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Show pipe. Almost all distribution- size pipelines ( 18- inch diameter or smaller) are now PVC or ductile iron. Utilities with corrosive soils favor PVC. Pipe diameter plays a major role in leak generation. In general, smaller diameter pipes have smaller wall thickness, and therefore seem to be more vulnerable to leaks. Significantly higher rates of repair are reported for smaller diameter water mains. Experience shows most leaks found in service lines. Pipe corrosion plays a significant role in generation of pipe leaks. As part of the Safe Drinking Water Act, Lead and Copper Rule ( LCR) promulgated in 1991, all water supply systems are required to implement corrosion control. The primary purpose of the LCR corrosion control program is to prevent leaching of lead and copper from piping systems into water supplies. Implementation of corrosion control should also act to reduce internal pipe corrosion, thereby reducing pipe failure and leak production. Fortunately, water supplies in Utah are not generally corrosive, and damage from internal corrosion is rare. External corrosion is due to the soil surrounding the pipeline acting as an electrical battery cell. Soil resistivity can indicate the potential for corrosion. Pitting corrosion can occur where the pipe is in contact with corrosive soil pockets. Pre- 1940 pipe installation practices did not consider corrosion potential of soils, therefore older pipes are more susceptible to this type of corrosion. Western soils tend to be fairly corrosive, and they have been implicated as major contributors to pipe corrosion in the intermountain west. External corrosion can be controlled by a variety of methods. Electrolysis control is conducted using galvanic and impressed current cathodic protection. Alternatively, the use of Stic and epoxy coatings on metallic pipe and fittings can provide a physical and electrical barrier between the pipe and corrosive soil conditions. Overview of Leak Detection and Repair Practices A variety of approaches are used to detect, prevent and repair pipeline leaks depending on the age and size of the distribution system, the operating budget and staff, and other factors. Based on surveys conducted within the last several years, the majority of utilities around the country do not have leak detection programs in place. There are two major reasons for the lack of leak detection programs: 1) the technologies currently available for leak detection are not universally effective for all types of pipes, and 2) leak detection programs have not proven to be cost- effective. Leak Detection Several methods have been used for leak detection in water distribution systems with varying degrees of success. Ultrasonic emission can be used to try to detect cracks and other discontinuities. This method is ineffective for cement- coated or lead pipes ( lead pipes are not common in Utah). Most water distribution pipelines are cement lined or coated. Another alternative is to conduct visual testing using horoscopes and TV cameras that can travel through piping to inspect the interior surfaces and identify zones of excessive corrosion and breaks. Magnetic methods can be used to generate low frequency magnetic fields that can detect cracks in the pipes and pipe wall thickness. Interference, however, sometimes makes it difficult to locate the exact site of a crack or leak. Remote- field eddy- current techniques can detect cracks due to disturbances in the flow of electric current. An excitor coil produces electrical and magnetic fields in the pipe wall, and a pickup coil detects the fields and can determine the pipe wall thickness. This technique is claimed to be applicable to steel, ductile iron- and cast iron pipe, but it has not been widely used. Sonic searching is the most common leak 47 |