Madsen Giersing (MG) was engaged by Canstruct to carry out the detailed design of the pipeline and the installation procedure. The upgrade of the 800mm diameter HDPE subsea outfall involved the replacement of a 3.6km section of the ballasted pipeline servicing Vale’s Goro Nickel Mine.
Key Challenges:
- Water depths up to 60m with some challenging subsea terrain
- Tight lateral tolerance to remain within the existing pipeline corridor
For the purpose of the sinking operation MG designed the temporary works required on the barge. This comprised a guide frame on the side of the barge to provide lateral control of the floating pipe with the ballast blocks. The barge was also equipped with davits able to lift the end of the pipe string and hold it elevated as the connection between two pipe strings was made.
The guide barge was able to sink the pipe in the very limited corridor and work to lateral tolerances not normally required for such installations.
The sinking operation was controlled by introducing water into one end and venting air out the other end. The over pressure in the pipeline was 4.5 bar which was then released as the water was introduced.
Extensive analysis of the strain in the pipeline during the sinking operation was carried out to ensure that the allowable stress in the pipe was not exceeded during installation. This resulted in MG developing a very detailed installation procedure which assisted the contractor.
Installation was completed from the surface in 10 pre-assembled segments with minimal dive support using an ROV to guide the precise placement of the pipeline.
Location
New Caledonia
Client
Vale New Caledonia
Contractor
Canstruct International P/L
