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| Fig. 1: A leaking concrete water pipe located in Wagga Wagga, New South Wales. (Source: Wikimedia Commons) |
Pipes are hermetically closed elements crucial to the transport of fluid-like substances in chemical processing and the transmission of water, oil, and gas. A leak in a pipeline which could be the result of an intended crack, hole or porosity in a wall or joint can lead to undesired consequences in a system such as a loss of pressure, contamination of a product, or a decrease in processing efficiency. [1] Radiotracers and thermography are two techniques used for leak detection that can help to identify leaks and thus mitigate the performance and economic issues associated with them.
A leak is a serious issue in processing plants or pipelines when it spoils the quality of a final product or drastically reduces the transport capacity of water, oil and gas. Water transmission pipelines which provide a critical resource for agriculture, manufacturing, electricity production, and human health lose an average of 20 to 30 percent of the water transmitted through them due to leakages. In old systems that are not maintained, the amount of water lost from a water transmission pipeline can reach 50%. [2] Similarly, leaks in gas pipelines can lead to large transmission losses but can be more hazardous and expensive than water leaks. [2]
In terms of safety, leaks can be very dangerous when pathogens or contaminants from the surrounding environment are introduced into a water pipeline, or if oil and gas are spilled into the surrounding ecosystem. A pipeline that leaks oil to the environment can contaminate groundwater and kill ecosystems. Furthermore, leaks not only lead to water waste but can drastically increase power consumption due to the energy that is needed to treat and transfer water. [1] There is an increasing demand for technologies that can detect leaks early and help improve the operational efficiency of pipelines, lower their operation costs, reduce potential for contamination, extend the life of related facilities, and reduce potential property damage and water outage events.
In 1895, X-rays were discovered by Wilhelm Conrad Röntgen while he was experimenting with cathode-ray tubes. Henri Becquerel in 1896 became interested in the mechanism of how X-rays are produced and in particular their links with fluorescence. During his investigations a couple months later, Becquerel showed that uranium, a natural element, spontaneously emits rays closely resembling X-rays, marking the discovery of natural radioactivity. An increasing understanding of X-rays and radioactivity over the next 4 decades led to the discovery of artificial radioactivity in 1934 by Irene and Frederic Joliot-Curie, which led to the ability to manufacture radioactive isotopes from most of the natural elements. [3] Some of these radioactive isotopes can act as radiotracers meaning that a radioactive species labels a substance or phase and is followed through a system using suitable detectors. Tracers are designed to follow a specific substance through a system and sensitive detectors are strategically placed on the outside surface of that system where they detect that tracer as it flows past. [4] Radiotracer technology has been used as a reliable technique since the 1980s in agriculture, medical, and petrochemical industries to monitor and track any abnormalities in a system, optimize processes, solve problems, improve product quality, save energy and reduce pollution. [5] The same radiotracer technique is also used to identify leaks in pipelines used for water, oil and gas.
Radiotracer methods are a non-intrusive technique for the early detection of leaks in pipelines. [4] The detection of leaks in buried pipelines (Fig. 1), complex subsea pipe networks, or in heat exchangers and chemical processing equipment with harsh operating conditions can be successfully achieved through the use of radiotracers. The advantages of using radiotracers for leak detection are numerous:
Radiotracers allow complex systems that are hard to physically access to be divided into and analyzed as individual components. Users can make accurate, informed decisions about a system that has been made transparent. [4]
Radiotracers can be detected in very small quantities due to the high sensitivity and effectiveness of existing detection systems. [5]
Tracer movement through a pipeline can be detected in real time, allowing troubleshooting and optimization to be performed in situ. [5]
Small teams of engineers can perform the technique quickly and accurately without the need for complicated or expensive preparations. [4]
Radiotracer techniques applied to pipelines and processing lines with leaks can help reduce shutdown time, ensure safe operation, protect the environment, and save money. The cost of fixing a leak or locating a blockage in a pipeline can be significant and would likely require help from special, third-party contractors. [4] Radiotracer tests can thus help to reduce routine maintenance, material and labor costs in the long term. The short-term investments of radiotracer techniques are extremely cost effective and are regularly used for leak detection by industrialists. Using radiotracers to detect leaks is a common routine in the petrochemical and chemical industries in both developed and developing nations.
In this technique, tracers are usually detected outside of the pipeline because ionizing radiation can project from the tracer as it flows through the substance being analyzed. By detecting leaks early, major pollution incidents can be avoided, especially in places where other detection methods cannot be used due to physical constraints. Leaks in pipelines can also cause large losses in the transportation capacity of the pipeline and inspecting these leaks is crucial for the performance of processing lines and the quality of the final products. The data collected through tracer methods can also determine whether local deposits have caused blockages and where they are located. The total volume of deposits and percentage bore restriction within the pipeline can be measured which allow users to identify if a pipe is dry or flooded with product. The fluid velocity, flow rate, phase distribution, and deposit inventory are also measured with tracer techniques. [4]
For tracing an aqueous phase, several types of radiotracers can be used. One common factor that is considered when selecting a tracer is its half-life or the length of time for half of a radioactive atom to decay which is related to the intensity and nature of the radiation transmitted by a radioisotope. [2] A study done by the Thailand Institute of Nuclear Technology performed a study of leak detection using radiotracer at the laboratory scale. The experimental setup consisted of water tanks, a non-buried piping system and the radiotracer injection system. A small opening valve in one of the water tanks was used to mimic the leakage of water in the system. The radiotracer, Br-82 (approximately 10 mCi), was used and injected into the test system. Three detectors were placed along a non-buried pipeline to measure the radiation signals but only the third detector was set up at the outlet pipe of the water tank in order to measure the flow leakage. A Residence Time Distribution (RTD) program distributed by the IAEA was used to calculate the ratio of the leakage to the main flow by processing radiation signals measured by the leak detectors. [6]
The first two detectors were used to measure the velocity of water in the pipe, and the pipe diameter at these detectors was about 5 cm. The first two detectors were located 100 cm apart and the radiation signals from them allowed the researchers to calculate the velocity of the water at about 6.54 cm/s. Before injecting the radiotracer into the system, the leak rate was directly measured by a glass flow meter and found to be about 0.5% of the main flow. Radiation signals collected at detector 1 were compared to the radiation signals compared at detector 3. The data collected from these radiation signals revealed that the leak rate was about 2.8% of the main flow, which is about 5.6 times larger than the result from the direct measurement. The main reasons for the discrepancy between the leakage results obtained by the two methods, as hypothesized by the researchers, are the accumulation of radiotracers at the leakage point and the effect of pipe size on the measuring efficiency of detectors. However, if the effects of radiotracer accumulation and measuring efficiency can be filtered out, researchers believe that the radiotracer method can provide consistent results with direct measuring methods. Despite conflicting results about what the flow rate was in the system, the research demonstrates that radiation signals from radiotracers are indeed effective at marking the location of and finding leakage points. [6]
Early leak detection is crucial for improving the operational efficiency of pipelines, lowering their operation costs, reducing potential for contamination and environmental damage, extending the life of related facilities, and reducing potential property damage and water outage events. Water, oil and gas pipelines deliver goods and services that are essential to several industries and the health of humanity. Until recently, being able to make direct, non-intrusive measurements of pipeline contents was not possible, but many operators have been adopting radiotracer technology worldwide.
© Amir Kader. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] B. Shakmak and A. Al-Habaibeh, "Detection of Water Leakage in Buried Pipes Using Infrared Technology: A Comparative Study of Using High and Low Resolution Infrared Cameras for Evaluating Distant Remote Detection," 2015 IEEE Conference on Applied Electrical Engineering and Computing Technlogies (AEECT), IEEE 7360563, 3 Nov 15.
[2] S. El-Zahab and T. Zayed, "Leak Detection in Water Distribution Networks: an Introductory Overview," Smart Water 4, 1 (2019).
[3] M. Tubiana, "The Discovery of Radioactivity," World Health 48, No. 3, 5 (1995).
[4] M. Wilson, "Radioisotope Technology Helps Ensure Pipeline Flow," Offshore Magazine, 1 Feb 11.
[5] M. A. S. Mohd Yunos et al., "Industrial Radiotracer Technology for Process Optimizations in Chemical Industries A Review," Pertanika J. Scholarly Res, Rev, 2, No. 3, 20 (2016).
[6] S. Wetchagarun , A. Petchrak and C. Tippayakul, "Preliminary Study of the Use of Radiotracers for Leak Detection in Industrial Applications," J. Phys. Conf. Ser. 611, 012018 (2015).
