The firing line comprises the fixed pipelay ramp, enclosed in the central housing, running along the longitudinal centreline of the vessel. It is connected to an internal and external ramp, both of which have adjustable inclination to facilitate pipelay in varying water depths. A ramp extension unit is available for use in deep water or for severe seabed conditions. Located along the fixed and internal ramps are three 110 tonne tensioners, nine work stations (Welding, X-ray and Field Joint Coating) and a number of support rollers.
Double Joint Lines
The pipe double-jointing system with six work stations is located in the deckhouse above the fixed ramp while the transfer and line-up station is enclosed within the superstructure at the stern.
The vessel has a twelve point mooring system to facilitate accurate positioning and movement during operations with a fully redundant control and monitoring system. It also has four Azimuthal variable pitch thruster units which can be utilised for propulsion or to further enhance position keeping if required.
A fully mechanised GMAW system known as "PASSO" is utilised for medium to large diameter pipe in the firing line whilst double joint line welding is accomplished using submerged arc equipment.
An aluminium helideck structure is located at the stern of the vessel. The helideck is designed to accommodate single main rotor helicopters up to and including the Sikorsky S61N type and is approved for use by the UK, Norwegian, Danish, German and Netherlands Civil Aviation Authorities.
Offices and stores are located on either side of the central housing at main deck level. A separate superstructure mounted at the bow of the vessel encloses the bridge, offices, computer room and radio room.
Source for the images and text, is owned by Nord Stream AG and Saipem
Pipe laying Methods
The most common installation methods are the S-Lay, J-Lay, and Reel-Lay methods.
In the S-Lay method, as the laying barge moves forward, the pipe is eased off the stern, curving downward through the water until it reaches the touchdown point. After touchdown, as more pipe is played out, it assumes the "S" shaped curve. To reduce bending stress in the pipe, a stinger is used to support the pipe as it leaves the barge. To avoid buckling of the pipe, a tensioner must be used to provide appropriate tensile load to the pipeline (Clauss,1998). This method is used for pipeline installations in a range of water depths from shallow to deep.
van Oord's Stingray uses the S-Lay method
In the J-lay method, the pipe is dropped down almost vertically until it reaches touchdown; after that it assumes the "J" shaped curve. J-Lay barges have a tall tower on the stern to weld and slip prewelded pipe sections. With the simpler pipeline shape, the J-Lay method avoids some of the difficulties of S-Laying such as tensile load forward thrust, and can be used in deeper waters.
Saipem's 7000 barge uses the J-Lay method
In the Reel-Lay method, the pipeline is installed from a huge reel mounted on an offshore vessel. Pipelines are assembled at an onshore spool-base facility and spooled onto a reel which is mounted on the deck of a pipelay barge. Horizontal reels lay pipe with an S-Lay configuration. Vertical reels most commonly do J-Lay, but can also S-Lay.
McDermott's North Ocean 105 uses the Reel-Lay method
Nord Stream Pipeline - Introduction
Nord Stream Pipeline - Preparation for pipe laying
Nord Stream Pipeline - Manufacturing of Large Steel Components
Nord Stream Pipeline - Logistics by the Numbers
Nord Stream Pipeline - Pipe Laying Vessel - Saipem's Castoro Sei
Nord Stream Pipeline - Pipe Laying Vessel - Saipem's Castoro Dieci
Nord Stream Pipeline - Pipe Laying Vessel - Allseas Solitaire
Nord Stream Pipeline - Pipelaying Processes
Nord Stream Pipeline - Tie-Ins and Hyperbaric welding
Nord Stream Pipeline - Pre-Commissioning and Pressure Testing