written by: Jayant R Row
• edited by: Lamar Stonecypher
• updated: 3/12/2011
Pipes are laid in the ground and soil conditions that are acidic can cause water mains to corrode and rupture. Breaks can also be occur when the pipes are subjected to very high pressures, which can even come from the water hammer cause by incorrect closing of valves.
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Causes for Breaks in Water Mains
Water main leaks and breaks occur from pipes that have been weakened by corrosion or when the network undergoes extreme pressures. The corrosion is a natural phenomenon occurring over years and can be caused by the water carried by the pipe or due to external soil conditions which may be acidic and can corrode the pipe. This corrosion can cause holes to develop in weaker sections of a pipe, which then leads to leaks.
Extreme pressures in pipe networks can be a result of incorrect closing of valves which can cause a phenomenon called water hammer, which results in very high pressures which can cause joints to become loose, thus leading to leakages. Pipes are also sometimes put under pressure by the freezing of the ground, which can cause the pipes to become dislodged from their original position, leading to additional pressure on the joints. Natural phenomenon like earthquakes or landslips can also cause water mains to break.
Detection and Repairs to Pipe Line Breaks and Leaks
Pipe line leaks and breaks are detected from visible indications of water on routes where pipe lines have been laid. They can also be detected when operators of the network notice unexplained drops in pressure or increases in consumption. While the first allows pinpointing of a leak easily, the second may involve quite detailed inspection of the route to find the exact location of the break. There are times when breaks occur close to surface drains and remain undetected because the drain carries away the extra water.
Leakages quite often occur at joints, and redoing the joint and resealing it can address the problem. Pipes laid decades ago will generally have joints that are made with lead. The repair of such joints would require the closing of the water supply, complete exposure of the joint, removal of the old joint material and re-caulking the joint with the necessary joint material. Older joints in cast iron mains were made with hemp dipped in tar, which was forced into the joint and then covered with lead.
Nowadays most water mains use press fit rubber caskets and leaks in such joints are difficult to repair. Newer techniques use carbon fiber along with polymers, and robots have been developed which can go into a pipe line, detect the leak, and repair it using carbon fiber. Repairs to joints and other holes causing leaks is sometimes effected by jacketing the defect and areas around it with concrete or polymer additives. Such jacketing is considered a temporary measure and would require planned shutdowns of the water mains to replace the defective pipe at a later date.
Quite often pipe mains are laid under roads and highways, and this can cause a lot of disruption when repairs are required. Such disruption also occurs in the supply of water to areas serviced by the mains. Pipe repair requires safety measures to be taken while work on roads or inhabited areas are in progress. The completion of water main repairs also requires the mains to be disinfected after the repair is completed. When restoring the supply, engineers also have to be careful in the operation of valves to prevent sudden surges in pressure.
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Newer Technologies in Water Main and Line Construction
Very large water mains are nowadays laid far below the ground, quite often in rocky strata by the use of tunneling techniques. The walls of the tunnel are concreted or lined with steel and other materials to ensure a section that is leak proof. Because of the huge diameters of such pipes, any leaks or problems in the future can be tackled by actually entering the pipe to effect repairs.
Most water mains of lower diameters are laid in trenches and such trenching is constantly in conflict with other utilities also laid in the area. A large proportion of water main breaks and leaks occur when other utilities dig their own trenches in conflicting areas. To overcome this problem, engineers have developed the technique of trenchless laying of pipes or other services that is done without disturbing the surface.