New cooling system copper corrosion inhibitors improves sustainability, performance and reliability and reduces total cost of operation at Petrochemical plant in Europe.

摘要

A Petrochemical plant in Europe had recurrent problems of copper galvanic corrosion in its carbon steel heat exchangers. Every year, 5 to 7 heat exchangers leaks have been identified, replaced or repaired. The associated cost of corrosion has been estimated at 210 K? per year excluding production loss and cooling-system impact. Heat exchanger leaks caused cooling water system contamination which reduced the acceptable concentration ratio and increased discharge volumes. The acidic contamination damaged the passivation layer. The copper corrosion inhibitor used in the cooling system was Benzotriazole, however a large excess of 7 mg/l as benzotriazole was required to control galvanic corrosion and carbon steel pitting corrosion. This excess is caused by particulate copper as well as dissolved copper contamination coming from the process activities. To solve the corrosion issues and lower the total cost of operation an innovative azole treatment was tested to try and provides a better copper corrosion protection. After a film building period of 4 weeks at high dosage (7 ppm as azoles), the dosage of the new product was decreased to 3 ppm of azoles. This dosage is the maintenance dosage. As the results of the new treatment the corrosion rate on carbon steel dropped below 15 μm/year and no pitting corrosion on carbon steel has been noticed. The copper solids contaminating the water generate a high surface filming demand hence the routine benzotriazole dosage (3mg/l free azole) was not enough to provide sufficient copper corrosion inhibition. The new azole treatment established a better and stronger film with few defects during the passivation period that enabled a lower dosage (3 mg/l) to be used as routine dosage. The copper corrosion is now under control (copper solids from process operation and yellow metal heat exchangers) and pitting corrosion on carbon steel heat exchangers has not occurred since 1.5 years. No carbon steel heat exchangers leak has been reported since the implementation of new azole treatment. This translates to 300k? cost avoidance since start of treatment.