A Multi-Electrode Approach to Evaluating Inhibition of Underdeposit Corrosion in Brine/CO2 Environments

Underdeposit corrosion of carbon steel pipeline in the oil industry develops under a mixed range of deposits, usually sand or sand in combination with oxides or sulphides and occasionally microbial deposits. To mitigate this problem different types of inhibitors, with different adsorption characteristics and at different concentration levels are commonly explored using laboratory simulations. The laboratory testing involves a carbon steel electrode in some form covered by a deposit and coupled to a larger external electrode to simulate the pipe wall. A ZRA is used to monitor the coupling current and LPR to estimate the actual corrosion rate. A limitation of existing methods is the relatively few comparative tests that are carried out and the limited range of pre-existing corrosion conditions investigated. To that aim a multi-electrode probe consisting of 24 individual electrode rods mounted in epoxy was developed and the assembly located in a cup to which the sand deposit is added. Using this assembly, tests of different inhibitors have been carried out at 60 °C in a simulated formation water environment in 1 bar CO₂ and in a mixed CO₂ and H₂S gas. The results will be reported and the importance of statistical evaluation of performance emphasised.