Underwater pipelines are most frequently used for transporting hydrocarbons from the off-shore reservoirs to shore. With such substances, it is important that the temperature within the pipeline does not fall below a certain level, otherwise hydrate and wax formation and deposition occur. The temperature of the hydrocarbons increases with the depth of the reservoirs. In the transportation of such materials it is necessary to prevent heat loss from the hydrocarbons and this is generally addressed by providing an insulating coating around the pipeline.

Underwater pipelines may also require a weight coating for several purposes including the need to weigh the pipeline down and so maintain the position of the pipe on the seabed and to form a protective cover around the pipeline.

In one known pipe coating method, the pipe is coated with extruded polyethylene or polypropylene together with one or more additional coatings to provide weight or anti-corrosion properties to the pipeline.

It is generally assumed that the coating of pipeline with extruded polyethylene could be done as to give uniform thickness circumferentially and longitudinally over the pipe body. This seems to be a reasonable assumption taking into account that the three main

factors governing the thickness of the application are mechanically controlled and should remain constant. The three factors being the pipe rotation, the pipe advancement and the extruder output.

The wastage % of applied polyethylene theoretically should be very close to zero but experience shows it can vary greatly depending on the degree of accuracy of the conveyor adjustments and certain other factors, the most crucial of which is the pipe weld seam.

The thickness of coating on the weld seam as opposed to a point perpendicular to the seam will most certainly vary, the lowest measurement will be found on the weld.

The degree of difference between the two measurements depends primarily on the height and width of the weld.

To combat this problem techniques have been developed which vary the flow of material onto the pipe, increasing the flow as the weld passes the extruder head and subsequently decreasing the output on the pipe body.

The changes in the flow rate are not governed by the extruder which retains a constant output continuously but by a roller system located between the pipe and the extruder head. The polyethylene sheet is"hung"over a geared roller which has two speeds. The two speeds should vary depending on the size and peripheral speed of the pipe, as well as the amount of increased coverage needed which depends on the height and shape of the weld.

Although widely used, this machine has two apparent disadvantages. The first disadvantage is that it is not adaptable for use on spiral welded pipe comparing the increase in thickness on spiral welded pipe to longitudinal welded pipe with the same parameters (weld shape etc). A gain in thickness on the spiral pipe is

expected to be in the region of 20% of the gain attained on the longitudinal pipe.

The second disadvantage of the known"stretch and pull"method is that unless the adjustment and speeds are precisely controlled there will always be a variation in the thicknesses around the pipe girth due to the difficulty in obtaining two different constant speeds of material between the gear roller and the pipe. As a minimum thickness for the coating is normally stated, the waste % will be dependent on the lowest measured thickness on the pipe (be it on the body or weld) and it is often found with this system that the lowest point on the pipe is located just after the weld at the point where the gear roller finishes its high speed cycle.

In order to overcome these limitations, a powder application unit has been proposed for applying powder to the surface of the PE coated pipes destined for concrete coating. This unit is linked to a timing device as to deposit a layer of powder as the weld passed. The unit functions as it was designed to however it is found that where sufficient powder is deposited to give any appreciable increase in coating thickness, voids or pockets of un-melted powder are discovered. Another problem with the system would be to overcome the problem of depositing enough material on the weld to give the desired increase in thickness.

The ideal system for increasing thickness over the weld area is one that can operate on both types of welded pipe with an equal degree of efficiency, and can operate without changing any of the above mentioned"governing factors"which have to remain constant if uniformity of thickness is to be achieved.

According to one aspect of the present invention there is provided an apparatus for applying a patch of material over the weld seam of a pipe, the apparatus comprising means for advancing the material towards the pipe, means for sensing the position of a weld seam on the pipe, means for applying the material onto the pipe, over the weld seam and means for cutting the material to the required length to cover the weld seam.

Preferably, the means for advancing the material through the apparatus comprises a plurality of rollers through which the material passes and a motor for operating the rollers. The rollers may be chain-driven.

The rollers may be adapted to contact the upper and lower surfaces of the material in order to feed the material through the apparatus.

Advantageously, the cutting means comprises a guillotine provided on one end of the apparatus, adjacent the pipe. The guillotine may be mounted within a support cradle which is mounted on the end of the apparatus.

Preferably, the guillotine is provided with a solenoid for actuation thereof. The solenoid is provided with a sensor which, when activated passes a signal to the solenoid to lower or raise the guillotine accordingly.

Advantageously, the apparatus is provided with an indented seat to receive the guillotine when in an extended position. This provides a secure and firm support for the guillotine during the cutting operation.

Conveniently, the means to apply the material to the pipe comprises a roller mounted on the apparatus, the roller being moveable between a retracted position when

not in use and an extended position when applying material to the weld seam.

Advantageously, the roller is mounted on the free end of a cylinder.

Preferably, the cylinder is either hydraulic or pneumatic. Alternatively, the cylinder may be replaced by an actuating arm upon which the roller is mounted.

Advantageously, the apparatus is provided with a control panel to enable an operator to control the functions of the apparatus.

According to a further aspect of the present invention there is provided a method of applying a patch of material over the weld seam of a rotating pipe, the method comprising the steps of advancing a sheet of material towards the pipe, sensing the presence of a weld seam on the pipe, applying the free end of the material to the pipe, pressing the material over the weld seam and cutting the material to the required length to cover the weld seam.

Advantageously, the surface temperature of the pipe during the application method is in the range of 180°C to 210°C.

Conveniently, the pipe is pre-coated with a layer of fusion bonded epoxy.

Preferably, the fusion bonded epoxy is applied to the surface of the pipe via a spray head.

Advantageously, the material is applied to the pipe at ambient temperature.

Conveniently, the primary coat is applied to the pipe at a temperature in the range 180°C to 220°C.

One embodiment of the present invention will now be described with reference to and as shown in the accompany drawings, in which : Figure 1 is a schematic side view of an apparatus for coating a pipe according to one aspect of the present invention ; Figure 2 is a schematic side view of the apparatus of Figure 1, and Figure 3 is a schematic side view of the apparatus of Figure 1 following application of the coating, and.

Figure 4 is a plan view of a section of pipe having a longitudinal weld seam coated with the apparatus of Figure 1.

Turning now to the Figures, there is shown in Figure 1, an apparatus 1 for applying a patch to the surface of a pipe in the region of the weld seam of the pipe, the apparatus comprising a housing 2 in which means are provided for supporting and advancing a sheet of material (not shown) to be applied to the surface of the pipe towards the rotating pipe as it passes the apparatus. It is envisaged that the housing will be manufactured from stainless steel. However, other suitable materials could be used.

A reel 3 is releasably supported within the housing at one end thereof, around which the sheet of material is wound.

A first motor 4 is provided for feeding the sheet of material from the reel 3, to the end of the apparatus adjacent to the rotating pipe, and remote from the reel, prior to being fed onto the pipe. A gravity loop system 5 may be incorporated to interact between the applicator 1 and the reel 3 as shown in Figure 2. This system allows the motor which feeds material into the applicator to be low powered. The loop may be fitted with a number of sensors (not shown) to monitor correct operation.

The housing 2 is provided with one or more pairs of chain driven rollers 6 which are adapted to contact the sheet of material on both the upper and lower surfaces thereof and to feed the sheet of material through the housing.

Adjacent the end of the housing remote from the reel, the apparatus is provided with a cutting means 7.

The cutting means comprises a support cradle (not shown) which is mounted on the housing. A cutting device 8, which in the embodiment shown is a guillotine, is mounted on the free end of the support cradle for movement towards and away from the upper surface of the sheet of material. The cradle may be suspended upon the housing through linear bearings from a twin shaft arrangement and is located by loading clamps.

A secondary motor (not shown) is mounted on the cradle, the purpose of which will be described below.

A solenoid 9 is mounted on the housing 2 for actuation of the guillotine.

The housing is provided with a seat 10, below the cutting means. The seat is indented to accept the blade 8a of the cutting means when it is in the lowered position. This provides a firm support for the blade during the cutting operation.

The cradle may also incorporate a support tray (not shown) which is designed to slide under the fixed sections on the in-feed section and the applicator section, for patch length setting.

An actuator 11 which may be in the form of a hydraulic or pneumatic cylinder is mounted adjacent the cutting means, on the cradle. A roller 12 is mounted on the free end of the actuator and is moveable towards and away from the surface of the rotating pipe as it passes the applicator. An electrically operated solenoid 13 is operationally connected to the roller to control this movement of the actuator during use of the apparatus.

A cooling drum (not shown) is located on the apparatus to engage with the roller 12 when it is relocated as will be described below.

A plurality of sensors are mounted on the apparatus, for detecting correct operation. A first sensor 14 is situated before the cutting means 7, a second sensor 15 is situated after the cutting means 7 and a third sensor 16 is situated at the end of the applicator apparatus.

A control panel will be provided on the apparatus to allow personnel operating the apparatus to control the operating parameters during use.

The operation of the apparatus will now be described with reference to the Figures. A sheet of suitable material such as polyethylene is wound around the reel 3 of the apparatus which is then loaded into the housing 2 of the applicator apparatus. A signal is generated from the control panel to operate the apparatus to feed the sheet of material through the housing to the end of the applicator adjacent the cutting means 7. Once the end sensor H is activated, by the sheet of material, the feed signal will cease. The applicator will now await a signal from the weld seam sensor.

A pipe is mounted onto the main coating apparatus and is rotated as it advances through the various stages of coating. Prior to application of the material over the weld seam, a pre-coat of fusion bonded epoxy is sprayed onto the surface of the pipe, which has a temperature in the range of approximately 180°C to 210°C.

As the pipe approaches the applicator apparatus, a sensor locates the position of the weld seam and sends a signal to the applicator apparatus 1 to feed a length of the material from the apparatus past the cutting means 7.

A signal is also sent to activate the actuator 11 and extend the cylinder 12 mounted on the cradle. As the cylinder is extended this brings the roller 13 into contact with the upper surface of the sheet of material.

The sheet is then pressed over the weld seam as the pipe rotates past the applicator apparatus. At the same time, the cutting means 7 is activated to lower the guillotine and sever the sheet of material at the required length to cover the weld seam.

It is envisaged that the resulting patch of material will be in the region of around 20cm in length. However depending upon the size of the pipe to be coated and the

weld seam to be covered, the length of the patch may be altered accordingly.

The cutting means 7 is then retracted and the roller 12 continues to apply pressure to the patch of material to firmly apply this over the weld seam. When the sensor signals that the patch has passed from the applicator, the cylinder 11 carrying the roller 12 is retracted and the pipe rotates, with the patch applied over the weld seam, past the applicator apparatus.

During the application process, the temperature of the roller increases due to the high temperature of the pipe and the coatings applied thereto. As the roller 12 is retracted it engages with the cooling drum in order to lower the temperature of the roller before it is brought into contact with the next patch of material to be applied over the weld seam.

As the pipe is rotating past the applicator, the first motor 4 will be reactivated to position the next strip of material at the end of the applicator ready for the next signal from the weld seam sensor.

The patch is applied to the surface of the weld seam at ambient temperature i. e. approximately 20°C.

In the case where the pipe is provided with a longitudinal weld seam as shown in Figure 3, upon each rotation of the pipe 18, and its advancement past the applicator head, a patch of material 19 is applied over the weld seam 20. The patches may be applied in an overlapping arrangement if required.

In the case where the pipe is provided with a spiral weld seam 21 as shown in Figure 4, each patch 19'is

applied to the pipe offset circumferentially from the last patch. This gives rise to a pattern of patches as shown in figure 4 covering the spiral weld seam.

Once the patch 19,19' has been applied, further layers of coating can be applied to the surface of the pipe. Such coatings may, for example, be spray applied, wound or moulded onto the pipe.

As the weld seam 20,21 is covered by a patch of material and no longer stands proud of the surface of the pipe, when the further coatings are applied, the depth of the coatings can be uniformly controlled thereby resulting in savings of up to 40% on the coating materials.

The patches may be applied to the surface of the pipe either under the first layer of coating or may, alternatively, be provided between the various layers of coating as they are applied.

The position of the applicator 1 can be altered in order to apply the patches at different times in the coating process.

It is envisaged that a level adjustment device will be incorporated in the apparatus for example by mounting the applicator structure on a floor mounted track with a suitable locking mechanism. Vertical movement of the apparatus may be achieved by hinging the applicator top section and providing a screw wheel manual adjuster.

Guarding will be provided on the apparatus where appropriate, for example in the region of the guillotine in order to provide for safe operation of the apparatus.

furthermore, a heat shield 17 may be provided on the apparatus in the region of the patch applicator.

It is envisaged that the patches will be applied to the surface of the rotating pipe between 20 to 35 times per minute.