PIPE ASSEMBLY METHOD AND SYSTEM FOR PRODUCING UNDERWATER PIPELINES, AND UNDERWATER-PIPELINE LAYING VESSEL COMPRISING SUCH A SYSTEM

TECHNICAL FIELD

The present invention relates to a pipe assembly method for producing underwater pipelines. BACKGROUND ART

More specifically, the present invention relates to a method comprising the steps of aligning, along the path of an assembly system supported by a structure, a portion of assembled pipeline, and a given number of pipes to define an in-process pipeline; jogging the structure forward parallel to the path and with respect to the in-process pipeline; and working end portions of the pipes of the in-process pipeline by means of a work unit forming part of the assembly system.

In other words, jogging the structure, and therefore the assembly system, forward with respect to the in-process pipeline jogs the pipeline along the path and with respect to the assembly system.

An underwater pipeline of the above type comprises a number of pipes joined to total lengths of hundreds of kilometers. The pipes are of normally 12-metre standard length, and relatively large diameters ranging between 0.2 and 1.5 metres, and each comprise a steel cylinder; a first coating of polymer material to protect the steel cylinder; and possibly a second coating of Gunite or

cement to weigh down the pipeline. In some applications, the pipes and underwater pipelines do not need and therefore have no second coating.

To weld the steel cylinders together, the end portions of each pipe have no first or second coating. The pipes are joined at on-land installations into multiple-standard-length pipes, as well as on pipeline- laying vessels, on which standard-length or multiple- standard-length pipes are joined to others, in turn already joined to other pipes to form the underwater pipeline, which is laid by the pipeline-laying vessel.

The assembly method comprises a series of assembly jobs performed on the assembly system. Generally speaking, "assembly work" is intended to mean both joining work, such as welding, and auxiliary work, such as non-destructive weld testing and preparation for further joining work.

The pipe assembly method for producing underwater pipelines comprises : welding the steel cylinders, normally in a number of weld passes; non-destructive weld testing; roughing the contiguous welded end portions; applying a protective cover joint; and possibly applying a weighting cover joint.

Once an annular weld is formed between two adjacent steel cylinders, the two end portions joined by the annular weld form an annular connecting portion known as a cutback, which extends astride the annular weld along a portion of the steel cylinders with no first or second

coating. In other words, the cutback is defined by the contiguous end portions of respective pipes and by the annular weld, extends axially between two end portions of the first coating, and must be roughed and covered with the protective cover joint to prevent corrosion.

Applying the protective cover joint to the cutback is known as "field joint coating", and comprises coating the cutback with three coats (in some applications, two coats) to ensure protection and adhesion of the coats to the steel cylinders.

Applying the protective cover joint to the cutback comprises first shot/grit-blasting to roughen the outer surface of the cutback; heating, e.g. induction heating, the cutback to 250 ⁰ C; spraying the cutback with powdered epoxy (FBE - Fusion Bonded Epoxy) resin, which, in contact with the cutback, forms a relatively thin first coat or "primer"; spraying the cutback, on top of the first coat, with a modified copolymer, which acts as adhesive and, in contact with the first coat, forms a relatively thin second coat; applying a third so-called "top coat", which also extends partly over the first coating; and then possibly applying the weighting cover joint.

Welding, non-destructive weld testing, shot/grit- blasting, and application of the protective and weighting cover joints are performed at joining stations set up along the path and forming a so-called "firing line" forming an integral part of the assembly system.

Jogging the in-process pipeline forward with respect to the structure comprises a stop period between two successive forward-feed steps or, using other techniques, slow-feed steps alternating with fast-feed steps; and the assembly work is carried out during the stop periods or slow-feed steps to allow respective work units to be set up at the end portions of the pipes. The assembly system is supported by a structure integral with the pipeline-laying vessel, and which normally extends below deck and defines a tunnel and the path of the in-process pipeline.

The jogging movement of the pipeline-laying vessel and the wave motion make it difficult to position the assembly system work units accurately at the end portions or, rather, the cutbacks.

Moreover, during the stop or slow-feed periods, in which assembly work is carried out on the contiguous end portions, pitching of the vessel may produce relative, normally oscillating, movements between the in-process pipeline and the structure. Such difficult operating conditions have so far prevented adequate automation of the assembly system and work units, with the result that the work carried out on the firing line is still largely labour-intensive . Shot/grit-blasting of the contiguous end portions, in particular, is performed using handguns, and, among other things, produces large amounts of dust requiring the installation of bulky dust-extraction equipment in

the vicinity of the shot/grit-blasting unit. DISCLOSURE QF INVENTION

It is an object of the present invention to provide a method of assembling pipes for producing underwater pipelines, designed to eliminate the drawbacks of the known art, and which, in particular, provides for greater automation of the assembly system, and particularly of the shot/grit-blasting stage.

According to the present invention, there is provided a method of assembling pipes for producing an underwater pipeline, the method comprising the steps of aligning, along the path of an assembly system supported by a structure, an assembled portion of pipeline, and a given number of pipes to define an in-process pipeline; jogging the structure forward parallel to the path and with respect to the in-process pipeline; and working end portions of the pipes by means of a work unit of the assembly system,- the method being characterized by comprising the step of moving the work unit with respect to the structure and/or in-process pipeline by means of a powered assembly for guiding and supporting the work unit, and as a function of control signals.

By means of the present invention, a high degree of automation can be achieved by enabling the work unit to be moved into line with a given point on the in-process pipeline; tracking the in-process pipeline if it is moving; and performing work cycles involving relative movement between the work unit and the in-process

pipeline.

The present invention also relates to a pipe assembly system for producing an underwater pipeline.

According to the present invention, there is provided a system for assembling pipes for producing an underwater pipeline; the system being supported by a structure, in which an assembled portion of pipeline and a given number of pipes are aligned along a path to define an in-process pipeline, and comprising at least one work unit for carrying out work on the end portions of the pipes; the structure being jogged forward parallel to the path and with respect to the in-process pipeline; and the system being characterized by comprising a powered guide and support assembly for guiding and supporting the work unit, and for moving the work unit with respect to the structure and the in- process pipeline as a function of control signals.

The present invention also relates to an underwater-pipeline laying vessel . According to the present invention, there is provided an underwater-pipeline laying vessel which is jogged forward in a given direction; the vessel being characterized by comprising said structure and said pipe assembly system as claimed. BRIEF DESCRIPTION OF THE DRAWINGS

A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which:

Figure 1 shows a side view, with parts removed for clarity, of an underwater-pipeline laying vessel comprising a pipe assembly system for producing an underwater pipeline, in accordance with the present invention;

Figures 2 and 3 show sections, with parts removed for clarity, of pipes at various assembly stages;

Figure 4 shows a larger-scale side view, with parts removed for clarity, of a detail of an underwater pipeline;

Figure 5 shows a side view, with parts removed for clarity, of the assembly system according to the present invention;

Figure 6 shows a plan view, with parts removed for clarity, of the Figure 5 assembly system,-

Figure 7 shows a partly sectioned front view, with parts removed for clarity, of the Figure 5 assembly system in a first operating position;

Figure 8 shows a larger-scale section of a detail in Figure 6;

Figures 9 and 10 show partly sectioned front views, with parts removed for clarity, of the Figure 5 assembly system in different operating positions;

Figure 11 shows a partly sectioned front view, with parts removed for clarity, of the Figure 5 assembly system;

Figure 12 shows a partly sectioned side view, with parts removed for clarity, of a detail of the Figure 11

system;

Figure 13 shows a partly sectioned front view, with parts removed for clarity, of the Figure 5 assembly system; Figure 14 shows a schematic of a control device of the Figure 1 assembly system;

Figure 15 shows a diagram of the operating steps in the method according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION THE PIPELINE-LAYING VESSEL

Number 1 in Figure 1 indicates a pipeline-laying vessel for producing and laying in the sea (SL indicates sea level) an underwater pipeline 2 comprising pipes 3 joined to one another. Vessel 1 comprises a bow, stern, and buoyancy hulls 4; an above-water structure 5; a partly above-water, inner ramp 6; an underwater outer ramp 7; and an assembly system 8 supported by and extending inside structure 5.

An assembled portion of pipeline 2 and a given number of pipes 3 ready to be joined to it are aligned along an axis Al and a path P in assembly system 8.

Assembly system 8 comprises a firing line 9 in turn comprising a number of assembly stations 10 arranged along axis Al and each for performing a given assembly job; a supporting device 11 for supporting pipes 3; and a tensioning device 12 for supporting the in-process pipeline 2.

Assembly stations 10 have respective work units 13,

14, 15, 16 for carrying out respective assembly work on pipes 3, and which comprise a welding unit 13; a nondestructive weld test unit 14; a shot/grit-blasting unit 15; and a coating unit 16. The term "assembly work" includes both actual assembly work on pipes 3 , such as welding and field joint coating, and assembly-related work, such as non-destructive weld testing and shot/grit-blasting .

The distance between consecutive assembly stations 10 equals the unit length - about 12 metres - or a multiple of the unit length of each pipe 3.

IN-PROCESS UNDERWATER PIPELINE

With reference to Figure 2, pipes 3 are aligned along axis Al and welded together to form underwater pipeline 2 (Figure 3).

Each pipe 3 comprises a steel cylinder 17; a first, normally polyethylene or polypropylene, coating 18 contacting and for corrosion-proofing steel cylinder 17; and a second coating 19 of Gunite or concrete to weigh down pipeline 2.

In an alternative embodiment not shown in the drawings, the pipes have no second coating.

Each pipe 3 has two opposite end portions 20 (only one shown in Figures 2 and 3) with no first coating 18 or second coating 19; and first coating 18 has a bevel 21 at each end portion 20.

With reference to Figure 3, pipes 3 are joined by

an annular weld 22 and form a cutback 23, which extends along axis Al, between two successive bevels 21 of first coating 18, and, in addition to the two end portions 20, comprises annular weld 22. In addition to welding steel cylinders 17, the method of assembling pipes 3 also comprises forming the protective cover joint and, more specifically, covering cutback 23 with polymer material to form a substantially seamless protective second coating 18 along the whole of pipeline 2. In the same way, the assembly method comprises forming a weighting cover joint, so the second weighting coating 19 is also substantially seamless along the whole of pipeline 2.

In some applications, the weighting cover joint is optional .

The assembly method comprises shot/grit-blasting the outer surface of cutback 23 to promote adhesion of the polymer material to cutback 23.

With reference to Figure 4, pipeline 2 comprises a relatively bulky item 24 extending about and fixed to a pipe 3. In the Figure 4 example, item 24 is a frame protecting a valve not shown in Figure 4. Alternatively, item 24 may be a branch connection or an on-off valve or an inspection device by which to inspect pipeline 2.

FORWARD JOGGING OF THE PIPELINE-LAYING VESSEL

With reference to Figure 1, vessel 1 jogs forward in a direction D determined by the ideal laying path of

pipeline 2, and, as it does so, produces relative movement between pipeline 2 on one side, and structure 5 on the other.

Vessel 1 jogs forward in basically two ways : a first go-stop mode, i.e. a cyclic succession of forward movements alternating with stops; and a second fast-slow mode comprising a cyclic succession of alternating fast and slow forward movements.

In other words, in go-stop mode, vessel 1 alternates forward movements - equal to the unit length or a multiple of the unit length of pipes 3 to be joined, and using a controlled mooring line traction system (not shown) - with stops also controlled by the mooring line system not shown. The length of the stops substantially depends on how long it takes to perform the longest assembly job.

In fast-slow mode, vessel 1 alternates fast forward movements - substantially equal to the unit length or a multiple of the unit length of pipes 3 to be joined, and using a thruster system (not shown) - with slow forward movements substantially depending on how long it takes to perform the longest assembly job.

Tensioning device 12 is supported by structure 5, and comprises two opposite tracks 25 looped about respective wheels 26 and clamped to pipeline 2.

Tensioning device 12 serves to control the movements between structure 5 and pipeline 2, and, in the example shown, clamps the in-process pipeline 2 with

respect to structure 5 and vessel 1 when the vessel is stopped, and allows relative movement between in-process pipeline 2 and structure 5 as the vessel moves forward, as well as controlled relative movement between pipeline 2 and structure 5 when the stress between structure 5 and pipeline 2 exceeds a given threshold value.

ASSEMBLY SYSTEM

With reference to Figure 1, assembly system 8 comprises tensioning device 12 and work units 13, 14, 15 and 16, which are fitted to structure 5 and jogged forward with respect to pipeline 2 together with vessel

1.

Connection of work units 13, 14, 15, 16 to structure 5 is described below with particular reference to shot/grit-blasting unit 15, but also applies to the other work units 13, 14, 16.

Assembly system 8 comprises a powered guide and support assembly 27 for each work unit 13, 14, 15, 16. And each powered guide and support assembly 27 is fixed to structure 5 of vessel 1, in particular to a base of structure 5 sloping downwards from bow to stern.

With reference to Figure 5, powered guide and support assembly 27 is located under shot/grit-blasting unit 15, and provides for making controlled movements of shot/grit-blasting unit 15 parallel and crosswise to path P.

Powered guide and support assembly 27 comprises : a

track 28 parallel to path P and fixed to structure 5; a carriage 29 which engages and runs along track 28; a track 30 parallel to track 28 and fitted to carriage 29; a carriage 31 which engages and runs along track 30; and a track 32 (Figure 6) crosswise to path P and along which shot/grit-blasting unit 15 runs.

Powered guide and support assembly 27 also comprises actuators 33 between carriage 29 and track 28

(Figure 7); actuators 34 between carriage 31 and track 30 (Figure 9); and actuators 35 between carriage 21 and shot/grit-blasting unit 15 (Figure 7).

With reference to Figure 6, track 28 comprises two rails 36, preferably two parallel IPE rails.

With reference to Figure 5, carriage 29 comprises a frame 37; and wheels 38 which engage rails 36 and are fitted to frame 37 to rotate about axes perpendicular to path P.

With reference to Figure 7, actuators 33 comprise, on carriage 29, an electric, preferably brushless motor 39; a motor reducer 40; a shaft 41; and two pinions 42 on the ends of shaft 41. In addition to the two rails 36, track 28 comprises two racks 43, each fixed to a respective rail 36 with its teeth facing downwards.

The two pinions 42 engage respective racks 43 , so that operation of electric motor 39 moves carriage 29 with respect to track 28 and parallel to path P.

In the Figure 9 example, track 30 comprises two rails 44, preferably two parallel IPE rails, fixed to

carriage 29 and of narrower gauge than rails 36. Track 30 and rails 44 are an integral part of frame 37 of carriage 29.

Carriage 31 comprises a frame 45; and wheels 46 which engage rails 44 and are fitted to frame 45 to rotate about axes perpendicular to path P. Actuators 34 comprise, on carriage 31, an electric, preferably brushless motor 47; a motor reducer 48; a shaft 49; and two pinions 50 on the ends of shaft 49. Track 30 comprises two racks 51, each fixed to a respective rail 44 with its teeth facing downwards.

The two pinions 50 engage respective racks 51, so that operation of electric motor 47 moves carriage 31 with respect to carriage 29 and parallel to path P. With reference to Figure 10, track 32 comprises two parallel rails 52 fitted to carriage 31, and which are an integral structural part of frame 45 of carriage 31.

Shot/grit-blasting unit 15 comprises two wheels 53, which engage rails 52 and are supported to rotate about respective axes parallel to path P.

Actuators 35 substantially comprise first and second hydraulic cylinders 54 and 55, in particular double-acting hydraulic cylinders, each supported by carriage 31 and shot/grit-blasting unit 15. More specifically, first and second hydraulic cylinders 54, 55 are located on opposite sides of axis Al of pipeline 2.

SHOT/GRIT-BLASTING UNIT

Shot/grit-blasting unit 15 performs a closed shot/grit-blasting cycle, i.e. using recycled shot/grit.

With reference to Figures 9 and 10, shot/grit- blasting unit 15 comprises a first and second supporting frame 56, 57 distinct from one another and movable independently of one another crosswise to path P and with respect to carriage 31. In the example shown, first supporting frame 56 is connected to carriage 31 by respective first hydraulic cylinders 54 and respective wheels 53 ; and second supporting frame 57 is connected to carriage 31 by respective second hydraulic cylinders

55 and respective wheels 53.

Shot/grit-blasting unit 15 comprises as a whole: - a first and second housing 58, 59 fixed to first and second supporting frame 56, 57 respectively, and connectable to each other to form a shot/grit-blasting chamber 60 (Figure 8) about pipeline 2 ; four turbines 61 for firing shot/grit onto pipeline 2 and fitted in pairs to first and second frame

56 and 57 (Figure 11) ;

- a shot/grit collecting device 62 fitted to second supporting frame 57 (Figure 13); and a feed device 63 for feeding shot/grit to turbines 61 and fitted partly to first supporting frame

56 and partly to second supporting frame 57 (Figure 13).

With reference to Figures 9 and 10, first and second housing 58 and 59 are substantially specularly

symmetrical, and each comprise a lateral wall 64 parallel to path P; a number of face walls 65 perpendicular to path P and fixed to lateral wall 64

(Figure 8); and a number of rubber partitions 66 fixed to face walls 65 and which rest on pipeline 2 to prevent shot/grit and dust escaping from shot/grit-blasting chamber 60 (Figure 8) .

With reference to Figure 11, when first and second frame 56 and 57 are brought together about pipeline 2, turbines 61 are equally spaced about axis Al of pipeline

2 to ensure even blasting about axis Al of the outer surface of cutback 23.

With reference to Figure 8, since turbines 61 can only blast a limited axial area, shot/grit-blasting unit 15 must be moved parallel to path P with respect to pipeline 2 to shot/grit-blast cutback 23 axially.

Shot/grit-blasting unit 15 is moved with respect to pipeline 2 by moving carriage 31 with respect to carriage 29. In other words, carriage 31 performs a shot/grit-blasting stroke and a return stroke with respect to carriage 29.

With reference to Figure 13, shot/grit collecting device 62 is supported entirely by second supporting frame 57, and comprises : - a collecting trough 67 (Figure 11) fixed to second housing 59, located beneath first and second housing 58, 59, and communicating directly with shot/grit-blasting chamber 60 (Figure 8);

- a screw conveyor 68 housed in collecting trough 67 and substantially parallel to path P; a substantially horizontal screw conveyor 69 connected to screw conveyor 68; - a cup conveyor 70 (Figure 11) for conveying the shot/grit upwards over turbines 61; and

- a screw conveyor 71 crosswise to path P and over turbines 61 to supply shot/grit feed device 63.

With reference to Figure 13, feed device 63 feeds shot/grit to the four turbines 61, and operates substantially by gravity.

Feed device 63 comprises a part fitted to second supporting frame 57 and comprising: a shot/grit screening and cleaning drum 72 located over turbines 61 and gravity-fed with shot/grit by screw conveyor 71;

- a feed conduit 73 connected to drum 72, and which supplies the two turbines 61 fitted to second supporting frame 57; and - a spout 74 connected to drum 72, and which feeds shot/grit to the turbines 61 fitted to first supporting frame 56.

Feed device 63 comprises another part fitted to first supporting frame 56 and comprising: - a feed conduit 75 for supplying the two turbines

61 fitted to first supporting frame 56; and

- a funnel 76 integral with feed conduit 75, and which can be positioned selectively under spout 74 to

receive shot/grit from drum 72.

ASSEMBLY SYSTEM CONTROL DEVICE

With reference to Figure 1, assembly system 8 comprises a control device 77.

With specific reference to shot/grit-blasting unit 15, control device 77 serves to coordinate the movements of carriage 29, carriage 31, first supporting frame 56, and second supporting frame 57 (Figure 7) with the forward jogging movement of vessel 1 moving in-process pipeline 2 with respect to structure 5.

With reference to Figure 14, control device 77 comprises : a control unit 78; a control console 79; sensors 80 for determining relative movement of pipeline 2 , in particular with respect to tensioning device 12; sensors 81 for determining the position of a reference point, e.g. annular weld 22 of pipeline 2, with respect to shot/grit-blasting unit 15; and a hydraulic central control unit 82 for selectively operating first and second hydraulic cylinders 54 and 55. Control unit 78 is connected to a control unit 83 for controlling the forward jogging movement of vessel 1.

Control unit 83 supplies control unit 78 with signals indicating the jog status of the vessel : for example, a "1" signal indicates forward movement of vessel 1, and a "0" signal indicates a stop or slow forward movement of vessel 1.

Control unit 78 controls operation and movement of

shot/grit-blasting unit 15 as a function of the signals from control unit 83 controlling vessel 1.

The Figure 15 diagram shows the operating modes with reference to go-stop jogging mode. In the example shown, Tl indicates the forward-movement time, and T2 the stop time. Times Tl and T2 are determined by control unit 78 as a function of the signals from control unit 83. At the end of the forward movement, sensor 81 transmits a signal related to alignment of annular weld 22 with a reference point on shot/grit-blasting unit 15, and control unit 78 compares this signal with a reference value. When the alignment signal departs from the reference value, control unit 78 emits a control signal E _A to operate electric motor 39, which moves carriage 29 until annular weld 22 is aligned with the reference point on shot/grit/grit-blasting unit 15, and the alignment signal substantially coincides with the reference value.

Alternatively, any misalignment (difference between the alignment signal and reference value) is displayed on control console 79, and, using a respective control, the operator operates electric motor 39 with a control signal to eliminate the misalignment. In the Figure 15 diagram, this alignment step is indicated T7 , which indicates the time taken to correct any misalignment.

Shot/grit-blasting unit 15 then commences the work cycle, which comprises the following steps: first and second supporting frame 56, 57 are

closed from the Figure 10 position to the Figure 7 position to close shot/grit-blasting chamber 60 about pipeline 2, and in particular about cutback 23 (Figure 8); closure is performed by first and second hydraulic cylinders 54, 55 (Figure 14) for a time T3 (Figure 15) which indicates the time taken to close shot/grit- blasting chamber 60; carriage 31 performs the shot/grit-blasting stroke, i.e. control unit 78 operates electric motor 47 (Figure 14) for a time T5 (Figure 15) indicating the time taken to perform the shot/grit-blasting stroke, which, in the example shown, is roughly 350 mm; at this step, control unit 78 operates a number of electric motors (not shown) to power turbines 61, collecting device 62, and shot/grit feed device 63; first and second supporting frame 56, 57 are opened from the Figure 7 position to the Figure 10 position, to open shot/grit-blasting chamber 60, by the first and second hydraulic cylinders (Figure 14) for a time T4 , which overlaps stop T2 and forward movement Tl (Figure 15) and indicates the time taken to open shot/grit-blasting chamber 60; carriage 31 performs the return stroke; i.e. control unit 78 operates electric motor 47 (Figure 14) for a time T6 (Figure 15) which indicates the time taken to restore carriage 31 to its original position; at this step, carriage 31 is restored to a position resting against a stop (not shown) on carriage 29. As shown in

the Figure 15 diagram, return stroke T6 is conveniently simultaneous with forward movement Tl of vessel 1.

The shot/grit-blasting cycle is preset on control unit 78, and comprises successively emitting a control signal C _c to command hydraulic central control unit 82 to close shot/grit-blasting chamber 60; emitting a control signal C _s to operate electric motor 47; emitting a control signal C _A to command hydraulic central control unit 82 to open shot/grit-blasting chamber 60; and emitting a control signal C _R to operate electric motor 47.

With reference to the Figure 15 diagram, during stop T2, closure T3 , and sand-blasting stroke T5, a tracking step T8 may be performed, in which sand- blasting unit 15 tracks pipeline 2 (Figure 14) .

Tracking comprises determining any relative movement between pipeline 2 and tensioning device 12, or other parts integral with structure 5, by means of sensor 80. Depending on the signal from sensor 81, control unit 78 emits a control signal E _τ to operate electric motor 39 and move carriage 29 by an amount equal to the relative movement recorded.

Control device 77 also allows operator intervention to let through items 24 of exceptional size, such as the one shown in Figure 4. That is, as an item 24 of exceptional size approaches sand-blasting unit 15, the console 79 operator, by means of an appropriate control signal, moves first and second supporting frame 56, 57

by the amount shown in Figure 9.

In other words, assembly system 8 described provides for aligning cutback 23 with sand-blasting unit 15; performing an automatic work cycle; tracking pipeline 2; and allowing throughput of items 24 of exceptional size.

Assembly system 8 thus combines a high degree of automation with a high degree of versatility, while at the same time providing a healthier workplace. Moreover, in the case of fast-slow jogging of the vessel , tracking is operative throughout the sandblasting stroke and during alignment.

In the exceptional event of tensioning device 12 losing control of in-process pipeline 2, sensor 80 emits an alarm signal to immediately release first and second supporting frame 56, 57.