Subsea inspection methods throwing up significant challenges

Michael Stephenson, Project Manager of the Foundations Working Area in the Offshore Wind Accelerator
Michael Stephenson, Project Manager of the Foundations Working Area in the Offshore Wind Accelerator
Clamp installed on jacket foundation to inspect complex node weld (Image: Oceaneering)
Clamp installed on jacket foundation to inspect complex node weld (Image: Oceaneering)
Oceaneering hybrid ROV/crawler deployed to inspect the monopile weld
Oceaneering hybrid ROV/crawler deployed to inspect the monopile weld

The Offshore Wind Accelerator (OWA) recently announced the winning projects of its recent innovation competition to find novel subsea methods to inspect offshore wind substructures, reports Andrew Williams.

One of the challenge winners is Oceaneering International Services, which impressed judges assessing bids for weld inspection for monopile foundations solutions with its proposal for the development of an inspection tool adapted from previous use in oil and gas.  Oceaneering was also one of two winners in the weld inspection for jacket foundations section, with a project that will utilise its experience in oil and gas to provide an innovative technique for the inspection of nodes.

The other winner was Kraken Robotics, a German company, which has developed a high resolution laser imaging sensor for the inspection of subsea assets.  A third competition for grout inspection for jacket foundations was won by Next Geosolutions UKCS in collaboration with Ashtead Technology and Hydrason, with a technique based on the use of innovative sonar to detect gaps, cracks and disbanding of grout.  Finally, projects under the grout inspection for monopile foundations section were awarded to Uniper Technologies, which has developed an ultrasonic interferometric technique with the British Geological Survey and has already shown its success in recent offshore trials, and Next Geosolutions UKCS with the same technology as for the jacket inspection competition.

As Michael Stephenson, Project Manager of the Foundations Working Area in the Offshore Wind Accelerator (OWA), explains, one of the main motivations for the scheme is the fact that offshore wind installations differ from those seen in the oil and gas sector, because a wind farm is composed of multiple individual structures installed at sea.  This results in a significant increase in requirements for subsea inspections and a need to understand the integrity and condition of sometimes up to 100 steel structures in a highly energetic and corrosive environment.

"By finding new ways to understand the condition of offshore wind substructures during operation, operators can reduce the cost of their offshore activities significantly and perhaps even extend the life of their assets, reducing LCOE further," he says.

"More importantly, the offshore wind industry is continually focused on health and safety and reducing the risk of incidents.  By reducing the number of offshore interventions required, or even automating the inspection process, a significant reduction in the number of offshore personnel hours can be achieved," he adds.

In Stephenson's view, improvements in the quality of data that operators receive from inspections will help them to make more informed decisions on the risk to assets, and therefore potentially move to 'Risk Based Inspection' methodologies, which he believes can provide 'significant operational improvements and efficiencies.'

"The project teams will have to tackle challenges similar to any new technology entering the offshore wind market, and especially understand the nuances and differences from other maritime and subsea markets that they may traditionally operate in. This is where their involvement in the OWA will really help as they will get visibility of the developer requirements are and will be able to align the development of the technologies in relation to real market needs," he says.

"The expectation is that all the technologies will be commercially developed.  The OWA is focused on technologies on the cusp of commercialisation and the market-pull approach shows the desire of the offshore wind market to bring these innovations into commercial viability and to be deployed at operational wind farms in the future," he adds.

One of the key beneficiaries of support under the competition is Oceaneering International, which was selected to participate in the programme based on its proposal for a crawler-based inspection technique with phased array ultrasonic sensors.  The technique, due for delivery in September 2018, will be used to inspect subsea monopile circumferential welds on offshore wind turbines.  A tool equipped with alternating current field measurement (ACFM) sensors installed on the end of a remotely controlled arm will also enable inspection of jacket nodal welds.

As Raj Venkatachalam, Product Development Manager at Oceaneering, explains, the monopile welds will be inspected using a crawler magnetically coupled to the structure, using a remotely operated vehicle (ROV), which will be capable of both cleaning and inspection activities.

"Cleaning the area is essential, as ultrasonic inspection requires the surface under inspection to be free of debris in order to collect accurate defect data.  The inspection method combines phased array and time of flight diffraction (ToFD) ultrasonics using sensors attached to the front of the crawler," says Venkatachalam.

"This inspection method will be able to detect surface flaws in circumferential butt welds of monopile cans, both internally and externally to the structure," he adds.

While this technology has already been proven for subsea inspections, Steven Cowie, Vice President & Country Manager at Oceaneering International, points out that the primary challenge now is to ensure that the tools can be reliably deployed in the splash zone.

"Our goal is to deliver a more cost-effective solution that meets the financial requirements of the customer.  We also envisage that, by using ROV technology, multiple work scopes can be completed simultaneously, thus eliminating additional equipment mobilisations and costs," he adds.

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