Internal corrosion prevention in slurry pipelines using nitrogen gas: a case study

Abstract

The transport capacity of the slurry pipelines is related to the internal roughness of the pipe. Thus, the application of corrosion protection methods is of fundamental importance, both in the operational phase and in times of temporary shutdown. In addition, corrosion also affects the service life of the duct. The studied pipeline was hibernated with nitrogen using the ABNT NBR 15280-2 standard as a reference and remained hibernated for 3.5 years. Chemical, mineralogical, and microstructural analyses were carried out on samples of materials removed from the pipeline interior during the hibernation period. The most striking phase found was magnetite, with botrioidal morphology, formed by the oxidation of steel in the pipeline. After reactivation, the pipeline was inspected by smart pigs with ultrasound and MFL technologies. It was found that the corroded regions are more concentrated in the initial kilometers of the sections, where important depths of corrosion were also observed, as well as higher rates of corrosion and erosion, which show the influence of the operational phase in the development of the pipeline corrosive process and wear. Thus, the application of the nitrogen hibernation process in long-distance pipelines proved to be feasible for long periods of time. However, improvements are suggested in this article to make the process more robust.