51314-3796-The Influence of Hydrodynamics on the Preferential Weld Corrosion of X65 Linepipe Steel in Flowing Brine Containing Carbon Dioxide

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Product Number: 51314-3796-SG

ISBN: 3796 2014 CP

Author: Michael Adegbite

Publication Date: 2014

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The Influence of Hydrodynamics on the Preferential Weld Corrosion of X65 Linepipe Steel in Flowing Brine Containing Carbon DioxideM. A. Adegbite M. J. Robinson and S. A. Impey Cranfield University England UKThis paper describes the use of a submerged jet-impingement flow loop to investigate corrosion control of an X65 steel weldment in flowing brine saturated with 1 Bar carbon dioxide containing a typical oilfield corrosion inhibitor. A novel jet-impingement target was constructed from samples of parent material weld metal and heat affected zone cut from the weldment using electrochemical machining. The samples were assembled and mounted in resin to form a target consisting of three concentric ring electrodes. The target was positioned beneath a nozzle in the flow loop and subjected to the flowing brine at velocities up to 10ms-1 to give a range of hydrodynamic conditions ranging from stagnation to high turbulence. The galvanic currents between the electrodes in each hydrodynamic zone were recorded using zero-resistance ammeters and their self-corrosion rates were measured using the linear polarisation technique.At low flow rates the weld metal and heat affected zone were shown to remain cathodic and were partially protected by the sacrificial corrosion of the parent material. However in certain conditions including high flow rates a current reversal took place leading to accelerated corrosion of the weld region. The most severe corrosion occurred when oxygen was deliberately admitted to the flow loop to simulate the situation of a leaking pump or valve. The results are explained in terms of the selective removal of the inhibitor film from different regions of the weldment at high flow rates and reasons for the apparent change in the corrosion mechanism with ingress of oxygen are discussed.Key words: carbon dioxide corrosion oxygen corrosion weld corrosion corrosion inhibition carbon steel electrochemical submerged jet impingement