Solution for Corrosion and Crack Detection in a Crude Oil Loading Line
First-time inspection of a loading line with focus on the long seam welds
A 2.5 km (1.6 mi), 42” loading line transporting crude oil from the pier to a tank farm needed an inspection for corrosion and cracks both along and within the long seam welds. A leak caused by an axial crack along the seam weld had made the inspection mandatory and urgent. Not having been designed for pigging, the line had never been inspected before. No traps existed on either end of the line. Nor were pumps available for moving a pig, as the oil was pumped from the tanker.
Our solution
The pipeline had two valves at the end of the tank farm, about 7 m apart from each other. These valves were closed, the pup joint in-between was removed, and a shorter spool piece, which was fitted to the length of the ROSEN tethered tool, was flanged on. The inspection tool was to be a tethered self-propelled bidirectional ultrasonic tool. It was equipped with:
- Strong tractor at the front
- UT inspection module for wall thickness/corrosion and geometry
- TOFD (time-of-flight diffraction) unit for crack detection and sizing
- Electronic and storage modules
After clarification of all technical details, the tailor-made tool was mobilized and launched via the new pup joint. Since there was not enough space behind the temporary trap, the winch was placed to the side, outside Ex-Zone 0, with a guiding wheel deflecting the cable. For the launch, the tool was inserted into the trap and the trap door closed. The cable through the stuffing box was then sealed and the trap filled air-free with oil before the inspection tool was switched on. The pig immediately switched into inspection mode, and the tractor moved forward, pulling the other modules into the line, which started measuring wall thickness/corrosion and geometry.
The inspection team monitored the movement and tension of the cable from the control cabinet in a container nearby, viewing the inspection data in real time. The pipe tally was prepared even as the tool travelled along the pipe. At the pier end of the line, the tool stopped. Data was downloaded and the tool switched into return mode. On the return inspection run, the tool stopped at every girth weld to precisely locate the long-seam weld position and scanned the area with the TOFD module. The operator received a first report still on site, directly after the inspection.
Your benefit
The imaginative approach offered by ROSEN rendered a pipeline piggable whose design had never included in-line inspection. Moreover, it provided a cost-effective alternative to the installation of conventional traps on both sides of the line and a pump plus connecting lines. Several data sets of the greatest reliability and accuracy were delivered in one run, providing all information necessary not only to immediately start urgent repairs but to create a detailed repair plan for the future. They enabled a corrosion growth assessment and a lifetime calculation. The results formed the basis of a sophisticated integrity management plan, including required inspection intervals.