The evolution of uncrewed subsea pipeline inspection

We are experiencing an industry-wide shift towards uncrewed and remote survey operations. However, recent developments in remotely operated vehicle (ROV) pipeline inspection methods have run in a converse direction. Technically demanding client specifications call for ROVs equipped with an increasing array of complex payload sensors. This combined with higher survey speeds results in larger volumes of more detailed data. Consequently, large survey teams are still required offshore. This has, so far, ruled out existing uncrewed options. Yet DeepOcean are now seeking to address this gap through the introduction of an uncrewed surface vessel, USV Challenger.

A network of pipelines traverses the world’s oceans. The first subsea pipelines were installed in the late 1940s, with larger-scale engineered subsea pipeline developments emerging in the mid-1950s. Subsea pipelines play a crucial role in transporting valuable fuel. Moreover, as long as subsea pipelines have existed, there has been an associated requirement for regular inspection of these assets. If these pipelines are not inspected, maintained and repaired, severe consequences could ensue. Subsea pipelines are arteries, most of which transport hydrocarbons. These hydrocarbons hold the potential to reap havoc and devastation should they leak from the pipelines. In addition to standard wear and tear, another serious threat to the integrity of these pipelines, which has grown more prominent in recent years, is human sabotage. Therefore, ensuring asset integrity is paramount and the demand for pipeline inspections is continually increasing.

The evolution of subsea inspection technologies

Demand for regular inspection of subsea pipelines has served to propel the development of subsea inspection technologies. Divers played a significant role in the early days, when alternative technologies were not available. However, there are obvious depth and speed limitations to diver surveys. One early alternative to diver surveys was the use of crewed submersibles. Both methods satisfied the requirement to visually inspect the pipelines, yet were limited in terms of the extent of data types that could be collected.

As the range of sensors expanded to include acoustic data, one challenge was clear: acoustic sensors need to be close to the pipeline assets being inspected. This ruled out the use of conventional vessel hull-mounted sensors for all but shallow pipelines. Furthermore, this requirement contributed to the development of towed acoustic systems, such as sidescan sonars (SSS) and sub-bottom profilers (SBP). The major breakthrough, however, came with the introduction of ROVs; one of the first documented uses of an ROV for pipeline inspection was in 1981. ROVs formed a direct replacement for diver and crewed submersible inspections, enabling visual surveys to be completed remotely in deeper waters. Since their introduction, ROV-mounted inspection technologies have evolved rapidly. It proved possible to equip ROVs with SSS and SBP, and the increased stability of ROVs, when compared to towed sensor arrays, also made them more suitable platforms for acquiring multibeam echosounder (MBES) data and high-resolution video, in addition to utilizing tools such as cathodic protection probes.

Contemporary ROV inspection approaches

Since the company’s formation in 1999, subsea survey at DeepOcean has been dominated by pipeline inspection. As a result, pipeline inspection has become a significant service offering, with the company inspecting approximately 10,000km of pipeline annually. As per industry standard, pipeline inspections have revolved around the use of ROVs. Over the years, DeepOcean has collaborated with clients to implement updated technologies and has been an early adopter of advances in payload, acquisition platform and data processing methods (further details provided in World Pipelines, 2024 – see here).

One prominent development has been the implementation of the Superior ROV (SROV), which entered use in 2015. Methodologies have also been developed to optimize the data products generated from inspections. One significant development was initially labelled fast digital imaging (FDI). This involves high-speed, high-resolution still-image capture, enabling photogrammetry processes and 3D model creation. Variants of this method have been routinely utilized in work scopes for many clients.

The SROV achieves survey speeds of four knots during high-fly surveys (4–5m above pipeline) and 2.5 knots for visual surveys – where speed is limited by video review requirements. At these higher speeds, larger quantities of data are generated, which has pros and cons. In FDI campaigns, the offline workload per hour of survey acquisition exceeds that associated with standard visual inspections. This places a heavy burden on the offline team and has necessitated structured production line workflows. Over the years, the survey team has introduced an efficient processing system, and this is now being supplemented by machine learning tools developed in-house to assist manual video and image review.

Despite these developments, there is still high demand for offline crew to handle the large quantities of data generated. And, given the imperative for immediate access to data as it is collected, large survey teams have been necessary offshore during pipeline inspection campaigns. This has proven a constraint to utilizing uncrewed assets for the current, highly detailed pipeline inspection campaigns. Nevertheless, this is not a complete barrier – just one of many challenges requiring solutions that are not currently available off the shelf.

Assessing uncrewed inspection options

The requirement for real-time access to pipeline inspection data, and thus proximity to its source, must be considered when selecting a remote survey method. But what uncrewed options are available for inspecting subsea pipelines? One obvious choice could be an autonomous underwater vehicle (AUV). DeepOcean has operated AUVs in the past but now mainly uses ROVs for pipeline inspections.

AUVs differ primarily by being untethered and free-swimming. There are clear merits and limitations associated with their use. AUVs are fast-flying, stable and achieve comparable survey speeds to the SROV. Yet, unlike the SROV, there is a time lag in gaining access to the data collected due to reliance on through-water acoustic communications. This can result in delays of two days before data can be checked. Issues have also been raised in relation to free-span classification from AUV datasets. Furthermore, while AUVs are suited to advanced payloads such as synthetic aperture sonar (SAS), they are unable to carry the full range of sensors typically required by clients. This is especially the case for the multi-camera setup (centre and boom cameras) utilized in standard ROV inspections, which provide the desired coverage around the pipeline. A single AUV camera only records top-of-pipe. There are also limitations in surveying and tracking buried pipelines due to the inability to mount conventional acoustic and magnetic pipe trackers. Depth is an advantage for AUVs, but even though SROVs have completed inspections in over 2,000m water depth, speed is constrained by the length of tether deployed.

Currently, AUVs are used to complete remote, not uncrewed, surveys, as most AUVs must be manually deployed from a support vessel. Attempts have been made to complete uncrewed AUV pipeline inspections. One of the most noteworthy occurred between 2018 and 2019, where Swire Seabed completed surveys of pipelines off Norway as part of a trial project using an AUV/USV solution. This comprised a Hugin AUV paired with a Sea-Kit Maxlimer USV. The trials were a partial success, but the methodology was not further progressed. The solution trialled was hampered by several issues. The inability to download data or recharge the AUV limited operations to single-dive missions. Automated in-water AUV retasking was also required, as was improved through-water acoustic communication. These and other issues would need addressing for this solution to become a viable uncrewed option.

Another option considered, but again not widely progressed commercially, is the use of a USV/ROTV (remotely operated towed vehicle) solution. ROTVs are used successfully for a range of specific survey scopes, in particular unexploded ordnance (UXO) surveys. These platforms offer advantages over conventional towfish related to stability and payload diversity. Yet ROTVs have limitations that have prevented widespread utilization for other seabed survey applications. Prominent among these, compared with ROVs, are constraints regarding control, stability and payloads. Video is not a standard payload mounted on ROTVs, yet it forms an essential component of most pipeline inspection campaigns. Although progress is being made, ROTVs do not currently appear to be an obvious contender to ROVs for pipeline inspections.

The USV/ROV approach and the Challenger platform

The final option explored here is the USV/ROV solution. This has proven a popular choice, with several companies progressing this combination in different forms and scales. It is this combined solution that has been pursued for USV Challenger.

USV Challenger is a 24m long, 7.5m wide, dynamically positioned vessel. It is powered by a diesel-electric engine, giving it 30 days endurance at sea. The vessel is equipped with an electric work-class ROV (WROV), deployed using an in-house-designed launch and recovery system (LARS). The WROV is recoverable in 3m significant wave height (HS) and the USV has a transit speed of ten knots. The vessel is fitted with a conventional bridge and can accommodate crew onboard for day operations. In progressing this endeavour, DeepOcean has partnered with Solstad Offshore and Østensjø Rederi to create a joint venture titled USV AS.

The vessel was successfully delivered to Norway in May 2025. It left the shipyard classified as a workboat, and throughout the remainder of 2025 the required systems have been configured onboard to gain certification as an uncrewed vessel. At the time of writing (1 December 2025), the vessel had successfully completed its first trial project involving a cable inspection work scope, and it is currently being prepared for its first pipeline inspection trial.

Not all of the technical aspects of DeepOcean’s SROV, crewed pipeline inspection solution form part of this USV solution. For example, Challenger is equipped with a standard WROV, not a fast-flying survey ROV. Given that this development is first-in-class, it was deemed prudent to first establish conventional ROV pipeline inspection capabilities before attempting to operate a fast-flying vehicle from an uncrewed platform. Challenger is also designed as a multi-purpose vessel, capable of being utilized for subsea inspection, maintenance and repair (IMR) operations in addition to survey. Future USV developments are under consideration that may be tailored more specifically to survey.

Enabling remote operations

In shifting to uncrewed operations, it is essential to recognize that the USV/ROV solution constitutes only the acquisition platform. To enable a complex pipeline inspection production line to operate remotely, it is necessary to provide the onshore survey team with real-time access to data as it is collected. DeepOcean have recognized this and are in the process of rolling out an automated remote IT architecture, capable of guaranteeing global data access.

USV Challenger is controlled from a remote operations centre (ROC) in Haugesund, Norway. The online survey team will be located in this ROC, alongside mariners, engineers and ROV pilots, and data processing will be undertaken in remote onshore data hubs.

Subsea pipeline inspection remains a crucial task. The field of pipeline inspection has progressed far beyond the early days of diver and crewed submersible surveys. However, the industry has now entered a new phase of technological development with service provision shifting to uncrewed platforms. The USV/ROV concept represents a meaningful step forward.