Limitations of Current Technologies

From the perspective of this research, a specific guideline is necessary to define leak detection systems and to identify what is expected from such systems. Geiger (2006) identified four main aspects to evaluate the performance of leak detection systems. The four main aspects are (1) reliability, which represents the extent to which the system is capable of detecting a leak and the accuracy of the received information, (2) sensitivity, which shows the capability of the system to identify leaks of various sizes ranging from big leaks and bursts to small leaks, (3) accuracy, which, unlike reliability, provides extra information such as leak location and leak size and (4) robustness, which displays the ability of the system to provide reliable data even under changing conditions within the network or in the case of data loss. Additionally, Geiger identified that externally-based leak detection sensors can pinpoint leak accurately, whereas, with internally- based leak detection systems, leak locations are estimated and are rarely as accurate as the values derived from externally-based leak detection sensors. When it comes to the costs, externally- based leak detection systems are considerably expensive and complicated to install. Thus, they are not used as much as internally-based systems that cost much less. Externally-based leak detection systems, as stated in section II.1, rely mainly on sensors for collecting various types of signals and data. However, externally-based leak detection systems have proven to be the most capable of leak pinpointing. Therefore, the limitations of such systems can come from the

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technologies they utilize. Thus, in this section, a brief discussion and a comparison of technologies and their limitations will be discussed.

Lately, multiple technologies are utilized to minimize the damage created by the leaks. One of the most popular technologies is acoustic detectors or listening devices. Listening devices rely on identifying the sound emitted by the leaks to detect a leak and, in some recently developed models, pinpoint the leaks. The primary tools in this category are geophones and hydrophones, described in section A.1 of the appendix. Those devices listen to audible sounds in the network mainly using listening sticks or microphones. Besides being popular, acoustic technology encounters multiple limitations that impair their effectiveness as follows: (1) Acoustic devices must go over or in the pipe, which might require opening the pipeline or drilling and digging sometimes; (2) acoustic devices are affected by ground dampening on the signal and thus their accuracy is reduced, (3) acoustic devices rely on well-trained operators to detect and pinpoint the leaks while listening and the human operators must be able to distinguish the signal from the background noise picked up by the devices pickup; (4) acoustic devices need to be close to the leak to be able to detect it, not functioning efficiently in plastic pipes such as PVC (Echologics Inc. 2006; United States Environmental Protection Agency 2009).

Another popular technology, considered an improvement in acoustic phones, is acoustic devices with correlation techniques such as noise loggers. Such devices rely on placing two acoustic listeners on opposite sides of the expected leaks with their data input into a correlator, as described in section A.2 of the appendix. This technology has shown promising results and received multiple contributions. Nevertheless, they are costly to utilize and they require the anticipation of the leak location to be confirmed. Besides, acoustic devices with correlators face difficulties in correlating small and low-sound leaks and tend to struggle detecting leaks within

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PVC pipelines and large diameter pipelines (Echologics Inc. 2006; Datamatic Inc. 2008; El- Abbasy et al. 2016).

Infrared thermography has been widely used for leak detection through sensing the infrared radiation and temperature change within surfaces where leaks are expected. Section A.3 of the appendix provides more details on this technology. However, infrared devices can be expensive and require well-trained operators for good results., Moreover, the accuracy of infrared devices can be impaired by external factors, mainly weather conditions that limit the operational capabilities of the technology to a specific temperature range (Echologics Inc. 2006; Fahmy and Moselhi 2009; Varone and Varsalona 2012). Another form of leak detection technologies is chemical leak detection. Chemical leak detection is performed using tracer gasses injected into the network and escaping through leaks to be detected at the surface as described in section A.4 of the appendix. Chemical leak detection, however, faces multiple challenges as it takes a substantial amount of time to detect a leak and thus a large number of resources and huge funds are needed. Moreover, the accuracy of chemical leak detection is affected by factors such as depth and inner soil paths that might render the leak to go out of another location or dissipate through the soil (Echologics Inc. 2006; KVS 2015).

Another technology widely used in leak detection is Ground Penetrating Radar (GPR). This device relies on emitting radar waves into the soil and generating an image of the soil based on the reflection of the emitted signals, as illustrated in section A.5 of the appendix. However, the images derived from the GPR data are hard to interpret and require extensive research to become viable (Eyuboglu et al. 2003; Echologics Inc. 2006; United States Environmental Protection Agency 2009).

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Multiple devices have recently been developed to solve the leak detection problem. This class of devices is known as leak detection robots that include devices such as Smart Ball, Beaver, Explorer and Pearpoint. As illustrated in section A.6 of the appendix, most of these devices are able to venture through pipelines on their own with little or no human aid. However, these devices are, in some cases, exclusive to the developer company. Additionally, leak detection robots fall under the risk of getting stuck in the pipeline and having a moderate accuracy level compared to other available technologies (Schempf et al. 2003; WCT Products 2015; Puretech Ltd. 2015).

Micro-electro-mechanical sensors (MEMS) have been extensively used in recent years as real- time leak detection devices. MEMS belong to a broad category of sensors, which contains various types of sensors as described in section A.7 of the appendix. MEMS in this research are accelerometers, as devices that can read vibration signals. Accelerometers still require more research in terms of plastic pipelines and metallic pipelines to become a standalone technology for leak detection., Studies are also required in terms of the signal interpretation to eliminate any noise within the signal, mainly due to the high sensitivity of accelerometers (Kim et al. 2011; MEMS and Nanotechnology Exchange 2015; El-Zahab et al. 2016).

Table II-2 provides a comparative analytical summary of all the aforementioned leak detection technologies and assesses the technologies based on their cost, accuracy, capabilities of detection in metallic and non-metallic pipelines, market availability, traffic interruption and susceptibility to external factors. Another factor is permanent installation determining whether a system is permanently installed in the network to provide real-time data or it is brought in when a leak is detected. For example, micro-electromechanical sensors (MEMS) provide a low-cost solution with high accuracy and they can be installed permanently in the network. However, MEMS are

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still experimental when it comes to experimental pipelines and plastic pipelines and their functionality needs further research. Leak detection using MEMS is affected by external factors that need to be addressed in signal analysis, yet this detection does not interrupt the traffic flow. Besides, the table indicates that MEMS are readily available in the market for purchase.

Table II-2: Comparison of the Available Technologies against Multiple Criteria.

Technology Cost Accuracy Perman_ent Metallic _Pipes Metallic Non- Pipes Market Available Interru pts Traffic External Factors Geophone/

Hydrophone Low Low No Yes Yes Yes Yes Yes

GPR High Operator _{dependent No} No Yes Yes Yes Yes

Infrared n/a Low No Yes Yes Yes Yes Yes

Leak noise

Loggers High High Yes Yes No Yes No Yes

Smart Ball Low Moderate No Yes Yes Company _Only No No

MEMS Low High Yes No No Yes No Yes