Corrosion failure analysis of galvanized steel pipes in a water irrigation system

The premature failure of a water irrigation system made of galvanized steel pipes installed in the orange orchards of a citrus farm located in the interior of the state of Sمo Paulo, Brazil, was investigated by onsite visual inspection, microstructural characterization of the Zn coatings based on SEM/EDS analysis, and chemical and physical analysis of the water used in the system. The irrigation water comes from a creek that runs through the farm, and the first pipe leakages were detected after the system had been in operation for only 2 years. The findings of this investigation indicate that the failure of the pipes before their expected service lifetime was caused by acid corrosion, which rapidly attacked the Zn coating of the inner walls of the pipes, exposing the entire steel surface in the first months of use. The deterioration of the pipes was intensified by the mechanical wear resulting from a substantial amount of suspended solids in the flowing water. In addition, the SEM/EDS analysis of the Zn coating suggested that some points of the galvanized pipes exhibited manufacturing defects, further impairing the corrosion performance of these pipes.