Introduction
Subsea inspection is essential for ensuring the integrity and safety of offshore assets. Welds, pipelines, and subsea structures must be assessed with precision, often in difficult environments where access is limited and downtime is costly. The industry continually seeks methods that provide reliable data while reducing inspection time and operational risk.
Ensuring the integrity of subsea welds has always been one of the offshore industry’s biggest challenges. Harsh conditions, limited access, and the high cost of intervention mean that operators need inspection techniques they can trust. Over the years, ultrasonic methods such as Phased Array Ultrasonic Testing (PAUT) and Time of Flight Diffraction (TOFD) have become widely recognised for their ability to deliver accurate weld assessments in onshore and topside applications.
Sonomatic were the pioneers of commercial TOFD in the 1980s and consider themselves leaders in this field. TOFD has been a cornerstone of our work both topside and subsea, with successful subsea deployments carried out for decades. In parallel, we have also been successfully applying PAUT to advanced geometry inspections for several years, proving its effectiveness in complex scenarios.
By combining our proven track record in subsea-deployed TOFD and advanced PAUT techniques, we are able to deliver a fully comprehensive system that can be deployed in the harshest of environments. This integration ensures operators benefit from the strengths of both methods, providing high-quality data to support critical integrity decisions.
Recent Validations
Sonomatic has recently completed a successful validation of diver-deployed Phased Array Ultrasonic Testing (PAUT) and Time of Flight Diffraction (TOFD) systems for a client in the Middle East. The validation was completed on a sample with a variety of weld flaws of different sizes and depths and demonstrated how advanced ultrasonic methods, applied with the right equipment and expertise, can set a new standard for subsea integrity management.
This validation builds on Sonomatic’s track record of more than 35 years of successful subsea inspections worldwide, reflecting a consistent focus on innovation and client assurance.
This particular validation was focused on weld inspection using Sonomatic’s Nautilus scanner. The Nautilus is deployed by a diver and can be used to conduct dual-sided scanning, where two probes operate simultaneously from opposite sides of the weld.
This method delivers several advantages:
- Maximum accuracy - Flaws are examined from both sides, reducing uncertainty.
- Faster inspections - Both sides are scanned at the same time, reducing overall duration.
- Repeatable and reliable data - Probe positioning and movement are controlled, producing consistent results.
The results were clear. All test flaws were detected, critically sized, and reported. The validation confirmed that the system can provide the level of precision required for critical subsea integrity assessments.
Why Dual-Sided Scanning Matters
By deploying probes on both sides simultaneously, the Nautilus scanner eliminates the limitations of single-sided approaches. Inspectors receive comprehensive data in one pass, improving both accuracy and efficiency. Scanning from both sides of the weld at the same time also maximises circumferential accuracy and repeatability of inspection data, giving operators greater confidence in integrity assessments. For subsea operations, where diver time is limited and costly, this represents a significant operational improvement.
Phased Array and TOFD
The validation used two complementary ultrasonic techniques:
- Phased Array Ultrasonic Testing (PAUT):
- Allows inspectors to electronically steer ultrasonic beams and create detailed images of weld structures. It is highly effective for detecting and characterizing flaws.
- Time of Flight Diffraction (TOFD):
- Measures the diffraction of ultrasonic waves at flaw tips, providing highly accurate sizing information. It is particularly effective for detecting and sizing cracks.
Used together, PAUT and TOFD provide a reliable system for weld inspection. PAUT offers wide coverage and detailed imaging of weld geometry, while TOFD provides highly accurate defect sizing and is particularly effective for crack detection. By combining both techniques, the benefits are maximised and the limitations of each method are addressed. This combined approach is widely regarded as best practice in topside and onshore inspections, and the successful subsea validation now demonstrates how these benefits can be extended to offshore subsea environments.
PAUT data indicating a toe crack
TOFD data indicating various weld flaws
The Nautilus Scanner – Proven Platform for Subsea Inspection
The Nautilus scanner is a Sonomatic-designed, bespoke, diver-deployed tool that has been in operational use for many years. While it has undergone several upgrades over time, the fundamental design has remained consistent: a solid and stable platform for scanning.
Key features include:
- Fixed scanning platform - Unlike magnetic wheel-based systems that can potentially suffer from wheel slip and skew, the Nautilus provides a stable base that eliminates this issue.
- No diver interaction during scanning - Once positioned, the scanner operates independently, reducing the chance of human error and improving safety.
- Ideal for dual-sided inspections - The fixed platform ensures precise alignment of probes on both sides, which is especially important for PAUT and TOFD applications.
This stability gives Nautilus a significant advantage in achieving highly accurate dual-sided weld inspections. By reducing potential sources of error and variability, the system ensures that inspection data is both reliable and repeatable, even in challenging subsea environments.
The i-CLAW – ROV-Deployed Advanced PAUT and TOFD
In addition to the above, Sonomatic also recently successfully completed a validation and field execution of the subsea i-CLAW PAUT and TOFD system, designed specifically for duplex I-tube weld inspection.
The i-CLAW is deployed via remotely operated vehicle (ROV), providing a robotic solution that was developed for an asset life extension project. Its purpose-built design enables accurate and reliable weld integrity assessments in areas where diver deployment is impractical or higher risk.
With custom PAUT and TOFD capabilities, the i-CLAW delivers unparalleled precision in detecting and sizing weld flaws and cracks in challenging duplex materials. This successful deployment demonstrates the versatility of Sonomatic’s inspection technologies, showing how both diver-deployed and ROV-deployed platforms can be tailored to project requirements while ensuring the same level of accuracy and reliability.
Benefits for Operators
The successful validations of both Nautilus and i-CLAW highlight several benefits for operators managing subsea infrastructure:
- Improved accuracy - Dual-sided scanning and complementary ultrasonic methods provide high confidence in detection and sizing.
- Time efficiency - Faster inspections reduce diver or ROV exposure and project duration.
- Reliable data - Repeatable results enable better-informed integrity decisions.
- Cost effectiveness - Accurate inspection data can reduce unnecessary interventions and extend asset life.
These benefits align with the industry’s need to manage costs while maintaining the highest standards of safety and environmental responsibility.
Full Matrix Capture Capabilities
Sonomatic’s subsea PAUT system can also perform Full Matrix Capture (FMC) with Total Focusing Method (TFM) algorithms. These techniques allow for advanced imaging and improved flaw detection, especially for small or complex defects.
The availability of FMC/TFM provides operators with options for higher-resolution inspection when required. This adds flexibility to subsea campaigns, ensuring the most suitable technique can be applied depending on asset condition and inspection objectives.
Building on 35 Years of Subsea Experience
These achievements are not isolated successes. Sonomatic has been delivering subsea inspections for more than 35 years, working with operators across the globe. Over this period, the company has developed a deep understanding of subsea challenges and built a reputation for providing inspection data that clients can trust.
The current validations are part of a continuous cycle of development, where new technologies are introduced, refined, and proven in real offshore conditions. Experience, combined with innovation, ensures that Sonomatic remains at the forefront of subsea inspection technology.
Team Expertise
Inspection technology is only one part of the solution. Both validations also reflected the capability of Sonomatic’s engineers and offshore inspection personnel.
The combination of advanced equipment and skilled personnel ensures that clients receive inspection results they can rely on. This expertise has been built up over almost 5 decades of work in ultrasonic inspection and integrity management.
Conclusion
The validations of Sonomatic’s diver-deployed PAUT and TOFD systems in the Middle East, together with the ROV-deployed i-CLAW system, reaffirm the company’s long-standing capability in subsea inspection. These systems consistently deliver accurate, efficient, and repeatable weld inspections, providing operators with the reliable data needed to manage asset integrity in demanding subsea environments.
The Nautilus scanner, with its proven track record, bespoke design, and solid fixed platform, continues to provide a clear advantage for dual-sided ultrasonic inspections. Meanwhile, the i-CLAW expands these capabilities into ROV-based applications, delivering the same level of accuracy and reliability for complex materials such as duplex welds.
Because all of Sonomatic’s inspection tools are designed and built in house, the company also has the flexibility to develop new solutions for specific tasks and to adapt existing tools to meet evolving project requirements. Tools such as the Stingray, ROV-iT, Barnacle, MAG-Rover, MAG-Nautilus, MAG-ST, Mini-MAG, Man-Scan, Nautilus and Raptor are just a few of the more commonly deployed systems, each tailored to different inspection challenges. This breadth of capability ensures that operators benefit not only from proven inspection methods, but also from solutions designed for the specific demands of their assets.
These achievements build on more than three decades of subsea inspection experience, reinforcing Sonomatic’s commitment to advancing subsea integrity management and providing operators with solutions that combine proven technology with expert application.
About the Author
Clayton Webb is the Regional Manager for Sonomatic across North Africa, the Middle East, the Caspian, and the Black Sea regions. With over 11 years at Sonomatic, he has progressed from Lead Technician offshore to Project Manager, and now Regional Manager, combining strong technical insight with effective leadership in subsea inspection and integrity management.
Author: Clayton Webb
