5.4 - Pipelay Operations

Many pipelay operations are conducted by DP lay barges.

Sketch 5.6 - Pipelay methods

In a typical S-lay barge, the pipe is constructed in a linear pipe fabrication facility called the "Firing Line" in which a number of stages of welding take place. Each operation is conducted at a "station". Further stations conduct X-ray and NDT testing on the welded joints, anti-corrosion coating, and weight-coating if necessary. At intervals, the DPO initiates a move ahead a distance equivalent to the joint-length. Once the move ahead has been completed, the firing-line operations continue.

It is essential that tension is maintained on the pipeline. At the back end of the firing line, the pipe is held by a number of pipe tensioners, or caterpillar tracks clamping the pipe. The tensioners control the movement of the pipe, maintaining a set tension on the pipe string. The pipe is supported aft of the firing line by the "stinger", which is an open lattice gantry extending beyond the stern of the vessel, sloping downwards. Tension on the pipe is needed to prevent pipe damage from buckling. The set tension is to ensure a smooth catenary to the touchdown point on the seabed. If tension is lost, then damage will occur at the touchdown area.

Pipe tension values are communicated to the DP system which is continually providing thrust commands to maintain tension, position and heading.