Inspection of Deep Water Offshore Flowlines

Our solution for providing operational flexibility

A recent success story began when ROSEN was asked to inspect two oil field flowlines for corrosion. The pipelines are located in West Africa 120 km offshore, in water depths of 1100 m. The customer requested an inspection for two 8 km flowlines, which have 10/12" dual diameters and wall thicknesses from 12.7 mm to 31.6 mm.

Section of map showing the location of the asset.

Asset Description

  • Location: Offshore
  • Product: Oil
  • Pipeline diameter: 10 & 12"
  • Survey Length: 2 & 8 km
  • Outer Diameter: 324 mm
  • Wall Thickness: 12.7 mm to 31.6 mm
  • Min. ID: 266 || Bend Radius: 5D
  • Operating Conditions: Max 62 bar, min 17 Bar & 1,5 m/s

Under ideal circumstances the customer could have inspected the complete 16 km pipeline system in one run. The tool would be launched into the first flowline, sent through a pigging loop at the Pipeline End Manifold (PLEM) into the second flowline, and received back on the deck of the Floating Production Storage and Offloading vessel (FPSO).

However, ROSEN engineers were informed by the pipeline operator of the possibility that a defective valve on the PLEM would not open completely, meaning that an inspection tool might not be able to pass through the PLEM. In such a case, a common approach is to determine the valve's likely position by using a gauge tool. Depending on the results of this run, the next tool to be launched would be selected. For example, a conventional in-line inspection (ILI) tool could be considered if the valve was sufficiently open. However, since these tool runs would require a shutdown of production in the flowlines, an approach based on a separate gauge run would require multiple production shutdowns before a full inspection could be performed.

The uncertainty on the valve's functionality, along with the deep-water offshore environment, the heavy pipe wall thicknesses, and the continuous operation demands, presented a challenging situation that required a unique solution.

Our solution

The uncertainty of the valve's position was a critical issue for the pipeline operator and it was absolutely essential to complete the full inspection in one shutdown. Therefore, ROSEN proposed an inspection solution that consisted of bidirectional cleaning and gauging tools, as well as a bidirectional UT tool.

If the results of the cleaning and gauging process showed no damage to the tools, then the UT inspection would be performed in a unidirectional run. However, if the gauge plate returned heavily damaged, indicating a partially closed valve or reduced diameter, the pipeline would be inspected bidirectionally. The UT tool would be pumped through the first flowline to the PLEM, and then the medium flow would be reversed so that the tool is pumped backwards and received at the FPSO. This process would be repeated for the second flowline, but only one shutdown would be required for the entire operation.

ROSEN's Challenging Pipeline Diagnostics Division took the lead on the project and developed a tailor-made 12" bidirectional (BiDi) UT tool that met the passage and corrosion inspection requirements. Constant stand-off and optimum sensor guidance was established by housing the UT sensors in flexible bidirectional polyurethane (PU) carriers. The unique design of the BiDi tool ensures that the data quality is equal to that of ROSEN's standard UT tools, thus providing the high-resolution data quality required to ensure the pipeline's integrity.

Two employees at a test field inspecting a tool.Testing the inspection solution at the RTRC test yard

It was manufactured in close cooperation between the ROSEN Technology and Research Centers (RTRC) in Lingen and Karlsruhe, both in Germany, and was subjected to pump testing through a simulated pipeline configured to have similar diameters, wall thicknesses, and bend radii as these flowlines. Once the manufacturing and testing was completed, the cleaning tool, gauging tool and inspection tool were transported to the FPSO for the inspection campaign. 

Specialized bidirectional inspection tool.Specialized 12" bidirectional inspection unit

The inspection campaign began by sending the cleaning and gauging tools through the pipeline to determine whether they could pass the valve. After launching the gauge tool into the pipeline and receiving it again, the gauge plates confirmed that valve was fully open at the time of inspection. Therefore, the BiDi UT tool was launched into the pipeline and completed the full inspection through the pigging loop in one unidirectional run. A detailed analysis of the recorded data was performed by ROSEN engineers and the final results were delivered to the pipeline operator to the satisfaction of all parties.

Your benefit

Maximized Uptime

The solution provided flexibility in allowing both a unidirectional or bidirectional inspection, whatever the situation required. This operational flexibility kept the downtime, and any production losses for the client, to an absolute minimum.


Complete data sets allowed for a full understanding of the pipeline condition and the ability to take measures for its integrity management. This ensures compliance with safety standards and regulations.

Minimized Risk Exposure

ROSEN's bidirectional approach assures the tool can be removed from the pipeline at any time, hereby minimizing the operational risk and effectively guaranteeing operational safety.