One of the main infrastructure items or assets of water or sewerage utilities is their pipeline network which functions to deliver or carry away fluids from discrete locations. Similarly, pipes and pipeline networks may be used to convey any number of types of fluids ranging from petroleum products to natural gas. Pipes in these networks may be located either above or below ground depending on requirements. Corrosion can occur on the inside wall of metallic pipes when protective linings deteriorate over time resulting in the subsequent formation of tubercules. Corrosion can also occur on the outside wall of metallic pipes when protective linings deteriorate over time with subsequent conversion of metal into corrosive by-products and pits. In the case of cement pipes, cement leaching can occur due to exposure (either internal or external) to soft water. Both of these effects can cause a wall thickness reduction or loss of elastic stiffness in the pipe wall resulting in a weakness at that location. These weaknesses increase the likelihood of a pipeline burst.
The consequences of a pipeline burst or failure, especially in the case of a large capacity pipe may often be catastrophic resulting in a serious disruption to those relying on the pipeline. As a result, a large amount of effort is often expended by utilities or other entities that manage pipe networks to determine the condition of pipes, and where a problem is detected, then engage in preventative maintenance. With the increasing age of many pipeline networks this task of ongoing maintenance is important in ensuring their reliability.
There are a number of different methods that are used to assess pipeline condition. The most intrusive method involves taking physical samples from a pipe section to determine the extent of any corrosion or cement leaching (this is termed “coupon sampling”). This destructive testing is not preferred by industry and requires the exposure of buried pipes and their subsequent repair after the coupon sample is obtained. Closed circuit television (CCTV) camera investigation is sometimes used but generally requires intrusive access and allows for only a visual classification of the extent of pipe wall deterioration.
Other non-destructive methods involve the use of ultrasonic gauge testing along a pipe to directly determine the wall thickness at a given location. This method however, relies on the pipe location being exposed i.e. the pipe is either above ground or excavation has been carried out to expose a section of pipe. In addition, this method will often rely on an initial estimate as to the location of an area of concern otherwise the cost and time involved in testing a large section at a series of discrete locations along the pipe is prohibitive. Both destructive coupon sampling and ultrasonic gauge testing provide information only at specific locations which may not coincide with points of damage to pipe walls. As a consequence, the condition of the pipe away from the sample or test locations can only be inferred using these methods.
Another method of non-destructive testing involves the transmitting of an acoustic signal along a pipe from a first location and then detecting these same signals at a location farther down the pipe. By noting the average propagation velocity of the acoustic signal as it travels from transmitter to detector, inferences may be drawn as to the average pipe condition along that section of pipe. While this process has the advantages of being non-destructive, it still is only able to provide a cumulative measure of pipe quality over the section being tested between measurement locations and hence is unable to indicate the location where weakness in the pipe wall may occur.
As a consequence, a large section of pipe may end up being needlessly replaced on the basis of this “average” measure. This is due to the distribution of pipe wall damage being often highly variable and often manifesting at individual localised sections of pipe that have a defect from manufacture or installation. Clearly, entities involved in the management of pipeline networks are focussed on finding and replacing these weak sections as opposed to the expensive process of replacing entire lengths of pipeline.
There is therefore a need for a method and system for assessing the condition of a pipe which allows improved location of potential variations in pipe condition.