GB873103A - Method and composition for inhibiting corrosion of ferrous metals - Google Patents

Abstract

The corrosion of ferrous metals in contact with an aqueous solution of a caustic alkali and a sequestering agent capable of forming water-soluble and alkali-stable iron complexes is inhibited by adding to said solution an inhibitor comprising chromic acid, a chromate or another chromium compound which provides chromate ions on addition to an aqueous caustic alkali solution The solutions may be used to clean surfaces of metal and would normally tend to corrode heat transfer elements which are in contact therewith. The caustic alkali is preferably sodium or potassium hydroxide and is present in a concentration of 0.25-20% w/v. The sequestering agent preferably has a concentration of 0.002-5% w/v., and may be (i) a compound having the general formula R1-(CHOH)n-R2 where n is at least 3 and R1 and R2 are-CH2CH or-COOH, e.g. sorbitol and mucic, saccharic, gluconic and glucoheptonic acids and salts and lactones thereof, (ii) a compound having the general formula <FORM:0873103/II/1> where n is 0-3 and R1, R2 R3, R4 and R5 are -CH2COOH or-CH2CH2OH, e.g. ethylenediaminetetraacetic acid, N-hydroxyethyl ethylenediaminetriacetic acid and diethylenetriaminotriacetic acid and salts thereof, (iii) an aromatic polyhydroxy compound such as pyrocatechol and 1,8-dihydroxy naphthalene, or (iv) an alkanolamine such as triethanolamine. The weight ratio of inhibitor to sequestering agent is preferably in the range of 0.02 to 0.5. Solid compositions and liquid concentrates to be dissolved in or diluted with water are disclosed.