Peaking (or roof topping) is an out of roundness anomaly at the longitudinal weld of a pipe joint. It is the result of improper forming of the steel plates in the manufacturing process and leads to a triangular apex at the long weld position. Peaking might be a threat to the pipeline integrity because it can result in cracks during the manufacturing process or under operational conditions.
In an inline inspection (ILI) of a pipeline, the measurement of the peaking height is a challenge because a sufficiently high circumferential resolution is required to get a realistic picture of the pipe geometry at the long seam. A direct measurement of the peaking height – especially with mechanical caliper tools - can be problematic since the weld cap is located at the highest point of the peaking. This can result in an underestimation of the true height of the peaking.
In this paper the effect of different circumferential resolutions on the measured peaking height is discussed. It is shown that measuring the peaking angle instead of the peaking height can better handle missing or problematic data points at the weld cap of a long seam. Furthermore, this method is less sensitive to an additional ovality of the pipe joint and a possible movement of the sensor carrier of the ILI robot. The latter is especially important and allows to utilize high resolution data of ultrasonic wall thickness / corrosion robots for peaking analysis.
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