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Woodside: Structural integrity assessment at the North Rankin Complex

OceanTech’s inspection solutions enabled Woodside to efficiently verify the structural integrity of the North Rankin A platform legs, circumventing the need for a costly cofferdam project.

Since its formation in 1954, Woodside has been a key player in shaping Australia’s energy sector, and is currently the largest independent oil and gas company in the country. Woodside operates the North Rankin Complex production platforms A and B, key parts of the prestigious North West Shelf Project – one of Australia’s most critical offshore gas production and liquefied natural gas (LNG) endeavours.

As offshore platforms age, ensuring continued safe and efficient operations becomes increasingly challenging. Deterioration of structural components due to corrosion and material fatigue poses a significant risk to the platform’s integrity. Marine organisms may also accumulate on submerged surfaces, resulting in heightened drag and potential equipment blockages. Regular inspections are therefore essential to ensure the safety, integrity, and operational efficiency of offshore platforms.

As a consequence of structural modifications to the North Rankin Complex facility, and the introduction of a new gangway connecting the platforms, Woodside needed to assess potential underwater corrosion and the structural robustness of the North Rankin A (NRA) platform legs. OceanTech specialises in conducting inspections in the splash zone, and determining the necessity of maintenance tasks. This led to their engagement with our team of engineers.

Choosing the right approach

Maintenance work often requires cofferdams that provide project personnel with a controlled and safe environment. However, constructing and installing a cofferdam involves several costs, such as:

  • Engineering and design costs
  • Material costs
  • Transportation and logistics
  • Labour costs for installation and removal
  • Equipment rental or purchase

Other costs include costs related to dewatering and maintaining the dry work area during the maintenance phase. 

Despite the relatively milder weather conditions in Commonwealth waters, tropical cyclones, hurricanes, and typhoons can still impact maintenance work. These events may substantially limit the operational timeframe available. 

Moreover, when maintenance work involves activities in the splash zone, additional safety risks and access challenges come into play. Divers face increased dangers due to turbulent waters and reduced visibility. Even remotely operated underwater vehicles (ROVs) may face manoeuvring challenges, which can escalate the risk of equipment damage and cause work delays.

OceanTech carefully considered these factors and recommended a robotic inspection of the platform legs. Our solutions empower operators to detect corrosion and fatigue accurately and measure wall thickness effectively, regardless of weather conditions. This approach enables well-informed maintenance decisions, providing a cost-effective, efficient method to ensure offshore platform integrity.

Leveraging vertical access tools and robotics

OceanTech offers a wide range of field-proven technologies and inspection techniques that we have refined to cope with the splash zone’s challenging environment. Our robotic solutions provide a fixed, stable platform for deploying sensors, cameras, probes, and other inspection tools. All our tools and techniques avoid using divers, ROVs, and support vessels.

Following testing at our Subsea Test Center in Trondheim, we decided on a pulsed eddy current (PEC) scanning of the NRA platform legs. PEC scanning provides a reliable means of assessing the condition of underwater structures with several benefits:

  • Non-destructive testing (NDT): PEC scanning ensures the inspected structures remain uncompromised throughout the assessment process.
  • Time-efficiency: PEC scanning enables rapid inspections and can measure wall thickness over large areas in a relatively short period. This minimises operational disruptions.
  • Early corrosion detection: PEC scanning is particularly effective in detecting corrosion and metal loss in submerged structures. This helps operators address these issues before they escalate into major problems.
  • Enhanced safety: PEC scanning with robotic solutions eliminates the need for ROVs and divers to physically inspect structures. This reduces risks associated with human intervention in hazardous environments.

At the NRA, OceanTech’s robotic systems guided the PEC probe along the platform legs from a control cabin topside. Our approach equipped Woodside with essential data for making well-informed decisions regarding maintenance requirements. 

Project outcome: Verified structural integrity

Leveraging OceanTech’s solutions allowed Woodside to verify the structural integrity of the NRA platform legs while avoiding an expensive cofferdam project. 

In our commitment to innovation, we are currently concluding a collaborative research project with SINTEF, DNV, and ConocoPhillips. The project aims to enhance our robotised inspection tools, incorporating advanced sensors and enabling autonomous inspections. We are revolutionising offshore inspections with the new ANDWIS (Automated Non-Destructive Weld Inspection Robot).

Beyond inspection services, OceanTech possesses the equipment and expertise to conduct marine growth cleaning on splash zone structures. We continually develop novel inspection techniques in collaboration with our specialist partners. Fostering cooperation with a diverse range of experienced underwater inspection specialists, engineers, and technicians is where we excel.