As jacket structures worldwide approach the limit of their estimated service life, discoveries, and improved production methods have bolstered the desirability of extended lifetimes. Extending the lifespan of these structures provides operators with many advantages spanning financial, operational, safety, and environmental domains, making it an appealing option for optimising offshore operations.
Life extension processes involve several inspection and modification requirements to verify the asset can continue operating safely and effectively beyond its planned design life. This includes weld inspections to ensure the asset can withstand anticipated loads, stresses, and environmental conditions while meeting specified standards.
However, weld inspections pose several challenges due to the splash zone’s distinctive characteristics:
- The splash zone has limited access points and confined spaces, making it difficult to reach and thoroughly examine all areas.
- Marine growth and fouling can further complicate inspection processes.
- Working in the splash zone involves inherent risks for personnel due to strong currents, slippery surfaces, and potential underwater hazards.
- The turbulent weather conditions, particularly in areas prone to rough seas, often limit weather windows for offshore operations.
- When performing eddy current testing, noise caused by wave action and other sources of interference can mask subtle indications of weld cracks. This reduces the signal-to-noise ratio and impacts the reliability of the inspection results.
- Water splashing around the weld areas can attenuate signals, making it more difficult to detect and evaluate cracks accurately.
- The water can act as a barrier, affecting the interaction between the test probe and the weld surface. This can potentially lead to reduced sensitivity and compromised signal quality.
In response to the demand for enhanced solutions, OceanTech collaborated with SINTEF, ConocoPhillips, and DNV to create an autonomous underwater robot and an advanced eddy current probe for non-destructive testing of welds in the splash zone environment.
“With operators increasingly seeking to extend the lifespan of jacket structures, we believe there is a demand for a solution that can conduct these tests with greater efficiency, safety, and reliability”, stated Karsten Husby, a researcher at SINTEF.
The innovation project behind the robot, known as Automated Non-Destructive Weld Inspection in the Splash Zone (ANDWIS), was launched in 2020. Several SINTEF research departments were involved in the project.
“To tackle critical industry challenges head-on, we engaged a diverse team of experts in 3D camera technology, cybernetics, electromagnetism, and non-destructive testing methods for metal surfaces”, Husby said.
According to Husby, the robot is a testament to collaborative innovation. A diverse range of expertise came together to address the precise requirements of the offshore industry. Reflecting on the experience, he expressed, «The project has fostered a seamless exchange of knowledge. Throughout this project, I genuinely felt like an integral member of the OceanTech team.”
After undergoing a series of tests in SINTEF’s underwater testing lab, the inspection robot is on the verge of being ready for deployment. Highlighting its distinctive features, Husby emphasises the addition of a cutting-edge 3D vision system specifically designed for splash zone operations, along with an advanced control system.
“These advancements are likely to reduce measurement time and elevate the quality of the data, further enhancing the robot’s effectiveness in inspection tasks”, he said.
Once securely attached to the welded brace, the robot can manoeuvre along the pipes while maintaining precise control over the position of the eddy current probe. Guided by the 3D vision system comprising two lasers and two cameras, the robot ensures accurate inspection and provides valuable visual information for the operator. The collected measurement data is stored alongside corresponding positioning information, allowing for comprehensive analysis and documentation.
The robot control system offers two operational modes: FPV (first-person view) and closed-loop control. In FPV mode, the pilot has full, intuitive control over the robot’s movements, facilitating easy manoeuvrability. Alternatively, in closed-loop mode, the robot autonomously positions the eddy current probe with utmost precision, ensuring optimal alignment against the weld. The probe incorporates multiple alternating current field measurement sensors to tolerate minor misalignments, lift-off variations, and fluctuations in permeability.
“This feature enhances the robustness and reliability of the inspection process, enabling accurate detection and characterisation of flaws in the weld”, added Husby.
A safer, faster, and more reliable option
The test results from the robot’s eddy current probe have been promising, demonstrating precision that surpasses other available solutions. Husby emphasised, «Our tests have revealed better signal quality and detection capability specifically for weld cracks.»
The findings highlight the technological prowess of the robot, and its potential to revolutionise non-destructive testing in the challenging splash zone environment.
The robot also provides operators with significant HSE benefits. It effectively addresses the key challenges associated with manual operations involving divers and remotely operated underwater vehicles (ROVs) in the splash zone. Conventional methods inherently carry substantial safety risks, exposing personnel to potential hazards. Moreover, the restricted time window for operations can prolong the inspection process, further impacting safety and operational efficiency. The robot effectively mitigates these challenges.
Husby highlighted the autonomous nature of the robot, stating, «By utilising the robot, operators can reduce the need for human intervention in hazardous environments, thereby enhancing operator safety.»
Its time-saving capability is perhaps the most significant advantage. The robot empowers operators to conduct tests efficiently even in the face of adverse weather conditions, enabling them to perform more frequent eddy current testing in a shorter period. This is paramount to expediting the inspection process, minimising operational downtime, and maximising resources. The robot provides a valuable solution that significantly accelerates data acquisition by eliminating the dependency on favourable weather windows. This leads to faster decision-making and more efficient life extension processes.
«The ANDWIS innovation project will be presented at the Offshore Europe Conference in Aberdeen in September. We are hopeful to get the robot to use by the end of the year,” Husby concluded.