Large resources of oil and gas are located offshore. Pipelines are often used to develop these offshore fields, used for both gathering lines in between subsea wells and as transportation to the mainland for commercial processing.

Offshore pipeline projects involve a different set of challenges to their onshore counterparts as discoveries are often made in remote locations, in deep water with hostile conditions. Some planned pipelines traverse unexplored waters, requiring extensive seabed surveys to determine appropriate route and design.

Construction of offshore pipelines is also considerably different to onshore, with pipe welded on a moving pipelay vessel before being lowered to the seabed. The most common methods for completing this are the ‘S-lay’ and ‘J-lay’ techniques.

The ‘S-lay’ method involves welding the pipe horizontally and lowering it into the sea supported by a curved pontoon structure known as a stinger, which forms an elongated ‘S’. It can be used for both shallow water and deepwater pipelines up to a depth of 3,000 m.

The ‘J-lay’ method involves vertical pipe welding and pipe lowering without the use of a support structure, forming a ‘J’ shape. This system is used to lay pipelines at depths between 400 and 3,500 m.