DN-17a – PE Single squeeze-off up to & including 180mm LP, & up to 63mm MP

Title Page

General requirements

Prior to commencing any work ensure that the following documentation is available and authorised where
appropriate.
1. Job instructions
2. Routine / Non-Routine operation procedures
3. Permit to work

Tools and equipment

Thoroughly clean the main where the squeeze-off and joints are to be made
Check diameter, Standard Dimension Ratio (SDR). Material type – information will be printed along the pipe barrel at 1m intervals on each side of the pipe. Check then pipe for ovalty and re-round as required.
All equipment must be checked, prepared and available for the work to be undertaken.
Ensure the correct distance is maintained from the existing fittings, joints, squeeze-off applied locations and any proposed future joints used for connection purposes.
Set out the squeeze-off operation by marking the exposed pipe with all positions for pressure points, by-pass connections, vent points, rider points and location of squeeze-off.

Install two pressure monitoring points on the PE main either side of the proposed flow stop section of pipe
Attach and commission pressure gauges.
Confirm Network pressure as specified within range of single squeeze-off operation, 75mbr for main up to and including 180mm diameter, and 2bar for mains up to and including 63mm diameter.

Construct the bypass in size and material as per written procedures.
Prior to tapping the main the bypass must be pressure tested with valves A and B in the open position with the vent pipes capped off above the vent valves C and D, these vent valves must be left in the open position. The bypass must be pressure tested to 350mbr, for 15 minutes. No pressure loss is accepted. On successful completion of the test the vents C and D must be closed, and the vent pipes erected. Close valves A and B, the main can now be drilled.
Vent pipes must be constructed as per Section H1, (SGN/WI/ML/2), and protrude 2.5m above the ground level. Metallic vent pipes must be earthed using approved electrical earth rods and straps from the metallic vent pipes to earth. Vent pipes must be adequately supported.

It is important that the bypass is confirmed free from blockages by purging both ways. Check all valves are closed, check network pressure.
Open vent valve C, then open bypass valve A,
Purge until two independent readings of 90% gas in air have been obtained from vent C, then close vent valve C and bypass valve A.
Open vent valve D then bypass valve B.
Purge until two independent readings of 90% gas in air have been obtained from vent valve D. Close vent valve D.
Open bypass valve A slowly and pressurise to network pressure.
Fittings not tested must be checked for soundness with approved leakage detection fluid, washing off pipe and fittings with clean water afterwards
The bypass is now fully commissioned.

Place squeeze-off units, 1 and 2, on the parent main at the marked positions.
Fit and connect vent E onto parent main upstream of squeeze-off 1 ensuring minimum distances from squeeze-off position and future tie-ins.
Check squeeze-off units are in good working order.
Set the stops to the correct pipe size and SDR. If the SDR of the pipe cannot be found, then set the stops to the size of pipe. For 90mm and 125mm SDR 17.6 pipe it is necessary to set the stops to one size below i.e. 125mm to 90mm and 90mm to 63mm.

Re-check Network pressure to confirm mains operating pressure.
Re-check bypass is fully open.
Slowly apply downstream squeeze-off unit 1, until it reaches its maximum position, monitoring the pressures at both mains pressure points to ensure the pressure is not falling. Monitor the pressure gauges for 10 minutes before proceeding. If the pressure starts to fall below that stated on the written procedure release squeeze-off and inform the Operational Manager
Apply squeeze-off safety stops.
Slowly apply upstream squeeze-off 2. Continuously monitor pressure.
Apply squeeze-off safety stops.
Open valve E and check at the vent between the squeeze-off units to establish whether there is any gas passing.
If no gas is passing continue with the operation
If gas is passing, refer to Section E1, (SGN/WI/ML/2)

Drape damp cloths around the pipe and ensure they are in contact with the ground on each side of the cut to prevent a spark from static electricity.
Cut pipe section as specified in the work instruction, continually monitor the network pressure and the atmosphere within the cut-out area. The cutting of PE mains must only be undertaken using approved equipment. Should a guillotine be used a re-rounding clamp should be put on the main prior to joining.
Install expanding stoppers whilst preparing fittings for installation.
Remove expanding stoppers.
Install new section as specified in the work instruction and in accordance with Appendix D, (SGN/WI/ML/2) Electrofusion.

Remove squeeze-off safety stops.
Monitor pressure gauges, open valve E, slowly release upstream squeeze-off 2 and purge through vent pipe until two independent readings of 90% gas in air is obtained.
Turn of valve E and allow section to pressurise to line pressure.
Test installed fitting with leak detection fluid and wash off with clean water.
Slowly release downstream squeeze- off 1.

Slowly close valve B whilst monitoring the pressure.
Monitor mains pressure for 10 minutes to ensure the new section is supplying gas downstream without any blockages.
Slowly close valve A and vent down bypass through vent C,
Disconnect vent pipe valve at C
Connect air supply at valve C, open valve D and direct purge to air at vent D.
Note. Air pressure must not exceed 1/3 of mains pressure.
Remove caps from the top of the top tees and reinstate PE cutter into main at bypass. Pressure point and vent connections. Check seal using leak detection fluid.
Remove bypass, pressure points and vents. Install electrofusion cap on to the outlet of the saddle fusion tees. Raise integral PE cutest and fit completion cap. Test electrofusion cap with leak detection fluid. Wash off with clean water
Recover squeeze-off units 1 & 2, re-round PE main and apply squeeze-off tape.