Overview
AISUS was engaged by a North Sea offshore operator to undertake external cleaning and Pulsed Eddy Current Testing (PECT) inspection of two 6″ OD risers through the splash zone.
The project presented several challenges, including restricted access, the presence of heavy marine growth and 50 mm thick passive fire protection (PFP) coating. To overcome these constraints, AISUS designed and manufactured a bespoke Clamshell inspection tool, creating a new solution specifically for riser inspection that can also be used for other diagonal tubular applications.
Requirement
The scope of work required AISUS to clean both risers from the splash zone down to the first subsea guide and perform a full circumferential inspection to assess their condition.
Heavy marine growth needed to be removed to allow the inspection system to travel along the risers, while the inspection itself had to be completed through the existing 50 mm PFP coating without causing any damage.
Challenges
The risers were located in close proximity to each other and the carrier caisson, leaving very limited clearance for any deployed equipment. This meant that any inspection tool had to remain extremely compact while still providing full cleaning and inspection capability.
In addition, thick marine growth on the subsea sections prevented direct access for inspection. The presence of 50 mm PFP coating also ruled out conventional UT techniques, requiring an alternative inspection method capable of assessing the condition through the coating.
Finally, the solution needed to be lightweight and simple enough to be installed and removed safely by a Rope Access team.
Solution
To meet the project requirements, the AISUS R&D team designed and manufactured a bespoke Clamshell tool specifically for the application.
The tool was engineered to fit the approximately 6″ OD coated risers while maintaining a compact profile that avoided clashes with adjacent assets. It was also designed to allow straightforward installation and removal by the Rope Access team.
Custom-designed dual jetting spray bars were incorporated into the system, providing full 360° cleaning coverage to remove marine growth and enable access to the inspection area. Jetting pressures were carefully controlled to ensure effective cleaning without damaging the existing PFP coating.
The Clamshell was also fitted with a multi-probe PECT system, allowing inspection through the 50 mm coating thickness. This provided a non-intrusive method of assessing the condition of the risers without the need for coating removal.
Results
- The bespoke AISUS Clamshell tool successfully completed both the cleaning and inspection phases of the project. Marine growth was removed from the risers down to the first subsea guide, enabling uninterrupted deployment of the inspection system.
- A full 360° PECT inspection was completed on both risers through the splash zone, providing a comprehensive overview of their condition.
- No areas of concern were identified, and the corrosion rates measured were consistent with corrosion rates observed elsewhere on the client’s subsea pipeline system.
Benefits
The project demonstrated AISUS’ ability to develop specialist inspection technology for complex asset configurations. The successful deployment of the new Clamshell tool not only met the immediate project requirements but established a proven solution for future riser and diagonal tubular inspections.
