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Scouring Effect at River Crossing Pipelines

Proceedings Title : Proc. Indon. Petrol. Assoc., 33rd Ann. Conv., 2009

This paper reviews the results of previous laboratory experimentation on the scouring phenomenon upon river crossing pipelines. Due to the dynamic condition of a rivers flow and its sediment abrasion, there will be degradation of the river bed, which condition could eventually lead to the exposure of the pipeline. A pipeline exposed to the current could be damaged, as a result of the abrasion by sediment carried by the river flow, especially in rapid currents. Protrusion of the pipeline above the bed level will lead to the formation of vortex shedding on its transversal axis, at the downstream end of the pipe. Critical flows, the result of significant difference in the pressure gradient between the upstream and downstream areas, will aggravate the scouring of the river bed below the pipeline. This condition will impose additional force on the pipe itself, i.e. drag force due to the river current, and probably debris flow as well. Preliminary data was obtained from existing conditions in the field where heavy scouring occurred on river crossing pipelines, resulting in their becoming suspended / hanging. Laboratory experiments and modeling to counter the scouring phenomenon on river crossing pipelines were carried out as well, at the Water Resource Laboratory - Civil Engineering Dept., ITB. These experiment made use of “Glass walled open channels / flumes with a water circulation system, and were conducted by applying a time-varied water discharge, controlled by a hydrograph to adjust the water discharge volume in sequence.Non-cohesive sediment (sand) was laid to model the river bed under conditions of clear water scouring. From the experiment it was observed that the maximum depth of the scouring effect will be practically the same as the pipe diameter. The length of the scouring influence may extend up to 6 (six) times that of pipe diameter, towards the downstream section of the pipeline. An alternative solution was proposed for protection, placing or constructing a weir / small dam at the downstream locus of the pipeline, this is anticipated to provide significant results in minimizing scouring effects.

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