Definition
Pipelay Vessel or Pipe Laying Vessel refers to the vessel used by the offshore oil and gas industry to install subsea all the connecting infrastructures such as pipelines, umbilicals or electrical cables
Comments
These subsea infrastructures may be installed to connect floating units on the surface to the seabed, or from shore to floating unit or from floating unit to shore or even from shore to shore.
All these connections may be done with pipelines or electrical power lines or umbililcals.
These infrastructures are made of steel and other materials having a limited flexibility which may be severely damaged if shocked or folded beyond their elasticity limit.
Their length and diameters increase in respect with the distance and the quantity of fluid or gas or energy and information to be carried out.
In addition the costs of these infrastructure is extremely high and may exceed $1 million per kilometer.
Therefore handling offshore these infrastructures requires dedicated vessels, the pipelay vessels or pipe laying vessels.
There are two types of pipelay vessels, the J-lay vessel and the S-lay vessel.
The J or the S refer to the shape of the pipe from the pipelay vessel to the seabed during the laying operation.
In the J-lay vessel the pipe or the cable is downloaded vertically or with limited angle from the vertical from the vessel to the seabed
The pipe makes only one curve when it is laid down on the seabed.
In the S-lay vessel, the pipe is downloaded horizontally and therefore bending behind the vessel in shaping the form of S when it reaches the seabed.
The S-lay vessel shall be used in shallow water in order to limit the bending forces on the pipe or the cables or umbilicals.
The J-lay vessel will be preferred after a certain water depth as the pipe or cable will have only one bending phase.
In the same project, the both type of vessels may be used, the S-lay vessel when laying the pipe near the shore and the J-lay vessel when getting closer to the floating unit.
