Avaliação da corrosão interna em minerodutos brasileiros para transporte de minério de ferro

Abstract

The transport capacity of long-distance slurry pumping systems is directly related to the roughness of the pipe. In this context, corrosion plays an important role, especially when dealing with old pipes. Corrosion also affects the useful life of these systems, because it compromises their mechanical integrity through thickness loss and possible formation of cracks. Chemical, microbiological, metallographic, mineralogical, microstructural and electrochemical analyses, among others, were performed on pipe samples, pumped fluid samples, specimens and materials removed from the inner of the pipe in order to identify and characterize the most significant types of internal corrosion that occur inside of Samarco Mining Co. pipeline 1. This pipeline has been operating since 1977, transporting iron ore slurry from the Germano unit in Minas Gerais State to the Ubu unit, in Espírito Santo State. It was found that the pipe has uniform corrosion, localized corrosion of alveolar type, differential aeration corrosion, corrosion with cavitation and corrosion with erosion. There is no evidence of microbiological corrosion inside the pipeline. The corrosion layer formed inside the pipe presents magnetite as a major mineral phase, and hematite and goethite as secondary phases. It is believed that this layer is, in large part, protective, as the pipe has a low failure rate due to internal corrosion. Mitigation of corrosive attacks suffered by the pipe can be accomplished by periodic cleaning of the duct with pigs, controlling the pH value of the different pumped water qualities, removing dissolved oxygen in water and operating the pipeline in an interconnected mode.