GB2258901A

GB2258901A - Coating pipes

Info

Publication number: GB2258901A
Application number: GB9116473A
Authority: GB
Inventors: Francis Lodowic Bartels; Damion Daykin
Original assignee: Pipeline Induction Heat Ltd
Current assignee: Pipeline Induction Heat Ltd
Priority date: 1991-07-31
Filing date: 1991-07-31
Publication date: 1993-02-24
Anticipated expiration: 2011-07-31
Also published as: GB9116473D0; GB2258901B

Abstract

An internal pipe coating machine or pig (10) comprises a surface preparation vehicle, means (34) for preparing an internal surface area of a pipe which is located between seals (36), means for heating the internal surface area of a pipe, and means (64) for applying surface coating material to the prepared surface area of the pipe. <IMAGE>

Description

PIPE COATING MACHINE The present invention relates to pipe coating machine, for example, a machine to apply coating to the interior surface of a pipeline in the region of the joint between adjacent lengths of pipe.

Pipelines for use under water and on land to transport oil and gas comprise a "string" or lengths of pipeline which are formed by welding together individual pipes. Each pipe being of a standard length. These lengths of pipe are coated internally with the material such as a fusion bonded epoxy in order to prevent the oxidation of the pipe material. However when the length of pipe are welded together the coating material is removed in the region of the weld before welding takes place, leaving portions of the "string" which are subject to corrosion.

The present invention seeks to provide a coating machine which can be located in a "string" in the region of the welded junctions between the length of pipe, the machine being capable of preparing the internal pipe surface and making good the internal surface coating of the pipe.

Accordingly the present invention provides an internal pipe coating machine comprising a surface preparation vehicle, means for preparing an internal surface area of a pipe, means for heating the said internal area and means for applying a surface coating material to the prepared surface area of the pipe.

The present invention will now be more particularly described with reference to the accompanying drawing which shows an elevation of one form of internal pipe coating machine according to the present invention.

Referring to the drawing an internal pipe coating machine 10 is shown located internally of a pipe "string" 12, of which two pipe lengths 14 & 16 only are shown. The pipe lengths 14 & 16 have been welded together at a junction 18 and the pipe lengths have previously been coated internally with a corrosion resistant coating. The coating in the region of the junction 18 is removed before the welding process takes place, and the machine 10 is constructed and operated to make good the corrosion resistant coating internally of the pipe "string", in the region of the junctions between the pipe lengths.

The machine 10 comprises a main chassis 20 a sub frame 22 attached to the front end of the chassis 20 which is itself mounted on two sets of wheels 24 & 26. The rear wheels 24 are driven by a motor 28 deriving power from a battery 30 and are also provided with a brake unit 32, the motor 28, battery 30 and brake unit 32 all being mounted on the chassis 20.

The motor 28 is preferably a dual speed reversible motor with an integral gearbox and is permanently rated for operation at high ambient temperatures and is self cooled.

The front wheels 26 are not driven or braked.

The sub frame 22 supports a shot blasting and vacuum recovery unit 34 which is located between two expandable seals 36. The unit 34 includes a centrifugal impeller (not shown) driven by an electric motor (not shown), the impeller receiving abrasive grit from a main grit store 38 which is provided with a grit level sensor (not shown). A reserve grit store 40 is provided in communication with the main grit store 38.

The seals 36 are expandable immediately before, and retractable immediately after an abrasive cleaning process.

The purpose of the seals 36 is to prevent the impact of abrasive particles on the internal coated surface of the pipe.

Abrasive particles from the main grit store 38, are fed to the impeller wheel by means of a supply of compressed air from a compressor 42 via a grit control valve 44 and a pipe 46. The abrasive is fed to the impeller wheel in a controlled manner after the impeller wheel has reached it's operating velocity and the feed system is arranged to ensure that the complete circumference of the pipes 14, 16 in the region of the joint 18 receives a supply of the abrasive material from the impeller wheel.

The combined grit blasting and vacuum recovery unit 34 is located between the seals 36 and is connected to the compressor 42 and a vacuum unit 48 both of which are driven by compressor and vacuum motor 50. The compressor unit 42 and vacuum unit 48 are provided with venting valves 52 and the compressor unit 42 is arranged to supply a flow of compressed air along the pipe 46 via the shot control valve 44 to the impeller wheel after the impeller wheel has reached operating velocity. The feed system is arranged so as to ensure that the complete circumference of the pipes in the region of the junction 18 receives a blast of abrasive material.

Two air reservoirs 54 are provided for use if required.

The vacuum recovery unit 34 comprises a number of nozzles 56 connected to the vacuum unit 48 which is arranged to draw material comprising spent abrasive and debris from the weld area into a separation unit 58 where re-usable abrasive material is separated from the lighter dust and spent abrasive particles. The re-usable abrasive material is returned to the main powder store 38 whilst waste material is stored separately in a debris store 60.

In order to ensure complete removal of particles from the weld area a circumferential brush assembly 62 is provided which will cover the entire surface to be cleaned.

The brush assembly 62 is mounted at the leading end of a coating head 64 and passes over the cleaned surface at the junction 18 immediately before the replacement coating is applied. The small number of particles removed by the brush assembly 62 are simply moved out of the area to be coated. No recovery system is provided for use in conjunction with the brush assembly 62.

The material to form the coating on the pipe in the region of the junction 18 comprises a fusion bonded epoxy which is kept in a powder store 66 comprising a sealed container.

A small fluidisation bed 68 is provided to extract coating powder from the store 66 and supply the coating powder to the coating head 64.

A tachometer 70 is provided to monitor the distance travelled by the machine and the direction of movement. The tachometer comprises a rotary encoder mounted on the axle of a wheel 72 in contact with the surface of the pipe 14. The information gathered by the rotary encoder is sent to a programmable logic control unit which is located in a control cubicle 74. The monitored wheel 72 is neither powered or braked in order to eliminate errors resulting from any lack of adhesion between the wheel and the pipe surface.

The data gathered by the tachometer 70 is used to locate the weld at junction 18.

The machine includes an uncoated weld detection module comprising a weld detection unit 76 including a combination of sensors to detect the protrusion of the weld bead into the pipe together with the lack of coating on the internal surface of the pipe. The sensors of the unit are triggered to generate a positive signal. The data provided by the weld detection unit 76 is used in combination with the output from the tachometer 70 to accurately locate the junction areas to be coated. The combination of several sensing elements in detecting a weld greatly enhances the integrity of the weld locating procedure.

A surface roughness gauge (not shown) having a piezo-electric probe is brought into contact with the pipe wall when required to measured the surface profile of the pipe after cleaning. The data provided by this gauge is used by the machine to verify the surface finish produced and the result can be stored to form part of a quality record.

A profile and coating thickness gauge 78 is also provided and comprises a probe which can be brought into contact with the pipe wall when required to measure the thickness of the coating on the finished surface. Again the data can be stored by the machine and can then can be used to form part of the permanent quality record.

A pipe surface temperature monitor 80 is provided to monitor the temperature of the pipe surface in the weld area during the period of time between cleaning and coating the weld area.

The monitor is a non-contact temperature measuring device and the data from the monitor is sent to the programmable logic control which is programmed to detect favourable conditions for the fusion bonded epoxy powder coating. These measures will ensure that the coating operations do not proceed unless the pipe wall is at a suitable temperature. An important coordinating link between the internal and external operations is established by this temperature sensing function. The surface temperature which coating operations commence can again be stored to form part of a quality record.

A video recorder 82 is mounted at the front end of the machine together with a suitable light source. The resulting video tape provides confirmation that the machine is operating satisfactorily and it also forms part of the quality control information for the pipe length of being coated.

The working shot and the coating material stores are provided with level detectors enabling the programmable logic control to check at the end of each operating cycle that sufficient materials are available for the completion of the next cycle.

Sensors are provided at each end of the machine in contact with the pipe wall and any loss of contact by these sensors will cause the machine to stop by means of the programmable logic control.

The outputs from the sensors are connected to a number of interface units which convert the signals from the sensors which can be input to the programmable logic controller.

An electronic recorder is provided to retain the various items information which form a permanent quality record for the pipe coating operation. At the end of each operating cycle the relevant information is recorded.

An interface module is also provided to allow convenient input of data governing the coating operations and extracting of quality data at the end of an operating cycle.

The programmable logic control unit is loaded with computer software appropriate to control all operational and quality functions. The data input from the various sensors on the machine together with an internal clock will run the programme.

The programme will contain a number of operational checks and is designed to halt operations and remove the machine from the pipe in the event of any data input being inconsistent with a normal operating cycle. The programme is free from open loop search/wait routines which could lead to loss of the machine in extraordinary circumstances. Where appropriate items of data will be transferred to the data logger unit and stored for later access.

Valves and relays are provided to convert the low power signal output from the programmable logic controller to useful control functions for the more powerful equipment on the machine.

The coating machine operates in a straight pipe in which the inside of the pipe is free from significant obstructions. The internal factory coating cutback areas of jointed pipe lengths are blast cleaned to an acceptable standard prior to welding. After the pipe lengths have been welded together the inside of the jointed pipe length is kept dry and in an uncontaminated condition.

All the girth welds will have a regular bead protruding into the pipe and around the circumference. The size of the internal weld beads is within pre-determined limits. If the internal weld bead size cannot be guaranteed an alternative system of weld location shall be adopted.

Before commencement of use of the machine, the programmable logic controller is loaded with predetermined functional parameters which control all operations.

The machine is initially located in a transport/launcher assembly (not shown) which is aligned with the end of the pipe 'string'. All routine maintenance inspection and replenishment of consumable materials are carried out with the machine in this assembly. A routine test sequence is performed immediately before coating operations begin.

On receipt of a valid start command the machine proceeds into the pipe under its own power. After a pre-programmed distance the machine slows down to a low velocity consistent with accurate positioning when a weld is detected. When the sensors of the unit 76 detect an uncoated weld the machine stops with the unit 34 positioned centrally over the weld bead.

If a coated weld is detected, the machine will revert to travelling speeds and proceed to the next weld. If no weld is detected within a short pre-programmed distance the control sequence will default to a weld located sub routine. If a weld is not detected within a short distance of the expected position the machine shall return to the launcher assembly.

When the machine is correctly positioned over the weld to be cleaned, the weld cleaning cycle will commence automatically.

The weld joint will be sealed by the seals 36 at each end to protect the internal factory coating on the pipes from abrasion and the blasting process is commenced by operation of the impeller drawing shot from the store 38. The quantity of abrasive used and the duration of blasting is automatically controlled. At the end of the blasting process, the end seals 36 are removed before the recovery process starts in order to eliminate the possibility of spent abrasive material remaining trapped against the seals. The recovery process consists of the vacuum nozzle 56 being moved along the bottom of the pipe in the weld area. The duration of the process is controlled by the programmable logic controller. Any reusable abrasive and dust is separated automatically by the recovery unit 60.

In order to verify the blast cleaning process the surface profile of the pipe wall is measured by the unit 78. If the measuring profile is inadequate the cycle will be repeated.

The surface profile data is stored.

On completion of the cleaning cycle the machine moves a short distance from the weld area and stops. An audible coordinating signal is sent externally of the pipe, and on receipt of this signal, an external induction heating coil (not shown) is applied externally on the pipe in the region of the joint 18 and the weld area is brought up to temperature.

The machine waits whilst periodically repeating the signal and monitoring the temperature of the inside surface of the pipe in the weld area. When the appropriate thermal condition is detected a second audible signal is generated and the coating cycle commences. The maximum duration of the waiting period is limited by the operating programme and if suitable conditions have not been encountered within a pre-set time the machine will exit the pipe. The actual pipe wall surface temperature once coating commences is measured and the data stored. On detecting thermal conditions suitable for fusion bonded epoxy coating the machine moves back into the weld area and positions the coating assembly 64 centrally over the weld bead. Simultaneously the compressed air supply to the powder fluidisation bed 72 is switched on.With the coating head 64 correctly positioned fluidised powder delivery is started. A measured amount of powder is deposited on each joint and the duration of the powder spraying process is automatically controlled by the programmable logic controller.

On completion of the coating cycle the machine pauses to allow the epoxy to cure before applying a dry film thickness gauge 78 to the coated surface. The resulting data is also stored.

On completion of surface preparation and coating cycle the machine checks the remaining levels of the consumable materials i.e. abrasive and fusion bonded epoxy powder.

Depending on the result of this check the machine either proceeds to the next joint to be coated or returns to the transport/launch assembly for replenishment of material.

In order to ensure correct co-ordination between internal and external coating operations, to eliminate operations with the machine incorrectly positioned and to prevent loss of the machine, the operating programme incorporates operational checks and fail-safe default procedures where appropriate.

In certain circumstances such a failure to locate a weld or failure to achieve the required surface finish the machine shall repeat the appropriate procedures a limited number of times in order to achieve the required result.

In all other situations when the machine encounters a sequence of events inconsistent with correct coating procedure it will return to the transport/launch assembly. All movements, actions and waiting periods are subject to pre-programmed distance and time limits to prevent loss of control in extraordinary circumstances.

On completion of an operating cycle the programmable logic control extracts the stored data from the machine and makes a permanent record. This record can incorporate the following information for each coated joint; a) weld identification number, b) distance from end of pipe, c) surface profile prior to coating, d) pipe internal surface temperature prior to coating, and, e) dry film thickness.

In addition a video tape record of the internally coated pipe length is available.

It will be appreciated that the machine performs all of the internal functions and it is anticipated that the cycle time will be approximately thirty minutes for each field joint.

The onboard sensors monitor the distance travelled, the surface profile, coating thickness and pipe surface temperature which assures the quality of the coating functions.

The provision of the programmable logic control permits complex and versatile operating sequences. As the data logger is connected to the input and output module this enables easy access to the quality assurance and quality control data.

The provision of a positive weld detection ensures correct positioning of the machine during cleaning and coating operations.

As the pipe surface temperature is measured internally thorough heating of the pipe wall is ensured.

As the weld areas are sealed during the factory blasting process any grit impact on the coated surface is prevented.

The provision of a two-stage abrasive removable removal ensures that the weld area is free from spent abrasive before coating.

The provision of the on-board video recorder enables a permanent visual record of the coating operations to be available. The monitoring of the consumable store levels prevents ineffectual operation of the machine.

Claims

1. An internal pipe coating machine comprising a surface preparation vehicle, the vehicle including means for preparing an internal surface of a pipe, means for heating the said internal surface area, and means for applying a surface coating material to the prepared surface area of the pipe.

2. A machine as claimed in claim 1 in which the means for preparing the internal surface area of the pipe comprises shot blasting and vacuum shot recovery means.

3. A machine as claimed in claim 2 in which the shot blasting and vacuum shot recovery means are located between expandable seals attached to the vehicle.

4. A machine as claimed in claim 2 or claim 3 in which the shot blasting and vacuum shot recovery includes a centrifugal impeller driven by a motor, a grit store and compressed air supply means to transfer grit from the store to the impeller.

5. A machine as claimed in any one of the preceding claims 2 to 4 in which the vacuum shot recovery means comprises a plurality of nozzles connected to a vacuum means and a separation device to extract reusable abrasive grit.

6. A machine as claimed in claim 1 including a brush assembly arranged to pass over the internal surface of the pipe which has been treated by shot blasting prior to a replacement coating being applied.

7. A machine as claimed in claim 1 in which the means for heating internal surface area of the pipe comprises an induction heating coil located externally of the pipe in the region of the internal surface area to be treated.

8. A machine according to claim 1 in which the means for applying a surface coating material to the internal surface area of the pipe comprises a coating material store, a fluidised bed to extract coating material from the store and a supply of coating material to a coating head, the coating head being arranged to deliver the coating material on to the heated internal surface area of the pipe.

9. A machine as claimed in any one of the preceding claims including means for monitoring the distance travelled by the machine and the direction of movement.

10. A machine as claimed in any one of the preceding claims including means for detecting a welded bead internally of a pipe.

11. A machine as claimed in any one of the preceding claims including means for measuring the surface roughness of the internal surface of a pipe.

12. A machine as claimed in any one of the preceding claims including means for measuring the profile and coating of the internal surface of a pipe and the thickness of any coating applied to the internal surface of the pipe.

13. A machine as claimed in any one of the preceding claims including means for measuring the internal surface temperature of a pipe.

14. A machine as claimed in any one of the preceding claims including a video recorder to provide information relating to the internal surface of a pipe and the operation of the machine within a pipe.

15. A machine as claimed in any one of the preceding claims including contact sensors at each end of the machine in contact with a pipe wall.

16. A machine as claimed in any one of the preceding claims including a programmable logic control programmable to control the operation of the machine and to receive inputs from a plurality of sources on the machine and to operate the machine in dependence upon those input signals.

17. An internal pipe coating machine constructed and arranged for use and operation substantially as herein described and with reference to the accompanying drawing.