ABSTRACT
A submerged jet-impingement flow loop was used to investigate corrosion control of an X65 steel weldment in flowing brine, saturated with 1 bar carbon dioxide, and containing a typical oilfield corrosion inhibitor. A novel jet-impingement target was constructed from samples of parent material, weld metal and heat affected zone, and subjected to flowing brine at velocities up to 10 ms-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 galvanic currents were small and in some cases the weld metal and heat affected zone were partially protected by the sacrificial corrosion of the parent material. However, at higher flow rates the currents increased and current reversals sometimes took place leading to accelerated corrosion of the weld region. The most severe corrosion occurred when oxygen was deliberately admitted into the flow loop to simulate typical oilfield conditions. 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 the corrosion mechanism in the presence of oxygen is discussed.
