being touched in using the same polyurea tank lining material.
Finally the termination of the polyurea lining was detailed using a chemical resistant polyurethane jointing compound to protect the edges of the coating.