Removal of impact damage using cutting tools to recover failed Flexible Riser/J-tube
With a failed flexible riser affecting production, Technip approached UCS to assist in the recovery and damage analysis of this critical component.
Due to impact damage on the J-tube, the riser end fitting could not be lowered down the structure, requiring cutting operations to be performed on both the riser and J-tube simultaneously.
The riser and J-tube were cut at three locations, using both air and saturation divers. A recovery saddle was used to lift the sections. Prior to cutting, the damaged flexible riser was secured by drilling and pinning to limit any movement while cutting was taking place.
As this cutting requirement had never before been executed offshore, it was agreed that a trial test would be carried out along with testing of the recovery clamps.
The trials showed that the 22” Diamond Wire Saw was more than capable of performing this task offshore and a cutting time of 45 minutes was achieved.
Four cuts were performed in various locations on the riser and J-tube. With the DWS set up to be diver-operated, divers only had to operate clamping, motor and feed functions. Once the DWS was deployed and the drive motor engaged, the diver was only required to operate the automatic feed and monitor the cutting operation.
In all, the project scope saw the riser and J-tube cut into three sections and removed, allowing damage-free recovery to the vessel deck for future analysis of its failure condition to be carried out.
The tool performed as expected, with an excellent average cutting time of only 46 minutes.