Effect of flow on corrosion and its inhibition in riser pipelines

摘要

The performance of a candidate corrosion inhibitor under conditions similar to the ones encountered in Catenary risers was evaluated in a 44 m long, 10.16 cm diameter, industrial scale multiphase flow loop. Flow characteristics (e.g. slug frequency), baseline corrosion and the performance of a corrosion inhibitor are presented in this paper. Electrical resistance (ER) probes for inhibitor screening tests and carbon steel corrosion coupons for inhibitor validation tests were used for the measurement of corrosion rates.Light condensate oil with a viscosity of 2.5 cP was used and water cut with 150,000 ppm of chloride and 55 ppm of bi-carbonate was 80%. The tests were undertaken in 3° and 45° inclined pipes.Visual observations showed that the flow is substantially changed when the pipeline is set at a 45 degree inclination. At superficial liquid and gas velocities of 1.5 and 0.7 m/s, plug flow was observed at 3°. However at same conditions, simultaneous plug and slug flow were observed at 45°.The corrosion rates for both bottom and top of the pipes increased significantly when the pipeline inclination was changed from 3 degrees to 45 degrees.A total inhibitor concentration of 200 ppm was required to achieve the target corrosion rate.