Technical feasibility of sacrificial anodes to avoid corrosion on galvanized steel during fertigation

Abstract

Corrosion, a recurrent problem in irrigation, can lead to leaks, interruptions in activities, reduced system efficiency, among others, and its magnitude is directly related to the chemical composition of the solution that is drained, and may be even greater with the use of fertigation, as fertilizers become corrosive when in contact with water, and its degree of corrosivity varies with the type of source and its concentration. Cathodic protection is a technique used to reduce or control corrosion, in which a less noble metal is inserted into the structure, which is consumed by corrosion. The use of this technique associated with the metallic piping coating can be used to achieve a significantly greater protection, which would ensure the integrity of the piping for a longer time, however, it is not a technique commonly used in irrigation networks, which makes studies are needed to verify your benefits. For this reason, we sought to evaluate the effectiveness of using cathodic protection using the sacrificial anode method to control corrosion caused by fertigation solutions. For this, immersion tests were carried out with solutions of Urea and Potassium Chloride (KCl), at 10 g L-1, in contact with galvanized steel specimens, with cathodic protection of zinc, aluminum and magnesium anodes, in addition to a treatment without protection, simulating 350 hours of operation, in order to obtain the mass loss per area of the galvanized steel specimens and anodes. The influence of the cathode/anode area ratio on the protection of galvanized steel and on the consumption of aluminum anode in KCl solution was also verified. The results showed that with the use of cathodic protection it is possible to reduce the mass loss of galvanized steel exposed to KCl fertirrigation solutions, and that the aluminum anode is the most effective, since, with its use, one can have up to a 78% decrease in weight loss compared to unprotected treatment; however, for solutions containing Urea, the use of this method was not effective. With the increase in the aluminum cathode/anode area ratio, there was no significant difference in the weight loss of the galvanized steel and in the aluminum anode weight loss, thus making it more feasible to use the higher ratio (44:1).