Copyright 2007 Bureau of Waterworks, Tokyo Metropolitan Government. All Rights Reserved 8-1 Nishi-Shinjuku 2-chome, Shinjuku-ku, Tokyo, Japan

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Hector McKinney
6 years ago
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4 Outline of leakage prevention Present situation The rivers flowing in this area, namely Tone, Ara, Tama and Sagami rivers are the main source of water used in the Tokyo Metropolitan area. The untreated water taken from these rivers is purified through such processes as coagulation, sedimentation and filtration at water purification plants. Then it is pressurized and supplied to the customers as tap water through underground pipelines. In the process of supplying tap water, some water leaks from the pipes into the ground. This is the leakage of water. Ten years ago, in FY1997, the amount of water leakage was about 140 million m 3 and the leakage rate was 8.4%. However, in FY2006, it was reduced to 58 million m 3, and the leakage rate decreased to 3.6% of the distribution water volume of billion m 3. (Fig.1, Table-1 and 2) Most of the leakage is caused by cracked or corroded service pipes and distribution pipes due to aging. The total number of cases of leakage repair in FY2006 amounted to about 18,000, and about 97% of them occurred in service pipes and the remaining 3% in distribution pipes. (Table-3 and 4) Leakage is classified into two types by its form; surface leakage flows out on the ground and underground leakage leaks out underground without appearing on the surface. Surface leakage is handled by mobile work and underground leakage by planned work. The ratio of two types of work is shown in Fig As a general rule, surface leakage (mobile work) is repaired on the same day. The number of cases in FY2006 was 16,460.On the other hand, the underground leakage (planned work) is invisible. Therefore the underground leakage continues for a long time, and accounts for a high percentage of the total leakage volume (Fig.2-2). Therefore, unless we identify and repair leakages systematically, valuable water will continue to leak and large accidents may occur. The number of repair cases in FY2006 was 1,287. 1

5 Water supply pipes are affected by, in addition to their own aging, earthquakes, irregular subsidence of the ground, corrosion, traffic loading and construction works. Leakage is always easy to occur. Although water leakages are repaired as soon as they are found, On the other hand, the new leakage increases gradually in accordance with time. This is referred to as the repetition phenomenon of leakage. As the solution to this repetition phenomenon may lead to leakage prevention measures, we are trying to understand this phenomenon. (Fig. 3) Leakage volume day prevention volume prevention volume Repetition volume Remained leakage volume Remained leakage volume The second last time The last time Now Recurring years Fig. Repetition of leakage Necessity of leakage prevention The Tokyo Metropolitan Government holds 6.23 million m 3 of daily water resources. However, there are resources that have problems such as difficulty intaking sufficient water due to changes in the riverbed. Particularly, the Tone River System, which accounts for about 80% of the water resource is not as stable against drought as other river systems, and water intake has been restricted three times in the past 10 years, in both summer and winter seasons. Also, future long-term water demand is expected to grow gradually. Thus, it is necessary to continue the development of water resources, but it requires a long time. There are about 25,000 km of distribution pipes laid in Tokyo as of FY2006. There is always a risk of the water supply pipes laid underground leaking. If leakage occurs, secondary disasters such as poor water flow, road collapse, flooding of the buildings and houses might occur. As measures for leakage prevention are not only as effective as developing new water resources, but are also effective in preventing secondary disasters, we are actively practicing such measures as one of our major activities. 2

6 Countermeasure of leakage prevention System of leakage prevention measures The leakage control measures that we take in Tokyo are classified as follows. Countermeasure of leakage prevention Corrective measures Mobile work Patrol work Preventive measures Planned work Technical development in leakage prevention Replacement of old distribution pipes with ductile cast iron pipes Material improvement work of service pipes Leakage volume measurement work Integration of service pipes under the private road and replacement with sub mains Reinforcement of seismic resistance of large-diameter service pipes Fig System of leakage prevention measures Corrective measures The corrective measures is the work of finding and repairing leakages that occur at the surface or underground. In the waterworks pipeline, distribution pipes are maintained and managed by the Tokyo Metropolitan Government. Services pipes that branch off from the distribution sub mains (diameter less than 350 mm) are to be maintained and managed by customers. However, it is difficult for customers to maintain and manage all the service pipes beneath the road. Therefore, for the purpose of leakage prevention, a leakage that occurs in a service pipe within residential land up to the water meter is repaired free of charge by the Waterworks Bureau except for special cases. Corrective measures include mobile work and planned work. Mobile work The work of repairing the surface leakage detected through the information from Tokyo residents or through patrol activities, etc. is called mobile work. In order to carry out this work effectively there are 7 branch offices (14 service station) in the division, where our staff and repair contractors are on call 24 hours a day. (Refer to Document-5). In Tama area, Tokyo Waterworks Service Co., Ltd., a supervised organization of Bureau of Tokyo Waterworks, and repair contractors keep a round-the-clock watch for the cities and towns with business operations carried out directly by the Bureau of Tokyo Waterworks. As for the cities with consigned business operations, the repair contractors of each city 3

7 remain readily available for the service. Information about water leakage, etc. is received in the day time of weekdays at the service stations of Tokyo Waterworks Service Co., Ltd., or at the concerned department of the city, and at Tama Water Control Center during night hours and on holidays. Planned work The planned work is Classification work and Patrol work that find and repair leakage by investigation deliberately inside some working blocks, which are parts of sub mains network divided by regular length, and the Leakage volume measurement work to presume of leakage volume and trend grasp of leakage. In ward districts, leakage prevention practices have been conducted for a long time, and leakage detection is under the direct management of 7 branch offices (14 enterprises). And most of the repair work performed under contract. As the leakage is less in the Tama area than in the wards because its waterworks facilities are relatively new and the start of planned work was fairly recent, the detection and repair is performed under contract. Patrol work (Circulating checking) The patrol work does not include the leakage volume measurement work and it involves block-wise detection and repair of water leakage from each house by applying an acoustic rod to the water meter, the detection and repair of leakage under the road by using an electronic water leakage detector during night hours when traffic is little and noise is nil. The blocks for patrol work are selected on the basis of past survey records and leakage condition. The work of each house in some blocks using a time integral type leakage detector has been consigned to private sectors since FY2003. Leakage volume measurement work To do presumption of leakage volume and trend grasp of leakage, the leakage measurement work is executed. In city which act for 24 hours, the measuring object is squeezed to about 300 to grasp a more accurate leakage volume, and minimum flowing quantity (leakage volume) at nighttime is measured. The presumption of the water leak becomes possible because it measures an accurate leakage volume, and it uses it to examine the water leakage prevention measures in the future. The Leakage volume measurement work has been consigned to the private company in a part of divisions from FY2005. (Annex) Classification work The classification work involves detection and repair of water leakage based on the result of measurement of the volume of potential underground leakage conducted in advance in order to ensure effective leakage prevention. The minimum flowing quantity (leakage volume) at night of a block is measured and then depending on the volume of water leakage, the leakage is detected using mainly the acoustic leakage sound detection method and correlation method before repairing. 4

Preventive measures Preventive measures are important and effective for identifying leakages early, suppressing repetition phenomena and also reducing the remaining leakage volume.

Replacement of the old distribution pipes with ductile cast iron pipes The cast iron pipe which low strength without inner surface lining, and the old steel pipe of all distribution pipes are

8 Preventive measures Preventive measures are important and effective for identifying leakages early, suppressing repetition phenomena and also reducing the remaining leakage volume. Major examples of preventive measures are as follows. Replacement of the old distribution pipes with ductile cast iron pipes The cast iron pipe which low strength without inner surface lining, and the old steel pipe of all distribution pipes are considered aged pipes. As aged pipes tend to develop leakage and turbid water and have low earthquake resistance, since 1973 they have been systematically replaced by ductile cast iron pipes, which have higher strength and better earthquake resistance, internally lined to suppress the development of turbid water. And, from FY2002, the complete replacement of aged pipes has been pursued in the K-zero Project. Further, from FY2004, the complete replacement of the early ductile cast iron pipes that is consist of Ductile cast iron and Cast iron has been pursued. As a result, as of the end of FY2006, about 99% of the total length of distribution pipe has been replaced by ductile cast iron pipes. (Note) Ductile cast iron pipe has increased material strength by the addition of magnesium to the traditional cast iron pipe and making graphite in the structure spherical. Cast iron Ductile cast iron Fig Micrograph of cast iron 5

9 Material improvement work of service pipe Approximately 97% of the water leakage repair works are concerned with the service pipes. Therefore, the prevention of water leakage from the service pipe is extremely important. Service pipes were conventionally made mainly of lead. Such pipes were not strong enough and were vulnerable to deterioration, causing water leakage. Hence, since FY1980 we have been replacing the lead pipe with stainless steel pipe for service pipes used under public roads (up to the stop cock installed in the house land 1m away from the distribution pipe), and availing of the opportunity of reinstallation of distribution pipes or of repair of water leakage from the service pipe, we have been replacing the lead service pipes under public roads with the stainless steel pipes. In preparation for the reinforcement of lead content level in water (from 0.05 mg/l to 0.01 mg/l, to be enforced in April FY2003), we drew up a plan in FY2000 to eliminate the lead service pipes under public roads by FY2002, and have successfully accomplished the job as planned. Since FY2003 we have expanded the material improvement project to private roads and up to the water meter inside the house land in order to eliminate lead service pipes. As a result, we have been successful in eliminating almost all of the lead service pipes under public and private roads and up to the water meter inside the house land. Fig Material improvement of service pipe 6

10 Integration of service pipes under the private road and replacement with sub main Since the service pipes are laid by customers, there are quite many private roads extending over a long distance and having a large number of service pipes. Most of the service pipes laid under such private roads are either lead pipes or vinyl pipes, which are likely to get deteriorated or broken. In order to solve this problem, we are making efforts to shorten the distance of service pipe by installing distribution sub main. This ensures steady water pressure and allows promotion of reinforced seismic resistance of the service pipe and preventive measures against water leakage. In the project that started in FY1994, the work started on the private roads having 3 or more service pipes drawn. Since FY2007 the scope of work has been further expanded to the private roads having 15 or more water meters installed. Public road Before the execution Housing land Public road After the execution Housing land Private road Sub main Private road Sub main Service pipes Sub main Service pipes meter Simple drain Valve (for service pipe Valve (for sub main) Fig Integration of service pipes under the private road and replacement with sub mains Reinforcement of seismic resistance of large-diameter service pipes Reinforcement of seismic resistance of service pipes with diameters larger than 75 mm has been promoted together with the replacement and leakage repair of distribution pipes since FY1998 with an aim of enhancing seismic resistance of water distribution network. The scope of the project has been further expanded since FY2007 to the route where the replacement of distribution pipes has been completed before FY1998, and where part of the large-diameter service pipes have yet to have the seismic resistance reinforced. Replacement of such pipes is under way as planned. 7

11 Technical development In order to advance efficient leakage prevention works and improve the leakage ratio further, research and development of related technologies is essential. So the Tokyo Metropolitan Government established the Training and Technical Development Center. On the area of piping test facility, various test and verification facilities for solving problems related mainly with piping are provided. Equipment related to water leakage prevention that has been developed or improved by researchers at the center is listed in Table-6. Leakage prevention construction system The Water Supply Section carries out electronic processing for calculating the construction cost, summarizing the records of the leakage cause and contents of work for the leakage repair project. The present system includes the processing given below. 1) Reception of leakage prevention measures 2) Calculation of construction cost for water leakage repair, material improvements, etc. 3) Summarization of the records of leakage causes and contents of the work done The data obtained through electronic processing are effectively used for budget-making of the next fiscal year and drawing out long-term plans, selection of planned work blocks, and calculation of leakage volume, etc., contributing largely to the execution of effective preventive measures against leakage. 8

12 The method of leakage investigation Presently, leakage investigation is performed by actually measuring the leak in a block (minimum night flow measurement) or detecting leaks by sound and locating the position of leak (acoustic leak detection, correlative leak detection, time-integrated leak detector, etc). Minimum night flow measurement method The minimum night flow measurement is a method that pays attention to the time period when there is no water usage in a block (Unoccupied hour). First, gate valves surrounding the block to be investigated are closed and the water from other blocks is shut down. Then the water is sent into the block through minimum flow measuring equipment set in the block water meter and the flow rate is measured. The minimum flow rate measured during the vacant period is considered to be the leakage. High precision portable minimum flow measuring equipment developed jointly by the Bureau and private industry is used in the measurement. Fig Theory of minimum night flow measurement method 9

Fig. Portable minimum flow meter Acoustic method In the acoustic method, the leak sound is detected by an acoustic rod or an electronic leak detector.

An inspector then presses an ear against a vibration diaphragm set at the other end of the rod, and listens for transmitted sound of the leakage.

13 Fig. Portable minimum flow meter Acoustic method In the acoustic method, the leak sound is detected by an acoustic rod or an electronic leak detector. The metal tip of the acoustic rod is pressed against the water meter, gate valve or fire hydrant. An inspector then presses an ear against a vibration diaphragm set at the other end of the rod, and listens for transmitted sound of the leakage. The acoustic rod can only tell whether the leakage is present in the neighborhood, and it is difficult to detect the position of leakage. Using an electronic leakage detector, a pickup to convert the leak sound into an electrical signal is placed on the ground, and the sound transmitted through the ground is amplified and heard through headphones. As the pickup is moved in order, the leak sound is heard most strongly directly above the point of leakage and thus the position of leakage can be detected. Fig. Acoustic rod 10

Fig. Electronic leakage detecter Acoustic rod Electronic leakage detecter Fig Acoustic method Correlation method In the correlation method, the position of leakage is detected by using a correlation

First, the sensor is placed on either side of the expected point of leakage in the pipeline and the time lag of leakage sound reaching the two sensors is obtained by the correlation analyzer.

14 Fig. Electronic leakage detecter Acoustic rod Electronic leakage detecter Fig Acoustic method Correlation method In the correlation method, the position of leakage is detected by using a correlation type leakage detector (a combination of correlation analyzer, sensor, amplifier, wireless transmitter, etc.). First, the sensor is placed on either side of the expected point of leakage in the pipeline and the time lag of leakage sound reaching the two sensors is obtained by the correlation analyzer. The position of leakage is calculated by the time lag, distance between sensors, and velocity of leaking sound transmitting through the pipe. The correlation type leakage detector was jointly developed by the Tokyo Metropolitan Government and private industry. It has the excellent characteristic of being largely unaffected by traffic noise or laying depth of the pipe. 11

amplifier with radio transmitter correlation leakage detector sensor valve C C A (standard point) leak point B (comparison point) La L Tm C Tm C L leakage

15 amplifier with radio transmitter correlation leakage detector sensor valve C C A (standard point) leak point B (comparison point) La L Tm C Tm C L leakage noise propagation time difference noise velocity on the pipe distance between A and B Fig Theory of the correlation method Fig Correlation type leakage detector 12

Time integral type leakage detector The time integral type leakage detector detects a leakage by utilizing the nature that leaking sound persists.

the pipeline for a certain time period (10 seconds to 3 minutes). The time integral type leakage detector was jointly developed by the Tokyo Metropolitan Government and private industry.

16 Time integral type leakage detector The time integral type leakage detector detects a leakage by utilizing the nature that leaking sound persists. In this detector, a sensor is pressed against the exposed part of the service pipe in the meter box and the leakage is detected by an automatic leakage detector, measuring transmitted sound through the pipeline for a certain time period (10 seconds to 3 minutes). The time integral type leakage detector was jointly developed by the Tokyo Metropolitan Government and private industry. It has excellent characteristics such as being largely unaffected by intermittent usage sound of the waterworks or traffic noise transmitted through the ground, and not requiring skill to operate. Automatic leakage detector meter Leak point Service pipe Sub main Fig Time integral type leakage detector Other methods Leakage investigation requires not only the technologies to identify the leakage but also those to detect the position of laid pipes or to test water quality to determine whether leaking water is tap water. Metal pipe detector, nonmetal pipe detector and Water hammer Generator are used to detect the pipe location. We are applying simple methods using a thermometer, residual chlorine meter, ph meter and electrical conductivity measuring equipment, or more precise methods of detecting trihalomethane and others to test whether it is the tap water or not Fig Metal pipe locator 13

Fig Water hammer Generator Problems and the future of leakage prevention The problem of lead service pipe that accounts for the major part of leakage repair work has mostly been eliminated for the

17 Fig Water hammer Generator Problems and the future of leakage prevention The problem of lead service pipe that accounts for the major part of leakage repair work has mostly been eliminated for the pipes under public and private roads, and up to the meters inside the house land by the end of FY2006. Further, the replacement of aged distribution pipes with ductile iron pipes has also been completed approximately up to 99% of the total extension of distribution pipe. With the aforesaid preventive measures taken, the leakage rate at the end of FY2006 was reduced to 3.6%, well below the target value of 4%. (Refer to Documents 2 and 7) The number of leakage repair works is decreasing and the leakage detection efficiency is declining year after year. In the future, measures are needed, with due consideration paid to the improvement in cost performance. Therefore, Tokyo Metropolitan Government has promoted, through collaborated research with universities since FY2005, studies on the future leakage preventing activities during the stage of low-rate leakage, such as estimation of the optimum term of pipeline replacement, etc. On the other hand, the high-level leakage prevention technology of the Bureau of Tokyo Waterworks is drawing world-wide attention. The low leakage rate in Tokyo was the center of attention of the cities participating in the C40 Large Cities Climate Summit held in New York in May FY2007. As for the international contribution in the field of waterworks, set as the major policy objective in the Waterworks Vision published in FY2004, the item is included in the major field in the Asia Gateway Initiative approved in a Cabinet meeting held in FY2007, and has become an important keyword in recent years. Taking account of the aforesaid items, Tokyo Metropolitan Government is determined to transmit to the world, as part of international contribution, the achievements in reducing water leakage rate, and the leakage prevention technology and know-how as a disclosure of information. 14

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20 Water volume (year) Component ratio () Distribution total 1,606,415, Effective 1,544,576, Account for 1,524,405, Charged 1,518,510, Supplied totama 5,853, Others 42, Unaccount for 20,170, Unmeasured 17,346, Waterworks use 1,945, Others 878, Ineffective 61,839, Leakage 58,423, Deduced consumption by settlement 2,649, Others 766,

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23 Leakage prevention subsect.(7) Leakage prevention subsect.(7) arrangement charge(7) coordinantion charge(7) Number of persons working in the Waterworks is 4,416 (at April 2007). 417 persons of them are engaged in leakage prevention of the 23 wards. 20

24 Freezing method This method suspends water by freezing up the water inside the pipe with liquid air in repairs. Electronic leakage detector This instrument can pick up the leakage noise electrically on ground surface. Portable minimum flow meter This flow meter is used at the minimum night flow measurement. orrelation type leakage detector This instrument locates the leakage by processing leakage noise picked up at two point on pipe. Underground radar This radar radiates electro-magnetic wave to ground so as to search the underground condition. Time integral type leakage detector Making use of the continuity of leakage noise, this instrument is able to check whether the leakage exists or not. Non-metal pipe locator Making use of the transmission noise, this instrument can locate the non-metal pipe. Endoscope Putting the camera into mains, this instrument can check the condition inside the pipe. Insert type flow and vector meter This instrument is put in the pipe through the hydrant, etc. so as to measure the flow and the vector. Transmission-type leakage detector (under development) It is a device to locate the place of water leakage by detecting the helium gas injected into the water pipe and then discharged through the leakage spot to the soil. 21

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Prevention of Leakage in Tokyo

Prevention of Leakage in Tokyo 2017 Bureau of Waterworks, Tokyo Metropolitan Government Contents 1 Outline of leakage prevention 1 (1) Present situation 1 (2) Necessity of leakage prevention 2 2 Leakage