The purpose of the equipment is to reinforce the subsea annular cavity in a flare stack.
To perform this activity the following equipment is provided per flare stack leg:
- 1-off ROV equipment shelf
- 3-off Flare Stack Clamps complete with ROV docking station, seal and isolation valve
- 1-off ROV operated subsea drill, 1-off ROV grouting probe and topside grout package
The ROV is initially installed with the lightweight equipment shelf on which is located Flare Stack Clamp number-1 and the preinstalled subsea drill connected into the ROV's hydraulic supply.
The ROV latches the clamp onto the pile towards the top of the flare stack and drills a 2” NS hole in the stack. The ROV then undocks leaving the clamp-1 mechanically held in position on the stack.
Towards the base of the flare stack the ROV positions clamps 2, 3 & 4 and also drills three more holes. This completes the subsea drilling operation with four clamps positioned on the flare stack.
At this point the grouting probe replaces the drill. The ROV re-docks onto the base clamp (clamp-4) and grout is injected from the topside into the annular cavity until grout is pumped from the clamp above (clamp-3). The ROV closes the isolation valve on clamp-4 and undocks. The ROV re-docks onto clamp-3 and closes the isolation valve. The ROV again undocks and the system is now left to allow the grout to set.
Once the grout has set and there is now a hardened slug of grout in the annular cavity, the ROV docks onto clamp-2. Grout is again pumped from the topside and the full cavity is filled until grout is evident at clamp-1. The ROV undocks and closes the isolation valve on clamp-3. The ROV redocks onto clamp-1 and closes the isolation valve.
The operation is now complete and once the grout has fully set the clamps can be removed by the ROV.
This equipment has been successfully used to repair three flare stack legs on July 10 off the coast of Egypt. All equipment is commissioned offshore by Subsea Innovation's service engineers prior to installation.
Client benefits provided by solution:
Long term reinforcement of severely corroded flare stacks ROV remote installation.