GB2509734A

GB2509734A - Conductivity tool for non-metallic pipeline inspection

Info

Publication number: GB2509734A
Application number: GB1300478.3A
Authority: GB
Inventors: Anthony Hugh Bond; Peter Henley; Stephen Russell
Original assignee: WRC PLC
Current assignee: WRC PLC
Priority date: 2013-01-11
Filing date: 2013-01-11
Publication date: 2014-07-16
Also published as: GB201300478D0

Abstract

An inspection tool for buried non-metallic pipelines which uses a conductive sensor head passed along the length of a pipeline to detect leaks and metallic pipe fittings as in Figure 1. The sensor head 1 may include a location device to enable the position of a leak or metallic fitting to be marked on the surface above the pipeline. The sensor head may also include a metal detector to discriminate between leaks and metallic fittings. Signals for the sensor head and a cable counter are used to generate a plot of conduction current against distance moved into the pipeline. Leaks and metallic fittings show as conduction peaks in the trace generated. Typically the sensor head with cable is pulled along the pipeline by the pipeline flow using a drogue 12 attached to the sensor head.

Description

I

CONDUCTIVITY TOOL FOR NON-METALLIC PIPELINE INSPECTION

This invention relates to the field of pipeline inspection.

Pipelines are an essential part of the infrastructure of life. Most cities include pipelines for gas, drinking water and sewage whilst industrial pipelines may be used to transport oil, foods, chemical reagents; heating/cooling liquids/gases and process wastewaters. Pipeline flow may be forced by pressure, or simply use a sloping pipe and the force of gravity to transfer liquid. Most pipelines are subject to deterioration by a range and often combinations of mechanisms such as corrosion, fatigue, loss of joint integrity and mechanical damage from excessive loads, Pipeline operators managing these assets'need information regarding their condition and their capacity for continuing service if they are to make sound economic decisions on repairs, renovations and replacement. To meet thi need, inspection tools have been developed to gather information such as wall thickness on corroding pipes, cracks in welded steel pipes, leaks, deformation and joint displacement. These tools are typically either pumped through the pipeline, gathering and logging inspection data between launch and capture points, or tethered at a launch point from which they are retrieved after the tool has passed along-the section of interest. Sensors have been developed to mount on inspection devices to gather pipeline data using for example ultrasonics, magnetic sensors or special cameras. Many of these sensors are highly sophisticated and the data generated is processed to present the operator with a clear and accurate understanding of the pipeline condition. A sensor which has been little used until, now is electrical conductivity.

Metallic pipelines which have an insulated coating may be inspected using a holiday detector. This device applies a high voltage between a probe, usuallyhandheld, and the pipeline metallic substrate.

The user passes the probe across the surface of the coating, noting any positions where the coating has deteriorated and a significant current passes between probe and pipeline. This may be on the inside or outside of the pipe. This is the main use of conductivity in existing pipeline inspection equipment.

Conductivity can also be used on non-metallic pipelines carrying conducting liquids to detect leaks and metallic fittings. This is of little practical interest on pipelines running above ground, but provides valuable information on buried pipelines. Acoustic detection of leaks on non-metallic pipelines is widely effective when the acoustic sensor is passed along the pipe so that is reaches the leak.

However it is not always successful, particularly on pressures below about 2 bar such as often occur on sewage rising mains. The conductivity method is thus a valuable additional inspection method.

Where records on a pipeline are poor, information about the number of previous repairs and their locations is also valuable inspection data for engineers considering repair or replacement options. A specific embodiment will now be described by way of example with reference to Figure 1.

The conductivity inspection system uses a sensor head I which has a conductive tip, and may also include a locator device It is attached to the end of an insulated cable 2 which-passes along the non-metallic pipeline 3 through a sealed entry 4. The electrical circuit consists of an alternating current source 5 connected to ground through an earth pin 6 and to the insulating cable through an alternating current meter 7. The conduction path is completed by current passing through the pipe wall and through the earth back to the earth pin. If there is a large metallic pipe nearby this can be used as an earth instead of the earth pin.. The cable is wound on a drum 8 which.has a slip ring 9 to connect to the AC èource and current meter. Entry to the pipeline is obtained at an access chamber enabling a sealed fitting 11 to be attached to the pipeline. In use the fluid in the pipe, flows, under pressure along the pipeline and provides sufficient force on the drogue 12 for the cable and sensor to be carried along the pipeline. Whilst one operator controls the cable drum and the speed of movement of the sensor head 1, a second operator trthcks the course of the sensor head above ground using a location receiver 13. When the sensor head 1 approaches a leak in the non-metallic -pipe, the current meter 7 registers a rise. The cable drum operator can adjust the position of the sensor until a peak current occurs. The second operator can then determine the position of the sensor head from above ground and if required mark the position on the ground surface. This can then guide repair work to access the leak with a small hole excavated at the correOt location.

A record of an inspection survey can be generated using a cable counter 14 which senses the length of cable which has passed into the pipe, the alternating current signal and a data logger and display device 15. A trace of the alternatirg current signal plotted against the distance moved along the pipe is useful for interpretation of the data.

Figure 2 shows a typical output trace from a survey along a pipeline. The features show lqcations at which increased conduction current occurs. They may be leaks, they may also be metal repair clamps or metallic air release valves fitted to sortie pipelines. The pipeline operator may have accurate records of previous repairs and the locations of fittings. The sensor head ican also include a simple metal detector to assist the operator in interpreting the output trace and deciding on any action needed following inspection. The metal detector output can be fed back up the cable to generate-a second trace, so that where peaks in conduction output and metal detection coincide, the operator can clearly identify conduction peaks caused by metallic fittings.

The operating frequen6y for the conductivity system is typically 800 Hz. This is above the mains supply frequency of 50 or 60 Hz and above its main harmonics. Operating at higher frequencies is rnfrfrundesirable as capacitance effects become more significant and can make interpretation of the trace difficult. Operating at relatively low frequencies will also avoid interference from the metal detector and locator devices. In this embodiment, the current measurement is made using synchronous detection rather than a broad band alternating current detection to minimise interference from mains installations in the vicinity.

The cable drum may require a powered winch to assist in recovering the cable at the end of a survey.

Additional equipment may be needed to gain entry for the sensor and cable if the pipeline cannot be temporanilyde-pressurised, such as is described in US2002148294 (Al), Deployment of equipment into fluid containers and conduits'. On some pipelines it may be difficult to control the flow and thus the speed of the passage of the sensor along the pipeline. Other means of moving the sensor through the pipeline may be used such asthreading a line through the pipeline from an open discharge end and winching it through, or using a self-propelled trolley to carry the sehsor.

The system may be used on pressunised or gravity pipelines. For gravity systems it will be necessary to fill the pipeline with conducting liquid to detect leaks at any point On the pipeIine. 3.

Claims

CLAIMS1. A method for detecting leaks and metallic fittings in buried non-metallic pipes carrying conductive liquids using electrical conduction between a sensor head passed along the pipeline and an earth at the entry point.
2. A method for detecting leaks and metallic fittings in buried non-metallic pipes carrying conductive liquids according to claim one which includes a location device to pinpoint the leak or fitting at the surface.
3. A method for detecting leaks and metallic fittings in buried non-metallic pipes carrying.conductive liquids according to claim one which includes a metal detector in the sensor head to discriminate between leaks and metallic fittings.
4. A method for detecting leaks and metallic fittings in buried non-metallic pipes carrying conductive liquids aOcording to claim one which uses alternating current and synchronous detection to measure the conduction current.
5. A method for detecting leaks and metallic fittings in buried non-metallic pipes carrying conductive liquids according to claim four which operates at about 800 Hz to avoid mains interference and minimise capacitance currents.
6. A method for detecting leaks and metallic fittings in buried non-metallic pipes carrying condudtive liquids according to claim one fitted with a cable counter to provide an electronic signal for logging and display of position along the pipeline.
7. A method for detecting leaks and metallic fittings in buried ron-rnetallié pipes carrying conductive liquids according to claim one fitted with a logging and display unit to provide a plot of conductivity against distance along the pipeline.
8. A method for detecting leaks and metallic fittings in buried non-metallic pipes according carrying conductive liquids according to claim one which uses a drogue to pull the cable and sensor head through the pipeline using the liquid flow.
9. A method for detecting leaks and metallic fittings in buried non-metallic pipes carrying conductive liquids accordingto claim eight which uses a line and winch to pull the cable and sensor head through the pipeline. .
10. A method for detecting leaks and metallic fittings in buried non-metallic pipes carrying conductive liquids according to claim eight which uses a self-propelled trolley to pull the cable and sensor head through the pipeline.