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Cathodic Protection System for Large Diameter Water Mains Water Supplies Department (WSD) uses steel pipes for large diameter water mains. However, when a steel pipe has been laid underground for a long time, its metal will lose its electrons to the soil surrounded and leads to corrosion. The steel pipe will become thinner and eventually fail to withstand the pressure and burst. Considering the more active the metal the easier it corrodes, one of the ways to prevent corrosion of large diameter water mains is to connect the steel pipe with a piece of more active metal (i.e. more easily corroded, such as magnesium), which acts as “sacrificial metal” to replace iron in the steel pipe to provide electrons to the oxide in the soil. The steel pipes will then be protected against corrosion. This principle is like the role of the cathode of an electrolytic cell, so it is named “cathodic protection system”. Another method of cathodic protection involves the connection of an external electric power source to the water main. In 2007, WSD introduced the cathodic protection system under the Replacement and Rehabilitation (R&R) Programme of Water Mains. Condition survey had been conducted on existing large diameter steel water mains and for those water mains that were found to be in satisfactory condition, they were designed to receive cathodic protection such that their service life could be extended considerably. The installation of cathodic protection system is relatively simple, fast track and more cost effective as compared with other types of R&R methods. In addition, it does not require isolation of the water mains and hence interruption of water supply to consumers can be avoided. In the cathodic protection system of the R&R project, magnesium sacrificial anodes in groups with chemical backfill are adopted. The said anode groups are installed up to approximately 10m deep underground by drilling and then connected to an existing water main by cables. For protection of the whole section of water main, similar anode group is installed for every 150m to 200m of the water main depending on the surrounding condition. In between the anode groups, copper and copper sulphate reference electrodes are installed as reference station for regular monitoring of long term performance of the cathodic protection system to ensure that the water main receives sufficient protection. • Magnesium anode, the sacrificial metal Delegation Date of Visit Location Department of Quantity Surveying, Universiti Teknologi MARA, Malaysia 17-10-2012 Sha Tin Water Treatment Works and Plover Cove Reservoir Delegation led by Governor of Shiga Prefecture, Japan 3-11-2012 Ngau Tam Mei Water Treatment Works PUB, Singapore’s National Water Agency 6&7-11-2012 WSD Customer Telephone Enquiry Center and Tuen Mun Water Treatment Works Vocational Training Council 4-12-2012 Tai Po Tau Raw Water Pumping Station Kunming Municipal People’s Government Water Resource Management Group 5-12-2012 Ngau Tam Mei Water Treatment Works Delegations During the past several months, the following delegations visited the department to exchange experience and knowledge on the latest water treatment technologies and water supply management: ENQUIRIES 24-hour telephone enquiry hotline: 2824 5000 Fax hotlines: 2519 3864 (for water supply and general matters) 2802 7333 (for billing and consumership matters) Website address: http://www.wsd.gov.hk E-mail address: [email protected] Correspondence address Water Supplies Department, Immigration Tower, 7 Gloucester Road, Wan Chai, Hong Kong (Fax: 2824 0578) Editor Public Relations Manager, Water Supplies Department Free copies of Waterlink can be obtained from the following locations: • Customer Enquiry Centres of the Water Supplies Department • Public Enquiry Services Centres of District Offices / Home Affairs Department All WSD publications can be browsed on the WSD website. • Installation of magnesium anode block The Ombudsman’s Awards 2012 – WSD Winning an Award for Public Organisations Introduced in 1997, The Ombudsman’s Awards aims to acknowledge professionalism in handling complaints and to foster a positive culture of service in the public sector. Over the years, staff from the Water Supplies Department (WSD) received several individual prizes for their significant contribution in providing quality customer services. The overall performance of the WSD was further recognised in 2012 for being one of the three awardees of the “Awards for Public Organisations”. Speaking at the Award Presentation Ceremony, The Ombudsman appreciated WSD’s cooperative and forthcoming attitude in response to the Office’s investigations or inquiries. The WSD was complimented on being “open- minded to recommendations” and “proactive in working for improvements”. The department’s customer-oriented and positive attitude helped enhance the service quality amidst rising expectations from the public. The Director of Water Supplies, Mr MA Lee Tak expressed that considering the close relation of WSD’s services to the daily life of the public, the department attaches great importance to the opinions and complaints of the public and regards their views as a good opportunity for the department to improve the efficiency and upgrade the service quality. The six core values of the department: customer satisfaction; reliability; environmental awareness; dedication; improvement; and teamwork, are upheld by every WSD staff, who will continue to provide high quality water supplies services to the community. Also attended the Ceremony was our Engineer, Mr Horace LEE, who received an individual award together with 40 public officers from other government departments and public organisations. • The Ombudsman with awardees at the Award Presentation Ceremony held on 31 October 2012 • Mr MA Lee Tak (right), Director of Water Supplies, receiving the Award for Public Organisations from The Ombudsman, Mr Alan LAI • Water Supplies Department believes that teamwork is essential in the provision of customer-oriented and quality service • “Dedication and Unity” are the motto of Mr Horace LEE (right), WSD Engineer Waterlink • January 2013 • Issue 64 Waterlink • January 2013 • Issue 64 FOCUS UPDATES INTERFLOW VISITS 64th Meeting The 64th meeting of the CLG was held on 28 September 2012. The first presentation was on the accomplishment of and progress on the Replacement and Rehabilitation (R&R) Programme of Water Mains, which started in 2000 for replacing and rehabilitating of some 3,000 kilometres of aged water mains among the 7,800 kilometres of total water mains in the territories in stages, in order to improve the performance of the water supply network. The benefits of the R&R programme were obvious. For example, the number of main bursts was greatly reduced by 87% from 2,480 in 2001 to 317 in 2012 while the water leakage rate had reduced from 25% in 2001 to 19% in 2011. It was anticipated that the leakage rate would be further decreased to 15% upon the completion of the programme. Members were also briefed on “Desalination in Hong Kong”. In 2008, the Government promulgated the Total Water Management (TWM) strategy which aimed to achieve an optimal balance between water demand and water supply in order to ensure sustainable use of water resources in Hong Kong. Given that Hong Kong had an abundant of seawater, desalination could be a new and reliable resource of water supply. Having carried out pilot plant studies using reserve osmosis (RO) technology at both Ap Lei Chau and Tuen Mun, the Water Supplies Department (WSD) found that the quality and salinity of the seawater at the eastern coast of Hong Kong were more stable than that at the west. Tseung Kwan O was thus selected as the site for the proposed desalination plant. At present, using RO technology for desalination requires much energy and thus it is not favourable in terms of price and impact to environment. In light of the rapid development of the desalination technology, there was a worldwide downward trend in both capital investment and operation cost for applying the RO technology. It was thus expected that the production cost of desalinated water would gradually decrease. Nevertheless, the WSD would look into the cost effectiveness and potential environmental impacts of setting up a desalination plant in Tseung Kwan O. The proposed plant would produce around 50 million cubic metres potable water per year (i.e. about 5% of overall water supply). The third presentation was on “Water Meter Replacement Works”. Most water meters in Hong Kong were mechanical meters, which were complied with international standard. The accuracy of water meters might deteriorate with time due to erosion of the mechanical parts and the consumption measured by an old meter might be less than the actual figure. As such, meters were required to be replaced periodically. Since 2006, WSD has accelerated to replace 15mm water meters and about 200,000 aged meters were replaced each year. Currently, WSD also speeded up the replacement of medium and large sizes meters. To facilitate the replacement programme, cooperation of members of public in making access available to the meters and repairing defective inside services would be most appreciated. Waterlink J A N U A R Y 2 0 1 3 I S S U E All treated water supplied by WSD - including desalinated water - was fully complied with the World Health Organization (WHO) Guidelines for Drinking-water Quality. Desalinated water would also go through a series of post-treatment processes including pH adjustment, post-chlorination, etc. Reserve osmosis is the process of forcing water from concentrated solution to less concentrated solution through a semi-permeable membrane under high pressure. The membrane allows fresh water to pass through while it retains salts and other impurities. Reserve Osmosis High Pressure Membrane Seawater Pure Water Direction of flow 64 Published by Water Supplies Department NEWS ON CUSTOMER LIAISON GROUP (CLG) Contents NEWS ON CUSTOMER LIAISON GROUP Sixty-fourth Meeting FOCUS The Ombudsman’s Awards 2012 – WSD Winning an Award for Public Organisations UPDATES Cathodic Protection System for Large Diameter Water Mains INTERFLOW VISITS Delegations
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