Case Studies

J-Tube Inspection & Messenger Line Installation

Project Overview

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 & Gauging

AISUS designed and fabricated a crawler driven inspection system, with gauge plates and subsea camera, which could capture visual inspection data and complete gauging of the J-Tube internal diameter, including around the J-Tube bend. Once the system was designed and manufactured, AISUS performed successful trials at its in-house testing facility.

The inspection system was deployed into the J-Tube with the existing messenger line in position. Visual inspection data confirmed that the messenger line had corroded, and would not be usable for the umbilical pull in operations. Silt and debris were also identified around the bend of the J-Tube, leading to the subsea termination. The silt and debris prevented the gauge plating from being completed over the full length of the J-Tube.

Cleaning and Messenger Line Retrieval

Following the gauging and visual inspection, AISUS removed the existing messenger line and mobilised internal high pressure cleaning systems in order to remove sand, silt and loose surface corrosion to ensure the completion of the gauge plate and visual inspection.

After the successful cleaning, the gauge plate and visual inspection were completed from the J-Tube entry point to its termination.

J-Tube Messenger Line Installation

Followed by the success of the inspection, the client tasked AISUS with installing a new messenger line by driving it with the crawler system to the termination. AISUS reconfigured the crawler tool to include a customised breakaway messenger line anchoring system, designed to secure the messenger line within the subsea bell mouth. The messenger line was installed successfully within the bell mouth, with the crawler system being recovered using a pneumatically driven air winch.


The job received extremely positive feedback from the client, as AISUS not only delivered an efficient and safe inspection, but were also able to design a crawler inspection system for the scope, remove the existing cable and complete the installation of a new messenger line, delivering more than the client had originally requested.

AISUS have the capability to design and implement bespoke solutions tailored to challenging projects.


  1. Previous Unblocking, Debris Retrieval And Coating Removal Project in the North Sea
  2. Next Successful J-Tube inspection campaign in the Mediterranean Sea

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