GB2237351A

GB2237351A - Coating the interior walls of pipes

Info

Publication number: GB2237351A
Application number: GB9021532A
Authority: GB
Inventors: William George Bradley
Original assignee: MERCOL DESCALING CO Ltd
Current assignee: MERCOL DESCALING CO Ltd
Priority date: 1989-10-26
Filing date: 1990-10-03
Publication date: 1991-05-01
Anticipated expiration: 2010-10-03
Also published as: GB2237351B; GB9021532D0; GB8924098D0

Abstract

So that a coating applied to the interior wall of a pipe can be of substantially uniform thickness regardless of any variations in the rates at which two-component substances eg. epoxies are pumped through respective hoses (20, 22), the rate of traverse of a distributor device (24) in the pipe is directly dependent on the rate at which the substances are delivered to the distributor device (24). Variations to be accommodated comprise viscosity changes and rotation of a drum (16) paying out hoses (20, 22). The rate of flow of resin through hose (20) from a pump (38, Fig. 3) drawing the resin from a tank (48) is the primary variable monitored. <IMAGE>

Description

Coating the interior walls of pipes.

The invention relates to the coating of the interior walls of pipes with liquid cold setting resin materials mixed with a liquid curing agent or initiator.

Underground pipes, for example water pipes, can be coated with a suitable plastics coating medium to be proofed againt leakage and can thereby also be protected against deterioration, or against further deterioration. An existing pipe may first require to be scoured free of rust or other deposits before the coating is applied. However, the invention is not only applicable to the coating of pipes underground but may be used for coating pipes at or above ground level, for example pipes forming part of chemical plant of various kinds, and of course in this case the pipes concerned are unlikely to require any prior scouring treatment.

Numerous cold setting resin materials have been used for coating the interior walls of pipes, notably the epoxy cold setting resins, but one disadvantage of using these materials is that the proportions in which they must be mixed with a liquid curing agent or initiator is critical. This is particularly so when using an epoxy cold setting resin where the proportion in which it is mixed with a curing agent or initiator must be very closely maintained, preferably within 1% and certainly within 5% of the correct proportion.The proportions are not easy to control since the epoxy resin and curing agent cannot be mixed in, for example, a tank for subsequent application in the correct proportions to the interior walls of pipes because, if the mixture was passed through a single delivery tube to the member which applies it to the pipe wall, premature curing or setting would occur and any resin still remaining in the tube after the process had been completed would also set. It has therefore been proposed to deliver the resin and curing agent or initiator through separate delivery pipes to a distributing device within the pipe to be coated, the materials being intimately mixed together within said device and then applied to the interior wall of the pipe concerned.It is also necessary to be able to vary the quantities of the materials flowing through the two delivery pipes, whilst still maintaining the proper quantitative relation between the two, so that the-thickness of the applied coating can be varied and so that an appropriate adjustment can be made when a different size of pipe is to be coated.

It has previously been proposed to use a pumping device for feeding the cold setting resin material and the curing agent or initiator to respective delivery pipes in the required proportions, said pumping device including two positive displacement pumps for the respective liquids, the swept volumes of the two pumps being in the same proportions as the proportions in which the liquids are required to be mixed, means being provided for driving the pumps at the same rate. However, it has been found that this is not a satisfactory solution to the problem when the materials concerned are highly viscous, thixotropic substances.This is thought to result from the fact that such substances do not flow readily into the pressure chambers of the pumps concerned so that pumping in the theoretical proportions, that is to say in the proportions according to the swept volumes of the respective pumps, is not possible. Even if, by trial and experiment, it has been found possible to pump the separate substances to a particular size of pipe to be coated in the required proportions, the pumping of the same two substances to a pipe of twice that diameter has not simply involved the doubling of the pump strokes as one would imagine. On the contrary it has been found that this has resulted in the separate substances being wrongly proportioned and this again is thought to result largely from the different flow characteristics of the substances concerned.A further complication is that the resin material has a different temperature/viscosity gradient to that of the curing agent or initiator so that variations in the ambient temperature as the coating process has taken place has resulted in wide variations in the proportions of the liquids being fed to the distributor device.

The invention has for its object to provide a method of and apparatus for coating the interior walls of pipes which will at least alleviate the problems referred to above.

According to one aspect of the invention, a method of coating the interior wall of a pipe with a liquid cold setting resin material mixed with a liquid curing agent or initiator includes the steps of feeding by means of a first pump a liquid or plastics coating medium through a flexible pipe connected to a distributing device, feeding by means of a second pump a liquid curing agent or initiator through another flexible pipe connected to said distributing device, controlling the operation of said first and second pumps so that the liquid or plastics coating medium and the liquid curing agent or initiator are delivered to the distributing device in the required proportions, and controlling the rate of rotation of a rotatable drum on which the two flexible pipes are coiled in accordance with the rate of operation of one or the other, or both, of the two pumps whereby the rate of traverse of the distributor device through the pipe to be coated is directly dependent on the rate at which the two substances are delivered to said distributor device to ensure that the applied coating is of substantially uniform thickness regardless of any variations in the rates at which the substances are pumped through the respective flexible pipes due to variations in their viscosity. The method may include the further step of feeding air under pressure through a third flexible pipe to a compressed air motor forming part of the distributor device for distributing the mixed substance upon the walls of the pipe to be coated, whereby the two substances are intimately mixed together before being flung outwards against the wall of the pipe being coated.

According to a further aspect of the invention, there is provided apparatus for use in coating the interior walls of pipes, the apparatus including a rotatable drum upon which at least two flexible pipes are to be coiled to traverse said two pipes through a pipe the interior walls of which are to be coated, a first pump for feeding a liquid or plastics coating medium through a first one of said flexible pipes and a second pump for feeding a liquid curing agent or initiator through a second one of said flexible pipes, a distributing device connected to the ends of the two flexible pipes for mixing together the liquid or plastics coating medium and the liquid curing agent or initiator and for distributing the mixed substance upon the walls of the pipe to be coated, control means for controlling the operation of the two pumps in step with each other and thus for controlling the delivery of the coating medium and of the liquid curing agent or initiator to the distributing device in the required proportions, and control means for controlling the rate of rotation of the rotatable drum in accordance with the rate of operation of the two pumps and thus in accordance with the rate at which the mixed coating issues from the distributing device.

In order that the invention may be fully understood and readily carried into effect, the same will now be described, by way of example, with reference to the accompanying drawings, of which; Figure 1 is a diagrammatic view of apparatus embodying the invention in use for coating the interior walls of an underground pipe, Figure 2 is a partly schematic perspective view of part of the apparatus, Figure 3 is a hydraulic circuit diagram, and Figure 4 is a schematic diagram of a control circuit.

Referring now to Figure 1 of the drawings, the apparatus there illustrated includes a mobile unit, generally indicated 10, which is mounted on wheels 12 and provided with a drawbar 14. At the rear of the unit is a rotatable drum 16 mounted for rotation about a horizontal axis between mounting brackets 18.

Flexible pipes 20 and 22 are coiled upon the drum 16 and are provided for conveying, respectively, a liquid or plastics coating medium and a liquid curing agent or initiator to a spraying or distributing device 24 being traversed along an underground pipe 26 by a pull applied to said flexible pipes.

Referring now in particular to Figure 2, the ends of the flexible pipes remote from said spraying or distributing device are connected to a shaft 28 at the axis of the drum, the connection being shown diagrammatically in the drawing. The liquid or plastics coating medium, and the liquid curing agent or initiator, are conveyed to the respective pipes 20 and 22 along passageways extending through the shaft 28, connectors 30 and 32 being provided at one end of said shaft for the connection thereto of non-rotatable conduits 34 and 36 for conveying the coating medium and liquid curing agent or initiator under pressure from respective pumps 38 and 40 (see Figure 3).

A further flexible pipe 42 is also coiled upon the drum 16 and is provided for conveying air under pressure from an air compressor 43 to a compressed air motor (not shown) forming part of the device 24, the latter being a device for intimately mixing together the liquid or plastics coating medium and the liquid curing agent or initiator and for distributing the mixed substance upon the wall of the pipe to be coated. (The device 24, which is illustrated diagrammatically in Figure 1, is shown to include a plurality of flails which are driven by the compressed air motor so as to make repeated impacts or rapid wiping actions upon the coated wall of the pipe 26 in the wake of a distributing member also driven by the compressed air motor).

The end of the flexible pipe 42 remote from the spraying or distributing device is also connected to the shaft 28 and air under pressure is delivered thereto along the axis of the shaft from the end remote from the connectors 30 and 32. A connector (not shown) is provided for the connection of a non-rotatable conduit 44 to said shaft, the conduit communicating with the air compressor.

A hydraulic motor 46 and a reduction gear unit 47 are provided for rotating the drum 16 at an appropriate and substantially constant speed during a pipe coating operation, the motor being fed with oil under pressure from a hydraulic pump 48 (see Figure 3). The pumps 38 and 40 which force the liquid or plastics coating medium and the liquid curing agent or initiator through the respective flexible pipes 20 and 22 are driven by respective double acting hydraulic rams 39 and 41 which are fed with oil under pressure from respective hydraulic pumps 35 and 37. The pumps 38 and 40 draw the substances concerned from respective storage tanks 49 and 50 which are mounted back to back on the unit 10 (see Figure 1).

A water cooled internal combustion engine 52 is provided for powering the apparatus, that is to say for driving the pumps 35, 37 and 48 which provide oil under pressure for powering the respective hydraulic rams 39 and 41 and for driving the hydraulic motor 46.

Referring now in particular to Figure 3, in the hydraulic circuit there illustrated it will be seen that there are three main sub-circuits, generally indicated 54, 56 and 58 respectively, in which the hydraulic motor 46 and the hydraulic rams 39 and 41 are contained.

The sub-circuit 54 includes a pressure relief valve 60 and an adjustable flow control valve 62.

The arrangement is such that during the operation of the apparatus the rate of rotation of the drum 16 is dependent on the setting of the flow control valve 62. A tachometer 17 monitors the rate of rotation of the drum.

The sub-circuits 56 and 58 include respective pressure relief valves 64 and 66, respective flow control valves 68 and 70, and respective spool valves 72 and 74 which are operable to reverse the flow of hydraulic fluid to the respective hydraulic rams 39 and 41. Proximity switches (not shown) are provided to detect the arrival of the respective pistons of the hydraulic rams 39 and 41 at the ends of their strokes and to cause the reversal of their associated spool valves 72 and 74 so that the pumps 38 and 40 can operate continuously. The rate of operation of each ram 39 and 41 is dependent on the setting of the respective flow control valves 68 and 70, the setting of said valves being constantly monitored as will presently be described.The control means for controlling the delivery of the coating medium and of the liquid curing agent or initiator to the distributing device 24 in the required proportions includes means which will presently be described for counting the number of reciprocations of respective meters 51 and 53 at the output side of each pump 38 and 40, the information being fed continuously to a computer 76 (see Figure 4).

Electronic control means including the computer 76 are shown in Figure 4 to include also actuators 78 and 80 for adjusting the flow control valves 68 and 70; electronic counters 82 and 84 associated with the meters 51 and 53 for counting the number of reciprocations of said meters; an actuator 86 for adjusting the flow control valve 62 by means of which the rate of rotation of the drum 16 is controlled; and a counter 88 by means of which the rotation of the motor 46 and thus the rate of rotation of the drum is constantly monitored.The arrangement is such that, at the commencement of a coating operation, a particular head of pressure can be caused to act in the pipe 20 conveying the liquid or plastics coating medium, being the safe maximum pressure which the pipe can withstand, and the coating medium is therefore forced through the pipe at a rate which is dependent on the viscosity of the substance. If the viscosity of the substance increases, due, for example, to a change of ambient temperature, the rate of flow will decrease and vice versa. Throughout the coating operation, the other variables are automatically adjusted in accordance with the rate at which the coating medium is forced through said pipe. In this way, regardless of variations in the rates of flow of the two substances brought about by, for example, changes of ambient temperature, the two substances are mixed in the correct proportions and issue from the distributing device at a rate which results in the correct thickness of coating being applied to the walls of the underground pipe.

Similarly, any slowing down (brought about by external means) in the rate of rotation of the drum will immediately affect the setting of the flow control valves 68 and 70 to vary the rates of flow of the substances through the flexible pipes.

It has been found that when coating the interior walls of pipes using the apparatus just described the standard of work is consistantly high because the materials are mixed together in the correct proportions and applied to the interior walls of the pipes at the required thickness. The operation is in addition carried out in a minimum of time and therefore at the lowest possible expense. The rate at which the coating is applied can be outside the control of the operatives and the computer signals can be recorded to be subsequently fed to a printer to give a read-out of all the relevant variables throughout the coating operation.

Various modifications may be made. For example, the distributing device connected to the ends of the flexible pipes for mixing together the liquid or plastics coating medium and the liquid curing agent or initiator and for distributing the mixed substance upon the walls of the pipe to be coated could be very different from that described and illustrated. In particular, the illustrated device 24 is shown to be provided with a plurality of flails which are driven by the compressed air motor so as to make repeated impacts or rapid wiping actions upon the coated wall of the pipe in the wake of a distributing member also driven by the compressed air motor. However, such a device may be replaced by means of a device which mixes the materials together and then flings the mixed substance against the walls of the pipe to be coated in the form of a fine mist or spray.

Claims

CLAIMS:

1. A method of coating the interior wall of a pipe with a liquid cold setting resin material mixed with a liquid curing agent or initiator, the method including the steps of feeding by means of a first pump a liquid or plastics coating medium through a flexible pipe connected to a distributing device, feeding by means of a second pump a liquid curing agent or initiator through another flexible pipe connected to said distributing device, controlling the operation of said first and second pumps so that the liquid or plastics coating medium and the liquid curing agent or initiator are delivered to the distributing device in the required proportions, and controlling the rate of rotation of a rotatable drum on which the two flexible pipes are coiled in accordance with the rate of operation of one or the other, or both, of the two pumps whereby the rate of traverse of the distributor device through the pipe to be coated is directly dependent on the rate at which the two substances are delivered to said distributor device to ensure that the applied coating is of substantially uniform thickness regardless of any variations in the rates at which the substances are pumped through the respective flexible pipes due to variations in their viscosity.

2. The method according to claim 1, including the further step of feeding air under pressure through a third flexible pipe to a compressed air motor forming part of the distributor device for distributing the mixed substance upon the walls of the pipe to be coated, whereby the two substances are intimately mixed together before being flung outwards against the wall of the pipe being coated.

3. Apparatus for use in coating the interior walls of pipes, the apparatus including a rotatable drum upon which at least two flexible pipes are to be coiled to traverse said two pipes through a pipe the interior walls of which are to be coated, a first pump for feeding a liquid or plastics coating medium through a first one of said flexible pipes and a second pump for feeding a liquid curing agent or initiator through a second one of said flexible pipes, a distributing device connected to the ends of the two flexible pipes for mixing together the liquid or plastics coating medium and the liquid curing agent or initiator and for distributing the mixed substance upon the walls of the pipe to be coated, control means for controlling the operation of the two pumps in step with each other and thus for controlling the delivery of the coating medium and of the liquid curing agent or initiator to the distributing device in the required proportions, and control means for controlling the rate of rotation of the rotatable drum in accordance with the rate of operation of the two pumps and thus in accordance with the rate at which the mixed coating issues from the distributing device.

4. A method of coating the interior wall of a pipe with a liquid cold setting resin material mixed with a liquid curing agent or initiator, substantially as hereinbefore described.

5. Apparatus for use in coating the interior walls of pipes, constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.