The present invention relates to a method of surveying pipeline and a pipeline survey apparatus for use in a method for surveying a pipeline.
Pipelines are often used for carrying gases or liquids from one place to the other. These pipelines are often provided with a protective wrapping and/or a cathodic protection system to enhance the life of a buried pipeline. However, over time faults may occur in the wrapping leading to damage of the pipeline. Possible causes of these faults are incorrectly applied wrapping, mechanical damage to the wrapping occurring before, during or after installation, decay of the wrapping due to soil conditions or disbonding of the wrap from the pipeline allowing water to reach the pipe.
Damage to or deterioration of the pipeline may be more or less serious depending on the nature of the gas or liquid that the pipeline is carrying and the areas through which the pipeline is carrying it. Of particular concern are those pipelines carrying hazardous fluids through high consequence areas. A high consequence area is defined as an area which contains a high level of permanent population, a transitional population (e.g. a football stadium, a school etc.), substantial property (buildings, museums etc) or unusually sensitive environment locations (wetland, bay areas, protected species habitats etc).
It is desirable to be able to monitor the state of the pipeline/wrapping in high consequence areas.
Also of concern are sections of pipeline which are identified as “could affect” sections of pipelines. These sections of pipeline have potential for causing death, damage, destruction or a combination of these at a location remote from the location of pipeline rupture. A section of pipeline may be a “could affect” section of pipeline due to the local terrain, the presence of ground or subsurface water, nature of local drainage (natural and man made), or the local weather conditions. Whilst a gas pipeline would not normally contain “could affect” sections of pipeline (since in general all the consequences of a leak or rupture would be local to the leak or rupture) an exception would be an LPG (liquefied petroleum gas) pipeline. A leak in an LPG pipeline would produce a vapour cloud which would stay close to the ground. This cloud is likely to flow to the lowest point in the local terrain, which may be several kilometres away.
Again, it is desirable to be able to monitor the pipeline and/or wrapping integrity in “could affect” sections of pipeline. Accordingly it is an object of the present invention to provide a method of surveying a pipeline which allows deterioration of sections of pipeline and/or wrapping to be monitored.
The Applicants currently market C-Scan survey systems for monitoring the location and condition of buried pipeline. In this system a signal generator is attached to a section of pipeline. The signal generator produces a constant AC current which passes down the pipeline, typically over a distance of 2 to 3 km. A hand held detector unit is used to measure electromagnetic signals, which radiate from the pipeline, at a series of locations spaced down the pipeline from the signal generator. The signals detected by the detector unit allow a user to monitor attenuation of the AC current down the pipeline from the signal generator. The rate of decline of the AC current is dependent primarily on the electrical resistivity of the wrap or coating used and the area of the wrapping in contact with the soil per unit length. However, if there is a low resistance electrical path between the pipeline and the soil at any point, a substantial increase in loss of signal current occurs. This increase in loss of signal current may be detected by the hand held detector unit. An increase in loss of signal current may indicate incorrectly applied wrapping, mechanical damage to the wrap, decay of the wrap due to soil conditions, disbanding of the wrap from the pipeline allowing water to penetrate through to the pipeline and or a leak in the pipeline itself.
However, this existing system requires identification of an appropriate point in the pipeline at which the signal generator may be attached. Further, the location of the signal generator may be determined by the points on the pipeline where it is possible to attach the signal generator. Thus a fault located near the signal generator can make it difficult to monitor sections of the pipeline beyond the fault.
It is an object of the present invention to provide an alternative method and apparatus for surveying a pipeline.
According to a first aspect of the present invention there is provided a method of surveying a buried pipeline, which pipeline comprises a tubular member with a protective wrapping, comprising the step of applying a signal to the pipeline from a first location, which first location is remote from the pipeline, and measuring the signal from a second location and a third location, which second and third locations are remote from the pipeline, the second location being spaced from the third location along the pipeline and using the signals received at the second location and third location to provide an indication of deterioration of the tubular member and/or wrapping.
According to a second aspect of the present invention there is provided a method of surveying a buried pipeline, which pipeline comprises a tubular member with a protective wrapping, comprising the step of selecting a plurality of spaced locations above and along the length of the pipeline, and sequentially from each spaced location applying a signal to the pipeline and measuring the signal at each of the other spaced locations.
The signal applied to the pipeline may be an AC electric current generated by electromagnetic induction. The step of applying a signal to the pipeline may comprise the step of using non-contact coupling means to apply a signal to the pipeline. The non-contact coupling means may be an electromagnetic signal transmitter. The advantage in being able to apply a current from a location remote from the pipeline is that it allows more freedom when selecting the point along the pipeline at which a signal is applied. This allows, for example, a signal to be applied from either side of a significant fault in the pipeline in order to determine the state of the pipeline lying either side of the fault.
Through out this specification “protective wrapping” shall be taken to mean any coating or wrapping applied to a tubular member to reduce or prevent damage to the tubular member.
In a method according to the first aspect of the present invention the difference between the strength of the signal measured at the second location and the signal measured at the third location may be representative of attenuation of the signal and along the tubular member and/or wrapping. The method may further comprise the step of comparing the attenuation of the signal along the tubular member and/or wrapping with a predetermined expected attenuation in order to provide an indication of deterioration of the tubular member and/or wrapping.
This method allows a user to examine a section of pipeline in which there may or may not be a fault and, by measuring attenuation along a chosen length of pipeline and comparing it with an expected attenuation along that length of pipeline, determine whether the section contains a fault. Alternatively, a plurality of measurements of attenuation along a chosen length of pipeline may be taken over time and changes in the measured attenuation monitored.
In a method according to the second aspect of this invention the difference in measured signal strength between a pair of adjacent spaced locations along the length of the pipeline in the direction of signal transmission may be a measure of the attenuation of the signal over that length of pipeline. The measurement of the signals applied to the pipeline from the plurality of spaced locations may generate a plurality of measured signal strengths and the method may comprise the step of calculating a plurality of attenuations for each of the plurality of lengths of pipeline located between respective pairs of spaced locations. The method may further comprise the step of averaging the calculated attenuations for each length of pipeline.
In this method because a signal is applied to the pipeline from several different locations, the attenuation along a particular length of pipeline may be measured several times. By taking an average of the measured attenuations along a length of pipeline, a more accurate measurement of attenuation may be obtained and more reliable identification of faults along that length of pipeline made.
The attenuation may be calculated in units which are independent of the applied signal strength. This makes comparison and averaging of different measured attenuations easier.
The measured attenuation across each length of pipeline may be expressed as a ratio of a predetermined expected attenuation to provide a plurality of attenuation ratios associated with each length of pipeline. These attenuation ratios may be multiplied together to produce an attenuation product for each length of pipeline. The method may further comprise the step of comparing calculated attenuation products to identify deterioration in each length of the pipeline. This has the effect of greatly increasing the resolution of the method so that it is much easier to identify a length of pipeline in which a fault is present.
In a method according to either the first or second aspects of the present invention the distance between each pair of adjacent spaced locations may be between 10 m and 100 m. The frequency of the signal applied to the pipeline may be between 5 kHz and 35 kHz and preferably between 10 kHz and 32 kHz.
According to a third aspect of the present invention there is provided a pipeline survey apparatus for use in a method according to the first or second aspects of the present invention, the apparatus comprising a plurality of sensor units, each sensor unit being spaceable from each other sensor unit above and along a length of the pipeline at a respective one of a plurality of spaced locations, at least one sensor unit comprising a non-contact coupling means for applying a signal to a pipeline and at least two sensor units each comprising a receiver for measuring signals emitted by a pipeline.
Preferably, each sensor unit comprises non-contact coupling means for applying a signal to a pipeline and receiver means for measuring signals emitted by a pipeline.
The non-contact coupling means may be an electromagnetic signal transmitter.
The apparatus may comprise a control unit, which control unit is arranged to receive data from each sensor unit and to perform calculations as referred to with respect to the second aspect of the present invention in order to measure deterioration in a pipeline.
The apparatus may comprise a sensor unit which is a master sensor unit, the master sensor unit comprising the control unit and further comprising a long range communication device. The long range communication device may be a GSM radio device.
Each sensor unit may comprise a short range radio system for communication with at least one other sensor unit.
The non-contact coupling means may be arranged to transmit a signal of between 5 kHz and 35 kHz and preferably to transmit a signal between 10 kHz and 32 kHz.
According to a fourth aspect of the present invention there is provided a pipeline survey system comprising a pipeline survey apparatus according to the third aspect of the present invention and a buried pipeline, which pipeline comprises a tubular member with a protective wrapping, wherein each sensor unit is spaced from each other sensor unit above and along the length of pipeline at a respective one of a plurality of spaced locations.
The sensor units may be regularly spaced along the pipeline with a spacing of between 10 and 100 m.
Each sensor unit, which is provided at a respective location, may be calibrated to take into account the distance between the sensor unit and pipeline at that respective location. Each receiver may have a sensor axis and each receiver may be arranged with its sensor axis orthogonal to the axis of the length of pipeline that passes under the respective location of that receiver. A sensor axis is a characteristic of the receiver which determines the strength of the signal detected.
The pipeline may comprise a cathodic protection system and each sensor unit may be arranged to monitor the voltage of the cathodic protection system.
Each sensor unit may be powered by a power unit, the power unit comprising a battery and a solar panel.
Throughout the specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of the stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
A method of surveying a pipeline and a pipeline survey apparatus which embody this invention are described now, by way of example only, with reference to the accompanying drawings.