Pipe Laying

Pipe carrier vessels will constantly supply the pipelay vessel. On board, the pipes will be welded into one continuous string and lowered onto the seabed. Once completed the pipeline will be thoroughly tested to confirm its mechanical integrity.

Reliable and Efficient Offshore Pipe Laying

The construction cycle on each pipelay vessel comprises several steps from loading the pipes onto the pipelay vessel to lowering the pipeline onto the seabed. There are exact procedures defined for each process to ensure consistent quality and compliance with health and safety regulations. On the Castoro 6 pipelay vessel, the process on board includes the following steps:

Single pipe joint supply: Pipes are unloaded from pipe supply vessels onto storage areas on each side of the pipelay barge. During the loading of pipes on to the pipelay vessel they are inspected for damage.
Single pipe joint storage on deck: Pipes will be stored on deck.
Activities in the Double-Joint Plant: Two 12-metre pipe joints are automatically welded together into a “double joint” of 24 metres length. All double joint welds are subjected to non-destructive testing. i.e automated ultrasonic testing (AUT).
Activities on the Main Line (firing line): The double joint is welded to the end of the pipeline. Every millimetre of each weld area is again examined by automated ultrasonic testing (AUT) in order to detect and assess all defects.
Pipelay barge move-up: The pipelay barge moves by hauling in on the stern anchor cables and paying out the bow anchor cables.
Pipeline advance to seabed: The completed pipeline runs down the stinger into the suspended span and will subsequently come to rest on the seabed.
Monitoring correct position: Periodically, touch down monitoring by remotely-operated vehicles will be conducted to monitor and confirm the pipeline’s position – in particular at cable crossing locations or near wrecks.

Using the method described above, approximately 2.5 kilometres of pipeline can be laid per day. For most of the offshore route, the pipeline will rest on the seabed. In some areas, for example near the landfalls, the pipeline will be laid in a pre-dredged trench which will be backfilled with the excavated material in order to assure sufficient on-bottom stability and protection. Similarly the pipeline maybe buried in areas with frequent shipping traffic in order to protect it from the risk of ship anchor impacts.