In a Nutshell:
New pipeline construction is a complex process in which many aspects have to be considered to ensure safe operation right from the start. An integral part of the process often is collecting baseline knowledge of the pipeline condition. Knowing the baseline condition provides reliable knowledge and allows improved integrity assessments in the future. Pre-commissioning processes of a pipeline are elaborate; in many instances, one element includes in-line inspection. During the manufacturing process, oils, greases, rolling imperfections and mill scale can contaminate the wall of the pipe. Oftentimes when constructing a new pipeline, internal coating is applied. In this case, it is vital to ensure correct coating thickness and proper bonding. This is particularly important if a corrosion resistant alloy (CRA) is used as internal protection of a pipeline. Pipelines exposed to high-temperature mediums and products containing highly corrosive components often are internally protected by metallurgical bonded corrosion-resistant alloy. Such preparation is very important for operational aspects, especially in offshore environments¹. This was also the case for a newly constructed 31-kilometer-long offshore gas pipeline in ROSEN’s Asia Pacific region.
The 16-inch pipeline was ready to commence operation with one of the final steps remaining to be carried out: the in-line inspection (ILI). As is so often the case, the ILI requirements did not come without their challenges. In this particular instance, the activities included providing access points for the inspection tool, as no traps were installed, as well as the specific condition for the inspection tool to have minimal contact with the internal coating to avoid damage to the CRA lining.
When selecting an in-line inspection solution for a pipeline, there of course are many conditions to be considered and questions to be answered. Common questions thus often include:
- How do we physically get a tool into and back out of the pipeline?
- What is the goal of the inspection, i.e. the type of anomalies expected?
- What measurement technology is best suited to gather much needed data?
- What customizations, if any, would have be done to the inspection tool to ensure success?
- What kind of testing needs to be completed prior to the actual inspection to minimize risk and increase confidence in the solution?
What Goes In Must Come Out
In this specific case, the launching and receiving of the tool was one of the primary challenges, not only due to the missing launcher and receiver but also because of the existing space restrictions. The limit area available did not allow for the connection of a suitable launcher barrel, allowing only work around the existing piping. It was also important to minimize any modifications. During site visits, suitable insertion and retrieving methods were reviewed before the most ideal solution was selected and agreed upon together with the operator. The agreed work methods allowed for all essential supporting equipment and tools to be mobilized.
The on-site crew disassembled a spool at the beginning of the pipeline in order to pull the tool directly into the pipeline, making it possible to safely launch the tool. The work could be carried out smoothly because of proper preparation and upfront agreements. At the receiver end of the pipeline, adaptations were also required but could be solved by adding a temporary – albeit shorter-than-standard – receiver barrel. The operation also included a specific lifting plan for the receiver barrel, as the crane at the receiver platform had not yet been commissioned for use. The operator, as well as ROSEN, carefully carried out every step to ensure safe operation for personnel, equipment and tools.
Technology and Modifications
The goal for this inspection was clear: to collect baseline survey data and verify the thickness of the CRA lining. Having a good understanding of an asset prior to commissioning allows for future improved integrity management decisions to be more educated and less of a guessing game. Verifying the thickness of the CRA liner is part of integrity assessment, particularly if the pipeline will be transporting highly corrosive products. Determining the best-suited technology to collect this initial ILI data ensures that it is best suited for future decisions – starting on the right foot. Given the inspection goal in this case, ROSEN experts recommended and chose ultrasound (UT) as a measurement technology. UT can measure the pipeline wall thickness. Depending on the orientation of the sensors mounted to the measurement carrier, sound waves propagate through the pipe wall by vibrating the particles that make up the material. The transducer generates these waves directly in the sensor through a liquid couplant, meaning a liquid batch was required for this specific case. The difference between the reflections caused by the front and back wall are also recorded, as they are directly related to wall and coating thickness. Based on these reflections, thickness can be assessed².
The specific tool chosen was a three-meter-long UT tool originally designed for waxy pipelines. This tool could address the need of minimal surface contact with the interior of the pipe wall. The sensors on this tool are designed with a polyurethane (PU) coating, reducing the tool’s metal contact with the inner pipe wall to less than 5% during the entire inspection. To eliminate additional risk and instill confidence in the solution, ROSEN additionally performed a scratch test on a test spool of the CRA section to ensure the remaining 5% metal contact (mainly odometer wheels) would not damage the internal coating surface.
Now that the baseline inspection, or pre-commissioning ILI, is complete, the pipeline can be put into operation. However, pipeline integrity management never stops, and the next question will be how future in-line inspections will take place. Again, the operator and vendor must ask themselves how to get a tool in and out of the pipeline, what technology is best applied and which threats need to be identified (i.e. corrosion, cracking, geometry threats, etc.). Given the CRA coating, this pipeline will be inherently challenging to inspect. Solutions may include creating odometer wheels in non-metallic materials to consistently avoid damage to the CRA layer, customizing geometry tools to have less metal contact with the pipe wall, using foam tools with geometry inspection capabilities and much more.
The Big Picture
Ensuring the integrity of this subsea pipeline prior to its commissioning not only allows for optimal operation and likely an extended lifetime, it also ensures its safety. Taking a comprehensive look at this line means not “just” sending a pig through the line but rather taking goals, operational needs and environmental circumstances into consideration. All elements of this solution have their purpose, both to ensure the success of the inspection and to provide a solid foundation for this pipeline’s future lifecycle.