Abstract

In Northern Chile, the use of carbon steel piping systems for seawater transport from the sea to desalination plants together with inhibitors for corrosion prevention is a common choice for mining plant designers. The aim of this work was to study the corrosion behavior of carbon steel pipe API 5LX65 immersed in seawater in terms of the performance of a commercial corrosion inhibitor under a broad range of conditions using electrochemical and weight loss testing and the economic assessment to choose a combination of pipe wall thickness and corrosion inhibitor. The electrochemical experiments are short-duration tests that serve the purpose to find an appropriate level of corrosion inhibitor dose for the seawater. In these tests, the API 5L X65 steel specimen was a 4 mm diameter disk rotating at 1200 rpm under a linear sweep voltammetry measurements in a three-electrode cell connected to a potentiostat. The weight loss experiments are long duration tests that allow examining the corrosion rate of API 5L X65 steel coupons exposed at a range of seawater velocities between 0.2 to 5.0 m/s. The main results were: a).- The appropriate range of inhibitor dose was between 10 to 30 ppm in the seawater with a corrosion inhibition efficiency up to 96 %, b).- The corrosion rate increased from 1.1 to 2.5 mm/year with sea water velocity between 0.2 to 3 m/s; at higher velocities, no higher corrosion values were observed, c).- The corrosion inhibition efficiency was maintained at high values at all seawater velocities, and d).- The morphology of corroded surfaces indicates a mechanism of pitting corrosion that propagates in the flow direction. From these results, recommendations are made for a correct piping selection.