Pipelay vessel

From EnergyWiki

A vessel used in offshore field construction work such as installing pipelines: A pipelay vessel is a complete seagoing plant that allows the pipeline to be assembled and laid continuously along the selected route either on top of the ocean floor or in dredged trenches on the seafloor.

Pipelay vessels are used in normal pipelay operations such as S-lay or J-lay, abandonment and recovery operations, sled installation, start-up via stab and hinge, start-up via sheave, as-laid span and steel catenary riser transfer.

Pipelay bury and flexed pipelay vessels are two examples of pipelay vessels. A pipelay bury vessel lays pipelines in a subsea floor trench. The sled, which is attached to the submerged line, moves along the line on the seafloor and uses a high-pressure jetting action to form a trench in which the pipeline will rest. Usually, the pipe is not covered at the time it is laid but is eventually covered by migrating fill material.

A flex pipelay vessel is used to lay rigid pipe. The pipe can be reeled onto the ship at a land-based spooling facility or lifted on the ship as a full reel. Flexibles and umbilicals can also be installed using a flex pipelay vessel.

Early pipelay vessels

Frank Motley of Brown & Root developed a practical machine - likely the first pipelay barge - for burying pipelines by using high pressure jets to dig the sea bottom out from under the submerged pipe, creating a trench into which the pipeline could sag under the guidance of a sled pulled along the pipe by a barge.

The first barges used to lay pipe were small and crude. Typically, several barges were hooked up end to end and equipped with side booms to stalk the pipe. Work proceeded slowly, and laying operation routinely damaged or lost pipe and equipment. In its descent from the barge to the sea floor, the pipestring often buckled due to excess stresses on the pipe and welds. To control bending stresses on the pipe, oil drums were lashed to pipe sections for buoyancy, but this method involved tremendous physical exertion and time.

In the early years, pipelines were "laid more by sheer muscle power than by efficient specially designed equipment". Until the early 1950s, offshore pipeline projects still were restricted to bays, rivers, and marsh areas of the shallow water Gulf.

Early innovations

However, the technology gradually developed as oil and gas operations moved into the deeper waters of the Gulf of Mexico.

In the early 1950s, Brown & Root took the lead in advancing the development of marine pipelining. The need to improve on the 'flotation system' fostered innovation. Frank Motley came up with the idea of attaching a ramp to the side of Brown & Root's vessel Herman B to allow the pipeline to angle more gently down to the ocean floor after 'losing the pipes for many times'. This was further developed to the "stinger" used in today's pipeline operations.

Motley's crew also developed a new assembly line approach that reduces the turnaround time for pipelay operations. The pipe went through four stations on the deck of the barge, where it was continuously prepared, welded, weighted and laid. The barge also was equipped with an eight-point mooring system. The new approach enabled the crew to lay an average of 2,500 feet of pipes a day while working on the Cameron field in water depths ranging from 14 to 30 feet.

Carl Langner advanced technology with the articulated stinger for the S-Lay technique used in deepwater. Sammy Collins (Submarine Pipelines Ltd.) was responsible for the development of controlled flotation pipe laying technology--pulling the pipeline out from shore supported by pontoon barges. Gurtler Hebert developed the fixed reel pipe laying barge in 1961. Dr. Yoram Goren was responsible for the development of the reel ship in 1975 and the Choctaw, the first semi-submersible pipelay barge.