In situations where pipe flushing does not result in improved water quality or improved flow capacity, pipe cleaning should be carried out. Reputable firms should be commissioned to undertake the work under the supervision of the operator.
Foam swabs and pigs are normally used to clean pipes. Other methods, including scrapers or brushes, are used to remove hardened scales and tuberculation. Swabs are made of polyurethane foam and can remove loose sediments, soft scales, and slimes. Pigs are also made of polyurethane but are heavier, harder, and less flexible than swabs. For general cleaning, swabs are used to remove sediments. A general improvement in water quality will be noticed after swabs are used. To improve both water quality and flow capacity, pigs are used. Pigs will remove the majority of the hardened encrustations. However, this may cause leaks at a later date in badly corroded pipe because of their abrasive cleaning characteristics.
Procedures for cleaning pipes are similar to those of pipe flushing except that services must be CLOSED. General procedures for cleaning include the following: 1) Planning and safety; 2) Water Supply; 3) Launch and exit points; 4) Valves; 5) Direction of flow; 6) Initial launch; 7) Progressive launches; 8) Record and open valves; and, 9) Open service connections.
- Planning and Safety
Read the section on Pipe Flushing.
- Water Supply
An upstream water source or an externally pressurized system is used. An adequate pressure to propel the swab or pig and sufficient supply of water for swabbing cycles is needed.
- Launch and Exit Points
On smaller mains, hydrants or special wyes and tees, are used to launch and retrieve the cleaning units. On larger mains, sections of pipes are removed because of the larger size of swab or pig needed. The removed section of pipe is fitted with a special wye fitting.
- Valves
Isolate the pipe to be cleaned by closing appropriate valves. Valves on the line to be cleaned must be fully open. Gate valves pose no problems but butterfly valves may require a different cleaning program.
- Direction of Flow
Turn on the water to verify the direction of flow through the pipe. Run a full-sized bare swab through the main to verify the direction of flow.
- Initial Launch
Run a bare squeegee through the main. Measure the diameter of the unit after it exits the receiving point. Launch a light cleaning unit that is the same size as the measured dimension followed by a full-sized bare swab. The bare swab provides a seal between the swabs and the pressurized water source that is used to propel units through the pipe.
- Progressive Launches
Increase the size of the pig in 2.5 cm (1 inch) increments using cleaning units until the inside diameter of the pipe is reached. Typical number of cleaning passes is three to five times. Units must be propelled at 0.70 to 1.3 m/s (2 to 4 ft/sec). For the final cleaning passes wire brush (do not use plastic wipes) units followed by a bare swab are propelled through the pipe to remove sediments.
- Record and Open Valves
Refer to the section on Pipe Cleaning.
- Open Service Connections
All service connections must be opened and flushed after the cleaning operation has been completed.
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