Ask the Expert Question-and-Answer Archive

by Ron Joseph

May, 2004

Preparation and Painting Recommendations for CS Tank Containing Siloxanes

Q. I have an underground carbon steel equilization tank used for cosmetic waste water storage before being discharged to the sewer. pH generally around 7 with spikes as high as 12 when process equipment is being disinfected. Water temperature ranges from a normal 85 deg F to a high of 150 deg F. Besides water, the main components in the wastewater are Dow Corning (DC) 245 - cyclopentsiloxane (Sp.G. 0.95), DC 345 - cyclomethicone (Sp.G. 0.957) cyclopentasiloxane & cyclohexasiloxane, DC 5225C - cyclopentasiloxane & PEG & PPG-18/18 demethicone w decamethylcyclopentasiloxane(Sp.G. 0.956), DC 593 - silicone fluid (Sp.G. 1.025), Medical Antifoam C Emulsion - simethicone (polydimethylsiloxane) & methyl cellulose. We are having problems keeping paint on the inside of the tank from bubbling and peeling off and I was wondering if you could make some recommendations as to the type/brand of paint and method of application for this purpose. Any information you could supply would be most appreciated.

A. We suggest a chemical resistant coating such as a 2 component catalyzed epoxy or a high bake phenolic coating such as Heresite. Either of these systems will provide the chemical resistance required. The tanks will require cleaning and abrasive blasting for the best results. Choosing a metal job shop that also applies the protective coating will be to your advantage because the protective coating should be applied as soon as the abrasive blasting is completed, at least within an hour or two at the most. We urge you to speak to your coating supplier before following any of the recommendations in this email. Every situation is different and we cannot guarantee that the coating we have recommended will perform well under your specific conditions.