Test reagent for verification of integrity of protective coatings on metal items, particularly with cathodic protection e.g. galvanizing, provides standardized corrosive environment and colorimetric indication

摘要

An item having a corrosion-resistant coating is tested by treatment with a solution, comprising one or more of each of the following : oxidizing agents, buffers, complexing agents, inhibitors colorimetric indicator compounds sensitive to ions of the base substrate and observed for colour development. Preferably the test item is immersed in an agitated, reagent filled, container, at 10-80[deg]C. The claimed test reagent comprises a pH3-7 solution of: (A) 0.1-30% by weight of an oxidizing agent of standard redox potential greater than 0.2V e.g. perchloric acid, hydrogen peroxide, or a peroxydisulphate such as sodium peroxydisulphate; (B) 70-95% solvent, particularly water; (C) 0.001-10% of a complexing agent e.g. disodium EDTA; (D) 0.1-5% of boric acid or citrate buffer; (E) 0.001-5% of a corrosion inhibitor e.g. butynediol, nitrate or nitrite salts; (F) 0.001-1% of a colorimetric indicator for Zn2+ ions, e.g. xylene orange; (G) 0.01-2% of colorimetric indicator for Fe+++, e.g. 5-sulphosalicylic acid-2-hydrate.