subject: Offshore Pipeline Challenges [print this page] Offshore pipeline and its laying process is one of the most challenging feats a steel pipe manufacturer and the steel pipe supplier can face. Not only are the elements the product will face a challenge, but deliver to a site is determined not by the shipping route or carrier, but by the process that is going to be used to lay the pipe. There are three main ways offshore pipeline is laid; tow-in, s-lay or j-lay. All are different and all require a different type of pipe and a different vehicle to deliver them to the site.
Tow in is just as it sounds. The pipe is actually towed to the site by a tug (sometimes two tugs). Even this has variants, because the pipe can be towed on the surface, just below the surface or drug across the bottom (this last one only used in shallow water with soft sea floor). Depending upon the buoyancy modules tied to the pipeline and the depth the installer wants to use, all of these methods can vary the type of pipe you use and the construction of that pipe.
Once the pipe is towed into place, the buoyancy is removed and the pipe is allowed to fill with water and slowly sink to the sea floor. In some cases it then has to be attached to the sea floor to keep it from moving around with currents. Most deep water pipeline is held in place by the simple pressure of the sea.
In the s-lay method of laying the pipe line the pipe is let slide off the back of a barge that has a boom extended underwater to keep the pressure off the pipe. The barge maintains thrust to keep the line taunt while each section is then welded into place and slipped off the end of the barge in a continuous line. The name comes from the s-shape the pipe makes as it's laid in the water. Again, the manufacturer must build the pipe to handle this type of installation and the supplier needs to know the installation particulars to recommend the correct pipe.
The last method is called the j-lay and is very similar to the s-lay method. The main difference is the j-lay uses a tall boom on the top of the boat to hold the pipe in a less stressful position. It forms a J as it is laid in the water. This method puts less stress on the pipe and is preferred over the s-method in deep water for that reason. It is sometimes used in depths of up to 6,500 feet.
The knowledge needed to understand all these variables, the engineering that goes into the design development of the pipe and the ability to deliver them to the site are all important reasons to choose your pipe manufacturer and your steel pipe supplier very carefully. Organizations like the API (American Petroleum Institute) and the ASTM (American Society for Testing and Materials) are great resources to assist you in finding the qualifications you should be looking for.
