The selection of GRP material for the laying of underwater pipelines offers many advantages connected to the material characteristics; GRP pipe is fully resistant to corrosion. The following methods are used for off-shore GRP pipeline installations:

• Towing method;
• Bottom pulling method;
• Installation by crane barge.

Towing method

The pipeline string is prepared on-shore, then launched at sea by pulling method but at a certain elevation on the seabed, where it is maintained and finally towed to the installation place. Spare buoys are generally used to limit the amount of surface motion transferred to the pipeline.

Bottom pulling method

This method is implemented by assembling on-shore strings of GRP pipe and by pulling them along the designed route axis trough a winch-cable system operated from a terminal located on barge.
The use of this technique implies the availability of an on-shore leveled area, where it is possible to pre-assemble flanked long strings of GRP pipe.
Strings are launched in sequence by transferring each string on the launch line. GRP pipeline is pulled trough a winch-cable system, hooked to a pulling head, connected to the source of the first string. Once a GRP pipe string has been launched, next string is transferred on the towing line and connected to the previous one. Joining operations are implemented on-shore.
This method allows the contemporary launching of more than one parallel pipelines. Pipes may be launched empty, flooded or lightened by means of floats. Pipeline may advance directly on the seabed previously prepared or inside a pre-excavated submarine trench.

Installation by crane barge

This is probably the most used method nowadays, specially for large diameter pipes. The semi-mobile or towed barge has to have suitable dimensions in order to contain all equipment required for stowing and joining pipe lengths. The barge dimensions, in addition to joining and launch operations, affect the progress of the work. Each pipe length is raised by the barge crane and lowered into to sea, where it is laid on the prepared seabed near the already laid pipe length. The connection of pipe lengths is performed by skilled divers by means of hydraulic jacks, which can be applied to collars mounted on the pipe ends.