Navigating Severe Diameter Reduction
Ultrasonic robotic inspection solution for a deformed offshore pipeline
A purpose-built ultrasonic robotic inspection system was engineered and deployed to inspect a severely deformed 42-inch offshore loading pipeline between a terminal and an offshore Pipeline End Manifold (PLEM). The asset presented multiple inspection challenges: absence of launching and receiving facilities, lack of bidirectional flow, and a significant internal diameter reduction caused by historical anchor damage. To overcome these constraints, a segmented UT scanner integrated with an electro-hydraulic propulsion unit and real-time fiber-optic communication was developed, enabling full-coverage, high-resolution wall thickness data while safely negotiating the restriction.
Asset description:
- Diameter: NPS 42"
- Length: 2,660 m
- Wall thickness: 12.7 - 16.6 mm
- Pipeline product: Crude Oil
- Obstruction: 230 mm (~22% of pipe diameter)
The challenge
An offshore loading pipeline runs from a terminal to an offshore Pipeline End Manifold (PLEM). As is typical for loading lines, the asset lacks launching and receiving facilities and is operated intermittently with potential product changes. These conditions do not provide the steady flow required for conventional in-line inspection.
The 42-inch line extends roughly 2.66 km and has only one workable access point. Compounding the challenge, a historical anchor impact caused a significant reduction in the internal diameter around 1,075 meters from the entry point. Prior inspections had also revealed internal corrosion concentrated at the six o’clock position. These factors together demanded a purpose-built inspection
approach that balanced tool negotiability with high-quality ultrasonic data acquisition.
Key challenges to overcome:
- Single access point and no traps, ruling out conventional ILI runs.
- Unsuitable operational conditions for conventional ILI due to intermittent operation and lack of propelling flow.
- Severe internal diameter reduction with uncertain geometry at ~1,075 m (historical damage), which posed a high risk of tool hang-up and potential loss of UT stand-off.
- Limited work envelope at the terminal and potential environmental/safety exposure if temporary pumping equipment were to be installed.
- Data quality requirements in nominal 42-inch sections while maintaining a compact configuration capable of safely negotiating the restriction.
Our solution
Several critical factors had to be considered when developing the solution, including selecting the appropriate propulsion system, choosing the right ultrasonic measurement technology for the asset, and integrating robust fail-safe mechanisms for the inspection tool itself.
A robotic inspection tool was the optimal solution because it enabled controlled traversal of the 42-inch offshore loading pipeline without relying on product flow or conventional launching and receiving facilities.
The inspection system features an electro-hydraulic propulsion unit with expanding arms that provide the necessary traction to navigate bends, elevation changes, and severe internal restrictions. The propulsion system was designed to deliver a pull force of up to 900 kg, ensuring reliable movement even through challenging pipeline geometry.
To address the unique internal diameter reduction caused by a historical dent, the ultrasonic sensor carrier was engineered as a three-module, segmented scanner. This design allowed the tool to maintain optimal sensor stand-off in nominal pipeline sections while collapsing to pass through the restricted area. Each of the three module housed high-resolution 160 ultrasonic probes, for a total of 480. This enabled accurate wall thickness measurements and enhanced detection of corrosion and laminations.
The inspection tool was connected to a cable, also referred to as tether, and a winch system. This setup provided power and realtime communication via a fiber-optic connection, as well as a robust retrieval mechanism. The buoyant, Kevlar-reinforced tether minimized friction, allowing for smooth movement through the pipeline. The entire system was monitored and controlled from the surface, enabling operators to adjust parameters in real time and respond dynamically to operational challenges.
This approach eliminated the need for temporary pumping equipment or extensive modifications at the terminal, reducing operational and environmental risks, increasing cost-effectiveness while ensuring high-quality data collection. The fail-safe tethered design also provided a reliable contingency for tool retrieval, further enhancing safety and project assurance.
Your benefit
Throughout the inspection process, the collected data was accessible in real time. This allowed onsite analysts to monitor tool performance and adjust inspection parameters as needed to enhance data quality. This real-time visibility allowed for immediate responses to operational challenges and supported the decision to conduct additional passes over areas of concern, ensuring comprehensive coverage and high-resolution results.
The inspection delivered high-quality, high-resolution wall thickness and geometry data, surpassing the results of previous inspections carried out by competitors.
The advanced ultrasonic technology and a flexible tool design enabled the detection of a greater number of corrosion and lamination features, providing a more detailed and accurate assessment of pipeline integrity.
Thanks to the inspection design concept, the need for temporary pumping equipment or extensive modifications at the terminal was eliminated, significantly reducing operational and environmental risks, increasing cost-effectiveness. The robust fail-safe mechanism provided by the cable connection ensured that the inspection tool could be reliably retrieved from the pipeline, if necessary, further reducing project risk and supporting safe and efficient operations.
A key benefit of this project was the ability to successfully negotiating a severe internal diameter reduction caused by historical damage, demonstrating the value of a flexible, segmented tool design. This adaptability allows for the application of similar inspection solutions to other pipelines with complex geometries, restrictions, or access limitations, enabling safe and effective integrity assessments even in the most challenging environments.