Coatings for tank interiors in the brewing industry and techniques to repair existing coatings.

Sanders, G.R.

Abstract
Tank linings are commonly classified as: aqueous or solvent dispersions (50-6250 um); flame spraying (75-500 um); hot melts (500-3100 um); and sheet (500-9400 um). Linings used in the brewing industry generally fall into thin film (less than 250 um) and thick film (between 250 and 725 um) categories of the aqueous or solvent dispersion classification. The thin film group includes some epoxies, vinyl formulations, bake phenolics, inorganic zinc and methane. The thick film group is comprised of epoxies (amine cured, polyamide cured and modified epoxy) and coal tar (epoxy and methane cured). Coal tar formulations do not satisfy the requirements of U.S. F.D.A. The unmodified baked phenolic linings are resistant to mild acids, heat and oils, and may be odourless, tasteless and non-toxic. Modified baked phenolic linings have the advantage of increased flexibility and resistance to alkali. A wide range of chemical resistance is achieved with epoxies through the judicious use of curing agents. Polyamide epoxies exhibit excellent resistance to dilute caustic, and if correctly cured, are non-toxic. They also offer excellent resistance to rubbing and scuffing. Some organic acids are, however, exceptionally penetrating. Amine cured epoxies exhibit excellent resistance to dilute caustic and have good retention of flexibility and resistance to impact. Their use with organic acids is limited. Microscopic examination reveals definite lattices of bubbles within the coating in the commonly available aromatic/aliphatic amine complexes. In some cases bubble diameters may exceed 25% of the thickness of the coating, thus reducing the effectiveness of the coating. Methods of repairing damaged coatings are described, covering surface preparation, application and curing.
Keywords: brewery brewing industry coating tank