Integrity assessment of buried pipe in erosive environment

Abstract

The integrity assessment of API 5LX42 carbon steel pipe in terms of erosion effect due to impaction of high pressure erosive slurry was studied. A water jet structure was analysed using a transparent perspex water filled tank . This was followed by buried pipe erosion study in a sieved sand as a backfilling material in a specially designed submerged experimental rig. Computational fluid dynamics (CFD) technique was applied to simulate numerically the pipelineerosion characteristics incomparison to the experimental findings. The sieved results indicated that majority of the backfilling mater ials; made up by quartz mineral having a size 0£0.2 to 2.0 mm, was in angular shape. The impaction of sand-water slurry on the pipe wall produc ed two peculiar regions; smooth surface in the middle and surrounded by rough wavy surface. The smooth surface was formed due to the high pressure water jet (potential core) perpendicular to the centre of the pipe surface. On contrary, the rough surface was formed due to the impact of sand-water in cutting action mode at the upper and bottom part of the pipe, as the wate r stream was being deflected radially. In comparison, the bottom part of the pipe experienced higher thickness reduction than the upper area . The average thickness reduction of the pipe wall due to the impaction of orifice jetting was 5.68% higher than that of the nozzle jet. The locations of ring type contours of water and sand wall shear from CPO simulation were found to be similar as the experimental findings. The contours of sand and water wall shear were found to be 68.67 kPa and 0.1054 kPa, respectively , at the upper and bottom sections of the pipe wall that corresponded to the higher thinning rate areas as in the experimental study. At the point of impaction that was perpendicular to the pipe surface, the sand and water wall shear stresses were found to be 13.73 kPa and 0.2208 kl'a, respectively, this concurred by the smooth convex region on the pipe surface from the experimental results. Percentage of wall thinning rate from the experimental study ( 10.74%) was found to be comparable to CFD simulation results with the percentage difference of sand and water were 11.1 2% and 11.02%, respectively, It is therefore concluded that at 400 mm separation distance, the pipeline was found to be safe from any erosion effect of 1000 kPa water jetting, this could be considered for gas industry application.