The Future of Offshore Integrity: Transforming Inspection with Data and Simulation

In the challenging world of offshore structural engineering, supporting clients in managing the risks to their offshore platforms from the relentless forces of nature is a never ceasing task. At Kent, our Global Offshore Structural team has developed extensive knowledge and insight from our experience supporting clients in the assessment, management and mitigation of the risks to offshore structures associated with a diverse range of loading scenarios and degradation mechanisms. This extensive experience has equipped us with comprehensive skills to guide our clients adeptly through these multifaceted challenges.

Offshore platforms are subjected to some of the harshest conditions on the planet. They need to resist the insidious effects of degradation, whether from metal fatigue resulting from the continuous assault on the offshore jacket from waves or corrosion from the harsh marine conditions. They also need to withstand extreme loading from the wind and rogue waves during large storms. Protecting people and the environment, as well as ensuring the continued integrity of the asset, is a continual battle involving the identification and management of these threats. Detailed inspection of structural components provides valuable information on the condition of those parts. Without these inspections, degradation or damage could lead to an unacceptable risks to offshore workers and to the environment and high costs associated with the structure's operational costs.

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Inspections can provide information of varying resolution, depending on the inspection method. For example, ultrasonic inspections of welds can detect fatigue cracks at an early stage in their growth. Detection of flooding in structural braces indicates a crack has formed and has grown sufficiently to allow water to enter a brace. Repairs and mitigation of the risks at this stage are more costly than if an early crack were discovered. Monitoring structural behaviour with accelerometers allows the detection of more severe damage by spotting changes in the structure’s dynamic signature, with the disadvantage of later detection of damage and more costly intervention.

Inspection methods that detect and anticipate damage allow for early intervention; however, they can prove more costly. Ultrasonic inspection may require saturation diving, which is expensive and potentially risky, with limited coverage. Flooded member detection can be performed by remotely operated vehicles without the need for divers and can give greater coverage. Monitoring structural behaviour by accelerometers is a continuous process, requiring relatively inexpensive equipment installed on the topside.

An effective life cycle programme for inspecting, repairing and managing the risks to an offshore structure needs to balance the costs of the inspection and monitoring and those associated with the repair of damage of differing severity. Throughout this, the potential hazards to the offshore workers, the environment and the operation of the structure must be managed so that they remain as low as reasonably practicable (ALARP). There are many possible strategies - how to inspect, where to inspect, how often to inspect, management of repairs, and risks to workers and the environment related to the potential damage based on whether it is discovered or not. The challenge is then to develop an inspection strategy which provides effective, practical, and optimal inspection and monitoring plans and associated repair and operational costs, always ensuring that risks to workers and the environment are ALARP.

From a financial perspective, Duty Holders are deeply invested in this battle. The costs associated with inspecting and maintaining the structural integrity of offshore platforms are substantial. For instance, a Remotely Operate Vehicle Support Vessel (ROVSV) costs five figures per day, and a Diver Support Vessel (DSV) is at least an order of magnitude more expensive than that.

At Kent, we support our clients in meeting these challenges by developing cutting-edge solutions. One such solution is our probabilistic risk-based inspection (RBI) method tailored for offshore oil and gas jackets.

This innovative approach makes use of Monte Carlo Simulation (MCS) and Bayesian inference methods to predict the probability of structural collapse due to fatigue degradation and extreme environmental loading. By integrating data from in-service inspections and online structural monitoring, the method refines inspection planning, ensuring that the risk of structural failure remains within acceptable bounds. This quantitative strategy marks a significant advancement from the traditional, semi-quantitative RBI methods, which, for ageing jacket structures with low fatigue lives, often result in impractical inspection demands. This probabilistic RBI method, by effectively quantifying the risks associated with the degradation and storm hazards, not only supports the effective management of life safety, environmental risk, and the longevity of offshore structures but also optimises inspection - a boon for platform owners in developing an optimal allocation of valuable subsea resources.

Figure 1: illustrates an example of the potential cost savings of applying our method for subsea inspection planning for an ageing jacket with low fatigue lives, where the semi-quantitative RBI resulted in annual subsea inspections. The costs of annual inspections are compared to the costs of inspecting every 3 or 4-years, justified by the Probabilistic RBI method.