The demand of fossil energy has boosted the construction of new oil facilities and the preservation of the physical and mechanical integrity of the already existing infrastructure. Corrosion is the main causes of failures in the hydrocarbons industry and half of them are produced by acid gases (CO2 and H2S) (Kermany and Harrop, 1996). Within this framework, a monitoring device was developed by PDVSA-Intevep, in order to study the internal corrosion mechanism in a real hydrocarbons production system. The results show the advantages offered by this tool, which allowed studying thoroughly the internal corrosion mechanism present in the system and their immediate causes. In this case, the main corrosion mechanism present is under deposit corrosion, which causes pitting damage at different positions along the pipeline. According to microscopic analyses, the pitting are related to the presence of sand and solids (iron carbonates and sulphides); and the location of the damage depends basically on the internal diameter of pipelines (the hydrodynamics of the system). (c) 2011 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.