Can Non-Destructive Testing Be Done Underwater?

Non-destructive testing, more commonly referred to as NDT, is a cornerstone of quality assurance and structural integrity across many UK industries. Its primary advantage lies in the ability to inspect, assess, and evaluate materials, components, and structures without causing damage. While most people picture NDT being carried out in factories, workshops, or controlled environments, there is a growing need for these techniques to be applied in more challenging conditions — including underwater.

Underwater environments present their own unique demands, from reduced visibility and strong currents to the challenges of corrosion and marine growth. Yet, the UK has a long history of engineering innovation in offshore and subsea industries, and the question of whether NDT can be done underwater is not just theoretical. The answer is an emphatic yes, but with significant caveats in terms of specialist techniques, equipment, and training.

Why Underwater NDT is Necessary

There are many situations in which structures or components that require inspection are submerged. Offshore oil and gas installations in the North Sea, for example, rely heavily on underwater NDT to ensure the continued integrity of subsea pipelines, risers, and platform legs. The same applies to the rapidly expanding offshore wind energy sector, where turbine foundations are often anchored deep below the waterline.

Maritime industries also depend on underwater inspections to maintain the safety of ship hulls, propellers, and other submerged components. Even inland waterways, reservoirs, and hydroelectric facilities may require underwater NDT to assess dams, sluice gates, and submerged infrastructure. In all of these cases, hauling the structure to the surface for inspection is either impractical or prohibitively expensive, so the work must be done in situ beneath the water’s surface.

Non Destructive Testing

The Challenges of Performing NDT Underwater

Carrying out NDT underwater is considerably more complex than conducting the same work in a dry, controlled environment. One of the primary challenges is the physical limitation imposed by water itself. Light behaves differently underwater, reducing visibility and making it more difficult for inspectors to visually assess components. Currents and tidal movements can also hinder precision work, especially at greater depths.

Another factor is the increased risk associated with diving operations. Many underwater NDT tasks require commercial divers, who must be trained not only in their inspection method but also in safe diving practices and emergency procedures. The equipment used must be designed to function reliably in submerged conditions, often at high pressures, and it must be resistant to corrosion from saltwater exposure.

Furthermore, marine growth and sediment can obscure the surfaces to be inspected, requiring cleaning or surface preparation before the NDT process can even begin. This additional step can significantly extend the duration and complexity of a job.

NDT Techniques Adapted for Underwater Use

Not all NDT methods can be adapted for underwater environments, but several have been developed or modified to work effectively in these conditions. Ultrasonic testing, for example, is widely used underwater because sound waves travel efficiently through water, making it possible to detect flaws beneath the surface of metals and other solid materials. Specialised underwater ultrasonic probes can be operated by divers or mounted on remotely operated vehicles (ROVs).

Magnetic particle inspection can also be carried out underwater using waterproof yokes and particles suspended in a suitable carrier fluid. This method is particularly effective for detecting surface cracks in ferromagnetic materials such as steel. Eddy current testing, which uses electromagnetic induction to identify flaws, can be adapted for subsea use as well, though it is more sensitive to surface preparation.

Visual inspection remains one of the most common underwater NDT techniques, often conducted with the aid of high-resolution cameras mounted on diver helmets or ROVs. While visual inspection alone may not be sufficient to detect all types of defects, it is an important first step in many underwater assessment programmes.

Diver-Operated vs Remote NDT Operations

Underwater NDT can be carried out either by divers physically handling the inspection equipment or by remotely operated vehicles equipped with NDT tools. Diver-operated inspections offer the advantage of human judgement and adaptability, allowing the inspector to adjust their approach based on what they see and feel in real time. This method is particularly valuable for complex structures where manoeuvring equipment is difficult.

However, diver operations come with increased safety considerations and logistical requirements. Working time is limited by depth and air supply, and there are inherent risks in sending humans into potentially hazardous underwater environments. For this reason, ROVs are becoming increasingly popular, particularly for deep-water applications. ROVs can be deployed for longer periods, operate in depths beyond the safe limits for divers, and reduce the overall risk to personnel.

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Industry Standards for Underwater NDT in the UK

In the UK, underwater NDT is carried out in strict accordance with industry regulations and safety standards. The British Institute of Non-Destructive Testing (BINDT) plays an important role in setting certification requirements for NDT personnel, while the Health and Safety Executive (HSE) provides guidance and enforces regulations for diving operations.

Divers performing NDT work must hold appropriate qualifications, both in their chosen inspection method and in commercial diving. Certifications such as PCN Underwater Inspection Diver qualifications are specifically designed to ensure that technicians can perform inspections safely and accurately in submerged environments. Additionally, offshore projects must adhere to international standards such as those set by the International Maritime Organization (IMO) and the International Organization for Standardization (ISO).

Training for Underwater NDT Professionals

Training for underwater NDT is more demanding than for standard NDT roles. Candidates must first become certified commercial divers, a process that involves intensive physical training, theoretical study, and practical assessments in diving safety, underwater tools, and emergency procedures. Only once this qualification has been achieved can they move on to NDT-specific training.

Underwater NDT training combines the theory and practical skills of conventional NDT with techniques adapted for subsea work. Trainees learn how to operate specialist waterproof equipment, deal with reduced visibility, and manage the additional complexity of working in currents or at depth. This dual qualification — in commercial diving and in NDT — makes underwater NDT technicians highly skilled and sought-after professionals.

The Role of Technology in Modern Underwater NDT

Technological advancements have significantly expanded the possibilities for underwater NDT. High-definition video cameras, sonar imaging systems, and 3D modelling software now allow inspectors to create detailed visual records of submerged structures without physically touching them. This is particularly useful in situations where physical access is limited or where surface cleaning would be impractical.

ROV technology has also improved dramatically in recent years. Modern ROVs can carry ultrasonic transducers, eddy current probes, and other NDT instruments, transmitting data in real time to surface operators. This not only enhances safety but also allows for more comprehensive and repeatable inspections. In some cases, autonomous underwater vehicles (AUVs) are now being deployed for routine inspection tasks, following pre-programmed routes to capture consistent data sets over time.

Underwater NDT in the UK’s Offshore Energy Sector

The UK’s offshore energy industry is perhaps the largest user of underwater NDT, particularly in the oil and gas and renewable energy sectors. North Sea oil platforms require constant inspection to ensure the integrity of their submerged structures. Similarly, offshore wind farms depend on regular NDT to verify that turbine foundations remain secure and free from significant corrosion or cracking.

These industries operate in harsh marine environments where saltwater, strong currents, and storms can take a heavy toll on structures. Underwater NDT enables operators to detect damage early, plan maintenance effectively, and prevent catastrophic failures that could result in environmental harm and financial loss.

Maritime and Shipping Applications

The UK’s maritime sector also relies heavily on underwater NDT. Ship hulls, propellers, rudders, and ballast tanks are all subject to wear, corrosion, and impact damage. Carrying out inspections underwater allows vessels to remain in service without the need for dry-docking, which can save both time and money.

Classification societies often require periodic underwater inspections as part of a ship’s certification process. These inspections are carried out by certified diver-inspectors or ROV operators who follow strict guidelines to ensure that the vessel remains seaworthy and compliant with international standards.

Inland Waterway and Civil Engineering Applications

Underwater NDT is not limited to offshore and maritime industries. In the UK’s inland waterways and civil infrastructure, submerged inspections are used to maintain bridges, piers, dams, and lock gates. Many of these structures are decades or even centuries old, and regular inspection is necessary to ensure they remain safe for public use.

Hydroelectric facilities also depend on underwater NDT to assess turbines, gates, and other submerged components. The ability to carry out these inspections without draining reservoirs or shutting down operations provides significant operational and economic benefits.

The Future of Underwater NDT

The future of underwater NDT in the UK is closely tied to advancements in technology and the growing emphasis on renewable energy. As offshore wind farms expand further into deeper waters, the need for reliable, efficient underwater inspection will increase. Improvements in ROV and AUV capabilities will likely lead to a reduction in diver-operated inspections, although there will always be situations where human judgement and adaptability are essential.

Artificial intelligence and machine learning are also expected to play a role, with inspection data being analysed automatically to identify potential defects more quickly and consistently. This could help operators predict when maintenance will be needed, reducing unplanned downtime and extending the lifespan of critical assets.

Conclusion

Non-destructive testing can indeed be performed underwater, and in the UK it is already a well-established practice across a variety of industries. From offshore oil rigs and wind farms to maritime shipping and inland waterways, underwater NDT provides a crucial means of ensuring structural integrity and safety without the need for costly or impractical removal of assets from their operational environment.

While the process is more complex than conventional NDT, requiring specialised equipment, training, and safety measures, it offers significant benefits in terms of operational efficiency and risk management. As technology continues to advance, underwater NDT will become even more capable, efficient, and essential to the UK’s industrial future.

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