TABLE OF CONTENTS The installation of pipelines and flowlines and their connection to platforms constitute some of the most challenging offshore operations. The level of engineering sophistication and effort required, as well as the size and cost of the various types of installation vessels used have reached such a level that pipelaying has developed into an engineering discipline of its own accord. The most commonly used installation processes and associated vessels are outlined in this section.
S-lay refers to an installation method in which the pipeline starts in a horizontal position on the vessel and acquires a characteristic S-shape on the way to the seabed, as shown in Figure 2.15 [2.55]. The first role of the vessel is to act as a work platform for assembling the line and for storing incoming pipe lengths. Usually, a linearly-arranged series of stations (firing line) weld 40 to 80 ft (12 24 m) lengths to the free end of the line. The welds are X-rayed and coated and the vessel moves forward, paying the line into the sea. The line leaves at the stern of the vessel via a sloping ramp (see Figure 2.16(b)). At the end of the ramp it comes in contact with a long boom-like curved structure known as a stinger. The stinger is an open-frame structure that supports the line on v-shaped rollers, providing a controlled-shape transition from the horizontal to the inclined suspended section. Older stingers were rigid, whereas modern ones are articulated,...
