Effect of phosphonate based corrosion inhibitors in a cooling water system

Abstract Various corrosion inhibitors, including: 1-hydrox y ethylene-1,1 diphosphonic acid (HEDP), sodium molybdate, and zinc ions with various concentrations of chloride ion, were added to an aqueous corrosive medium, and the corrosion rate of the carbon steel was measured at various temperatures. It is shown that the corrosion rate is increased when the temperature or chloride ion concentration is enhanced, while if the concentration of HEDP or molybdate is increased, the corrosion rate is lowered. Furthermore, it is observed that in presence of more than 1200 ppm of the chloride ion and temperatures greater than or equal to 42·5°C the combination of HEDP, molybdate and zinc cannot control the corrosion in a cooling water system. Ultimately, a formulation consisting of HEDP, 2-phosphono butane-1, 2,4 tricarbox ylic acid, tolyltriazole, zinc, and polymeric compounds has been developed and tested in an industrial cooling water unit. Results have shown that the corrosion rate may be lowered to less than 25 μm per year.