Ultrasonic Air Leak Detection: An Investigation to Improve Accuracy of Leak Rate Estimation

A compressed air test rig was designed to develop new procedures and improve the reliability of results that are obtained when conducting a leak survey using an Ultrasonic leak detector such as the UE Systems Ultraprobe. A test rig was designed that allowed the pressure of air in a compressed air system to be controlled by a regulator. This allowed experiments to be conducted that were able to recreate leak situations in a controlled environment. The pressure of the air through the test rig was measured both at the supply end and at the proximity of the leak site, while the volume flow rate was measured at the supply end of the rig. A number of leak geometries were examined, with compressed air being passed through open ended tubing and also discs with different leak geometries, some round holes and some rectangular. Initial studies were also carried out on flange leaks and pinpricks and slits in lengths of tubing. These were omitted from the study at this stage to allow further experimentation to be conducted in both areas. The experimentation was carried out using an Ultraprobe 9000 leak detector which was positioned at a set distance from the leak at a series of angles to the flow. The ultrasound level was measured at each point and compared with the pressure and volume flow rate of the air in the system. The results showed that the ideal angle to ensure the maximum level of ultrasound is at 30 to the axis of the leak. While the optimum distance for ensuring a consistent level of ultrasound is 150mm from the leak. The length of any air lines branching from the main distribution network is shown to be an important factor when quantifying the volumetric flow rate of air from an open ended tube or tubing with a significant orifice in it. The pressure drop in a 1m length of tubing was shown to be approximately 50%, and if you consider that often the flow rate being used has been obtained using the outside diameter of the tubing rather than the inside diameter this can become a considerable over estimation of leak rate. The geometry of a regular shaped orifice, such as a round, or rectangular hole was shown to have little to no effect on the flow rate through it for a constant area. However a coefficient of discharge to account for imperfections in the flow was developed for round and rectangular geometries, these were 0.74 for a round hole and 0.79 for a rectangular hole. These correction factors in tandem with the length effect factor for tubing and the improvements to the measurement procedure, allow a higher degree of accuracy to be obtained when conducting a leak survey

Towards practical pressure-based leakage characterisation of water distribution pipes with a novel pipe condition assessment device

Leakage detection and management have been proposed as effective ways of mitigating and managing water losses in an age where water scarcity has become prevalent. To this end, several methods have been developed and suggested with different benefits and drawbacks The presently available leakage detection methods, however, fail to identify and characterise the leakage while simultaneously assessing the condition of the water distribution network (WDN). This function is imperative for understanding and addressing leakage. WDN assessments are also important as knowledge of the network parameters helps in reducing water losses through planned infrastructure maintenance programmes. A pipe condition assessment device (PCAD) was thus developed which can detect, characterise leakage and assess the condition of the WDN. However, the efficacy and reliability of this device had not yet been established. In this study, the device was used to characterise leakage and assess system conditions in water networks. Initially, laboratory tests on six known leak types were conducted on a standardised laboratory setup. The leakage characteristics of these pipes were found through regression analysis. The results from the tests established that to 95% level of confidence; the standardised setup can produce repeatable and comparable results to previous studies. The accuracy of the PCAD instrumentation was verified and the device calibrated, the same pipes were then tested on the standardised setup using the PCAD. An overlap of the results from the laboratory experiments and the PCAD revealed that to 95% level of confidence, the device could adequately characterise leakage in pipes. A low variance of less than 4% of the mean parameter, across all tests conducted using the PCAD, informed that the results obtained through using the PCAD are repeatable and reliable. Field tests in the Kensington DMA were done and revealed the limitations of the device, such as its inability to characterise leakage in pipe sections that cannot be successfully isolated. However, in pipelines that were successfully isolated, the PCAD was able to detect and identify leakage characteristics in water networks and aid in conducting maintenance runs. Consequently, this study contributed to the body of knowledge by statistically establishing that the PCAD could adequately, and reliability characterise leakage in real water distribution networks

Leakage Characterisation in Bulk Pipes using Pressure Tests

The supply of water is becoming increasingly strained as the demand for this essential and limited resource continues to increase. A significant amount of this resource is, however, lost through leakage. Not only does this result in a waste of a precious resource, but it also leads to a direct loss of revenue, especially considering that value has been added to the leaking water through collection, storing, purifying and pumping. A great deal of research has been done on reducing water leakages in distribution networks, however, leakage in bulk pipelines has received comparatively little attention thus far. In this study, bulk pipelines in the field were tested with a pressure testing device developed by the University of Cape Town. With this device, a range of pressures were applied to various pipeline sections and the corresponding leakages were measured, resulting in characteristic pressure-leakage relationships. The Fixed and Variable Area Discharge (FAVAD) and the empirical N1 leakage models were then applied to interpret the pressure-leakage relationships. Thirteen tests were attempted on pipeline sections ranging from 300 mm to 600 mm in diameter, and pressure tests were successfully performed on eight of the thirteen sections. Even though the effectiveness of the testing technique is dependent on the sealing capability of the isolation valves, it was found that most valves sealed effectively, with only two pipelines sections failing to isolate. The high elevation differences along the length of the pipelines were found to have a dominating effect on the characteristics of the leak, which made it possible to roughly estimate the most likely leak locations by comparing the observed leak characteristics to those found in literature for similar conditions. The dependence of the leak characteristics on the location means that both have to be determined simultaneously. This can benefit the analysis, as some locations may be excluded based on their unrealistic leakage characteristics. However, it also means that there will be uncertainty with regards to the true location and leakage characteristics for sections of the pipe where the leakage characteristics are realistic. Nonetheless, the measured leakage rate together with the estimated leak characteristics provided valuable information on the pipeline conditions, making it possible to rank the pipelines according to the severity of their conditions, for optimal allocation of maintenance resources. Through practical tests, the study shows that pressure testing is an effective, simple and low cost technique to assess leakage in bulk pipelines. It causes minimal interference to the pipe operation, requires little downtime and the data can be processed in minimal time

Recent advances in pipeline monitoring and oil leakage detection technologies: principles and approaches.

Pipelines are widely used for the transportation of hydrocarbon fluids over millions of miles all over the world. The structures of the pipelines are designed to withstand several environmental loading conditions to ensure safe and reliable distribution from point of production to the shore or distribution depot. However, leaks in pipeline networks are one of the major causes of innumerable losses in pipeline operators and nature. Incidents of pipeline failure can result in serious ecological disasters, human casualties and financial loss. In order to avoid such menace and maintain safe and reliable pipeline infrastructure, substantial research efforts have been devoted to implementing pipeline leak detection and localisation using different approaches. This paper discusses pipeline leakage detection technologies and summarises the state-of-the-art achievements. Different leakage detection and localisation in pipeline systems are reviewed and their strengths and weaknesses are highlighted. Comparative performance analysis is performed to provide a guide in determining which leak detection method is appropriate for particular operating settings. In addition, research gaps and open issues for development of reliable pipeline leakage detection systems are discussed

Recent Advances in Pipeline Monitoring and Oil Leakage Detection Technologies: Principles and Approaches

Pipelines are widely used for the transportation of hydrocarbon fluids over millions of miles all over the world. The structures of the pipelines are designed to withstand several environmental loading conditions to ensure safe and reliable distribution from point of production to the shore or distribution depot. However, leaks in pipeline networks are one of the major causes of innumerable losses in pipeline operators and nature. Incidents of pipeline failure can result in serious ecological disasters, human casualties and financial loss. In order to avoid such menace and maintain safe and reliable pipeline infrastructure, substantial research efforts have been devoted to implementing pipeline leak detection and localisation using different approaches. This paper discusses pipeline leakage detection technologies and summarises the state-of-the-art achievements. Different leakage detection and localisation in pipeline systems are reviewed and their strengths and weaknesses are highlighted. Comparative performance analysis is performed to provide a guide in determining which leak detection method is appropriate for particular operating settings. In addition, research gaps and open issues for development of reliable pipeline leakage detection systems are discussed. Document type: Articl

Creep and thermal ratcheting of soft materials under compression

A rapid increase in the utilization of polymer and FRP materials over conventional metallic materials in the production of pressure vessel and piping components has become a global trend. However, factually, the design standards of ASME and its European counterpart for non-metallic materials are not material specific and as a whole vaguely follow the standards of metallic materials. Contrary to metallic PVP components, polymer components are of recent ages and this limits the statistical data available on the materials. Among polymer PVP components, polyvinylchloride (PVC) and high-density polyethylene (HDPE) constitute the majority. The inherent excellent corrosion resistance, lightweight and ease of manufacturing make these two polymer materials the ideal replacement over corrosive and heavy metallic structures. The objective of this research is to characterize the long-term creep and thermal ratcheting of soft materials. The research revolves around the analysis of thermal ratcheting behavior of the selected PVP polymer materials including PTFE and fiber based gasket materials. The core intent of this thesis is to characterize polymer materials used in bolted flange connections. For the investigation of thermal ratcheting performance of the selected materials, meticulous experimentations were carried out using test rigs equipped with high accuracy sensors. As the operating temperature range of selected flange materials are much different from the considered gaskets, the thermal ratcheting evaluation of flanges and gaskets were performed, separately. All the selected materials were subjected to different compressive loads, various ratcheting temperature and few pre-exposure creep to evaluate the thermal ratcheting phenomenon. The characterization tests of polymers were performed with ring shaped samples. Furthermore, full-scale tests of NPS 3 Class 150 PVC and HDPE flanges were conducted to evaluate the short-term relaxation and the results are compared to the finite element counterpart. The results provided significant insight on the vulnerability of polymer and soft materials to thermal ratcheting phenomenon. The study on the behavior of selected materials to thermal cycling highlighted the intensification of creep damage on the materials, the magnitude of which varied depending on each material. In addition, thermal ratcheting alters other fundamental properties of flange and gasket materials such as creep modulus and coefficient of thermal expansion