The O-lay technology is due to its fast installation and remote construction yard applicable in situations that would normally take a considerable time to construct the pipeline on a laybarge Taking a long time for production entails a large risk for not staying within a short working weather window. O-lay has the advantage to work in a relative small weather window even under these difficult situations.
Some of these situations are explained here.
For transport of corrosive gas (gas with a certain H2S and/or CO2 content) often lined pipe is used. This is a pipeline with an internal liner of a high not corrosive material like stainless steel.The welding comes very accurate and on an onshore location ample time is available to achieve a very high standard that is verifyable.
Pipe in Pipe
Pipe in Pipe (PiP) is a technology that is used in deep water and shallow waters and allows optimal thermal insulation performance for the pipe. Because of the longer installation times offshore it would be an advantage if the welding offshore would not be part of the laying process anymore. O-lay gives the posibillity to reduce the offshore time and prepare the complete PiP pipeline onshore. Then during a very small weather window in which the weather is optimal the pipeline can be transported and installed in a relative small time frame.
When sub-sea pipelines are connected to floating production structures often the pipe is raised as in a catenary shape. A Steel Catenary Riser (SCR) is a prolongation of a rigid subsea pipeline that is connected to a floatinbg structure.
With the O-lay method it is relatively easy to install such a SCR.
To increase the resistance on fatigue, special treatment can be applied in the onshore production yard to improve the weld geometry. Processes like Ultrasonic Impact treatment, Needle Peening and Weld Toe Dressing can increase the resistance against fatigue with more than 300% and will increase the life of the SCR.
Extreme shallow water installation
To install pipeline in extreme shallow water, with a water depth of less than 3 meters, the O-lay method has enormous advantages due to the shallow draft of the floating pipeline.Instead of using a laybarge, special build tractors can be used to install the pipeline. When the water becomes deeper installation can be taken over by a laybarge. In the video it shows how the pipe is installed in shallow water.( video shallow water installation )
Construction under good weather conditions
Because the pipeline can be constructed more than 1000 km away from the installation area it is possinble to choose the area of construction. In some cases an area with a milder climate has advantages above harsh winter conditions, at the installation site. Typical example is the Caspian Sea were the differences between the Northern and the Southers Caspian can differ in winter enormous and while in the north you would have only a few months of unfrozen waters, in the south you will have no froozen waters at all. This gives the advantages to prepare the pipeline in advance in the south and wait for good weather in the north and install it in a very short period of time.