Gauge pigging runs are performed to detect restrictions, dents and other deformations within pipelines. After a gauge tool is run, the gauge plate is examined to see if there are any impressions or damage on the plate which would indicate deformation or restrictions within the pipeline. It is important to note however, that in the process of the gauge pig traveling through the pipeline, collisions can occurs at locations where no deformations are present. Such locations can include pipeline elbows. Therefore, precautions in both the pig design as well as in the pipeline operation should be taken to prevent this from happening. For example, a U-shaped pipeline is often designed, with a series of 90° elbows, for pipeline river crossings. When a gauge pig passes through such elbows, the plate may incur damage if the pig velocity is too high or the pig’s design is inadequate. This can lead to erroneous judgment calls with regard to the presence of deformations within the pipeline. This paper describes the analysis performed on the motion of a gauge pig as it passes through the elbows of a U-shaped pipeline segment. And the geometric properties of elbow and caliper pig have been analyzed too.

It is concluded that if the velocity of the pig exceeds a specific threshold value, the centrifugal force of the pig as it travels through the elbow becomes large enough such that the supporting disks will yield and allow plate damage to occur. If the front support plates of the pig are deformed enough, the plate will collide with the outside arc of the elbow. A variety of factors, described in this paper, determine this critical pig velocity threshold value. Additionally, it is concluded that the plate can be damaged at the inside arc of the bend if specific geometric relationships exist between the gauge plate, pig and the bend itself.

Based on these conclusions, required modifications to both pig designs, as well as to pipeline velocity can be determined in order to avoid damaging gauge plates at pipeline elbows.

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