J-Tube Inspection & Messenger Line Installation




AISUS were approached by a client to complete a full visual and gauge plate inspection, within a J-Tube on a fixed platform located in the North Sea. The J-Tube had been open to sea since installation, and the internal condition and integrity was unknown. The J-Tube needed to be inspected to ensure the pull-in of a new control umbilical would be completed without incident. After a successful completion of the initial inspection, the client tasked AISUS with additional work to remove the existing messenger line, clean out silt and debris, and install a new messenger line.

Internal Visual Inspection and Gauging

AISUS designed and fabricated a crawler driven inspection system equipped with gaude plates and a subsea camera to capture visual inspection data and measure the J-Tube’s internal diameter, including around bends. Following successful trials at our in-house testing facility, AISUS deployed the system into the J-Tube with the existing messenger line in place.

The visual inspection revealed that the messenger line had corroded and was unsuitable for umbilical pull-in operations. Additionally, silt and debris were found around the J-Tube bend, leading to the subsea termination. This obstruction prevented the gauge plates from being used along the entire length of the J-Tube.

Cleaning and Messenger Line Retrieval

After gauging and visually inspecting, AISUS proceeded to remove the current messenger line and deployed internal high-pressure cleaning systems to eliminate sand, silt, and loose surface corrosion, ensuring thorough completion of the gauge plate and visual inspection process. Following successful cleaning, the gauge plate and visual inspection were conducted from the J-Tube entry point to its termination.

J-Tube Messenger Line Installation

After a successful inspection, the client assigned AISUS to install a new messenger line using the crawler system to drive it to the termination point. AISUS modified the crawler tool to incorporate a personalized breakaway messenger line anchoring system, ensuring the messenger line’s secure placement within the subsea bell mouth. The installation of the messenger line within the bell mouth was accomplished successfully, and the crawler system was retrieved using a pneumatically driven air winch.



The client provided highly positive feedback for the job, acknowledging AISUS for delivering not just an efficient and safe inspection but also for designing a crawler inspection system tailored to the scope and successfully completing the new messenger line installation, exceeding the client’s initial requirements. AISUS demonstrates the capacity to design and execute customised solutions for complex projects.


  • AISUS delivered the full work scope reducing the client’s need to coordinate with multiple vendors.
  • The project was completed in advance which reduced risk of costly vessel downtime.
  • Custom designed and developed crawler driven inspection system meeting all of the client’s needs.
  • Cost-effective project solution.




Recent Case Studies

Underdeck Inspection: PEC Technique

    Overview AISUS carried out an inspection using the Pulsed Eddy Current (PEC) technique on the underdeck of an offshore platform, inspecting the East and West accommodation module seal plates. The purpose of this inspection was to obtain visual and wall thickness data to identify any anomalies. Visual inspection, ultrasonic testing and PEC Technique […]

Remote Visual Inspection & Fluid Sampling

AISUS were approached by a current client of ours to provide Remote Visual Inspections (RVI) and Fluid Sampling in various carrier caissons.
Stairs in Rig

AISUS completes caisson inspection and cleaning in the North Sea

AISUS was tasked by a client to carry out Remote Ultrasonic Inspection on a maintenance scope of a severed caisson in the Norwegian North Sea.