Eye in the sky2 May 2018
Philip Buchan discusses how a drone has been used for a first-of-a-kind structural inspection of the concrete domes at the Cook plant in the USA.
Since 2008 Cyberhawk Innovations has been using unmanned aerial vehicles (UAVs), otherwise known as drones, across a variety of industrial sectors and has completed over 25 UAV inspection world firsts. This includes the first onshore and offshore UAV flare inspection, the first onshore and offshore UAV wind turbine inspections, and the first UAV inspection of an internal tank on board a floating production and storage vessel (FPSO).
This experience led to Cyberhawk being appointed by American Electric Power (AEP) to inspect two concrete PWR containment domes at the Cook plant, located on the eastern shore of Lake Michigan. Cook comprises two Westinghouse four-loop pressurised water reactors with a combined capacity of 2191MWe. Cook 1 started commercial operation in August 1975 and is licensed to operate until 2034, while Cook 2 began operation on 1 July 1978 and is licensed until 2037.
UAVs in the nuclear sector
UAVs are not new to the thermal power generation sector; there has been rapid progress and a wide uptake of this technology across power, oil and gas, utilities and infrastructure industries.
The case of Cyberhawk and AEP, however, was the first to use a drone to conduct a structural inspection to the American Society of Mechanical Engineers (ASME) Section XI Code.
This Code sets the rules for the inspection and testing of nuclear power plant components, including concrete structures and steel vessels, piping, pumps and valves. The Code includes the requirements for non-destructive evaluation (NDE) such as the type and frequency of inspection required and subsequent frequency of testing if defects are located.
The Code refers to several American Concrete Institute standards for completing an examination and this inspection has been recognised within the nuclear industry as a best practice based on these standards.
The project specifics
One of the main aims in using a UAV to conduct the containment dome inspection was to avoid the need to use a large crane and man-basket for the task, because the latter can cause significant disruption on site. However, for the UAV to be used instead of a crane, a detailed hazard and operability (HAZOP) study had to be carried out as part of the project planning. This HAZOP allowed the AEP and Cyberhawk team to identify and overcome potential operational challenges, including working around the live plant’s other scheduled projects without causing any disruption.
The inspection quality criterion of the ASME code for this particular visual inspection was to be able to identify cracks or indications as small as 0.8mm (1/32th of an inch) in diameter. In order for the inspection to meet the rigorous code requirements, Cyberhawk had to devise a specific data capture methodology and modify its hardware. The team also had to develop a rigorous quality check process to ensure all images taken during the inspection were of high enough resolution to spot any indications, while ensuring 100% of the structure requiring inspection had been covered.
Once the data-capture process had been developed and accepted by AEP and the US Nuclear Regulatory Commission (NRC), the next stage was to develop reporting criteria and a reporting structure that fitted with AEP’s existing reporting procedures. Cyberhawk’s visual asset management software – iHawk – was already set up for this task. iHawk allows the vast amount of visual data captured by a UAV to be converted easily into meaningful inspection information that allows the end user to source and review critical information without trawling through thousands of images.
For the execution of the project itself, an experienced pilot and inspection engineer from Cyberhawk undertook the work, operating around the plant’s scheduled projects without causing any disruption.
The main operational challenges included strong magnetic interference in the plant caused by high voltage transmission lines and ferrous magnetic materials in the dome concrete, and GPS multi-pathing. These interferences meant that the UAVs had to be flown manually without the assistance of GPS positioning. This required a high degree of piloting skill.
Despite the challenges, work was completed safely, efficiently and according to the ASME code examination requirements.
When compared with traditional methods of inspection utilising a large crane, the benefits of UAV or drone inspection are vast.
As above, an inspection of this type would usually involve using a man basket with a 60m (180ft) crane. Specifically designed equipment exists to allow personnel to work safely at height, but the UK’s Health and Safety Executive notes that “people can be at greater risk of harm when they are lifted by machinery”. Using a UAV to conduct initial structural inspections means maintenance technicians are only required to work at height when defects have been identified.
A further consideration when using lifting equipment is the time and cost required to send the equipment to site and get it set up for the inspection. Including time to set-up, carry out the inspection and dismantle the equipment, this would usually take in excess of two weeks. Using UAVs, Cyberhawk was able to inspect both Cook reactor containment domes in just five days, with minimal site disruption.
The most significant cost savings can be generated through UAV inspection. This particular inspection for AEP incurred direct cost savings of over 66% for the client, as well as significant indirect cost savings through reduced site disruption.
Sceptics are sometimes unconvinced that the quality of data captured by a UAV can match what is obtained from traditional inspection techniques. Cyberhawk has consistently proven this is not the case; in the AEP project, the team captured images of 100% of the dome’s surface, all to the ASME Code standard. Furthermore, the results were digitised into a 3D point cloud that will allow direct digital comparison for any future inspections.
All of the data captured was subjected to engineering analysis at Cyberhawk’s inspection centre being before uploaded to iHawk, the company’s cloud-based visual asset management solution. This shows visual data with a traffic-light colour-code to highlight the severity of any defects and allows users to drill into detailed photographic evidence behind each defect.
As well as allowing comprehensive access to inspection results, iHawk also allows users across multiple locations to view the recordable and suspect conditions of the domes. This means data can not only be shared by project teams, but also by third party suppliers such as maintenance providers.
Cyberhawk has one of the UAV industry’s most comprehensive pilot training programmes. The four-tier programme builds up extensive experience through on-site training. At the highest tier in pilots have over 500 hours of flight experience on live projects. These pilots are trained to operate in hazardous environments, including offshore and at nuclear sites.
The varied and experienced skillset of Cyberhawk’s pilots and engineers allows them to undertake challenging projects that have not previously been attempted.
Chris Fleming, CEO at Cyberhawk, commented: “It’s important to remember that whilst drones collect a huge volume of data, a high-quality engineering report is what makes all the difference. This allows the client to easily assess the condition of the structure and plan any maintenance based on the data. The final reports provided 100% visual coverage of the dome with exact sizing of defects and a 3D model of the structure.
“The uptake of drones will continue to grow in the thermal power generation sector as a result of the increasing applications of the technology, as well as regulation becoming less restrictive. Major improvements to safety and efficiency are offered by UAVs and we expect more and more companies to begin introducing this technology into their asset management programmes.”
Philip Buchan is Commercial Director at Cyberhawk