This invention relates to a method of laying an underwater pipeline, and to a vessel for carrying out the method.

It is known to lay the pipelines on the seabed from a floating vessel such as a ship or barge. This may be done by loading lengths of pipe on to the vessel proceeding to the lay site, and then welding the pipe sections end to end as the pipeline is laid from the vessel. This procedure has the disadvantage that the welding must be accomplished on the deck of the vessel in frequently adverse conditions, which makes it difficult to ensure that a high quality of weld is always obtained. It also entails carrying out a relatively labour intensive operation afloat and remote from support facilities.

It is also known to lay underwater pipelines by use of a reel ship. This allows most of the welding to be carried out ashore under controlled conditions and may allow the laying operation to be carried out more quickly. However, reel ships are extremely expensive to build and operate and the action of reeling and down

unreeling the pipe may be detrimental to the quality of the pipe.

According to one aspect of the present invention, a method of laying an underwater pipeline comprises providing a plurality of pipe sections each having a mechanical connector at either end, loading the pipe sections on a floating vessel, and traversing the vessel along a desired line of lay while laying the pipeline overboard from the vessel, pipe sections being coupled into the pipeline one by one as it is laid by interlocking the mechanical connectors thereon on board the vessel.

The pipe sections preferably have the connectors secured to their ends, for example by welding, before being loaded aboard the vessel; but the invention encompasses carrying out this step aboard the vessel.

Preferably the pipeline is laid under tension applied by the vessel to establish a launch angle, and each section is elevated into the launch angle before being connected.

Preferably, the mechanical connectors are snap connectors, for example those supplied by Hunting Oilfield Services under the trade mark Hunting Merlin S. By "snap connectors" is meant connectors which can be mated to form a fluid-tight joint without relative rotation of the pipe sections and without the use of separate applied fasteners such as nuts and bolts.

From another aspect, the invention provides a vessel for laying an underwater pipeline, the vessel having pipe storage means for storing a plurality of pipe sections, means for launching a pipeline from the

vessel, and means adjacent the launching means for interconnecting mechanical connectors previously secured to the ends of the pipe sections.

The launching means preferably comprises a pipeline tensioner for applying tension to the pipeline and thereby establishing a launch angle.

Preferably, the vessel is provided with pipe elevating means for raising each succeeding pipe section into alignment with the launch angle. The pipe elevating means may comprise an elongated pipe support mounted on a pair of elevator towers. The pipe support may suitably be provided with driven rollers for moving the pipe section along its length.

Most preferably, the vessel has a deck area having a storage rack for carrying pipe sections side by side, and the pipe support is movable between a lower position adjacent one side of the storage rack and an upper position aligned with the launch angle.

An embodiment of the invention will now be described, by way of example, with reference to the drawings, in which:

Fig. 1 is a side elevation of a ship used in one example of the invention;

Fig. 2 is a plan view of the ship shown in Fig. 1;

Fig. 3 is a longitudinal section in a radial plane of a snap connector;

Figs. 4, 5 and 6 are successive stages in the mating of a snap connector;

and

Figs. 7, 8 and 9 are successive stages in the de-mating of a snap connector.

A ship 10 has a deck area 12 which is provided with storage racks 14 for storing and handling lengths of pipe or spools 16.

The spools 16 are typically 20 to 30 metres in length. Each spool 16 is provided at its ends with connectors 18 and 20 as will be described in more detail below.

The deck 12 carries an elevating pipe support 22 by means of elevator towers 24 and 26. The elevator towers 24 and 26 are provided with means such as cable hoists or hydraulic rams for moving the pipe support 22 between an elevated position shown in Fig. 1 and a lower position indicated in broken lines.

In its lower position, the pipe support 22 is adjacent one edge of the storage rack 14 and horizontally aligned with the spools 16. This allows the adjacent spool 16 to be skidded sideways into the pipe support 22.

The pipe support 22 is then elevated to the desired angle and the spool thereon is brought into abutment with the inboard end of the previous pipe section, which now forms the inboard end of a pipeline 28. Suitably, the pipe support 22 is provided with a series of driven rollers (not shown) for moving the spool into such abutment. The connectors 18 and 20 are suitably male and female connectors of the product sold by Hunting Oilfield Services under the designation Hunting Merlin S, although other forms of snap connector may be

used. The Hunting Merlin S connectors are joined by use of a oveable clamp device and applied fluid pressure, and these are provided in a make up station 30.

The inboard end of the pipeline 28 passes through a holding station and tensioners of known kind indicated at 32. The holding station and tensioners 32 apply the required tension to the pipeline 28 while being laid and also the pipeline 28 to be held with respect to the vessel 10 while the connection is made.

The vessel is also provided with a start up winch 34 and an abandonment and recovery winch 36 as is conventional in pipeline vessels.

The pipe spools 16 will typically be formed ashore by welding together three or four lengths of standard pipe sections and welding the connectors 18 and 20 to the outer ends, together with any desired anti-corrosion or insulation treatments. Although described with reference to a self propelled ship, the invention may equally be used on board a barge or any other suitable floating vessel.

The construction and operation of a suitable snap connector will now be described in greater detail with reference to Figs. 3 to 9.

Referring first to Fig. 3, this is a section through one side of a made-up snap connector 100 comprising a box 1 and a pin 2. Facing circumferential surfaces of the box 1 and pin 2 are formed with interengaging formations in the form of circumferential teeth 4. It is to be noted that the teeth 4 are purely circumferential and not helical, ie they can not be

screwed together.

In order to force the toothed portions of the box 1 and the pin 2 mutually apart such that the connector 100 can be disassembled, hydraulic fluid is pumped and high pressure through a port 6 in the skirt (see Fig. 8). This pressurisation radially separates the respective toothed formations 4, and by applying axial forces through circumferential grooves 5 (see Fig. 9) the connector 100 can be pulled apart.

When the connector 100 is in its made-up configuration (Fig. 3), fluid tightness is assured by metal-to-metal seals 3 which are vented during make-up by pressure relief ports 7. If necessary or desirable, seal rings (not shown) can also be incorporated to augment sealing.

Fig. 3 shows only the connector 10 and not the two pipes to which the box 1 and the pin 2 would be respectively connected by circumferential fusion welds (not illustrated) applied around the welding bevels 8.

Fig. 4 shows the connector 100 in its initial stage of being made-up, with the pin 2 stabbed into the box 1 until the respective toothed formations 4 collide (being in an undistorted shape) .

In Fig. 5, hydraulic pressure is applied from an injector 120 through the port 6 to force the toothed skirts radially apart, and at the same time, clamp jaws 140 engage the grooves 5 so that the box 1 and the pin 2 can be pulled together, resulting in the made-up connector configuration shown in Fig. 6.

Making-up of the connector 100 is reversible, de-mating

of the box 1 and pin 2 taking place in a reverse sequence of the Fig. 4-6 operations, and is separately illustrated in Figs. 7, 8 and 9.

Modifications may be made to the foregoing within the scope of the present invention.