APPARATUS

Abstract

There is provided an apparatus for controlling a run of a pig (20) through a tubular object (22), the apparatus comprising: a propulsion device (32) for propelling the pig (20) inside the tubular object (22); a recording device (30) configured to, in real-time, record operating steps and operating parameters of a human-controlled reference run of the pig (20) through the tubular object (22); and a controller (30) programmed to selectively carry out an automatic control mode in which the controller (30) automatically controls a subsequent run of the pig (20) through the tubular object (22) in accordance with the recorded operating steps and operating parameters of the reference run, wherein the automatic control mode includes control of the propulsion device (32) to propel the pig (20) through the tubular object (22).

Claims

1. An apparatus for controlling a run of a pig through a tubular object, the apparatus comprising: a propulsion device for propelling the pig inside the tubular object; a recording device configured to, in real-time, record operating steps and operating parameters of a human-controlled reference run of the pig through the tubular object; and a controller programmed to selectively carry out an automatic control mode in which the controller automatically controls a subsequent run of the pig through the tubular object in accordance with the recorded operating steps and operating parameters of the reference run, wherein the automatic control mode includes control of the propulsion device to propel the pig through the tubular object.

2. An apparatus according to claim 1 including: a pig launcher arranged at a tubular end of the tubular object; and a first position sensor arranged at or adjacent the pig launcher, wherein the first position sensor is capable of detecting a presence of the pig, wherein the controller may be programmed to carry out the automatic control mode in which the controller automatically controls the subsequent run of the pig through the tubular object in accordance with the detection of the presence of the pig by the first position sensor.

3. An apparatus according to claim 1 including: a pig receiver arranged at a tubular end of the tubular object; and a second position sensor arranged at or adjacent the pig receiver, wherein the second position sensor is capable of detecting a presence of the pig, wherein the controller is programmed to carry out the automatic control mode in which the controller automatically controls the subsequent run of the pig through the tubular object in accordance with the detection of the presence of the pig by the second position sensor.

4. An apparatus according to claim 1 wherein the recording device is configured to, in real-time, record at least one duration of a propulsion of the pig during the human-controlled reference run of the pig through the tubular object, and the controller is programmed to selectively carry out the automatic control mode in which the controller automatically controls the propulsion device during the subsequent run of the pig through the tubular object in accordance with the or each recorded duration of the propulsion of the pig of the reference run.

5. An apparatus according to claim 1 wherein the recording device is configured to, in real-time, record an increase or decrease in propulsion force applied to the pig during the human-controlled reference run of the pig through the tubular object, and the controller is programmed to selectively carry out the automatic control mode in which the controller automatically controls the propulsion device during the subsequent run of the pig through the tubular object in accordance with the recorded increase or decrease in propulsion force applied to the pig of the reference run.

6. An apparatus according to claim 5 wherein the recording device is configured to, in real-time, record a timing of the increase or decrease in propulsion force applied to the pig during the human-controlled reference run of the pig through the tubular object, and the controller is programmed to selectively carry out the automatic control mode in which the controller automatically controls the propulsion device during the subsequent run of the pig through the tubular object in accordance with the recorded timing of the increase or decrease in propulsion force applied to the pig of the reference run.

7. An apparatus according to claim 1 including an engine or motor that is capable of being mechanically or hydraulically coupled to the propulsion device so as to enable the engine or motor to drive the propulsion device, wherein the recording device is configured to, in real-time, record a timing of mechanical or hydraulic coupling between the engine or motor and the propulsion device during the human-controlled reference run of the pig through the tubular object, and the controller is programmed to selectively carry out the automatic control mode in which the controller automatically controls the mechanical or hydraulic coupling between the engine or motor and the propulsion device during the subsequent run of the pig through the tubular object in accordance with the or each recorded timing of the mechanical or hydraulic coupling between the engine or motor and the propulsion device of the reference run.

8. An apparatus according to claim 7 wherein the engine or motor is capable of being mechanically or hydraulically decoupled from the propulsion device, wherein the recording device is configured to, in real-time, record a timing of mechanical or hydraulic decoupling between the engine or motor and the propulsion device during the human-controlled reference run of the pig through the tubular object, and the controller is programmed to selectively carry out the automatic control mode in which the controller automatically controls the mechanical or hydraulic decoupling between the engine or motor and the propulsion device during the subsequent run of the pig through the tubular object in accordance with the or each recorded timing of the mechanical or hydraulic decoupling between the engine or motor and the propulsion device of the reference run.

9. An apparatus according to claim 1 including a valve arrangement for directing a flow of a fluid inside the tubular object, wherein the recording device is configured to, in real-time, record one or more states of the valve arrangement during the human-controlled reference run of the pig through the tubular object, and the controller is programmed to selectively carry out the automatic control mode in which the controller automatically controls the valve arrangement during the subsequent run of the pig through the tubular object in accordance with the or each recorded state of the valve arrangement of the reference run.

10. An apparatus according to claim 1 including a fluid contamination level sensor configured to detect a contamination level of a returned fluid from the tubular object, the apparatus further including a fluid flow control device for directing a flow of the returned fluid from the tubular object into a selected one of a clean fluid storage tank and an effluent storage tank, wherein the controller is programmed to selectively carry out the automatic control mode in which the controller automatically controls the fluid flow control device during the subsequent run of the pig through the tubular object in accordance with the detection of the contamination level of the returned fluid from the tubular object.

11. An apparatus according to claim 1 including at least one sensor configured to detect a condition of an interior of the tubular object, wherein the controller is programmed to selectively carry out the automatic control mode in which the controller automatically controls the propulsion device during the subsequent run of the pig through the tubular object in accordance with the detected condition of the interior of the tubular object.

12. An apparatus according to claim 1 wherein the at least one sensor includes at least one pressure sensor configured to detect a pressure parameter of an interior of the tubular object, wherein the controller is programmed to selectively carry out the automatic control mode in which the controller automatically controls the propulsion device during the subsequent run of the pig through the tubular object in accordance with the detected pressure parameter of the interior of the tubular object.

13. An apparatus according to claim 1 wherein the at least one sensor includes at least one flow sensor configured to detect a flow parameter of an interior of the tubular object, wherein the controller is programmed to selectively carry out the automatic control mode in which the controller automatically controls the propulsion device during the subsequent run of the pig through the tubular object in accordance with the detected flow parameter of the interior of the tubular object.

14. An apparatus according to claim 1 including an input device for manual input of a stop command by a human, wherein the controller is programmed to stop the automatic control mode in response to the input of the stop command into the input device.

15. An apparatus according to claim 1 wherein the controller is programmed to selectively carry out the automatic control mode for a single run or a fixed number of consecutive runs.

16. An apparatus according to claim 1 wherein the controller is programmed to selectively carry out the automatic control mode for a fixed duration of time.

17. An apparatus according to claim 1 wherein the recording device includes a processor and memory including computer program code, the memory and computer program code configured to, with the processor, enable the recording device at least to, in real-time, record the operating steps and operating parameters of the human-controlled reference run of the pig through the tubular object.

18. An apparatus according to claim 1 wherein the controller includes a processor and memory including computer program code, the memory and computer program code may be configured to, with the processor, enable the controller at least to carry out the automatic control mode in which the controller automatically controls the subsequent run of the pig through the tubular object in accordance with the recorded operating steps and operating parameters of the reference run, wherein the automatic control mode includes control of the propulsion device to propel the pig through the tubular object.

19. A computer-implemented method of controlling a run of a pig through a tubular object, the computer-implemented method comprising the steps of: recording operating steps and operating parameters of a human-controlled reference run of the pig through the tubular object; and carrying out an automatic control mode in which a subsequent run of the pig through the tubular object is automatically controlled in accordance with the recorded operating steps and operating parameters of the reference run, wherein the automatic control mode includes control of a propulsion device to propel the pig through the tubular object.

20. A computer program comprising computer code configured to perform the computer-implemented method of claim 19.

Description

[0076] Preferred embodiments of the invention will now be described, by way of non-limiting examples, with reference to the accompanying drawings in which:

[0077] FIG. 1 shows an apparatus according to an embodiment of the invention; and

[0078] FIG. 2 shows a pig inside a serpentine heater tube.

[0079] The figures are not necessarily to scale, and certain features and certain views of the figures may be shown exaggerated in scale or in schematic form in the interests of clarity and conciseness.

[0080] The following embodiments of the invention are described with reference to their use in cleaning of tubes and tubing, such as fired heater, furnace or boiler process tubes, but it will be appreciated that the following embodiments of the invention may also be used in other pigging and inspection operations and other tubular objects, such as clustered small bore heat exchangers, pipes and pipelines.

[0081] An apparatus according to an embodiment of the invention is shown in FIG. 1 and is for controlling a run of a scraper pig 20 inside a serpentine heater tube 22. FIG. 2 shows the pig 20 inside the heater tube 22. The apparatus comprises first and second pig launchers 24,26, a sensor arrangement, a desk control system 28 and a programmable logic controller (PLC) 30. It will be appreciated that each of the desk control system 28 and the PLC 30 may be replaced by other types of controllers that provide the same controller functions.

[0082] The first and second pig launchers 24,26 are respectively connected to inlet and outlet ends of the heater tube 22. The pig launchers 24,26 also function as pig receivers. In use, the pig 20 is launched from and received by each pig launcher 24,26. The apparatus includes a fluid propulsion device 32 in the form of a fluid pump for providing fluid pressure (e.g. water pressure) to drive the pig 20 through the heater tube 22. Alternatively the pig may be driven by an on-board drive, such as a motor. The pig 20 is preferably driven in both directions through the heater tube 22 but in other embodiments may be driven in only one direction through the heater tube 22.

[0083] The apparatus includes an engine 34 and a clutch mechanism 36. Other drive connections may be used in place of the clutch mechanism 36. In use, the clutch mechanism 36 is operable to mechanically couple the engine 34 and the fluid pump 32 so that the engine 34 may drive the fluid pump 32, and the clutch mechanism 36 is operable to mechanically decouple the engine 34 and the fluid pump 32 so that the engine 34 is physically separated from the fluid pump 32.

[0084] In some embodiments of the invention, a motor may be used to replace the engine 34. When using a hydraulic or electric motor, the clutch mechanism 36 will not be required. Various drive connections may be used to couple the motor to the fluid pump 32 so that the motor may drive the fluid pump 32. The hydraulic or electric motor may be permanently connected to the fluid pump 32. The motor is controllable to reduce its RPM to 0 by means of a hydraulic or electric motor controller.

[0085] The apparatus includes a valve arrangement 38 for directing a flow of a fluid inside the heater tube 22. In use, the valve arrangement 38 may include a single control valve or multiple control valves, and the or each control valve is operable to direct the fluid to flow from the inlet end to the outlet end or from the outlet end to the inlet end.

[0086] The apparatus further includes a fluid flow control device 40, e.g. a valve configuration, for directing a flow of the returned fluid from the heater tube 22 into a selected one of a clean fluid storage tank 42 and an effluent storage tank 44. Optionally the apparatus further includes a fluid contamination level sensor 46 configured to detect a contamination level of the returned fluid.

[0087] The apparatus includes pressure and flow sensors 48,50 for respectively monitoring pressure and flow parameters of the interior of the heater tube 22. The pressure and flow measurements may be shown on a display screen of the desk control system 28 or a separate display screen or a gauge. When the pig 20 enters the heater tube 22 from a pig launcher 24,26, changes in pressure and/or flow may take place due to, for example, the pig 20 transitioning between sections of the heater tube 22 of different shapes and/or sizes or due to the pig 20 approaching a bend or end section of the heater tube 22. The extent of the changes in pressure and flow parameters of the interior of the heater tube 22 will be vastly different depending on the feature of the heater tube 22 towards which the pig 20 is travelling. For example, a significant increase or decrease in pressure and flow indicates that the pig 20 has reached an end of the heater tube 22. Also, for example, as the pig 20 travels through the heater tube 22, a pressure line chart may appear as a series of “beats” or “spikes”, with each beat or spike being associated with a bend.

[0088] Operating steps of a decoking or “pigging” run in an exemplary heater tube 22, such as a serpentine furnace tube, is carried out as follows when manually controlled by a human operator using the desk control system 28. The run is described with reference to an initial launch of the pig 20 from the first pig launcher 24 but applies mutatis mutandis to an initial launch of the pig 20 from the second pig launcher 26. [0089] 1. The operator inserts a pig 20 into the first pig launcher 24. [0090] 2. Via the desk control system 28, the operator sets the valve arrangement so that any fluid pumped into the heater tube 22 flows from the inlet end to the outlet end. [0091] 3. Via the desk control system 28, the operator operates the clutch mechanism 36 to mechanically couple the engine 34 and the fluid pump 32. Via the desk control system 28, the operator then starts the engine 34 to drive the fluid pump 32 so that water begins to flow through the heater tube 22. [0092] 4. Via the desk control system 28, the operator increases the engine's RPM (e.g. using an electronic potentiometer or Hall effect potentiometer) to apply a fluid propulsion force to the pig 20 and thereby launch it from the pig launcher 24 and drive it through the heater tube 22. The RPM level may vary depending on pig size, interior conditions of the heater tube 22 (such as contamination level), size of the heater tube 22 and so on. The RPM level may change throughout the run as the operator adapts the RPM level in response to variable and/or unexpected conditions of the heater tube 22. [0093] 5. The operator monitors the pressure and flow measurements and timings on the display screen of the desk control system 28 as the pig 20 moves through the heater tube 22. [0094] 6. When the pig 20 reaches the second pig launcher 26, the operator will observe a drop in pressure and a discolouration of returned water. The discolouration is caused by the fouling removed by the pig 20 during the run. [0095] 7. Via the desk control system 28, the operator operates the fluid flow control device 40 to divert the returned fluid so that the returned fluid flows into the effluent storage tank 44 instead of the clean fluid storage tank 42. Meanwhile the fluid pump 32 is controlled to pump water through the heater tube 22 until the returned fluid returns to a clean colour. [0096] 8. Once the returned fluid returns to a clear colour, the operator operates the fluid flow control device 40 to divert the returned fluid so that the returned fluid flows into the clean fluid storage tank 42 instead of the effluent storage tank 44. [0097] 9. The operator decreases the engine's RPM to switch the engine 34 to an idle state before operating the clutch mechanism 36 to mechanically decouple the engine 34 and the fluid pump 32. [0098] 10. The operator reconfigures the valve arrangement 38 so that any fluid pumped into the heater tube 22 flows in the opposite direction from the outlet end to the inlet end. [0099] 11. Steps 3 to 9 are repeated, with the fluid flowing and the pig 20 moving in the opposite direction through the heater tube 22.

[0100] In embodiments where the motor replaces the engine 34, the RPM of the motor is increased and decreased using a motor RPM controller.

[0101] The run can be repeated as many times as required (typically greater than 200 individual runs) as part of an overall decoking process before the heater tube 22 is fully cleaned. Pigs may be changed or renewed after several runs (typically after 10-30 individual runs). It is envisaged that, in other embodiments of the invention, the operating steps may vary, the sequence of operating steps may vary, and/or the operating parameters may vary. For example, steps 10 and 11 may be omitted from the run.

[0102] However, there are inherent reliability and inefficiency problems associated with manual control of the decoking run, especially when the run is repeated continuously. Such problems may arise due to, for example, operator error, limited operator reaction time, distractions, operator break/rest requirements and so on, non-limiting examples of which are set out as follows: [0103] The operator might forget to reduce the engine's RPM before disengaging/engaging the clutch mechanism 36, which can cause mechanical damage to components of the apparatus. [0104] The operator might forget to divert the contaminated returned fluid into the effluent storage tank 44, thus causing the supply fluid in the clean fluid storage tank 42 to become contaminated. [0105] When the pig 20 reaches a point of restriction in the heater tube 22, it is usually necessary to reduce the engine's RPM and disengage the clutch mechanism 36. Since the pig 20 reaching the point of restriction can be an unexpected occurrence, there is a risk of the pig 20 getting stuck if the operator is too slow to take the necessary actions. [0106] Time can be lost when an operator is interrupted (e.g. by clients, engineers or visitors) or takes a rest or break, which may be scheduled or unexpected.

[0107] To address these problems, the apparatus of the invention is configured and operated as follows.

[0108] The sensor arrangement includes a pair of position sensors. A first position sensor 52 is arranged at the inlet end of the heater tube 22 and adjacent to the first pig launcher 24. A second position sensor 54 is arranged at the outlet end of the heater tube 22 and adjacent to the second pig launcher 26. Each position sensor 52,54 is an electromagnetic pig signaller that is capable of detecting the passage of the pig 20. The pig 20 is fitted with a magnet, such as a neodymium rare earth permanent magnet. The magnet is cast inside, or bolted to an outer core of, the pig 20 at the manufacturing stage. It will be appreciated that other types of sensors may be used as position sensors to detect the passage of the pig 20 travelling inside the heater tube 22. It will be further appreciated that one or more further position sensors (e.g. a third position sensor, a fourth position sensor, a fifth position sensor and so on) may be arranged at other locations along the heater tube 22. For example, a pair of position sensors may be arranged at inlet and outlet ends of each section of the heater tube 22 and/or multiple position sensors may be arranged and spaced apart along a length of each section of the heater tube 22.

[0109] The PLC 30 functions as a recording device and a controller. More specifically, the PLC is configured to, in real-time, record the operating steps and the operating parameters of a run of the pig 20 through the heater tube 22 that are controlled and inputted by the operator via the desk control system 28, and the PLC 30 is configured to selectively carry out an automatic control mode in which the PLC automatically replicates the recorded run of the pig 20 through the heater tube 22. In order to carry out the automatic control mode, the PLC 30 is able to control components of the apparatus directly, via the desk control system 28 or a combination of both.

[0110] The pig signallers 52,54 are configured to be in wireless communication with the PLC 30, which is exemplarily achieved through a low-power wide-area network (WAN) protocol that is capable of linking battery-operated units. A signal from each pig signaller 52,54 is transmitted through an antenna mounted directly to the pig signaller 52,54 and received at a receiver, e.g. a base station, that is connected to or associated with the PLC 30.

[0111] The PLC 30 may be programmed to identify the pig signaller 52,54 from which a given wireless signal originated through evaluation of: [0112] unique identifiers (such as serial numbers) encoded in the wireless signals transmitted by the pig signallers 52,54; and [0113] a sequence of the wireless signals transmitted by the pig signallers 52,54. The receipt of a wireless signal from a given pig launcher 24,26 after receiving a wireless signal from the other pig launcher 24,26 indicates that the pig 20 is being received by the corresponding pig launcher 24,26. The receipt of two consecutive wireless signals from a given pig signaller 52,54 indicates that the pig 20 is being launched by the corresponding pig launcher 24,26.

[0114] It is envisaged that, in other embodiments of the invention, the wireless communication between the sensor arrangement and the PLC 30 may be carried out using Bluetooth™ or Wi-Fi equipment. It is also envisaged that, in still other embodiments of the invention, the sensor arrangement may be configured to be in wired communication with the PLC 30 or configured to be in wired and wireless communication with the PLC 30.

[0115] After the signals are received by the PLC 30, the signals are interpreted by a computer program that acts as a serial bus emulator. The information from the pig signallers 52,54 are deciphered and formatted into useable pieces of information that can be recognised and processed by the computer program.

[0116] Operating steps of a decoking run are carried out as follows when automatically controlled by the PLC 30 after a decoking run manually controlled by the human operator using the desk control system 28. The run is described with reference to an initial launch of the pig 20 from the first pig launcher 24 but applies mutatis mutandis to an initial launch of the pig 20 from the second pig launcher 26. [0117] 1. The operator manually carries out a reference run of the pig 20 through the heater tube 22 using the desk control system 28 as described above. [0118] 2. While the human-controlled reference run is being carried out, the PLC 30 at the same time records the operating steps and operating parameters of the human-controlled reference run. [0119] 3. After the human-controlled reference run has ended, the PLC 30 ends the recording process. [0120] 4. The first pig signaller 52 detects that the pig 20 is in the first pig launcher 24, and sends a signal to inform the PLC 30 about the detected presence of the pig 20 in the first pig launcher 24. [0121] 5. The PLC 30 sets the valve arrangement 38 so that any fluid pumped into the heater tube 22 flows from the inlet end to the outlet end. The automatic setting of the state of the valve arrangement 38 by the PLC 30 follows the recorded manual setting of the state of the valve arrangement 38 by the human operator in the reference run. [0122] 6. The PLC 30 operates the clutch mechanism 36 to mechanically couple the engine 34 and the fluid pump 32. The PLC then starts the engine to drive the fluid pump so that water begins to flow through the heater tube 22. The automatic control of the timing of the mechanical coupling between the engine 34 and the fluid pump 32 by the PLC 30 follows the recorded manual control of the timing of the mechanical coupling between the engine 34 and the fluid pump 32 by the human operator in the reference run. [0123] 7. The PLC increases the engine's RPM (e.g. using an electronic potentiometer) to apply a fluid propulsion force to the pig 20 and thereby launch it from the pig launcher 24 and drive it through the heater tube 22. The automatic control of the increase in the engine's RPM and the timing of the increase by the PLC 30 follows the recorded manual control of the increase in the engine's RPM and the timing of the increase by the human operator in the reference run. The RPM may vary during the automated run in the same way as the reference run. The automatic control of the duration of the propulsion of the pig 20 by the PLC 30 follows the recorded manual control of the duration of the propulsion of the pig 20 by the human operator in the reference run. [0124] 8. When the pig 20 reaches the second pig launcher 26, the second pig signaller 54 sends a signal to inform the PLC 30 about the detected presence of the pig 20 in the second pig launcher 26. [0125] 9. At this time the PLC 30 controls the fluid flow control device 40 to divert the returned fluid so that the returned fluid flows into the effluent storage tank 44 instead of the clean fluid storage tank 42. Meanwhile the PLC 30 controls the fluid pump 32 to pump water through the heater tube 22 so that the returned fluid returns to a clean colour. Thereafter, the PLC 30 controls the fluid flow control device 40 to divert the returned fluid so that the returned fluid flows into the clean fluid storage tank 42 instead of the effluent storage tank 44. The automatic control of the fluid flow control device 40 and the fluid pump 32 by the PLC 30 follows the recorded manual control of the fluid flow control device 40 and the fluid pump 32 by the human operator in the reference run. [0126] 10. The PLC 30 decreases the engine's RPM to switch the engine to an idle state before operating the clutch mechanism 36 to mechanically decouple the engine 34 and the fluid pump 32. The automatic control of the timing of the mechanical decoupling between the engine 34 and the fluid pump 32 by the PLC 30 follows the recorded manual control of the timing of the mechanical decoupling between the engine 34 and the fluid pump 32 by the human operator in the reference run. [0127] 11. The PLC 30 reconfigures the valve arrangement 38 so that any fluid pumped into the heater tube 22 flows in the opposite direction from the outlet end to the inlet end. Again, the automatic setting of the state of the valve arrangement 38 by the PLC 30 follows the recorded manual setting of the state of the valve arrangement 38 by the human operator in the reference run. [0128] 12. Steps 6 to 13 are repeated by the PLC 30, with the fluid flowing and the pig 20 moving in the opposite direction through the heater tube 22.

[0129] In embodiments employing the use of the fluid contamination level sensor 46, any discolouration in the returned fluid may be detected by the fluid contamination level sensor 46 during the automated run, which results in the fluid contamination level sensor 46 sending a signal to the PLC 30 so that the PLC 30 operates the fluid flow control device 40 to temporarily divert the returned fluid so that the returned fluid flows into the effluent storage tank 44 instead of the clean fluid storage tank 42.

[0130] The configuration of the apparatus of the invention enables the automation of the run of the pig 20 through the heater tube 22 by way of automatic recording and replication of the previous human-controlled reference run of the pig 20. By automating the run of the pig 20 through the heater tube 22, the decoking process becomes more efficient whilst simultaneously reducing risk induced by human operator error and limited reaction time during manually controlled runs. Furthermore, recording the human-controlled reference run in real time enables the automated run to replicate the human operator's controls that might vary depending on the conditions of the heater tube 22 on the day of the decoking process. On the other hand, an automated run based on standard pre-programmed setpoints is designed for a fixed set of conditions of the heater tube 22 and thereby results in a sub-optimal run of the pig 20 through the heater tube 22 if the conditions of the heater tube 22 differs from the fixed set of conditions.

[0131] The automatic control mode by the PLC 30 may be carried out for a single run, for multiple runs or indefinitely without operator involvement until such time as, for example, the pig 20 needs to be replaced by a different pig, e.g. a newer pig, a sharper pig, a larger diameter pig or until such time that the operator feels it necessary to change the operating steps, the operating parameters and/or the sequence of operating steps by recording a new human-controlled reference run.

[0132] In addition to the above, the controller of the apparatus may be programmable with desired run setpoints, such as RPM, runtime, pressure, flow or a combination thereof.

[0133] Optionally the apparatus may include an input device, such as a button, a lever or an electronic icon on a human-machine interface, for manual input of a stop command so that the operator may manually stop the automatic control mode. In this case the PLC 30 is programmed to stop the automatic control mode in response to the input of the stop command into the input device.

[0134] Further the PLC 30 may be programmed to selectively carry out the automatic control mode for a single run or a fixed number of consecutive runs, or may be programmed to selectively carry out the automatic control mode for a fixed duration of time.

[0135] The PLC is preferably programmed to record the data about the pig's travel inside the heater tube 22 and automatically generate log sheets with details about the pig's travel through the heater tube 22, e.g. quantity of runs, duration of runs, operating parameters, pressure measurements and timings, flow measurements and timings, etc.

[0136] It is envisaged that, in other embodiments of the invention, the PLC 30 may be programmed so that, during the automatic control mode, the PLC can control the fluid pump 32 responsive to pressure measurements and/or flow measurements received from the pressure sensor(s) 48 and/or the flow sensor(s) 50. This enables the PLC 30 in the automatic control mode to, if required, react to changes in the interior condition of the heater tube 22.

[0137] The pig 20 may become stuck if it enters a section of the heater tube 22 with reduced internal diameter, which may be caused by internal fouling, use of an oversized pig or a change in tube internal diameter. Therefore, if a pig enters a restriction (high coke build up, or a smaller tube/concentric reducer), the PLC 30 will receive information about a pressure spike and thereby control the fluid pump 32 to reduce or stop the propulsion force. This will lessen the risk of the pig 20 being forced into the restriction and getting stuck.

[0138] The interior of the heater tube 22 may be more heavily contaminated in one particular section. Consequently it may be desirable to operate the pig 20 to move back and forth inside the particular section to remove the heavy contamination. Therefore, when the pig 20 arrives at the heavily contaminated section, the PLC 30 will receive pressure and/or flow information corresponding to the heavily contaminated section and thereby control the fluid pump 32 to drive the pig 20 to move back and forth inside the heavily contaminated section.

[0139] The invention is applicable to an apparatus in the form of a single pumping unit, a double pumping unit, a quad pumping unit or a unit having a different number of fluid pumps. In embodiments employing the use of multiple fluid pumps, each fluid pump may be used to drive a respective pig to decoke a respective one of a plurality of heater tubes. The recordal of the operating steps and operating parameters of the human-controlled reference run and the subsequent automatic control mode may be carried out in respect of each heater tube independently. Alternatively the recordal of the operating steps and operating parameters of the human-controlled reference run may be carried out for one of the heater tubes, and the subsequent automatic control mode may be carried out for multiple heater tubes based on the same human-controlled reference run.

[0140] It will be appreciated that the above numerical values are merely intended to help illustrate the working of the invention and may vary depending on the requirements of the apparatus and the associated application.

[0141] The listing or discussion of an apparently prior-published document or apparently prior-published information in this specification should not necessarily be taken as an acknowledgement that the document or information is part of the state of the art or is common general knowledge.

[0142] Preferences and options for a given aspect, feature or parameter of the invention should, unless the context indicates otherwise, be regarded as having been disclosed in combination with any and all preferences and options for all other aspects, features and parameters of the invention.