February 2018, Vol. 245, No. 2
Features
New Pipelines Pre-Commissioning Inspection
Prior to the commissioning of any pipeline system, it is critical for both the construction company and the asset owner to verify that the pipeline’s construction conforms to standard regulations, and that no damages have occurred during the construction phase.
The timing of these inspection services is critical to ensure that any repairs that may be required can be executed before the pipeline is placed in operation. These testing practices, which range from pipeline gauging and hydrotesting to inline inspection, are of great benefit to the owner/operator, since they ensure safe operation not only during the actual commission of the pipeline, but throughout the life of the asset.
Further, these inspections create a reference baseline for future inspections to allow for the proper assessment of anomalies that may emerge from the operation of the pipeline or be caused by environmental factors.
Although inline inspection (ILI) is a well-established technique in the oil and gas pipeline industry, its implementation during the pre-commissioning phase is not prevalent, since the operating conditions required to properly run inspection tools are not available. Though adequate conditions can be produced, this typically requires high volumes of gaseous medium, such as nitrogen, at high pressures, which results in excessive project expenditures.
A result of this easy attainability and often low-cost, owners/operators frequently request geometric inline inspections over more comprehensive technologies such as magnetic flux leakage (MFL) or ultrasonic testing (UT) during the pipeline pre-commissioning phase. Due to the robustness of the tools and the reduced operational conditions required to run the tool, caliper inspections have become more of a standard practice during pre-commissioning.
Though caliper technologies require less operational support in terms of flow and pressure, minimum operating criteria still need to be met to ensure that data quality standards are achieved. These operational conditions are often overlooked during the pre-commissioning phase due to budget constraints and equipment availability. As a result, standard caliper technologies are often propelled by air with limited flow and pressure, resulting in excess speed excursions and poor data quality.
As running caliper technologies in air has increasingly become the standard for these services, operational considerations and customized tool configurations need to be evaluated to ensure that the data captured will be within the acceptable levels.
Challenge
The ROSEN Group was contracted to inspect a newly constructed 116-mile (187-km), 14-inch pipeline in Australia. The focus of the integrity assessment was to search for geometric integrity concerns related to the construction of the pipeline.
As so often with challenging pipelines, there was not merely one issue to contend with, but a combination of issues that made the inspection a challenge. With this particular pipeline, many challenges were present, including:
- The extreme length of the pipeline with only two points of access, forcing the inspection to be completed in one run
- Most of the pipeline was underground with numerous bends and passes or crosses houses
- Steep pipeline profile
- 3 check valves and 10 gate valves
- Dewatering and drying had already been completed
- No flow, no propellant
In providing a propellant for ILI tools to ensure stable run behavior, liquid mediums such as water, diesel, etc., or gaseous mediums at high pressures are preferred. While liquids tend to offer the best conditions for inline inspection tools, compressed air (oil-free and dry) was the only practicable choice due to readily available equipment and lower cost.
Although, in comparison to nitrogen, air compressors are a less costly method for bringing the pressure to more ideal levels (i.e., 20 bar @ 1m/s), the volume of equipment adds significant cost to the project.
To reduce cost while still providing acceptable conditions, four air compressors with dryers were contracted locally by the client with a combined air delivery of 4,350 standard cubic feet per minute (scfm) at 12.5 bar, resulting in average tool speeds of 0.6 meters per second (m/s), which is considered below optimal speed at such low pressures. Since the receiving site was situated near a well-populated area, the installation of mufflers was required to keep noise disturbance to a minimum.
Solution
ROSEN established the Challenging Pipeline Diagnostics Division to respond to inspection challenges by providing solutions that enable operators to inspect the majority of their pipeline networks.
The division consists of highly experienced engineers, specialists and service technicians able to provide unparalleled value through ingenious, tailored solutions. Through the division and the ROSEN Toolbox approach, which includes a broad range of proven technology elements, ROSEN is able to provide individual solutions to meet clients’ specific requirements under available pipeline conditions.
The major challenge in this case was the combination of various tasks relating to the dry media for propulsion, low speeds, and tracking of the inspection tool, as well as the length and passage of the pipeline through many bends, wall thickness changes, check valves and elevation changes.
During the inspection, inline inspection tools tend to stop or get hung up on various obstacles due to a lack of sufficient pressure (force) to move the tool through these obstacles. As time passes, the pressure behind the tool builds up and forces the tool through. As a result of this sudden dislodgement, inline inspection tools tend to travel at a higher rate of speed due to the immense pressure differential that was required to force the tool through the obstacle.
In some cases, tool speeds of greater than 108 km per hour (km/h) (30 m/s) are reached, whereas most inline inspection tools have a maximum target speed of 10.8 km/h (3 m/s) to ensure data quality specifications are met. Furthermore, after the tool starts to move again, the pressure in front of the tool is typically low, thus extending the high-speed phase.
The impact of exceeding the tool target speed is twofold. First of all, the mechanical dippers are no longer running smoothly on the interior pipe surface, which may affect the size or even the identification of geometric features, with the tool’s resolution typically also being effected.
Secondly, ILI tools typically record data based on the tool’s speed. When the tool is run outside of its measuring parameters (about 5m/s), it cannot record the data at the speed that the data is being measured. This often results in data loss and gaps in the data set.
The main challenge for low-pressure pipeline inspection is to create stable run behavior under the existing operating conditions. Since the geometric integrity of the pipeline was unknown, and the passage of an instrumented tool could be at risk, a cleaning tool with gauge plate specifically configured for long pipelines and dry environments was prepared. The gauge tool was also equipped with a pipeline data logger to gather information on pressures, differential pressures, temperature and accelerations throughout the entire run.
The data collected allowed proper evaluation of the actual running conditions under the prevailing circumstances. This data was used to adjust the operating conditions before the inline inspection tool was run.
During the run of the cleaning tool with gauge plate, tool passage track points were determined, covering all critical points, such as gate/check valves, major road crossings, populated areas and changes in elevation. Pressures at launching and receiving traps were continuously logged to identify the actual air compressors’ capabilities and efficiency throughout the gauge run. The results were evaluated and used to make adjustments in order to provide adequate conditions for the instrument tool run.
After the gauge run, it was noticed that the required air flow was not being met. Although the compressors were rated at a combined flow of 4,350 scfm @ 12.5 bar, the actual flow encountered was only 2,000 scfm at about 11 bar. This condition allowed the tools to be run but introduced additional challenges during the inspection, increasing accelerations at various locations. The expected overall run time of 48 hours was exceeded by 10 hours, adding difficulty to tool tracking due to night work.
Once all information and cleaning tool condition were evaluated, the appropriate configuration of the inline inspection tool was determined based on the pipeline’s physical and operating conditions. Having already considered a specific setup from the toolbox, it was decided to proceed with the run of a high-resolution/extended-geometry tool under the evaluated conditions.
The pull unit of the tool was specifically configured for long runs, and the extended-geometry technology tool was chosen in lieu of standard-geometry technology due to its proven design and capability to handle larger velocity ranges of 0.3 to 5 m/s.
Although this was a standard measurement technology, the inline inspection tool was optimized to improve run behavior. This was achieved by concentrating on three core objectives:
- Minimizing and maintaining constant friction, which assists in reducing unwanted speed variations
- Minimizing the difference between static and dynamic friction, which reduces acceleration after tool stops, and ensures that tool velocity returns to normal as quickly as possible
- Optimizing sealing components, which is necessary to ensure that minimum flow of the propellant bypasses the tool during the inspection
The preparation and consideration proved to be fruitful, and the high-resolution geometric inspection run was successfully completed. Optimal data was recorded for the entire length, and data evaluation showed no anomalies requiring repairs.
Further during this run, tracking passage points covering all critical points and pressures at launching and receiving traps were logged and further evaluated for correct identification of the run conditions. The recorded conditions were similar to those experienced during the single-body gauge pig run, proving that the setup for the much heavier multi-segment tool was correctly implemented.
Benefits
The overall benefits of the inspection were compelling. It provided the operator with reliable, high-quality data to complement the pipeline commissioning process and safely put it into operation.
In addition, the combined operation (cleaning and inspection) propelled by air provides the following benefits:
- Free swimming tool – able to pass unlimited distance and bends
- XGP technology provides a proven design
- High resolution
- Wide velocity range of 0.03 to 5m/s
- Inspection under low-flow, low-pressure pipeline conditions
- Cost-effectiveness
Conclusion
The newly constructed 14-inch pipeline posed a combination of hurdles that made completing a successful inline inspection a challenging task. A tailored solution, through the ROSEN Toolbox method, was conceived in order to establish stable run behavior. Propelled by compressed air, the optimized high-resolution/extended-geometry tool performed extremely well.
The tool maintained constant friction and optimal sealing, and therefore successfully completed the 187-km inspection run with complete data recording and no sensor loss. ROSEN experts transformed this challenge into a success – enabling the customer to confidently put this new pipeline into safe operation. P&GJ
Authors: Jaime Alejandro Lopez is a mechanical engineer and the Challenging Pipeline Diagnostics Division’s coordinator and technical solutions lead for the ROSEN operational unit located in Mexico. Within the ROSEN Group, he has acted as both an operations manager and special projects coordinator.
Corey Richards is business development manager for ROSEN’s Challenging Pipe-line Diagnostics Division based out of the Technology and Research Center in Lingen, Germany. His focus is on creating tailored solutions for pipelines deemed unpiggable in the Oceana and Asia Pacific regions. Richards has a comprehensive qualification as a certified electronics engineering technologist and Level 2 ILI tool operator.
Frank J. Mueller, advanced solutions expert for the Challenging Pipe-line Diagnostics Division, has been in the pipeline industry for over 33 years and holds a degree in mechanical engineering from TU Kiel, an aircraft engineering technician degree from the Technical University of the Air Force III in Germany
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