Water Lines. Materials

Transcription

1 Water Lines Materials Cast iron The Evansville Water distribution system includes almost 1,000 miles of water lines. Approximately 58%, or 580 miles, of the water mains in Evansville are made of cast iron which was the material of choice until the early 1970 s. Since Evansville s first water plant was completed in 1873, the oldest pipes also date back that far. Around the mid 1940 s, cast iron pipe with a cement lining started being installed in the system. Prior to that, there was no protection on the inside of the pipe to prevent tuberculation, as shown in photo 12.1, from forming due to the corrosive properties of the water against the iron pipe. Photo 12.1 Tuberculated Cast iron Pipe Tuberculation of a pipe can severely restrict the amount of water that flows through the pipe not only from the decreased area but also because the inside of the pipe is extremely rough which creates more friction loss. Cast iron pipes were joined together by packing oakum into the joints. Molten lead was then poured into the joint, creating a seal. As the demand for lead increased during times of war, a substance called leadite became the material of choice to join the cast iron pipes together. The use of leadite created problems with the water mains. It is more corrosive to the pipe and it expands and contracts at a different rate than the iron pipe. If the leadite expands faster than the bell of the pipe, it could split the bell and allow water to escape the pipe. 44

2 In the early 1950 s cast iron pipe was introduced to the system that used a rubber gasket joint, eliminating the need to use lead or leadite to seal a joint. One end of a pipe was simply pushed into the bell end of the next pipe which contained a gasket preventing the pipe from leaking. Ductile iron Ductile iron pipe resembles cast iron but it is a much stronger material. Due to the strength of the ductile iron, the pipe can be much thinner than cast iron, as shown in photo 12.2, yet still maintain the same pressure rating. Evansville experimented with the use of ductile iron in 1960 but did not start using it system wide until the early 1970 s. Evansville s distribution system contains approximately 9%, or 90 miles, of ductile iron. Ductile iron pipe is still being installed today in the Evansville distribution system, primarily for larger transmission mains 16 inches or larger and for fire hydrant leads that are installed between the water main and the fire hydrant. Photo 12.2 Ductile Iron Pipe Cast Iron Pipe Asbestos Cement A small amount of asbestos cement, sometimes referred to as transite, pipe was installed in the Evansville system during the 1940 s when iron products became scarce during the war. There are approximately 15 miles of asbestos cement pipe in the distribution system. Pre stressed Concrete Cylinder Pipe Evansville has approximately 30 miles of pre stressed concrete cylinder pipe, or PCCP, in its system. This pipe is reserved for large diameter transmission mains typically 30 inches and larger. PCCP is a very durable pipe with the potential to last an extremely long time. It is composed of a steel cylinder with an inner concrete liner and an outer concrete jacket. The outer concrete layer has a pre stressed wire hoop poured into the concrete which provides the structural integrity of the pipe. Once the pipe is 45

3 installed, it requires special fittings to install a tap on the line and due to its limited use in the area; there are very few contractors available with the equipment necessary to drill into the pipe. Due to its expense, and the expertise required to work on the pipe, Evansville has opted to use ductile iron pipe in lieu of PCCP for the larger transmission mains on recent projects. Photo 12.3 Preparing to make a tap on 48 PCCP Photo 12.4 Drilling into the 48 PCCP Main 46

4 PVC PVC pipe is by far the most widely used type of pipe that is installed in the Evansville system today. It currently makes up about 28% of the system or approximately 280 of the 1,000 miles that Evansville uses to transport water from point to point. Installation of PVC pipe started in the early 1980s in the Evansville system and is the pipe of choice for sizes up to and including 16 inch diameter pipe. High Density Polyethylene Pipe Evansville has a very small amount of high density polyethylene pipe, or HDPE, in its system. Evansville has used it exclusively for applications where the directional drilling method of pipe installation is necessary and/or a large degree of pipe flexibility is required for the installation. Examples of HDPE installations in the Evansville system would be the 24 inch water main that was drilled under Pigeon Creek along the Lloyd Expressway or the dual 36 inch diameter water mains that were drilled under Veterans Memorial Parkway. HDPE, like PCCP, requires specialized equipment to weld, install, and work on the pipe after installation. Photo 12.5 shows a 36 inch diameter HDPE pipe joint that was welded, or fused, together to form one continuous piece of pipe. Evansville does not install this type of pipe on a routine basis due to its expansion and contraction characteristics. Photo inch HDPE Pipe Joint 47

5 Fittings & Valves All fittings that are used in the installation of water mains in the Evansville system are made of ductile iron. Like the ductile iron pipe that is used, the fittings also have a cement lining to prevent corrosion and improve flow. The valves have a cast iron body that is encapsulated with an epoxy coating, inside and out, to prevent corrosion. Care has to be taken when handling and installing the fittings and valves so that the cement lining or epoxy coating is not damaged or compromised. If the coating is chipped and the cast or ductile iron is exposed to the water or surrounding soil, electrolysis will be concentrated in that small area of the chip and the fitting or valve will corrode much quicker than normal and over time will create a leak. Photo 12.6 shows some ductile iron fittings bolted to some epoxy coated gate valves. Notice the square operating nut on top of the valves shown. The red color of the operating nut indicates those valves open by turning them clockwise. If the operating nuts had been black, the valves would open by turning them counterclockwise. Almost all valves and fire hydrants in the Evansville system open by turning them clockwise which is backwards from the most common direction of opening a valve. Even most of the oldest valves in the system use this open right method of operation. Therefore, in an effort to maintain consistency throughout the system, Evansville still orders valves that open clockwise. Photo 12.6 Fittings and Valves Assembled and Awaiting Installation Fire Hydrants There are more than 5,700 fire hydrants in the Evansville distribution system that are owned and maintained by the Utility and another 300 fire hydrants that are privately owned. Fire hydrants are typically made of cast iron and are epoxy coated similar to the valves. The internal parts are most commonly made of either brass, stainless steel, or some type of iron encapsulated in rubber. The fire hydrants that Evansville uses are referred to as dry barrel hydrants because there is no water in the riser of hydrant until it is opened for use. This prevents freezing problems from occurring. 48

6 Photo 12.7 Typical Fire Hydrant Installation Photo 12.7 shows what a fire hydrant looks like prior to backfilling. There is normally four to five feet of riser pipe underneath the part of the hydrant you normally see above ground. At the base of the riser pipe is the shoe that contains the actual valve which controls the flow of water as you turn the operating nut on top of the hydrant. There is a piece of ductile iron pipe that extends from the shoe of the hydrant towards the water main where it connects to a gate valve that is used to turn the water off to the hydrant, for maintenance, without shutting down the main. Evansville also paints the top of the hydrant different colors indicating the size of the water main that feeds the hydrant. A red top indicates the fire hydrant is on a four inch main. A green top indicates a six inch water main and an all yellow hydrant indicates the water main is eight inches or larger. Service Lines Evansville requires the use of copper tubing for ¾ and 1 inch service lines that extend from the water main to the property line. A valve, referred to as a corporation stop, corp stop, or corp cock, is installed at the main and a valve, referred to as a stop cock, is installed at the property line. Both of these valves are made of brass and the tapping saddle that is placed on the main where the valve connects is made of stainless steel. The Utility maintains the service up to the stop cock and the customer owns and maintains the line from the stop cock to the house which includes the vault or pit where the meter is located. The utility does own and maintain the meter that is installed in the customer owned pit. Services larger than one inch are installed by the owner or owner s contractor but are maintained by the Utility up to and including the meter and vault. Two inch services are typically HDPE pipe and three inch 49

7 and larger services are typically ductile iron or PVC. All saddles are made of stainless steel and valves are either brass or epoxy coated cast iron depending on size. Construction Department The Evansville Water Department includes a construction department that is responsible for the maintenance of the distribution system with the exception of the storage facilities and booster stations that are maintained by the filtration plant staff. Construction department employees perform a variety of tasks. These tasks include: Repair and replace water mains Repair and replace service lines Repair and replace fire hydrants Repair and replace valves Inspect and paint fire hydrants Exercise valves to ensure they are accessible and usable when needed Repair and maintain all of the vehicles and equipment used by the Utility Set up and maintain traffic control and safety barricades for all Utility jobsites Complete restoration work in yards where work was performed Maintain and issue a parts inventory needed for system maintenance and repairs Diagnose system issues such as low pressure Locate leaks where point of failure is unknown 50