TECHNICAL FIELD

The present invention relates to a method of applying protective sheeting of polymer material to a pipeline, and in particular about a cutback on the pipeline.

The method according to the present invention forms part of a pipeline construction method, in particular for constructing underwater pipelines laid on the bed of a body of water.

BACKGROUND ART

Pipelines are normally constructed by joining the free facing ends of two adjacent, longitudinally aligned pipe sections to form a cutback; and winding protective sheeting about the cutback. Pipelines are made of pipe sections joined to cover distances of hundreds of kilometers. Each pipe section is normally 12 metres long, with a relatively large diameter ranging between 0.2 and 1.5 metres, and comprises a metal cylinder; a first coating of polymer material to protect the metal cylinder; and possibly a second coating of Gunite or concrete, which serves as ballast and is not always needed. To weld the metal cylinders together, the free opposite ends of each pipe section have no first or second coating; and the pipe sections are joined either at land-based installations or on board laying vessels designed to lay the pipeline as it is being built.

Joining the pipe sections comprises welding the metal cylinders, normally in a number of passes; and restoring the first and second coating (if any) . Once an annular weld bead is formed between each two adjacent metal cylinders, the cutback extends astride the annular weld bead, along a bare portion with no first or second coating. In other words, the cutback is substantially defined by the free ends of the pipe sections, extends axially between two end portions of the first coating, and must be covered with a protecting coating to prevent corrosion .

Restoring the first coating along the cutback is known as 'field joint coating', and normally comprises coating the cutback with three coats of polymer material to protect and ensure adhesion of the coats to the metal cylinders. More specifically, it comprises heating, e.g. induction heating, the cutback to a temperature of 250 °C; spraying the cutback with powdered epoxy resin (FBE - fusion bonded epoxy) 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; and applying a third so-called 'top coat', which also extends partly over the first coating. The second coating, if any, is then also restored.

Welding, non-destructive weld testing, and restoring the first and second coating are all performed at work stations equally spaced along the path of the pipe sections (or the pipeline being built, if the pipe sections are joined to this) , so the pipe sections are advanced in steps and stopped for a given length of time at each work station.

One known method of applying the third coat to restore the first coating comprises extruding and simultaneously winding thick protective sheeting about the cutback, as described in the Applicant's Patent Application WO 2008/071773 and in Patent Applications EP 1,985,909, WO 2010/049353 and WO 2011/033176. In the methods described, the protective sheeting is applied by an extrusion port mounted on a carriage, which runs along an annular path about the longitudinal axis of the pipeline; and the polymer material is plastified by a plastifying device located close to the pipeline and either selectively connectable to or hose-connected to the extrusion head. Both methods of feeding the soft polymer material to the extrusion head have drawbacks, on account of the physical characteristics of the polymer material, which, to remain soft, must be heated to within a given temperature range. DISCLOSURE OF INVENTION

It is an object of the present invention to provide a method of applying protective sheeting of polymer material to a cutback on a pipeline, designed to eliminate the drawbacks of the known art.

According to the present invention, there is provided a method of applying protective sheeting of polymer material to a pipeline, the method comprising the steps of advancing a carriage along an annular path extending about the longitudinal axis of the pipeline; extruding the protective sheeting on the carriage; winding the protective sheeting, as it is extruded, about a cutback on the pipeline; and plastifying the polymer material on board the carriage.

The method according to the present invention has the advantage of applying the protective sheeting at very high temperature, and therefore in a highly plastic state capable of adapting to uneven surfaces. Moreover, the polymer material is fed easily to the carriage in the solid state; and the relatively short distance travelled by the soft polymer material simplifies temperature and pressure control and reduces the amount of energy required to heat it .

In a preferred embodiment of the invention, the method comprises storing the plastified polymer material on the carriage. This solution frees the sheeting application stage, which is normally relatively fast, from the plastifying stage, which is normally relatively slow and related to the size and the heating power of the plastifying device. By storing the plastified polymer material on the carriage, the polymer material can be plastified during the downtime between applications.

In a preferred embodiment of the invention, the method comprises advancing the pipeline, with respect to the carriage, in a direction parallel to the longitudinal axis of the pipeline to position the carriage at the next cutback; and the polymer material is conveniently plastified mainly as the pipeline advances with respect to the carriage, i.e. when the carriage is idle.

The method preferably comprises feeding the polymer material in the solid state to a feed port of a plastifying device on the carriage as the pipeline advances .

The method preferably comprises selectively securing the carriage in an axial direction to the pipeline; and advancing the carriage about the cutback with the carriage secured to the pipeline.

In a preferred embodiment of the invention, the method comprises plastifying the polymer material and extruding the protective sheeting by means of a plastifying and extrusion assembly mounted on the carriage and comprising an extrusion head with an extrusion port. The plastifying and extrusion assembly is preferably a one-piece block, which is mounted adjustably on the carriage, and is preferably connected to the carriage to permit remote control of the position of the block and adjust the distance between the extrusion port and the cutback as a function of the position of the carriage along the annular path.

In a preferred embodiment of the invention, the method comprises pressing the protective sheeting onto the pipeline by means of a rolling assembly hinged to the carriage and comprising a roller; and adjusting the pressure exerted by the roller on the protective sheeting.

The roller is preferably powered to rotate about its axis; and the method comprises adjusting the rotation speed and reversing the rotation direction of the roller.

The roller plays a vital role in correctly restoring the first coating, and in preventing air bubbles forming between the protective sheeting and the cutback. Adjusting the pressure exerted by the roller enables pressure to be adapted to the physical condition of the protective sheeting; by adjusting the speed of the roller, rotation of the roller can be synchronized with the travelling speed of the carriage, to avoid shear stress as the roller rolls over the protective sheeting; and inverting the rotation direction of the roller enables it to be used even when the carriage is travelling in the opposite to application direction.

In a preferred embodiment of the invention, the method comprises extruding an initial portion of the protective sheeting with the carriage stationary and so positioned that the initial portion of the protective sheeting is inserted by force of gravity between the pipeline and the roller; and gripping the initial portion between the roller and the pipeline.

In this way, the initial portion of the protective sheeting is clamped immediately to the pipeline by the roller, with sufficient pressure to prevent air bubbles forming .

The method preferably comprises advancing the carriage about the cutback when the initial portion of the protective sheeting is gripped between the pipeline and the roller.

So doing keeps the portion of the protective sheeting between the extrusion port and the roller taut, thus reducing the risk of air bubbles forming between the protective sheeting and the pipeline.

In a preferred embodiment of the invention, the method comprises cutting the extruded protective sheeting at the extrusion port; and closing the extrusion port, preferably by means of a blade.

So doing has the advantages of forming a neat, clean end of the protective sheeting, and preventing soft polymer material from dripping from the extrusion port.

In a preferred embodiment of the invention, the method comprises adjusting the travelling speed of the carriage as a function of the position of the carriage along the annular path, to ensure optimum application of the protective sheeting.

Because the carriage makes at least one complete turn about the pipeline, and given the considerable weight and delicate nature of the soft protective sheeting, it is advisable to regulate the travelling speed of the carriage at least along the more critical points.

For the same reasons, it is also advisable to adjust the distance between the protective sheeting extrusion port and the pipeline as a function of the position of the carriage .

In a preferred embodiment of the invention, the step of pressing the protective sheeting onto the pipeline by means of a rolling assembly comprises rolling the roller, directly downstream from the extrusion port, in a first rotation direction of the carriage when extruding the protective sheeting; and keeping the roller pressed onto the protective sheeting in a second rotation direction of the carriage opposite the first rotation direction.

This solution has the advantage of improving adhesion of the protective sheeting to the pipeline, and is made possible by rotation of the roller being reversible, and by the pressure of the roller being adjustable. That is, as the roller rolls in the first rotation direction of the carriage, the polymer sheeting has just been laid and is highly plastic. Whereas, as it rolls in the second rotation direction of the carriage, the roller encounters increasingly firmer, longer-laid portions of the protective sheeting, so the pressure of the roller is increased gradually as it rolls in the second rotation direction of the carriage.

It is a further object of the present invention to provide a device for applying protective sheeting of polymer material about a cutback on a pipeline, designed to eliminate the drawbacks of the known art.

According to the present invention, there is provided a device for applying protective sheeting of polymer material to a pipeline, the device comprising a carriage, which moves along an annular path extending about the longitudinal axis of the pipeline to apply the protective sheeting to a cutback on the pipeline; and a plastifying and extrusion assembly mounted on the carriage to plastify the polymer material from which the protective sheeting is made, and to extrude the protective sheeting on board the carriage .

Preferably, the plastifying and extrusion assembly is a one-piece block having a feed port for solid, preferably granular, polymer material; and an extrusion port for applying the protective sheeting.

The soft polymer material thus travels a very short distance, and is therefore easily controllable.

In a preferred embodiment of the invention, the device comprises a contoured roller, in turn comprising a central portion; two lateral portions smaller in diameter than the central portion; and a groove formed in the central portion to adapt the roller to the shape of a central weld bead on the cutback.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figures 1 and 2 show sections, with parts removed for clarity, of pipe sections at various joining stages;

Figures 3 and 4 show larger-scale sections, with parts removed for clarity, of pipe sections at various stages in the method according to the present invention;

Figure 5 shows a view in perspective, with parts removed for clarity, of the device for applying protective sheeting of polymer material according to the present invention;

Figure 6 shows a larger-scale side view, with parts removed for clarity, of a component part of the Figure 5 device; Figures 7 and 8 show larger-scale views in perspective, with parts removed for clarity, of a carriage of the Figure 5 device;

Figure 9 shows a view in perspective, with parts removed for clarity, of a detail of the device;

Figure 10 shows a schematic of the control system of the Figure 5 device;

Figures 11-14 show schematics, with parts removed for clarity, of an operating sequence of the Figure 5 device. BEST MODE FOR CARRYING OUT THE INVENTION

Numbers 1 in Figure 1 indicate two pipe sections, each of which comprises a metal cylinder 2; a first coating 3 of polymer material, normally polyethylene or polypropylene, contacting and for corrosionproofing metal cylinder 2; and a second coating 4 of Gunite or concrete for ballast.

In an alternative embodiment not shown, the pipe sections have no second coating.

Each pipe section 1 has two opposite free ends 5 (only one shown in Figures 1 and 2) with no first coating 3 or second coating 4. First coating 3 has a bevel 6 at each free end 5. Two successive pipe sections 1, aligned along a longitudinal axis Al (Figure 1), are positioned with free ends 5 together, parallel and facing each other, and are welded, possibly in a number of passes at successive work stations, to form an annular weld bead 7 in between (Figure 2) . As shown in Figure 2, the two welded pipe sections 1 form a cutback 8 extending along longitudinal axis Al, between bevels 6 on first coating 3, and along annular weld bead 7.

When joined, pipe sections 1 form a pipeline indicated generically by P, and which, in the present description, also includes the pipeline being constructed and formed, for example, by only two joined pipe sections 1.

In addition to welding metal cylinders 2, joining pipe sections 1 also comprises restoring first coating 3 and possibly also second coating 4. Restoring first coating 3 comprises grit-blasting the surface of cutback 8; induction heating cutback 8 to roughly 250 °C; and applying in rapid succession onto cutback 8 a first coat 9, second coat 10, and third coat 11 of polymer material (Figure 3) .

As shown in Figure 3, first coat 9 is a 100-500 micron thick coat of epoxy resin (FBE - fusion bonded epoxy) sprayed in powdered form onto cutback 8 using a spray gun not shown. Second coat 10 is a 100-500 micron thick coat of modified copolymer, normally CMPE or CMPP, sprayed in powdered form on top of first coat 9 on cutback 8 using a spray gun not shown. And third coat 11 is a 2-5 mm thick coat of polymer, preferably polyolefin, CMPE or CMPP, applied by winding a single piece of protective sheeting 12 of polymer material about cutback 8 at a work station 13, as shown in Figure 5. In the example shown, protective sheeting 12 is wound about cutback 8 at station 13 (Figure 5), is wider than cutback 8 (measured along longitudinal axis Al - Figure 2) so as to overlap first coatings 3 and bevels 6 of both joined pipe sections 1, and is long enough to wind completely about cutback 8 and overlap at the ends.

Protective sheeting 12 is actually extruded as it is wound about pipeline P.

With reference to Figure 4, second coating 4 is restored with a coat of cement C.

Number 14 in Figure 5 indicates a device for plastifying the polymer material from which protective sheeting 12 is made, and for extruding and simultaneously winding protective sheeting 12 about pipeline P.

Constructing pipeline P, in particular on board a laying vessel (not shown) , comprises feeding pipeline P in steps in a direction Dl parallel to longitudinal axis Al; and fixing device 14 to pipeline P at cutback 8. Device 14 is located at work station 13, and comprises a frame 15; a carriage 16 movable along frame 15; a plastifying and extrusion assembly 17 mounted on carriage 16; a rolling assembly 18 mounted on carriage 16; a hopper 19 for feeding solid polymer material to plastifying and extrusion assembly 17; and a control unit 20 connected to carriage 16. Frame 15 comprises two facing grippers 21 spaced apart; and beams 22 for rigidly connecting grippers 21. Each gripper 21 is annular, and has one sector 23 and two sectors 24 complementary with one another to define a ring. Sectors 23 of grippers 21 are connected rigidly to one another by beams 22; and the two sectors 24 of each gripper 21 are hinged to corresponding sector 23 about hinge axes parallel to longitudinal axis Al, and are operated by actuators 25 to rotate from the closed position in Figure 6 to an open position (not shown) to release device 14 from pipeline P. Sectors 23, 24 have adjustable spacers 26 facing and designed to be positioned contacting pipeline P, and which are adjusted accurately to centre frame 15 on pipeline P.

As shown in Figure 6, in the closed position, sectors

23, 24 of each gripper 21 define a circular guide 27 for carriage 16 (Figure 5) ; and a circular rack 28 which cooperates with carriage 16 (Figure 5) to move it forward.

As shown in Figure 5, frame 15 is designed to selectively connect device 14 to pipeline P; to centre guides 27 with respect to longitudinal axis Al of pipeline P; and to support and guide carriage 16 along an annular path .

As shown in Figures 7 and 8, carriage 16 comprises two actuators 29 for moving carriage 16 forward; two facing, sector-shaped plates 30; and two beams 31 connecting facing plates 30. The outer face of each plate 30 is fitted with rollers 32 for engaging guide 27 (Figure 6); and a pinion 33 operated by respective actuator 29 and designed to engage rack 28 (Figure 6) to move carriage 16 along the annular path about pipeline P (Figure 5) . Carriage 16, in fact, serves to support and move plastifying and extrusion assembly 17 and rolling assembly 18 about pipeline P (Figure 5) .

As shown in Figure 9, plastifying and extrusion assembly 17 comprises a plastifying device 34, a storage tank 35, and an extrusion head 36, which, in the preferred embodiment of the invention, form a single rigid block mounted on carriage 16, between plates 30, to rotate about an axis A2 parallel to longitudinal axis Al (Figure 7), to adjust the position of extrusion head 36 with respect to pipeline P (Figure 5) . For this purpose, as shown in Figure 7, plastifying and extrusion assembly 17 is connected to carriage 16 by an actuator 37 for accurately adjusting the position of plastifying and extrusion assembly 17 about axis A2.

As shown in Figure 9, plastifying device 34 is a screw type driven by a motor 38 and reducer 39, and comprises a cylinder 40, in turn comprising a portion 43, and a portion 41 with a feed port 42. Portion 41 is preferably cooled by a water circuit, and portion 43 is preferably heated by electric resistors. Cylinder 40 is connected by a U-fitting to storage tank 35, which comprises a chamber 44, preferably a cylinder, in which a piston 45 is operated by a preferably electromagnetic drive 46 to alter the volume of storage tank 35. The rod (not shown) of piston 45 is preferably defined by a screw operated by a helical gear (not shown) .

To reduce its size and weight, plastifying device 34 is designed to supply a maximum amount of soft polymer material smaller than the maximum capacity of extrusion head 36.

Extrusion head 36 comprises a slit-shaped extrusion port 47 designed to form protective sheeting 12 of the required width and thickness, and is connected directly to storage tank 35. Plastifying and extrusion assembly 17 also comprises a blade 48 fitted to extrusion port 47 of extrusion head 36 to selectively cut the extruded protective sheeting 12, and which is operated by an actuator 49 fitted to extrusion head 36, and also serves to close extrusion port 47 to prevent the soft polymer material from dripping.

As shown in Figures 7 and 8, rolling assembly 18 is fitted to carriage 16, and comprises a roller 50; a supporting structure 51 fitted adjustably to carriage 16; an articulated link 52, in particular an articulated quadrilateral, connecting roller 50 to supporting structure 51; and an actuator 53 between articulated link 52 and supporting structure 51. Supporting structure 51 provides for accurately adjusting the position of the whole of rolling assembly 18 with respect to carriage 16.

As shown in Figure 8, rolling assembly 18 comprises an actuator 54 fitted to the articulated link; and a transmission 55 for connecting actuator 54 to roller 50, and rotating roller 50 at selectively adjustable speeds and in opposite directions. Roller 50 is made of rigid material, preferably metal, and has a contoured profile substantially defined by a central portion 56 designed to contact cutback 8, and by two smaller-diameter lateral portions 57 designed to contact protective sheeting 12 at coating 3. Roller 50 has a contoured groove 58 formed in central portion 56 to adapt the roller to the shape of annular weld bead 7 (Figure 3) .

As shown in Figure 5, hopper 19 is located over device 14, and is connectable selectively to feed port 42 to feed the solid, preferably granular, polymer material to plastifying device 34 when carriage 16 is in a rest position over pipeline P.

As shown in Figure 10, control unit 20 is connected to actuators 25 to selectively open and close sectors 24; to actuators 29 to move carriage 16 along the annular path; to actuator 37 to adjust the tilt of plastifying and extrusion assembly 17; to motor 38 for driving plastifying device 38; to drive 46 of piston 45; to actuator 49 of blade 48; to actuator 53 for adjusting the position of roller 50; and to actuator 54 for rotating roller 50.

Control unit 20 is also connected to thermocouples TC fitted to the whole of plastifying and extrusion assembly 17 to keep the soft polymer material at the temperatures required to plastify and feed it to extrusion port 47; and to temperature sensors T and pressure sensors P fitted to plastifying and extrusion assembly 17 to determine the condition of the soft polymer material and adjust thermocouples TC accordingly.

As shown in Figure 5, carriage 16 is connected to a cable bundle 59, which comprises signal cables, power cables, compressed-air feed pipes, and cooling circuit pipes for cooling feed port 42.

With reference to Figure 5, in actual use, pipeline

P, when released from device 14, moves one step forward with respect to device 14 in direction Dl parallel to longitudinal axis Al . At this stage, carriage 16 is in the rest position over pipeline P, and the hopper feeds the polymer material to plastifying device 34, which plastifies and feeds it to storage tank 35. Moving pipeline P forward takes much longer than to extrude and apply protective sheeting 12, so the time allotted to plastify the polymer material is long enough to employ a relatively small plastifying device 34 to plastify enough polymer material for protective sheeting 12. Next, device 14 is clamped to pipeline P, with extrusion head 36 positioned over cutback 8 (Figure 2) .

With reference to Figure 11, in the rest position, extrusion port 47 is located to one side, in an upper quadrant of the annular path, and roller 50 is located a given distance from pipeline P. At the initial extrusion stage, carriage 16, i.e. extrusion head 36, is maintained stationary in the rest position, and a first portion of protective sheeting 12 is extruded and drops freely by gravity into a position between pipeline P and roller 50. With reference to Figure 12, when the first portion of protective sheeting 12 is located between pipeline P and roller 50, roller 50 is activated to press it against pipeline P. At this point, carriage 16, i.e. extrusion head 36, can start moving along the annular path, so infeed of the solid polymer material is cut off, and plastification continues as long as there is polymer material inside plastifying device 34.

With reference to Figure 13, as carriage 16 moves forward, extrusion of protective sheeting 12 continues by gradually expelling the soft polymer material from storage tank 35 through extrusion head 36 and extrusion port 47. Roller 50 is moved in time with carriage 16, so as to roll over and press protective sheeting 12 onto pipeline P without generating shear stress in protective sheeting 12, which is still soft when applied. The speed of piston 45 is also synchronized with the speed of carriage 16 to form protective sheeting 12 of constant thickness. At this stage, the protective sheeting 12 being extruded is kept substantially taut between the extrusion port and the grip point between roller 50 and pipeline P, so that protective sheeting 12 is pressed firmly onto pipeline P to prevent air being trapped between the pipeline and protective sheeting 12, and which would be hard to expel once protective sheeting 12 is applied.

Particularly effective is adjusting the travelling speed of carriage 16, and therefore the speed of piston 45 and the rolling speed of roller 50, as a function of the position of carriage 16. In fact, the speed with which protective sheeting 12 is applied is affected by two factors connected with the position of carriage 16 and therefore of protective sheeting 12 itself : the force of gravity on protective sheeting 12 issuing from extrusion port 47; and the fragile nature of the soft protective sheeting 12. The position of extrusion port 47 with respect to pipeline P therefore affects the form of protective sheeting 12, and carriage 16 must be accelerated or decelerated at given points along the annular path. This variation in speed may conveniently be programmed, for example, by dividing the path into sectors and assigning each a given travelling speed.

For the same reasons, and to prevent protective sheeting 12 from contacting pipeline P downstream from the grip point by roller 50, the distance between extrusion port 47 and pipeline P when applying protective sheeting 12 is conveniently adjusted as a function of the position of carriage 16.

Given the width of protective sheeting 12, one turn of carriage 16 about pipeline P is enough to restore first coating 3 (Figure 3) . In actual fact, carriage 16 travels over 360° to allow roller 50 to compress and possibly overlap the opposite ends of protective sheeting 12 as shown in Figure 14.

With reference to Figure 14, once extruded, protective sheeting 12 is cut by blade 48, which closes extrusion port 47 to prevent the soft polymer material from dripping.

At this point, carriage 16 is returned to the initial rest position (Figure 11), travelling along the annular path in the opposite direction (clockwise in Figure 14) to that travelled when applying protective sheeting 12. At this stage, roller 50 is kept pressed against protective sheeting 12 and rolled in the opposite direction.

When carriage 16 reaches the initial rest position, device 14 is released from pipeline P to allow it to move freely with respect to device 14; and plastifying and extrusion assembly 17 is ready to start the next cycle.

The advantages of the method as described and illustrated are obvious.

Clearly, changes may be made to the preferred embodiment described of the present invention without, however, departing from the protective scope of the accompanying Claims.