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Show detection method. Sound waves result from pipe vibrations due to a high- pressure leak, the impact of water on the soil in the vicinity of the leak, and by formation of a water cavity in the soil near the leak. Leak detection involves a systematic recording and mapping of sound vibration patterns within segments of the water distribution system. Discontinuities are investigated in more detail. The major problems associated with this technique include the variation of sound transmission by pipe size and pipe materials and significant interference due to background noises. In addition, the approach is fairly time consuming, and it is usually not possible to test the entire distribution system on a regular basis. As mentioned previously, large leaks from corrosion damage usually develop quickly enough that routine leak detection surveys rarely detect them before the leak surfaces. Hydrostatic pressure testing is frequently used to pressurize a section of pipe and record the rate of pressure drop. This method can identify leaks, cracks or joint failures within the test section. Like sonic searching, it is usually not possible to frequently test the entire distribution system. It is an effective method to determine if a newly constructed pipeline has been installed properly before it is put in service. Construction standards in Utah require hydrostatic testing of new pipelines. An alternative pipe inspection approach is the use of submersible remotely operated vehicles ( ROVs). These vehicles can relay information about pipe systems under maximum head and full pressure conditions. Current technologies are capable of inspecting up to 30,000 foot stretches of pipe. Pipe diameters must be over 24 inches. Leak Prevention and Repair Based on currently available technologies, leak prevention programs generally are much more cost- effective than leak detection programs. The approaches used for leak prevention vary depending on the size and age of the water utility. A summary of the major leak prevention and repair approaches used by utilities across the country as reported in a AWWA research report is given in Table 3. Table 3 indicates, and experience has shown, that an emphasis on leak prevention programs is preferred and more effective than leak detection programs. The majority of approaches used for leak prevention are fairly low technology and involve design and construction standards for new pipelines and systematic record keeping to identify old pipelines in need of replacement. Currently, there is no standardized approach used for maintenance repair records. Depending on the extent of record keeping and the accessibility of records, repair records can provide information on potential problem pipe locations and evaluate repair patterns and trends. Records can provide a basis for cataloguing failure types according to pipe size, material, soil type, location and season. Corrosion Leak Prevention Methods Corrosion control methods and practices have been effectively used for over 75 years with little change, except where technology has improved the performance of the various corrosion control methods. Corrosion protection methods currently available for the water industry are coatings, cathodic protection and material selection for corrosion resistance. Material Selection Corrosion is commonly associated with metallic pipelines. Depending upon pressure, pipe size and specific preferences of the water utility, waterlines could be constructed using plastic pipe materials such as PVC or polyethylene. Plastic pipe offers corrosion resistance to most corrosive soil and water conditions and effectively reduces or eliminates corrosion related leaks. 48 |