Inline inspection: hydrogen edition

Chris Johnson, Managing Director, SMB Bearings, UK, explains the challenges and opportunities when using drones to monitor and inspect oil and gas pipelines.

Abee can travel over five miles and then remember its way home, despite possessing a brain the size of a pinhead. Scientists have been putting them in virtual reality simulators to help improve unmanned aerial vehicle (UAV) or drone technology. While the honey bee currently has the edge, drone technology is catching up.

The small UAV market was worth approximately US$2.84 billion in 2019 and is projected to grow to US$11.3 billion by 2027, according to Precedence Research.1 Currently, around 70% of this market is made up from rotary blade type UAVs. For the oil and gas drone service market specifically, ReportLinker has forecast a 60% compound annual growth rate between 2020 and 2025.2

Drones are being employed in a wider range of sectors and for myriad purposes. As a technology that was nurtured by the military, it is no surprise that they are widely used in defence applications. In 2018, they were even used in an attempted assassination of Venezuelan President Nicolas Maduro.3

Less sinister uses of the technology include assisting with policing, fire-fighting, search and rescue missions and delivery of medical supplies in remote locations. The technology has also

spawned a cohort of enthusiastic hobbyists. The nascent sport of drone racing is also rapidly taking off.

The further growth and adoption of this technology will be encouraged by consumer market growth, spill overs from the military sector and the possibilities opened up by 5G. The potential for drones to revolutionise the world of maintenance is clear. They certainly pass the ‘D test’: tasks that are dirty, dangerous and dull could all be left to drones.

BP, Shell and Exxon have already begun using drones for asset inspection and other tasks. Following an incident in 2008, where Exxon’s use of sonar technology was implicated in the deaths of 100 whales near Madagascar, the company recently used drones to help monitor the locations of whales off the coast of Santa Barbara.4 But what about the benefits for pipelines?

Opportunity in pipelines From Alaska to the Niger Delta, oil pipelines are often located in inhospitable or even dangerous environments. In addition to their vast size, this fact makes maintenance through visual inspection a dangerous task. By handing the task of visual inspection over to drones, human workers are no longer in harm’s way. Improved safety is one of the key benefits being touted by advocates of drone uptake in the oil and gas industry.

Making the task of maintenance safer is not the only incentive. Early investors in the technology are seeing significant cost savings. Although it is difficult to quantify the precise saving, research by Roland Berger has estimated that drone-based inspection of oil and gas rigs leads to cost savings of around 90%. The same research estimated that the use of drones has cut maintenance times from eight weeks to five days.5

Calculating the precise costs for pipeline inspection and maintenance is not easy. It will vary from pipeline to pipeline. That’s why many companies begin testing or piloting the use of UAV systems before fully committing to their adoption. However, precise calculations seem superfluous. The bottom line is that drones will provide a more cost-effective alternative to traditional asset inspection methods such as helicopters and ground vehicles.

Furthermore, drones are not simply replacing existing methods. Their agility allows them to offer visualisation and data analysis that existing methods cannot compete with. For example, satellites are limited by their orbit and weather can disrupt the accuracy of the images they provide. An engineer would have to assemble scaffolding to physically access a potential problem.

Drones, in contrast, can provide thousands of images from every conceivable vantage point, generally unhindered from the restraints imposed by traditional methods. In addition to helping improve safety and cut costs, they also improve the efficiency of asset inspection and maintenance programmes.

Scientists now claim that sophisticated sensors are developed enough and small enough to be mounted on UAV systems.6 As well as capturing high resolution visual data, drones can be equipped with other sensors to monitor pipelines, such as thermal imaging or ultrasound inspection. Challenges for take off Given the evident benefits of drone-based asset inspection, what is holding companies back from adopting this technology? One issue is regulation. As with any new technology, there is a struggle for regulators to keep up with the pace of innovation.

Companies wanting to adopt this technology must also make sure they understand this evolving regulatory environment. Those that already use aviation, for example with helicopters, are probably in a better position to confront this hurdle due to their existing knowledge of aviation regulation.7

Beyond visual line of sight (BVLOS) is among the most discussed things in the drone industry. This refers to where a drone is operating beyond the pilot’s line of sight. BVLOS activity will be necessary to enjoy the full benefits this technology could offer for asset inspection of pipelines, but in some countries it is not permitted.

In the United States, for smaller drones flying below 400 ft above ground level (AGL), BVLOS is currently not permitted without the necessary authorisation from the Federal Aviation Administration (FAA). To navigate around this restriction an FAA waiver is required. According to Geospatial World, 99% of waiver applications fail.8

The restrictions are different when you enter different airspace classifications (those above 400 AGL). Here, operators require either an FAA authorisation or waiver to enter controlled airspace. The necessity of understanding these rules is another obstacle that slows the uptake of drone technology in many commercial applications. For pipelines that traverse national boundaries, these regulatory issues become even more complex.

Another consideration many businesses must make is what business model to adopt. In its guidance for the industry, the American Petroleum Industry outlines three alternative models.9 The first model is an ‘internal model’. As the name suggests, this means utilising internal assets, purchasing equipment and training pilots to develop drone capabilities in house.

The second, alternative model is an external model. This means outsourcing to a company that specialises in running UAV programmes for this purpose. Although companies would still need to understand operator liability and insurance, this reduces some of the risk and means fewer costs up front. The third option is a hybrid model, containing elements of both.

Although the technology is constantly improving, there are limitations that are relevant to their potential for surveying pipelines. The limitations of the batteries that power the vehicles gives rise to range anxiety, a problem that is more significant for pipelines that cover significant distances. It is likely the industry will focus on using drones for inspection of oil rigs and other infrastructure before taking on the challenge of vast pipelines.

Another key issue that cannot be overlooked is that of cyber security. Cyber vulnerabilities can impact both the operation of the drones themselves and the data they gather and store. This is another risk factor that has to be properly calculated for any company embarking on the path toward adoption.

Something to bear in mind If maintenance engineers are to exploit the benefits of UAV technology, keeping the drones in tip-top condition will be essential. Understanding the maintenance needs of these vehicles will be important for those companies who adopt the internal model referred to above. Engineers will need to be quick to acquire fresh expertise in this area.

Maintaining and replacing the bearings in drones will be an essential part of this. Many oil installations face significant risks from corrosion. Bearings too, need protection from corrosion. If your drone is operating in an environment where this risk exists, speak to a reputable supplier like SMB Bearings for the best information on bearing choice for your application.10

In applications where the cost of bearing failure is high, quality precision bearings are required. The bearings for drone motors should offer inherent low noise and vibration characteristics. Many suppliers of drone bearings would offer lifetime lubrication to reduce the risk of accidentally over lubricating or under lubricating your bearings, as this is among the leading causes of bearing failure.

Drones and honey bees are becoming more alike. The buzz surrounding drones is only set to grow and their use in monitoring and maintaining oil installations will allow the oil industry to improve worker safety, reduce the time taken to complete key maintenance tasks and realise substantial cost savings. If you are thinking of adopting an unmanned aerial vehicle programme to monitor your assets, consider the benefits of partnering with a reliable supplier of high quality precision bearings to help keep your drones in the air.

References

1. Global Newswire (2021) ‘Small UAV market size worth around US$11.3 billion by 2027,’ 6 January, available at: https://www.globenewswire.com/newsrelease/2021/01/06/2154368/0/en/Small-UAV-Market-Size-Worth-AroundUS-11-31-Billion-by-2027.html 2. ReportLinker (2019) Oil and Gas Drone Services Market – Growth, Trends, and Forecast (2019-2024). 3. BBC News (2018) ‘Venezuela President Maduro survives ‘‘drone assassination attempt’’,’ 5 August, available at: https://www.bbc.co.uk/news/world-latinamerica-45073385 4. ROKER, S. (2016), ‘Exxon Mobil using drones to track whales,’ 13 July, available at: https://www.worldpipelines.com/equipment-and-safety/13072016/ exxon-mobil-using-drones-to-track-whales/ 5. BERGER, R. (2019) ‘Drones: the future of asset inspection,’ available at: https://www.rolandberger.com/de/Insights/Publications/Drones-Thefuture-of-asset-inspection.html 6. ROKER, S. (2017), ‘Scientists advocate the use of drones in monitoring oil and gas pipelines’, World Pipelines, 7 June, available at: https://www. worldpipelines.com/equipment-and-safety/07062017/scientists-advocatethe-use-of-drones-in-monitoring-oil-and-gas-pipelines/ 7. American Petroleum Institute (2019) API Guide to Developing an Unmanned Aircraft System, available at: https://www.api.org/~/media/Files/Policy/ Safety/API-Guide-for-Developing-a-UAS-Program-in-the-Oil-and-NaturalGas-Industry.pdf 8. CHOUDHARY, M. (2019) ‘What is BVLOS and why is it important for drone industry?’ Geospatial World, 11 June, available at: https://www. geospatialworld.net/blogs/what-is-bvlos-and-why-is-it-important-fordrone-industry/ 9. American Petroleum Institude, API Guide. 10. https://www.smbbearings.com/

Dr Aidan O’Donoghue, Pipeline Research Limited, UK, outlines a study examining pipeline pig motion and behaviour in pure hydrogen and hydrocarbon/ hydrogen mixtures.

Hydrogen is likely to be one part of a greener future in combination with other green technologies and existing fossil fuels, at least in the near term. Burning hydrogen only produces water vapour and this is an important step in emission reductions. Since hydrogen does not exist in a natural state, how the hydrogen is produced will determine its green credentials – if formed from water or electrolysis, then when using renewable energy, this is close to zero ‘carbon intensity’, whereas if formed from hydrocarbons, it is less than that of the natural gas but certainly not zero.1

Figure 1. Model used for dynamic pigging. The line is 16 in. and is 118 km in length. An inlet flow is provided and the outlet pressure is controlled. The middle graph shows the pig differential pressure along the pipeline (an input file). The nominal pig differential pressure (DP) is 1 bar but with 2.5 bar at river and road crossings due to thicker walled pipe. The pipeline elevation profile is shown on the lower graph.

Figure 2. Steady state output with pressure (top), gas velocity (middle) and pipeline elevation profile (bottom).

Figure 3. PIGLAB output for the base case 500 kg pig run in 50 bars pure hydrogen. The top graph shows the pig velocity profile along the route. The middle graph shows the pig differential pressure with peaks at the river and road crossings. The lower graph is the line elevation profile.

Transportation of hydrogen efficiently using existing gas infrastructure is an attractive prospect either as 100% hydrogen or in a mix with natural gas. Such pipelines will still require inspection and servicing and as a result pigging will be required. At atmospheric pressure, hydrogen is very light and even at high pressure, the density is much less than that of natural gas. Since pig motion in gas pipelines relies on pressure (or more specifically density) to dampen the motion and keep speed under control, then pig motion in hydrogen lines is likely to be less controlled. Barker provides a good example in his paper of high peak velocities during inspection of hydrogen lines with an MFL (magnetic flux leakage) tool.2

A study has been undertaken and the initial results are published in this paper. Several aspects of pigging in hydrogen have been examined but only velocity and leakage are covered in this article. Wear and material selection are not presented at this stage. Firstly, a description of the pig motion model (PIGLAB) is provided.

Pig motion model To determine the gas behaviour upstream and downstream of the pig or indeed with no pig in the system, it is necessary to solve a couple of partial differential equations (PDEs), namely the continuity and momentum equations. These equations couple pressure and gas velocity and allow their variation with distance and time to be calculated.

Solving for pressure, p and gas velocity u in space (x) and time (t) enables the behaviour of the gas upstream and downstream of the pig to be determined. Inlet and outlet boundary conditions set the incoming flowrates and pressures for the line but can also change with time. This upstream and downstream pressure around the pig can be determined.

An overview of the pipeline in question is as shown in Figure 1. The elevation profile of the line against distance and the pig differential pressure against distance are inputs in the form of a data file.

Cases It is assumed that an ideal mixture of the hydrogen and hydrocarbon gas occurs and that the specific gravity and molecular weight are based on a combination of the gas properties.3 This is a realistic starting point. The base case input for the pipeline is as follows: • 100% hydrogen. • 50 bar outlet pressure. • 500 kg pig mass. • Inlet velocity is 2 m/s and for the sake of this study, the flow is adjusted such that this is the maintained for all cases considered to facilitate comparison.

The following cases are then examined using the model:

Effect of hydrocarbon content • BASE CASE: 100% hydrogen, 50 bara outlet pressure, inlet flow of 1 Sm3/sec with 500 kg pig mass. • 75% hydrogen, 25% hydrocarbon gas.