Case Studies

Putting theory into practice

The Challenge

BP Angola needed a highly accurate baseline inline inspection (ILI) of its 36 km (22 mile) Plutao offshore deep water (up to 2,000 m/6,500 ft) flowline and riser systems. The baseline inspection is part of BP standard practice and provides a true blueprint of the pipeline, giving exact internal inspected status following commissioning. 

When the BP Subsea Projects Team began the ILI campaign, its first challenge was to thoroughly prepare for every eventuality. Unexpectedly the Plutao operation experienced an unplanned shutdown; giving the team a new window of opportunity to start the project ahead of the initial schedule, with the condition that mobilization had to start within 24 hours to coincide with this unforeseen shutdown. 

To run the ILI equipment first requires cleaning the line with a series of pigs, each designed for a specific task. The first is a foam pig to ensure all valves are fully open. Then, a de-sanding pig was used to dislodge accumulated sand and wax. This was also used to sweep away any debris. Finally, a gauge plate pig with a special disc matching the diameter of the pipeline is run to verify the pipeline has the required bore for the inspection tool. 

Once the team was mobilized, initial cleaning pigs in the line went as planned. The debris returned was minimal, indicating the line was cleaner than expected. A decision was then taken to run the gauge pig ahead of schedule. 

When it returned to the surface after its subsea odyssey, the gauge disk resembled a bowl rather than the flat plate that had set out on the journey. This identified a problem. The challenge now was to engineer a solution in record time to safely run the ILI tool below its current design limit, keeping risks within acceptable levels.

The Solution

BP has a worldwide agreement with NDT Global to provide intelligent pigging services. After a review of requirements an advanced ultrasonic tool was selected to accurately measure wall thickness and metal loss. The use of ultrasonic measurement is particularly important as it ensures accuracy in thick wall pipes, which other technology cannot achieve. 

For this project the UMp configuration was selected. This provides a true high-definition picture of the pipeline including any pitting corrosion, general corrosion or mid-wall flaws such as lamination's or inclusions. Due to the heavy walled nature of the pipeline, a custom configuration was required. 

NDT Global's tools are designed to be customized to specific customer requirements. However, any tailor-made tool still requires both testing and qualification. A test loop that replicated the pipeline characteristics and flows was built onshore at the large test yard in Stutensee, Germany. The project tool followed a meticulous test program before being delivered to site. 

When the gauging pig returned showing a reduced minimum diameter a rapid response was required. This new diameter was below the qualified diameter of the intelligent ILI tool but the team needed to complete the planned inspection during the shutdown window. Thanks to the NDT Global engineering team, and work by the Sunbury flow lines team, a plan was conceived to ‘put the pig on a diet’. NDT Global and the Sunbury engineering team worked together to identify and mitigate risks for design changes to the tool. Thankfully, there was a lot of experience with tool variations and the confidence level in the modifications was very high. After 96 hours of re-modeling, design assurance and risk assessments, the green light was given to launch the modified UMp tool.

The Results

  • Reduced operations downtime due to speed and reliability. Stopping production at such an important facility is hugely expensive (The operation has a production rate of 150,000 barrels per day). The project team successfully leveraged an unexpected shutdown to conduct the ILI with minimal disruption to flowlines. This was only possible due to the responsiveness of the team and reliability of the tool.
  • A successful campaign 11 months of planning permitted 10 successful pig runs to be safely executed over 18 days, while overcoming a bore restriction that could easily have destroyed the campaign on the 5th run. NDT Global has a long track record of offshore projects and understands the key requirements for success. One of these is enabling excellent open communication when critical issues arise.
  • First run success. The new flexible tool achieved a first run success. The tool returned safely to the floating production, storage and offloading unit (FPSO) and first run was completed in the planned 16 hours. The modifications that had been made did not adversely affect the inspection run which was essential for the overall project plan.
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