There are two major types of pipeline: on-shore, pictured
in Figure 1, and subsea pipelines. Two methods of
installing subsea pipelines are used. One is called the
S-Lay or J-Lay method, in which pipes are girth-welded
on board a ship and then lowered to the seabed. In
contrast, the spooled pipe method has the pipes
girth-welded into one long pipe (a few km in length). It is
wound or spooled onto a bobbin and carried to a ship for
installation under the seabed.