Jmse 11 02172
Jmse 11 02172
Jmse 11 02172
Marine Science
and Engineering
Review
Exploring Autonomous and Remotely Operated Vehicles in
Offshore Structure Inspections
Maricruz Fun Sang Cepeda 1 , Marcos de Souza Freitas Machado 1 , Fabrício Hudson Sousa Barbosa 1 ,
Douglas Santana Souza Moreira 1 , Maria José Legaz Almansa 2 , Marcelo Igor Lourenço de Souza 3
and Jean-David Caprace 3, *
1 Department Naval and Fisheries, Rio de Janeiro State University (UERJ), Rio de Janeiro 23070-200, Brazil;
cepeda.maricruz@ce.uerj.br (M.F.S.C.); machado.marcos@graduacao.uerj.br (M.d.S.F.M.);
barbosa.fabricio@graduacao.uerj.br (F.H.S.B.); santana.douglas_1@graduacao.uerj.br (D.S.S.M.)
2 Department of Applied Physics and Naval Technology, Polytechnic University of Cartagena (UPCT),
30202 Cartagena, Spain; mariajose.legaz@upct.es
3 Department of Naval and Oceanic Engineering, Federal University of Rio de Janeiro (UFRJ),
Rio de Janeiro 21941-611, Brazil; migor@lts.coppe.ufrj.br
* Correspondence: jdcaprace@oceanica.ufrj.br
Abstract: Operators of offshore production units (OPUs) employ risk-based assessment (RBA) tech-
niques in order to minimise inspection expenses while maintaining risks at an acceptable level.
However, when human divers and workers are involved in inspections conducted at high heights,
the operational risks can be significant. Recently, there has been a growing trend towards the use of
unmanned aerial vehicles (UAVs), autonomous surface vehicles (ASVs), remotely operated vehicles
(ROVs), and autonomous underwater vehicles (AUVs) for inspections of offshore structures as a
means to reduce exposure to human risk. This article provides an analysis of these vehicle inspection
Citation: Fun Sang Cepeda, M.; capabilities and their potential to enhance robustness and safety within the oil and gas industry. The
Freitas Machado, M.d.S.; Sousa review assesses both the advantages and the drawbacks associated with these innovative systems,
Barbosa, F.H.; Santana Souza Moreira, providing valuable comparisons and assessments on their potential use as viable alternatives to
D.; Legaz Almansa, M.J.; Lourenço de conventional inspection methods.
Souza, M.I.; Caprace, J.-D. Exploring
Autonomous and Remotely Operated Keywords: ASV; AUV; ROV; UAV; drone; inspection; offshore platform; risk; maintenance
Vehicles in Offshore Structure
Inspections. J. Mar. Sci. Eng. 2023, 11,
2172. https://doi.org/10.3390/
jmse11112172
1. Introduction
Academic Editors: Marco Cococcioni, 1.1. Context
María Isabel Lamas Galdo,
The offshore industry is experiencing rapid growth and technological advancement
Juan José Cartelle Barros
in exploration, collection, and storage. This progress is accompanied by a commitment
and Luis Carral
to improving safety measures to minimise the risk of accidents [1]. Although occasional
Received: 16 August 2023 incidents pose environmental and human risks, the industry has adopted preventive
Revised: 17 October 2023 measures and response strategies, demonstrating ongoing commitment to safety [2].
Accepted: 23 October 2023
Published: 15 November 2023 1.2. Challenges of Traditional Offshore Inspection Methods
The current offshore inspection methods face several issues that hinder their effec-
tiveness and efficiency. One of the main issues is the reliance on traditional inspection
techniques, such as visual inspection and nondestructive testing (NDT), which are often
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
time-consuming, costly, and limited in their ability to access hard-to-reach areas [3]. These
This article is an open access article
methods require human intervention and are subject to human error, which makes them
distributed under the terms and less reliable [4]. Furthermore, offshore installations are subject to perpetual fatigue loading
conditions of the Creative Commons and harsh marine environments, which can cause structural degradation and damage [5].
Attribution (CC BY) license (https:// Current inspection methods may not be able to accurately detect and assess the extent of
creativecommons.org/licenses/by/ such damage, putting the integrity and safety of offshore structures at risk [6].
4.0/).
Another issue is the lack of comprehensive risk-based inspection planning (RBI) for
offshore installations [4]. RBI involves assessing the risks associated with the operation
of offshore facilities and developing inspection plans based on the identified risks [7].
However, the implementation of RBI in the offshore industry has been limited and a more
systematic and integrated approach to RBI is required [4]. This is particularly important for
offshore wind turbines, which are expected to continue to develop in deep ocean areas in
the coming years [8].
Furthermore, current inspection methods may not be able to effectively monitor the
health and safety of offshore structures in real time [8]. Traditional inspection techniques
often provide a snapshot of the current condition of the structure, but do not provide
continuous monitoring or early detection of potential problems [3]. This can lead to
unexpected failures and higher maintenance costs [9]. Advanced monitoring systems are
needed to continuously collect data on the structural health of offshore installations and
provide real-time feedback on their condition [8].
Moreover, current inspection methods may not be cost-effective, especially considering
the large number of offshore structures and the challenging marine environments in which
they operate [10]. Traditional inspection techniques require significant resources, including
manpower, equipment, and time, which can result in high inspection and maintenance
costs [10]. It is essential to find a cost-effective way to plan inspection and maintenance ac-
tivities that takes into account the probability, consequences, and cost of these activities [10].
It is necessary to investigate alternative methods to reduce expenses while still maintaining
a high level of accuracy and quality both above and below the water.
by the HUGIN© endurance AUV. Lastly, waves and impacts of underwater currents on the
tether are of great concern for ROVs because they may cause them to be swept away or
limit their controllability. AUVs are immune to this limitation, allowing operations under
more challenging weather conditions.
Similarly, the industry has shown a recent interest in using autonomous surface vessels
(ASVs) and unmanned aerial vehicles (UAVs) for the inspection of ocean structures that
are above the sea water, as shown by [21]. These emerging technologies have established
themselves as essential tools due to their distinct advantages and benefits.
As widely discussed by [22], ASVs are highly adaptable for collecting data on both
the ocean surface and the subsurface environment, making them a reliable choice even in
harsh sea conditions. These vehicles have the ability to navigate independently around
offshore structures while collecting data using integrated sensors including multibeam
echosounders and side-scan sonars [23]. By minimising human error and reducing risks
associated with manned operations, ASVs greatly improve the efficiency of maintenance
schedules and potential threat assessments. These vehicles are designed to operate in
harsh ocean environments and reduce human participation in offshore infrastructure
monitoring [20].
Autonomous UAV technology, also called drones, has emerged as a crucial tool for
conducting inspections above the waterline. These UAVs possess the ability to access
difficult-to-reach areas on floating platforms and other ocean structures, enabling them to
capture detailed high-resolution imagery that offers essential information for structural
health monitoring, as shown by [24,25]. With their agile manoeuvrability and advanced
imaging technologies, drones can quickly detect problems such as corrosion or mechanical
damage, allowing for prompt remedial actions. Some even have the capacity to climb
structures [26]. Furthermore, by reducing the need for inspectors to work at great heights
or in hazardous conditions, drones significantly improve safety during inspections.
optimal selection and prioritisation of inspection and maintenance activities [10]. These
frameworks use structural reliability methods and Bayesian reliability methods to establish
fatigue design criteria and update inspection plans during operation [31]. RBI involves
prioritising inspections based on the level of risk associated with each subsea asset, thus
reducing the need for systematic periodic inspections where they are unnecessary. By
conducting a thorough risk assessment, operators can determine which assets require
frequent inspections and which can be inspected less frequently.
Another approach is to take advantage of advanced technologies such as artificial
intelligence (AI) and machine learning algorithms to improve the efficiency and effec-
tiveness of subsea inspections. Several authors discuss the use of AI to improve vehicle
self-awareness [32] or the ability to detect and follow objects [33].
For instance, the authors of [34] discusses the automation of the detection and classifi-
cation of marine growth in offshore structures using deep learning and sensors to obtain
a 3D representation of thickness and composition. The study also highlights the need
for further development given the impact of marine growth on structural integrity due
to increased hydrodynamic loads. Similarly, ref. [35] discuss the use of AUVs and AI in
inspecting, maintaining, and detecting damage in subsea oil and gas pipelines that com-
promise their structural integrity. Despite improvements in image-based inspections and
computer vision methods for subsea environments, the authors underline the challenges of
the lack of training data for image analysis and the incorporation of risk-based knowledge.
In essence, the combination of ROV, AUV, ASV, and UAV technologies provides a
holistic approach to reduce inspection costs, particularly for large structures and deep-sea
operations. Utilizing autonomous vehicles, implementing risk-based inspection strategies,
and leveraging artificial intelligence (AI) and machine learning can enhance inspection
efficiency and reduce expenses. Careful planning ensures optimal inspection schedules
that maintain desired risk levels at minimal costs. Using these methods, companies can
efficiently monitor total structural health, ensuring extended operational longevity and
safety while reducing operational costs.
aims to ensure the long-term reliability and durability of physical structures [12,28,37]. It
encompasses various aspects such as human resources, systems, procedures, and assets.
In order to adhere to the inspection needs of offshore production units, it is essential
to comprehend and address the unique obstacles and circumstances that these structures
encounter. Maintaining the SIM plays a critical role in ensuring the safety and reliability
of OPUs. This is achieved through regular inspections conducted in various areas of the
platform (see Section 2.1) with the objective of identifying potential risks or damages that
could jeopardise personnel, assets, and environmental integrity. These inspections are not
only obligatory for regulatory compliance, but also serve as proactive measures aimed at
avoiding costly incidents and failures.
Offshore production units can be divided into several zones of inspection depending
on the accessibility of the asset and methodologies available to perform the inspection.
(a) (b)
Figure 1. Inspection zones of offshore structures. (a) Fixed platform; (b) Floating platform.
to identify potential problems or defects without the need for direct physical inspection.
Similarly, mini ROVs have become popular for inspections in zone 3, as they can navigate
the subsea area near the water line with greater agility and flexibility compared to human
divers. Advanced inspection systems and autonomous underwater vehicles are used in
zones 4 and 5, respectively. These advanced technologies offer the advantage of collecting
data on the states of the subsea structure without the need for humans to operate them.
The following section aims to provide an overview of the possible use of autonomous
and remotely operated vehicles for inspecting offshore structures.
(a) (b)
Figure 2. Scientific publications and citations over time, based on [app.dimensions.ai]. (a) Number of
publications; (b) Number of citations.
Drones have become increasingly popular for inspection of offshore structures, par-
ticularly in zones 1 and 2. Equipped with high-resolution cameras and sensors, drones
offer enhanced visibility and remote monitoring capabilities. They can capture detailed
visual imagery and data for analysis, allowing operators to identify potential problems
or defects without the need for direct physical inspection. Drones can be used to inspect
various zones in offshore structures, including the following:
1. Hull: Drones can provide a detailed view of any part of the hull of a ship, identifying
sections with corrosion, cracks, or other damage.
2. Riser balconies: These are critical points on an offshore platform. Drones can reach
difficult-to-access places to inspect these areas.
3. Topside: The upper portion of an offshore structure can be easily inspected by drones
to check for structural integrity, leakage, weather-induced damage, etc.
4. Flare stacks: Inspections of flare stacks are necessary to check for corrosion, cracks, or
blockages. Drones can perform this task without the need to stop operations.
5. Internal tanks: Specialised drones can even inspect the interiors of large storage tanks
on ships and units, including corrosion and leakage detection assessments.
6. Hard-to-reach areas (underdecks, cranes, etc.): Drones can reach places that would
be dangerous or difficult for humans to access, enabling inspection of complex areas,
such as underdecks or cranes.
In essence, drones have significant versatility and can be used for most inspections in
practically all upper areas of naval and offshore infrastructure.
Kneipp (2018) alongside Santos (2023) present the potential of using drones for inspec-
tion in the naval and offshore industry, particularly within the Brazilian context [43,44].
It discusses the time-optimising benefits of drone inspection methods, highlighting their
ability to reach difficult-to-access places and detect issues like corrosion, cracks, and leaks.
The author proposes possible applications of drone inspections on a floating production
storage and loading (FPSO) platform. It also outlines the best types of drone for such
applications and navigates the regulations surrounding drone operations. Finally, it encom-
passes discussions on solutions such as 360-degree videos, 3D modelling for measurements
and volumes, and image-based structure analysis.
Drones provide a variety of benefits in terms of agility, cost-effectiveness, flexibility, se-
curity measures, and the ability to provide frequent information updates. These unmanned
aerial vehicles are equipped with active and passive sensors to enhance their functionality.
Active sensors such as LIDAR and RADAR enable them to collect data through signal
transmission, while passive sensors such as visual spectrum and thermal cameras capture
images without the need for signal transmission [45]. Moreover, photogrammetry is a
J. Mar. Sci. Eng. 2023, 11, 2172 9 of 27
common method used by drones for image analysis in inspections. This involves capturing
a series of overlapping images from different angles and using computer algorithms to
stitch them together, creating detailed 3D models that can be used for further analysis and
measurements [46].
Drones can also be used for confined space inspections on ships where human access
is limited. It includes the inspections described by Frederiksen et al. (2018) and Krystosik
(2021), including examinations of hulls, ballast and cargo tanks, coating systems, and
structural integrity. Drones are also used to inspect crane tops, flares, confined spaces, and
inaccessible areas during routine inspections, such as the exterior of the hulls (inaccessible)
or the interior of tanks. Additionally, drones may aid in damage inspection following
incidents and assessments before reactivating ships [47,48].
Poggi et al. (2020) identified challenges for the use of robotics and autonomous systems
(RAS), including drones, in offshore inspections [49]. This includes the management of
electromagnetic field disturbances, the limitation of GPS in internal space, the detection of
obstacles, the management of reflective surfaces, and the negotiation with air turbulence.
To address these challenges, various technologies are deployed, including vision-based
camera inspections, 2D and 3D laser scanners, depth and RGB-D cameras, along with
wireless-based location methods. The study finds several advantages to using RAS, leading
to important conclusions. First, RAS significantly reduces human risk during inspection
processes, as machines are deployed in areas where human access could be hazardous.
Second, RAS inspections generate larger volumes of data in a shorter period, fostering
efficient inspection processes. Finally, human-based inspections are often more expensive
than RAS inspections, reaffirming the cost-effectiveness of using automated systems for
offshore evaluations.
Numerous research teams have developed their own assortment of drones equipped
with inspection functions. In the ROBINS project [49], a diverse range of RAS platforms
were chosen to address the comprehensive needs of ship inspection, except underwater
vehicles, which have been actively adopted for underwater inspections for some time now.
The variety included two distinct types of aerial drones and a magnetic crawler, harnessing
the unique capabilities of different robotic solutions to fulfil various inspection requirements.
Moreover, the project anticipates conducting open trials with other robotic platforms in the
future. The specified RAS units, conceptualised and created by Universitat de les Illes Balears
(UIB), Flyability Sa (FLY), and Ge Inspection Robotics (GEIR), are depicted in Figure 4. These
platforms showcase the potential synergies and capabilities offered by combining different
robotic technologies to meet the extensive and varied needs of ship inspections.
The ADRASSO project, led by DNV Maritime, has undertaken extensive research
and development in the field of semi-autonomous drone navigation. Furthermore, the
project has focussed on utilising AI-based computer vision techniques for automated crack
detection and hyperspectral imaging analysis to evaluate the condition of protective paint
used in steel tanks as well as identify their chemical composition [48,50]. Demonstrations
were successfully conducted onboard floating production, storage, and offloading platforms
(FPSO) during this initiative (Figure 5). Notably, several other partners have collaborated
with DNV Maritime on this endeavour including Jotun, Norsk Elektro Optikk, Idletechs
Scout Drone Inspection, and NTNU.
The REDHUS project, which began in January 2021, is an ongoing initiative following
the previous project. Its acronym stands for “Remote Drone-based Ship Hull Survey”. The
primary objective of this effort is to showcase a streamlined procedure for conducting ship
hull or tank surveys remotely through automated drone inspections and analysis of video
data captured by the drones. By establishing this method as a standard practice in the future,
ship owners can experience improved safety measures and economic gains. Furthermore,
consistent delivery of high-quality inspection data improves the classification process
while also allowing room for long-term advances. As a result of these developments, new
market opportunities emerge not only for drone service providers, but also for technology
suppliers, a mutually beneficial outcome.
J. Mar. Sci. Eng. 2023, 11, 2172 10 of 27
(a)
(b)
(c)
Figure 4. Representative examples of robotic and autonomous systems developed for offshore
structure inspections. Based on [49]. (a) Drone from Universitat de les Illes Balears (UIB); (b) Drone
from Flyability Sa (FLY); (c) Crawler from Ge Inspection Robotics (GEIR).
Figure 5. Scout 137: A highlight on the autonomous drone-Based surveys within the ADRASSO
Project context. Based on [51].
J. Mar. Sci. Eng. 2023, 11, 2172 11 of 27
With technology similar to the REDHUS development, we can highlight the ELIOS 3
drone (Figure 6), which has recently performed an inspection in FPSO tanks and ballast
tanks for offshore companies and shipyards.
Figure 6. Elios 3: a versatile indoor drone to perform regular inspections remotely. Based on [52].
In conclusion, the use of drones in the maritime sector has proven to be highly benefi-
cial. Advances in drone technology have enabled efficient inspections and surveys of ships
and offshore structures. Drones offer advantages such as accessibility, easy operation, good
camera control, and operation in confined areas for multi-rotor drones. Several successful
demonstrations have already been conducted using autonomous drone technology in the
maritime sector.
• Work class: Designed specifically for construction work, the work class ROV is capable
of operating at depths that reach a maximum of around 3000 m. With robust lift
capabilities and ample payload capacity, work class ROVs enable efficient execution of
various underwater tasks. These vehicles use power systems with a capacity greater
than 75 kW.
• Heavy work class: At the top end is the heavy work class category, comprising highly
specialised vehicles that can operate at depths up to 5000 m. With ultra-high payload
capacities, these ROVs are capable of performing complex tasks such as deep-sea
exploration, underwater construction, and oil rig maintenance. These heavy work
class ROVs require powerful power systems, often exceeding 110 kW, to handle
demanding tasks in challenging deep-water environments.
Inspection techniques used in the evaluation of offshore installations, such as pipelines
and risers, consist mainly of the use of specialised tools to assess the structural integrity of
these entities and identify any potential damage. A commonly used method involves visual
inspections that aim to detect signs of degradation, corrosion, or surface irregularities [54].
The evaluation of pipeline integrity often involves the implementation of various non-
destructive testing techniques (NDT) [49]. These strategies employ a range of NDT modali-
ties, including ultrasonic testing (UT) [55,56], magnetic particle inspection (MPI) [57,58],
magnetic flux leakage (MFL) [59–61], eddy-current testing [62], guided wave pipeline in-
spection (GWPI) [63,64], and cathodic protection measurement (CP) [65,66]. Each technique
offers unique advantages in its ability to inspect pipelines without causing damage or
disruption. Ultrasonic testing uses high-frequency sound waves to detect defects or faults
within the material composition of the pipeline. This method is particularly effective for
identifying internal corrosion, cracks, and other forms of structural damage. Similarly,
magnetic particle inspection involves magnetising the tested area before introducing iron
particles, creating visual indications when they accumulate around areas with surface
breaking defects, such as cracks. Magnetic flux leakage operates by inducing a strong
external magnetic field onto the pipe’s surface and then identifies variations caused by
localised wall loss due to corrosion or cracking using sensors designed specifically for
this purpose. Eddy-current testing relies on electromagnetic induction principles where
electric currents are induced into conductive materials like pipes, generating opposing
fields that respond differently depending upon their condition; deviations from normal
patterns indicate potential problems requiring further examination, sometimes leading to
the identification of small pits creeping under coatings as well as the presence of cracks
or corrosion.
It should be emphasised that while there has been considerable development in
autonomous nondestructive testing technologies for external inspection, a substantial
amount of robotics research in the oil and gas industry has focussed on internally inspecting
pipelines (ILI). Special attention has been paid to the advancement of tools used for in-line
inspection [67,68]. However, it is important to note that ILI technology is only suitable for
rigid pipelines and cannot be applied effectively to flexible pipelines.
Several companies have devised their own array of subaqueous vehicles equipped
with inspection capabilities. These vehicles are designed to operate in underwater environ-
ments and can navigate the pipeline to perform thorough inspections.
Saab Seaeye has designed a variety of remotely operated vehicles specifically for the
purpose of inspecting and maintaining submerged oil and gas facilities. A notable ROV
from their collection is the Tiger ROV, similar to Figure 7c. This particular model has been
optimised to operate effectively at depths up to 1000 m [69]. Equipped with advanced
features such as cameras, manipulators, sonars, and CP probes, the Tiger ROV enables
seamless execution of tasks related to observation, inspection work search operations, and
survey assignments [70].
Similarly, Soil Machine Dynamics (SMD Ltd.) of Newcastle, UK, has developed
Holland I (Figure 7a), an ROV capable of performing operations at depths up to 3000 m [71].
This state-of-the-art ROV can accommodate a wide range of equipment and sensors through
J. Mar. Sci. Eng. 2023, 11, 2172 13 of 27
its I/O ports. The Holland I robot is equipped with instruments to measure conductivity,
temperature, and depth, as well as advanced multibeam sonar systems. Additionally, it
features a high-definition underwater camera that records excellent-quality footage for
various purposes. Moreover, this versatile ROV can be enhanced with two manipulators
that enable it to perform various tasks.
Another product offered by Fugro Subsea Services Ltd., Leidschendam, Netherlands,
is the work class ROV FCV 2000D, designed to provide real-time visual monitoring of
subsea work environments at depths up to 2000 m. On top of that, it is capable of carrying
out quantitative measurements for cathodic protection surveys and acoustic inspections.
One notable application of this ROV is its ability to inspect pipeline structures with a daily
coverage distance of up to 25 km, as well as being used to remove marine growth [72].
(a) (b)
(c)
Figure 7. Four models of ROVs used for offshore structure inspection. Based on [71,73]. (a) Holland I
ROV; (b) VideoRay Pro 4; (c) Work class ROV.
exercised. It is crucial to follow best safety practices during any modifications and ensure
that rigorous testing and validation procedures are undertaken. In this case, reliability
analysis using fault tree may be used, as suggested by [74].
In Figure 8, ROVs can be equipped with magnetic crawlers or robotised inspection
tools. These crawlers have the ability to traverse on wheels that magnetically adhere
to steel structures or plates, allowing inspections of horizontal and vertical surfaces in
an aquatic environment. Typically, these units are remotely controlled from either a top-
side location or a ship through a tether connection. The versatility of these crawlers is
enhanced by their ability to be fitted with various operational attachments, such as pressure
washers, to remove debris, remove rust, and prevent fouling. Additionally, they can
incorporate nondestructive testing equipment and cameras for comprehensive inspection
purposes. In cases where tubular members need to be evaluated, special tools designed to
encircle them while crawling along or around them provide a viable solution (Oceantech,
Oceaneering) [75].
(a) (b)
Figure 8. ROV installation of robotised inspection tool. Based on [76]. (a) ROV; (b) Robotized
inspection tool.
It should be recognised that the selection of ROVs discussed in this section (ROV
Tiger, Holland I, Fugro FCV, and VideoRay Pro 4) is not exhaustive. Other ROVs utilised in
previous studies and industry applications are not explicitly mentioned here.
In conclusion, remotely operated vehicles have proven to be highly valuable tools in
the offshore industry. One of the main advantages of ROVs is their ability to access harsh
environments that are difficult for humans to reach. Their versatility allows them to observe
and detect defects in subsea pipelines using acoustic or optical imaging techniques. They
can also be equipped with magnetic crawlers or robotised inspection tools to effectively
inspect and evaluate underwater structures.
seafloor imaging and broad-area surveying of oceanic features [82]. These vehicles are
equipped with suitable acoustic and imaging systems that enable them to gather data for
detailed inspections [18].
The use of AUVs for inspection purposes has gained significant attention in the petroleum
industry. Previously, human divers were used for dangerous and capital-intensive opera-
tions, but now AUVs equipped with advanced sensory devices are being used, as discussed
in [83,84]. These vehicles are capable of performing close visual inspections on subsea struc-
tures within oil and gas fields [85]. They are also used for the inspection of risers to identify
defects and ensure the structural integrity of offshore structures [81].
The inspection of offshore structures using AUVs requires advanced control systems.
Efforts have been made to develop distributed networked communication systems to
meet the control requirements of precision rotary scanners for inspection purposes [81].
Additionally, the use of fieldbus technology has been proposed to enhance actuator control
for automated inspection of offshore structures [81].
In terms of navigation, AUVs are capable of autonomously mapping and planning
collision-free paths in unknown environments [80]. They can navigate in close proximity to
underwater structures and the seafloor, allowing for imaging and inspection of different
structures such as underwater boulders [80]. A unified task priority approach has been
proposed for AUVs, which integrates various behaviors such as path following, terrain fol-
lowing, obstacle avoidance, homing, and docking manoeuvres [85]. This approach enables
AUVs to perform a wide range of missions without the need of humans interventions [85].
The design and instrumentation of AUVs play a crucial role in their effectiveness for
offshore structure inspection. The structure of an AUV, typically composed of a cylindrical
shell, needs to be analyzed for buckling resistance under high hydrostatic pressures [78].
Sliding stiffeners have been proposed as an alternative to welded stiffeners to increase buck-
ling resistance while maintaining the inner space for equipment [78]. The use of vectored
thrusters based on parallel manipulators has been investigated to improve the control and
manoeuvrability of AUVs [86]. Additionally, the development of wireless low-frequency
vibration inspection systems has been explored for offshore platform structures [87].
Continuous improvement in battery capacity and significant progress in hydrogen
fuel cell technology have significantly extended the operational capabilities of AUVs.
Consequently, AUVs can now carry out tasks that were previously carried out exclusively
by manned vehicles or remotely operated tethered vehicles [88]. With their enhanced
endurance and autonomy, AUV technology has become a key focus area for conducting
efficient and effective inspections of underwater structures.
The use of autonomous underwater vehicles for subsea inspection also eliminates the
need for large and costly support vessels, as AUVs can be launched directly from shore or
from smaller, more agile vessels.
Regardless of these advantages, AUV usage in offshore inspections also has limitations
and challenges. These lie in the areas of battery life, control in strong water currents [89],
avoidance of obstacles [17], and the high cost of advanced models. Furthermore, the oppor-
tunity for remote intervention is minimal compared to tethered systems, increasing the risk
of lost AUVs.
Despite these challenges, with technological advancement, AUVs are becoming more
efficient and reliable. Ongoing research and development focus on improving operational
range and duration, as well as the AUV’s ability to conduct more complex and diversi-
fied tasks.
Some industrial solutions are already available. For example, the REMUS 6000 devel-
oped through cooperation between the Naval Oceanographic Office, the Office of Naval
Research, and the Woods Hole Oceanographic Institution (WHOI) (Figure 9b) has been
used for extensive underwater searches and ocean floor mapping [90]. This AUV can
complete missions lasting up to 36 h at a cruising speed of 1.8 m/s. Its primary sensor is
the Kraken SAS aperture sonar. The vehicle design caters to longer missions and carries
advanced sensors, including new sonar systems and high-resolution stereo cameras. These
J. Mar. Sci. Eng. 2023, 11, 2172 16 of 27
data can be used to redirect the vehicle using AI algorithms. With its modular architecture,
the vehicle facilitates customisation of payload configuration.
Konsberg company with HUGIN family product and Eelume Underwater Intervention
Vehicle are probably the leading edge of this kind of technology today; see Figure 9a.
The HUGIN AUV solution, depending on the model, may be equipped with a flexible
set of navigation methods, including GPS surface fix, DGPS-USBL, Underwater Transpon-
der Positioning (UTP), and bathymetric terrain navigation [91]. One of the key features
of the AUV is its integrated inertial navigation system (INS) assisted by a Doppler Veloc-
ity Log (DVL). This system provides high-accuracy position updates and helps maintain
the AUV’s position during autonomous operations. These techniques allow for accurate
positioning and navigation in different underwater environments.
In subsea inspection, the AUV is used for high-resolution large-area seabed sur-
veys [92]. Its ability to glide just a few metres above the ocean floor allows the creation of
high-quality images of the seabed and subsurface.
To ensure the mission implementation of the AUV, fault localisation and detection are
crucial. Faults that occur in the propulsion and attitude control systems of the AUV can
be analysed and located using selective features of the defined fault parameters [93]. This
allows prompt detection and localisation of faults, ensuring reliable control strategies and
inputs for the AUV.
Therefore, given its potential to transform offshore inspections, investing in the devel-
opment of AUV technology promises substantial benefits.
(a) (b)
Figure 9. Autonomous underwater vehicle (AUV). Based on [94–96]. (a) AUV: HUGING ENDURANCE;
(b) AUV: REMUS 6000.
applications, such as search and rescue operations [100], seismic surveys [101], structural
health monitoring [87,102], and asset management of offshore facilities [103].
The development of ASVs has been driven by a growing need for efficient data collec-
tion methods and enhanced capabilities in these domains. As such, research centres from
different sectors have come forward to contribute their expertise towards creating intelligent
marine systems that can automate tasks previously performed by human operators.
In recent times, there has been an increase in the availability of commercial options
designed specifically for underwater exploration. In particular, products such as the Z-Boat
1800 RP, Teledyne Marine, Houston, Texas, United States, (Figure 10a) and the seafloor
system HydroCat-180 have gained prominence in this regard. These solutions are primarily
classified as remotely operated or fully autonomous vehicles that meet diverse requirements
within the underwater environment.
Presently, most commercially available systems tend to focus on acquiring perception
data from a singular domain, with greater emphasis placed on conducting detailed surveys
beneath the water’s surface. Ref. [104] proposes a solution that uses cameras for monitoring
and surveillance of inshore scenarios such as harbours, and [105] proposes an ASV which
allows the acquisition of 2D data from the surface using a two-dimensional laser scanner,
mainly used for localising the ASV in GPS-denied scenarios. In recent times, certain so-
lutions have emerged which facilitate the collection of data from both underwater and
surface domains. Two notable studies have employed 3D point clouds derived from LiDAR
technology to study the surface domain, while also utilising multibeam echosounders for
gathering information about the underwater environment [106,107]. Similarly, ref. [21] pro-
poses an unmanned surface inspection and maintenance vehicle, the SENSE (autonomouS
vEssel for multi-domaiN inSpection and maintEnance), which provides the versatility to
adapt to the most suitable payload to observe above and below the sealevel environment
according to the task requirements.
(a) (b)
(c)
Figure 10. Models of ASVs used in coastal surveys and port and harbor security. Based on [72,108,109].
(a) ASV Z-Boat 1800RP; (b) ASV W TUPAN 1 boat; (c) ASV FUGRO ORCA.
J. Mar. Sci. Eng. 2023, 11, 2172 18 of 27
Finally, we can mention the TIDEWISE company that developed the ASV TUPAN
(Figure 10b), which is specifically designed for environmental monitoring and surveying.
The TUPAN ASV may be equipped with a range of sensors, including LiDAR, multibeam
echo sounders, or even a micro-ROV, which allows for accurate and comprehensive data
collection. The FUGRO company with FUGRO ORCA (Figure 10c) today has similar
capabilities.
In conclusion, the use of autonomous surface vessels (ASVs) for offshore platform
inspection and monitoring offers significant potential for improving efficiency, safety,
and cost-effectiveness in the maritime and offshore industries. These vehicles can per-
form a wide range of tasks, including monitoring, surveying, and inspection of offshore
infrastructures.
Table 3. Summary of offshore production unit inspection, including information about zone, elements, risks, challenges, and methods.
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