Offshore O-lay pipe laying
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Abstract
The pipe laying technique described here is very different from the common technique used at present.
The operational production costs can be reduced compared to the existing general methods of pipe laying and the pipe laying operations can be faster than other methods used today. Experts say that pipe laying as fast as 15 to 25 km per day is obtainable with this method. The main reason for this high speed has to do with the bottleneck of welding and testing which is not a procedure that is part of the laying itself anymore.
The main difference between the new, state of the art, “O”-lay system and the existing systems is that the total length of the pipe is welded and tested onshore on an site that is near the waterfront and that the pipeline will be transported as a whole, in a huge floating spiral to the location where it will be laid.
Depending on the local situation, series of “pipe pieces” with a length of 50 to 1000 meter are produced and temporarily stored in the pipe yard.
The “pipe pieces” are welded together in the final pipe line string and then transported into the water. They will be kept afloat with the help of floatation devices. A spiral will be formed with the floating pipe with a diameter that is sufficiently large to prevent the pipe from deforming in its plastic area. Normally the diameter of the floating circle is 500 times the pipe diameter (Example: A pipe with OD 20 inch will form a spiral of 250 meter diameter). The spiraled pipe can form a total length of more than 100 km pipeline.
When the pipe spiral has reached its predetermined length, the whole spiral can be transported (towed by tugboats) to the place where the laying has to be done.
When the spiral has arrived at the location where the pipe will be lowered, the spiral shall be unwound and with the help of a special prepared vessel it will be lowered to the seabed. This method of pipe laying is especially interesting for water depths where S-lay methods are used.
Several tests in laboratory and under real conditions have shown that the method described is feasible for pipelines of all diameters.
The operational production costs can be reduced compared to the existing general methods of pipe laying and the pipe laying operations can be faster than other methods used today. Experts say that pipe laying as fast as 15 to 25 km per day is obtainable with this method. The main reason for this high speed has to do with the bottleneck of welding and testing which is not a procedure that is part of the laying itself anymore.
The main difference between the new, state of the art, “O”-lay system and the existing systems is that the total length of the pipe is welded and tested onshore on an site that is near the waterfront and that the pipeline will be transported as a whole, in a huge floating spiral to the location where it will be laid.
Depending on the local situation, series of “pipe pieces” with a length of 50 to 1000 meter are produced and temporarily stored in the pipe yard.
The “pipe pieces” are welded together in the final pipe line string and then transported into the water. They will be kept afloat with the help of floatation devices. A spiral will be formed with the floating pipe with a diameter that is sufficiently large to prevent the pipe from deforming in its plastic area. Normally the diameter of the floating circle is 500 times the pipe diameter (Example: A pipe with OD 20 inch will form a spiral of 250 meter diameter). The spiraled pipe can form a total length of more than 100 km pipeline.
When the pipe spiral has reached its predetermined length, the whole spiral can be transported (towed by tugboats) to the place where the laying has to be done.
When the spiral has arrived at the location where the pipe will be lowered, the spiral shall be unwound and with the help of a special prepared vessel it will be lowered to the seabed. This method of pipe laying is especially interesting for water depths where S-lay methods are used.
Several tests in laboratory and under real conditions have shown that the method described is feasible for pipelines of all diameters.
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