Multiphase flow characteristics can be altered with the change of pipeline topography in deep offshore oil and gas production. The increase of corrosion rate and decrease of inhibitor performance in the risers can occur due to the change of multiphase flow characteristics (e.g. severe slugging).
For the simulation of offshore flow lines and risers, the experiments were carried out in a 44 m long industrial scale multiphase flow loop equipped with three different pipeline inclinations of 0, 3 and 45 degrees. The effectiveness of three commercial corrosion inhibitors were analyzed using 25 cP oil at 20% water cut with three different gas velocities (0.7 m/s, 3 m/s, and 6 m/s). All tests were carried out at a liquid velocity of 1.5 m/s, a system pressure of 6 bar (76 psig) using carbon dioxide gas as the gas phase, and a temperature of 50°C.
Also, the effect of inclination on the flow characteristics (e.g. flow pattern) and their subsequent effect on corrosion rates are described. The results indicated that severe pitting corrosion was noticed in the 3 and 45° weight loss coupons for baseline testing. Severe slugging and high slug frequency were seen in 45 degree upward flowing conditions. The tests differentiated between three corrosion inhibitors. In most of testing conditions, high inhibitor concentration was required to achieve the target corrosion rate.