There may be occasions where PE pipes require repair, either temporary or permanent, both be made depending on the site conditions and ability to shut the main down and secure a dry environment to fuse in.
PE pipes can be shut off in emergency situations without a valve using the 'Squeeze-off method' this is where the PE pipe is clamped (usually hydraulically) between two steel rollers or half-round shapes in a 'squeeze off machine' until the pipe is completely flat, stopping all flow. This method is commonly used in PE gas pipes and is perfectly acceptable for use on PE pipes and gives maintenance crews a lot of flexibility to control burst situations. In Hong Kong, the Water Supplies Department require approval this method is used.
After squeeze-Off when the pipe is released, the PE will return to its original shape over a short period of time, depending on the pressure and temperature. Although not necessary, it is good practice to reinforce the squeeze off area of the pipe with an electrofusion repair clamp to remove any long term risk of Slow Crack Growth, especially if the pipe is not a PE100 RC (resistant to Crack) compound.
Other repairs including physical damage can be repaired with electrofusion repair saddles and patches, however, electrofusion is absolutely conditional on the pipe and fusion area being completely dry. Electrofusion must never be performed in a wet environment, tiny amounts of moisture turn to steam when headed at fusion temperatures and expand causing large voids in the weld area.
If the area cannot be maintained in a dry condition throughout the fusion process, then mechanical repairs must be conducted until such time as the line can be shut down and repaired properly. These can be performed with mechanical end restraint couplers or temporary wrap around clamps.
Repair balloons provide a method to stop ongoing minor water flows in a shutdown situation in smaller diameter pipelines to allow electrofusion to be performed.