GB2285596A

GB2285596A - An apparatus for coating a pipe weld joint

Info

Publication number: GB2285596A
Application number: GB9400332A
Authority: GB
Inventors: Joseph Crichton Duncan; John Wallace Betteridge
Original assignee: Pipeline Induction Heat Ltd
Current assignee: Pipeline Induction Heat Ltd
Priority date: 1994-01-10
Filing date: 1994-01-10
Publication date: 1995-07-19
Anticipated expiration: 2014-01-10
Also published as: GB9400332D0; GB2285596B

Abstract

An apparatus 1 for coating an pipe weld joint with a pre-formed thermoplastics shell 5, comprising a die set 23, heater means 25 for heating the die set 23 and clamping means 27 for closing the die set 23 onto the pipe 3, wherein, in use, a pre-formed shell 5 is mounted on a pipe weld joint, the pipe 3 and shell 5 are inserted into the apparatus 1, the heating means 25 heat the pre-formed shell 5 and the clamping means 27 close the die set 23 to mould the shell 5 onto the pipe weld joint. By using such an apparatus, the coating of pipe weld joints to produce a pipeline which is completely protected against corrosion and is fully insulated is simplified and facilitated. <IMAGE>

Description

AN APPARATUS FOR COATING A PIPE WELD JOINT This invention relates to apparatus for coating pipe weld joints.

The use of thermoplastics for anti-corrosion and insulation coatings for pipelines is becoming more common worldwide.

It is well known to coat lengths of pipe during manufacture prior to welding adjacent pipes together on site. The thermoplastics factory coating systems tend to be based on a two or three layer system whereby a primer or primary anti corrosion layer of fusion bonded epoxy (FBE) is sinter applied to the pipe followed by an adhesive layer of thermoplastics (either sintered or extruded) and optionally an outer layer of thermoplastics (usually polyethylene or polypropylene, although not limited to these polymers). The overall thickness of the coating is generally around 3mm, although insulation systems for sub-sea use may be as thick as 100mm or more.

Pipes are generally coated in 12 meter lengths within the factory and shipped to construction sites where they are welded together to form a pipeline. The pipeline may be laid on land or underneath the sea.

The factory coating is generally cut back at each end of each pipe to allow the pipes to be welded together without damaging the coating through excessive heat build up during welding. Once welding has taken place, it is necessary for the cut back regions to be made good to ensure overall anti-corrosion protection or, in the case of insulated lines, both anti-corrosion protection and insulation.

To date, there are two known methods of completing a coating layer over a pipe weld joint. Firstly, it is known to apply a layer of fusion bonded epoxy to the pipe weld joint and to heat shrink a sleeve of cross-linked polymer over the fusion bonded epoxy layer. An adhesive layer is also sometimes included between the FBE and the crosslinked polymer to improve the seal between the two layers.

Such heat shrinking is difficult to perform and requires complicated machinery. The second known method is to apply a fusion bonded epoxy coating prior to placing a steel mould around the pipe weld joint and injecting polypropylene or some other polymer sideways into the mould. Once the polymer has set, the mould can be removed. This second method is highly expensive to undertake and requires a very large and bulky machine which cannot readily be moved around from site to site.

In view of the foregoing, there is a clear need for a pipe weld joint coating apparatus which is easy to erect, simple to use and relatively cheap in comparison with the prior art apparatus. The present invention has been devised to meet this need.

According to the present invention there is provided an apparatus for coating a pipe weld joint with a thermoplastics coat, the apparatus comprising a die set, a frame for supporting the die set, means for heating the die set and/or pipe and clamping means for closing the die set onto a pipe, wherein in use a thermoplastics coat is mounted on a pipe weld joint, the pipe and coat are inserted into the apparatus, the heating means heat the coat and the clamping means close the die set to mould the coat onto the pipe weld joint.

In practice, the coat may be a pre-formed shell or simply a sheet of thermoplastics material which is wrapped around the pipe prior to the swaging operation. Further, the sheet or shell may be formed by extrusion or moulding, and may consist of a single material or multiple layers of different polymers or copolymers.

If desired, a base coating of fusion bonded epoxy can be applied to the pipe weld joint prior to the application of the thermoplastics coat. An adhesive layer may also be applied to the fusion bonded epoxy layer, if it is considered advantageous.

The die set preferably includes means for cooling the coat after the coat has been moulded onto the pipe weld joint. As a result, the moulded coat can be cooled more quickly so that the pipe weld joint can be removed from the apparatus shortly after the coating has been completed.

Thus, the time taken to complete the coating process can be kept within the bounds set by the number of coatings to be achieved per hour, for example.

The cooling means preferably comprise at least one cooling jacket. The or each cooling jacket is preferably adapted for connection to a supply of water, although any other suitable cooling medium could alternatively be used.

The die set preferably comprises three parts, each part being inserted into the frame from inside the frame. If the die set comprises three parts, each part preferably includes a cooling jacket.

The frame is preferably hinged to allow the die set to be opened and closed. More preferably, the frame comprises essentially three portions, one of the portions being separated from the other two portions by means of support shafts which act as hinges between the frame portions.

The heating means may comprise at least one heating coil mounted on the frame. More preferably, each portion of the frame supports a separate heating coil. Alternatively, the or each heating coil may be formed as part of the die set.

The clamping means preferably comprise a plurality of pneumatic or hydraulic cylinders. Any other suitable clamping means could alternatively be used, although it must be appreciated that significant pressure needs to be applied to the die set to force the thermoplastics coat into close contact with the pipe weld joint. In this regard, compression equivalent to at least half a tonne may need to be applied.

More preferably, a pair of cylinders act on each end of the frame to open and close the die set. Each pair of cylinders may act between one side of the frame and an end plate of the frame on the other side of the frame.

Further, each cylinder preferably includes a plunger carrying a hook for engaging a bar carried by the frame prior to closing of the die set. Alternative interlocking means for closing the frame can, of course, be envisaged.

The frame preferably comprises two end plates and a plurality of tie bars extending therebetween.

The die set may be manufactured from either metallic or non-metallic materials or, indeed, may be composite in construction.

A heater may be provided for heating the pipe weld joint prior to closing the die set.

Sensors may be included in the die set or on the frame for sensing the temperature of the thermoplastics coat during coating of the pipe weld joint.

According to another aspect of the present invention, there is provided a method for coating a pipe weld joint with a thermoplastics coat, the method comprising the steps of (a) applying a thermoplastics coat over a pipe weld joint, (b) inserting the pipe weld joint and coat into a coating apparatus, (c) heating the coat using heating means mounted on the apparatus, (d) closing a die set of the apparatus about the pipe weld joint, (e) applying pressure to the die set to mould the coat onto the pipe weld joint, and (f) removing the coated pipe weld joint from the apparatus.

When using such a method, it is preferable to apply a primer and/or adhesive layer to the pipe weld joint prior to applying the thermoplastics coat over the joint.

Furthermore, as above, the thermoplastics coat is preferably a pre-formed shell or a sheet of thermoplastics material.

A specific embodiment of the present invention is now described, by way of example only, with reference to the accompany drawings, in which: Figure 1 is an end view of an apparatus according to the present invention; and Figure 2 is a side view of the apparatus of Figure 1.

With reference to the drawings, an apparatus 1 for coating a pipe weld joint of a pipe 3 with a thermoplastics pre-formed shell 5 comprises two lower frame portions 7 and an upper frame portion 9 at each end of the apparatus 1.

The frame portions 7, 9 at each end of the apparatus 1 are joined by a plurality of tie bars 11, thereby defining a rigid frame of the apparatus 1. The upper frame portion 9 at each end of the apparatus is hingedly connected to each lower frame portion 7 by means of a bearing 13, as shown in the Figures. Each bearing 13 includes a shaft 15 passing through yolks 17 defined by the lower frame portions 7 and a plate 19 extending from the upper frame portion 9.

The upper frame portions 9 each include a pair of lifting eyes 21 for lifting the upper frame portion 9 off the lower frame portions 7 during disassembly of the apparatus 1.

The apparatus 1 further includes a die set 23, heating elements 25 and pneumatic clamping cylinders 27. The die set 23 is formed in three parts and is mounted within the frame of the apparatus 1, as shown in Figure 1 of the drawings. Each part of the die set 23 can be introduced into the frame from within the frame and his held in position by means of screws, bolts or simple stud fixings.

Each part of the die set 23 includes a cooling jacket 29 comprising a pipe adapted for connection to a water supply via a nipple 31, as shown in Figure 2. The cooling jacket 29, which may extend continuously through all three of the parts of the die set 23, is formed within the die set 23 as shown in Figure 1.

The heating elements 25, which may simply be sheathed wire elements, are mounted on the outside of the die set 23.

Each heating element 25, of which there are three shown in the drawings, has end connections 33 for connection to an electrical power supply. Each heating element 25 preferably has a rating of somewhere in the region of 76 kW, so that a thermoplastics shell mounted within the die set 23 is heated relatively quickly into a partially molten state.

Towards the bottom of the apparatus 1, four pneumatic clamping cylinders 27 are provided for closing the frame, and hence the die set 23, to apply pressure to the thermoplastics shell 5 to seal the shell 5 to the pipe 3.

The cylinders 27 are arranged in pairs at either end of the apparatus 1, as shown in Figure 2. Each cylinder 27 includes a plunger 35 for engaging a hook 37 pivotally mounted about a shaft 39. Each pair of cylinders 27, via hooks 37, acts on a bar or shaft 41 straddling an end plate of the apparatus 1. Strengthening webs 43 are also provided to support the shafts 41.

A brief description of the use of an apparatus as described above is now provided.

As mentioned above, sections of pipe, which may by 12 meters in length, are coated whilst in a factory with fusion bonded epoxy (FBE) and an outer coating of a thermoplastics, such as polyethylene or polypropylene. The plastics coating at the end of each pipe is cut back in the factory to facilitate welding of adjacent pipe sections on site.

Hence, when a pipeline is being assembled on site, two adjacent lengths of pipe are welded together and the area around the weld must then be coated with thermoplastics materials up to the edge of the cut back regions to ensure that a completely corrosion resistant and insulated pipeline results. Accordingly, when the welding has been completed, layers of FBE and adhesive are applied to the pipe weld joint prior to a thermoplastics sheath or shell 5 being placed over the weld joint with sufficient material on either side of the weld joint to reach the end of the cut back region of the factory coating. The shell 5, which may be formed in pieces, may be slipped along the pipe or, alternatively, the shell 5 may have a split down one or more sides so that it can be clipped or wrapped over the weld joint. In any event, once the shell 5 has been mounted on the weld joint, the portion of the pipeline adjacent the weld joint, together with the shell 5, are inserted into the apparatus 1 of the present invention. The cylinders 27 then arrange for the hooks 37 to engage the shafts 41 to partly close the die set 23. Electrical power is then supplied to the heating elements (or coils) 25, which heat the die set 23, so that the thermoplastics shell 5 is heated up and becomes malleable. Pressure is applied throughout this period by the cylinders 27 such that the shell 5 is effectively swaged over the pipe weld joint forming a satisfactorily bond with the fusion bonded epoxy and adhesive layers which have previously been applied to the surface of the pipe 3.

If necessary, prior to the coating of the weld joint and cut back regions, the edges of the remaining factory coatings may be heated to enable a better seal to be formed between the new coating and the edges of the existing factory coatings.

When the shell 5 has been swaged into position, so that the surface coating of the pipeline is essentially continuous along the pipeline (i.e. the cut back regions of the coating are filled), the electrical power is cut off from the heating elements 25 and a supply of coolant water is passed through the cooling jacket 29 of the die set 23.

This helps to cool the shell 5 so that the die set 23, and hence the complete apparatus 1, can be disengaged from the pipeline as quickly as possible. It may, however, take a few minutes for the complete operation to occur. In any event, when the heating, moulding and cooling operation has been completed, the cylinders 27 are released to allow the apparatus 1 to be moved along the pipeline to the next pipe weld joint.

If necessary, sensors could be included in the apparatus 1, possibly in the die sets 23, for sensing the temperature of the shell 5. As a result, improved control and timing of the swaging operation can be achieved. Furthermore, although it is envisaged that the pipe weld joint will have some residual heat due to the welding operation before the thermoplastics shell 5 is applied thereto, it may be beneficial to incorporate a heater (not shown) to reheat the weld joint to enable a better bond to occur between the thermoplastics shell 5 and the fusion bonded epoxy coating overlaying the pipe weld joint.

Piercing spikes and vents may also be provided by the frame and/or die set for piercing the shell 5 to allow air trapped within the shell 5 to escape during swaging of the shell 5 onto the pipe weld joints. As a result, improved sealing of the thermoplastics shell 5 over the pipe weld joint can be achieved.

It will of course be understood that the present invention has been described above purely by way of example, and that modifications of detail can be made within the scope of the invention.

Claims

1. An apparatus for coating a pipe weld joint with a thermoplastics coat, comprising a die set, a frame for supporting the die set, means for heating the die set and/or pipe and clamping means for closing the die set onto the pipe, wherein, in use, a thermoplastics coat is mounted on a pipe weld joint, the pipe and coat are inserted into the apparatus, the heating means heat the coat and the clamping means close the die set to mould the coat onto the pipe weld joint.

2. An apparatus as claimed in claim 1, wherein the die set includes means for cooling the coat after the coat has been moulded onto the pipe weld joint.

3. An apparatus as claimed in claim 2, wherein the cooling means comprise at least one cooling jacket.

4. An apparatus as claimed in claim 3, wherein the or each cooling jacket is adapted for connection to a supply of water.

5. An apparatus as claimed in any preceding claim, wherein the die set comprises three parts, each part being inserted into the frame from inside the frame.

6. An apparatus as claimed in any preceding claim, wherein the frame is hinged to allow the die set to be opened and closed.

7. An apparatus as claimed in any preceding claim, wherein the heating means comprise at least one heating coil mounted on the frame.

8. An apparatus as claimed in any preceding claim, wherein the clamping means comprise a plurality of pneumatic or hydraulic cylinders.

9. An apparatus as claimed in claim 8, wherein a pair of cylinders act on each end of the frame to open and close the die set.

10. An apparatus as claimed in claim 9, wherein each pair of cylinders acts between one side of the frame and an end plate of the frame on the other side of the frame.

11. An apparatus as claimed in any one claims 8-10, wherein each cylinder includes a plunger carrying a hook for engaging a bar carried by the frame prior to closing of the die set.

12. An apparatus as claimed in any preceding claim, wherein the frame comprises two end plates and a plurality of tie bars extending therebetween.

13. An apparatus as claimed in any preceding claim, wherein the die set is manufactured from non-metallic material.

14. An apparatus as claimed in any preceding claim, wherein a heater is provided for heating the pipe weld joint prior to closing of the die set.

15. An apparatus as claimed in any preceding claim, wherein sensors are included in the die set for sensing the temperature of the thermoplastics coat during coating of the pipe weld joint.

16. An apparatus as claimed in any preceding claim, wherein piercing spikes and/or vents are provided by the frame and/or the die set for releasing air trapped between the thermoplastics coat and the pipe weld joint during swaging of the coat onto the weld joint.

17. An apparatus as claimed in any preceding claim, wherein the thermoplastics coat is a pre-formed shell.

18. An apparatus for coating a pipe weld joint with a thermoplastics coat substantially as herein before described with reference to and as shown in the accompanying drawings.

19. A method of coating a pipe weld joint with a thermoplastics coat, the method comprising the steps of (a) applying a thermoplastics coat over a pipe weld joint, (b) inserting the pipe weld joint and coat into a coating apparatus, (c) heating the coat using heating means mounted on the apparatus, (d) closing a die set of the apparatus about the pipe weld joint, (e) applying pressure to the die set to mould the coat onto the pipe weld joint, and (f) removing the coated pipe weld joint from the apparatus.

20. A method as claimed in claim 19, wherein the thermoplastics coat is a pre-formed shell.

21. A method as claimed in claim 19 or claim 20, wherein a primer and/or adhesive layer is applied to the pipe weld joint prior to step (a).