Protection structure removal and J-tube flange separation

Sabratha Platform, Mediterranean Sea


Client: Technip UK

Location: Sabratha Platform, Bahr Essalam Field, Mediterranean Sea

Equipment: Flange removal tool (FRT) ; Protection structure removal tool (PSRT)

Technip had a requirement to install bellmouths onto the subsea ends of J-tubes located on the Sabratha  platform offshore Libya. The J-tubes are positioned within the jacket support caissons in the NE leg of the platform. The J-tubes are around 5m from sea bed in a water depth of approx 185m.

Proserv UK were awarded the ROV tooling scope in mid- August 2016. Two new tool designs were produced and tested and delivered to client within a tight 6 week deadline.


Proserv were approached to design, build and test tools to firstly cut the protection structures separately off the 10” and 16” Jttube caissons, then another tool to separately cut off the bolts on the back of both flanges. The bolts had been tack welded onto the flanges.

Project teams were set up in both Aberdeen and Perth locations and project managed from Aberdeen with regular client contact and updates. The tools were supplied to Technip on a rental only basis and then added to the asset portfolio after completion of the project.

Proserv were tasked to design and build 5 tools in total:

  • 3 x FRT (10”, 16”, spare)
  • 2 x PSRT (10” and 16”)

The FRT and PSRT were designed to be interchangeable between 10” a and 16”, by changing the lower arms, with same motors giving them great flexibility and redundancy.

All functions are controlled by hydraulic rams and motors, directly connected to the ROV. Tool deployed by ROV using 5 function manipulator.


  • FRT to suit flange sizes 10” and 16”
  • PSRT to suit caisson sizes for 10” flange and 16” flange
  • Tools all interchangeable in size and function and can be used as spares for each other, great flexibility
  • Tools can index around pipe or flange
  • Circular cutting blade with choice of friction disk or diamond tipped blade
  • Tools are ROV deployed on 5 function manipulator
  • Operated through 6m umbilicals connected directly to ROV hydraulics
  • FRT cutting blade can be adjusted +/- 12mm axially by ROV to find right cutting spot at back of flange
  • Camera attached to tool to view blade position (client supplied)
  • 4 hydraulic functions on each tool. Interchangeable umbilicals (no hot stabs)
  • Tool umbilicals also have a quick release system that can be installed to release ROV from tool in an emergency


The tools were designed, built and tested in the Perth location based on previous experience with this type of disk cutting tool. A factory acceptance test (FAT) was successfully carried out on mock up J-tube test pieces. The tools were then shipped to Aberdeen to the Birchmoss base where a further client witnessed FAT was carried out on more test pieces, which was carried out successfully followed by client sign off.

This was all completed within a tight 6 week period and delivery was met 1 day early. A technician from Birchmoss was sent to Perth to be involved in building and testing the tools from the start of the project and followed it through to completion of the offshore phase, minimising project risks.

The offshore phase was completed successfully. The PSRT tool performed very well with all 4 protection structures cut off within 24 hours. The bolt cutting phase took longer due to the time taken to land the tool on the flange. However, the FRT performed as expected once landed on the flange and all flange bolts were cut off. The client was very happy with what Proserv achieved as they knew this phase was high risk.


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