EDDY CURRENT PIPELINE INSPECTION DEVICE AND METHOD

Abstract: A pipeline inspection vehicle (10) can be towed through a pipeline (11) via cable (12). The vehicle includes a power unit (20), a master processor module (21) and a coil (24) which generates an eddy current field which passes along the pipe. The resultant field is detected by master sensor ring (22) and slave sensor ring (25). Information on amplitude and phase of the detected field together with vehicle orientation information is sent to the base station and hence to computer (31). A distance encoder (32) assists in locating the position of any faults detected.

Description: EDDY CURRENT PIPELINE INSPECTIONDEVICE AND METHOD The invention relates to pipeline inspection and more specifically to a vehicle which can be towed through a pipeline to allow analysis of its wall structure. Large diameter pipes can be tested using complex pipeline pigs which may even operate when the pipes are 'live', i.e. when gas, for example, is flowing through the pipe. The present invention seeks to provide an arrangement which allows both ferrous and non-ferrous small diameter pipes to be tested for defects. According to the invention there is provided a pipeline inspection device for travelling through a pipeline and including means for generating an eddy current field within the pipeline; and means for detecting the resultant field following passage through the pipe structure. Further according to the invention there is provided a method of testing a pipeline comprising generating an eddy current in a coil, moving the coil through the pipeline, ana detecting the eddy current induced in the wall of the pipeline to allow faults in the pipeline to be determined. The invention will now be described by way of example in which: Figure 1 shows an embodiment of the pipeline vehicle of the present invention; Figure 2 shows the control and data handling arrangements of Figure 1 m more detail; Figure 3 shows a sensing configuration with associated processing; and Figure 4 shows a flow chart associated with system operation. The pipeline inspection arrangement of Figure 1 comprises a towed vehicle 10 shown within pipe llwhich can be towed by a winch (not shown) via cable 12 to allow testing of a pipe through which it passes. The towed vehicle comprises several linked devices. These include a power unit 20 and master processor module 21 and a master sensor ring 22. A coil 24 generates a remote field edαy current which is detected via sensor ring 22. The coil is separated from the sensor ring 22 by means of separator 23 to attenuate any directly transmitted field between the coil 24 and sensor 22. A slave ring 25 is also provided separated from the coil 24 by attenuating separator 26. The sensor ring 25 is connected to slave processor module 27. A base station 30 provides the link between the vehicle 10 and a computer 31 so as to initiate testing and to receive resulting information. A distance encoder 32 s provided to generate distance information as the vehicle travels through the pipeline. The distance encoder can conveniently be mounted on the cable wheel (not shown) associated with the winch so that as the vehicle is towed the distance travelled is continuously updated back to the base station 30. The arrangement is configured to induce eddy currents into the wall of the pipeline due to the a.c. field generated by coil 24. We have determined that such eddy currents can be used in both ferrous and non- ferrous pipelines (i.e. magnetic and non-magnetic) and with a smooth pipe wall a uniform field decaying with distance is provided. When non uniformity in the surface is present due to pitting, cracks, etc., then changes in the detected eddy currents field occurs and these are αetecteα via sensors 22 and 25. By utilising two sensor array sets the ability to pinpoint the defect point is enhanced. In addition each sensor array have typically twenty-four sensors n each so that m total 48 amplitude sensing and 48 phase sensing measurements can be made covering the periphery of the pipe. We have determined that by taking phase measurements m addition to the amplitude measurements it is possible to discriminate between internal and external pipe wall defects. The information to and from tne base station can be passed on 48 analogue and 48 digital channels. The arrangement described is capable of operating within small pipes of 4" diameter or less and has capability of coping with 1.5D bends m the pipeline. The system can typically provide a 6mm scan interval with a winch speed of about 6 metres per minute. An x and y accelerometer is incorporated within the vehicle to allow orientation information to be sent to the computer as the vehicle may partially rotate during its travel through the pipeline. The towing range can be several hundred metres so providing a very useful and cost effective inspection mechanism. The information passed to computer 31 via oase station 30 allows a number of parameters to be determined from the detected information. This can give a display of: 1. amplitude and phase 2. azimuth 0-360° 3. velocity In addition the defects can be calculated to mcluαe the size and position of defects using the computer. The vehicle of Figure 1 will have electronic control, power and data transmission requirements which are shown m more detail m Figure 2. The vehicle power requirements are received on line 35 and pass to power unit 20. The input can be 110V a.c. supply and the power unit output will be 150V d.c. for the coil drive requirements using line 33. Low voltage d.c. will be available for the electronics circuits within the vehicle (e.g. ± 5V) . Communication to and from the vehicle and the base station will be via connection 30. A suitable communication protocol will be employed (e.g. RS 232) . The master processor 21 will be microprocessor controlled and include data links between the master sensor assembly 22 and the slave processor to ensure synchronism as well as control 32 to the coil drive. Serial data passes oetween master processor 21 and sensor 22 via line 31. There is also passage of data between slave processor 27 and sensor 25 via line 34. Rather than incorporating all the processing requirements within the slave and master processors 27 and 21, it is possible to provide signal conditioning and processing within the sensor assembly as shown in Figure 3 for the master sensors 22. Here dedicated acquisition hardware (signal conditioning 22d, e and microcontroller 22f) give improved noise performance and reduced processing load to the processor in the master pack 21, and allow increased front-end processing. Timing of data sampling will be controlled by the phase reference input. Sample rate will be dependent upon the excitation frequency selected. The microcontroller will be implemented using an 8 bit microcontroller with minimum port capability. The serial data interface will adopt a standard protocol. Channels will be paired as shown, each microprocessor 22f supporting t./o sensor cnanne.s 22a, 22b with associateα signal conditioning 22d, 22e. Returning to Figure 2, the single drive coil 24 provides fielα excitation and the sensors are maintained in close proximity to the pipe wall with x and y orientation sensors in each sensor assembly 22, 25 to compensate for rotation within the pipe and skew between the t^o censor assemces. Prior to operation, the vehicle identification is read and data is loadeα into a calibration file within the computer 31. Vehicle configuration is then set up v a the computer to give the number of channels and sensor address requirements . In addition the coil current s set to meet operational requirements. Finally the coil excitation frequency s set. This may be within the range of 20Hz to IKHz and selected dependent on the pipeline material under investigation as both ferrous and non-ferrous pipel tes are to be tested. In operation the vehicle is towed through the pipe and as it does so the distance encoder 32 of Figure 1 will produce data for distance travelled. To determine defects n the pipeline, a data scan command is sent from the computer and received via the base station in the vehicle master controller. Th s information is then repeated to the slave controller by the master. Scanning to the channels is then effected. The slave sends the data to the master in packet format and the master receives data also from the master sensors. The master assembles the data including amplitude and phase information and orientation data from both sensor rings and sends this to the host computer for display and processing. A flow chart of typical system operation is shown in Figure 4. In addition the master controller synchronises the slave and generates t e drive coil excitation signal. Compensating time delays can oe incorporated to ensure synchronisation between master and slave.

Claims: CLAIMS 1. A pipeline inspection device f r travelling througn a pipeline and including means ::r generating an eddy current field within the pipeline; and means for detecting the resultant field following passage through the pipe structure. 2. A device as claimed m claim 1, including means for determining faults within the p pe from the detected information. 3. A device as claimed in claim 1 or 2, including a first detector on the device for detecting eddy current information at a first location and a second detector spaced longitudinally therefrom for detecting eddy current information at a second location. 4. A device as claimed n claim 1, 2 or 3, including means for determining eddy current information concerning both amplitude and phase. 5. A device as claimed in any one of claims 1 to 4, including means for determining the orientation of the inspection device as it travels through tne pipeline. 6. A device as claimed in any one of claims 1 to 5 including mear.s for determining the distance travelled by the inspection device. 7. A device as claimed m any one of claims 1 to 6 including means for generating data packets for transmission to a remote computer for eva_uatιon. 8. A device as claimed in any one of claims 1 to 7 including means for determining the αimensions of a fault when present on the pipeline. 9. A device as claimed n any one of claims 1 to 8 including means for discriminating between faults on the inner and outer surface of the pipeline wall. 10. A device as claimed in any one of claims 1 to 9, wherein the means for detecting the field comprises a ring of sensors each spaced around its periphery. 11. A method of testing a pipeline comprising: generating an eddy current m a coil, moving the coil through the pipeline, ana detecting the eddy current induced m the wall of the pipeline to allow faults in the pιpel_ne to be determined. 12. A methcα as ciaimeα m claim II, including the step of detecting the induced eαdy current at two longitudinally spaced locations. 13. A methoα as claimed in claim 11 or 12, wherein the detecting step includes detecting the amplitude and the phase of the eddy current. 14. A method as claimed in claim 11, 12 or 13, including the step of determining the orientation of the detector oosition in the pipeline. 15. A method as claimed in any one of claims 11 to 14, including the step of determining the distance travelled through the pipeline. 16. A method as claimed in any one of claims 11 to 15, including the step of determining the dimensions of a fault ιr. the pipeline from detected information. 17. A method as claimed in any one of cla rs 11 to 16 including the step of discriminating between a fault on the inner and outer surface of the pipeline. 18. A pipeline inspection device substantially as described herein with reference to the accompanying drawings . 19. A method of testing a pipeline substantially as described herein.

Inventors: BURD JOHN FERRIS, RAMSHAW JAMES EDWARD, BURD, JOHN, FERRIS, RAMSHAW, JAMES, EDWARD
Applicants: BRITISH GAS PLC, BURD JOHN FERRIS, RAMSHAW JAMES EDWARD, BG PLC, BURD, JOHN, FERRIS, RAMSHAW, JAMES, EDWARD
Application year: 1998
Main classification: G01N27
IPC codes: G01N27