Determination of pipeline movement caused by tidal currents

Pipeline Description:

The 4” pipeline (steel X52, OD= 114,2mm) extends over 14 km from the mainland coast to an island straight through the tideland with maximum water depths of not more than 4 m below mean sea level. In 2006 it was pulled from the mainland towards the island and, therefore, was initially dead straight. Since then, it supplied low pressure natural gas to the island. The environment is exposed to tidal currents heading across the pipeline route since located behind the island. No known integrity issues have occurred since commissioning.

Why is it challenging?

Usually pipeline movement is identified by high accuracy inertial measurements that are performed twice, with an “observation period” of time in between. The comparison of the two data sets shows the movement that happened in between. In this particular project no previous data from inertial ILI measurements were available for comparison. Since the client needed a result on short notice, other ways had to be chosen.

Target of the inspection:

Following 15 years of uninterrupted operation without any in-line inspection the client was focussed to strengthen his ability for pro-active risk determination regarding his natural gas pipeline. General motivation was to protect the sensitive UNESCO world heritage environment of the Wadden Sea, the crossing coastal ship traffic and maintain natural gas supplies to the island. Specific inspection task was to identify, size and locate any horizontal pipeline movement caused by tidal currents or possible displacement by storms, waves, ground fishing activities, boat anchors, among others.