Inhibition of Corrosion of a Carbon Steel By the Aliphatic Fatty Polyamines in Association With Organic Phosphorous Compounds in 3% Sodium Chloride Solutions^★

In this paper, we give an account of an attempt to develop a neutral inhibitor of corrosion of a carbon steel in stirred 3% sodium chloride solutions. For this purpose, we studied the combined action of a fatty poly amine of molecular weight greater than 320, oleylamino-propylene amine, and an amino-phosphonic acid, amino-tri [methyl-phosphonic] acid. The inhibitor efficiency was determined by two types of methods: indirect measurements of the electrochemical type, potentiostatic voltamperometry and determination of polarization resistance by means of a rotating disk electrode and direct measurements of the gravimetric type by means of a semi-pilot scale circuit simulating the conditions existing in a closed industrial circuit. For a product concentration of 1 g/l⁻¹, the inhibitor efficiency determined by electrochemical tests is of the order of 80%, and 50% when determined by long term gravimetric tests (immersion times greater than 50 hours); examination of the condition of the surface in the latter case shows that it is protected, with no evidence of localized attack. The difference in efficiencies observed according to the type of method used for the evaluation, may be explained both by the difference in the actual principles of these methods, and by the difference in the hydrodynamic conditions involved.