DN - 15b - Live mains insertion on low pressure mains up to 180mm

Title Page

Site conducted
Conducted on
Prepared by
Location
Operative being assessed

Tools and equipment

Pipe pushing equipment
Pipe insertion protection
Pipe coil trailer
Pipe rollers
Butt fusion control unit
Re-rounding clamps, scraper and marker pen
CCTV camera (optional)
Metallic pipe cutters
Damp sacks / cloths
Mains break out tool
Foam off isolation equipment
End seal kit

General requirements: Insertion

Carryout the flow stop operation in accordance with Section B3, (SGN/WI/ML/2) and cut
out a section of main ensuring that the launch excavation dimensions are as recommended in Table 8
(SGN/WI/ML/2). Fit a cap end to the main not to be inserted and provide temporary anchorage, refer to Section
B, (SGN/WI/ML/2) for temporary restraining of the cap end. Fit gland box to the section to be inserted.
A bypass must be constructed and remain commissioned throughout the insertion process unless its omission is
authorised by the Operational Manager.
The exposed host main must be supported throughout its length during the preparation and insertion process.
The launch excavation from which the PE main is to be pushed should be as per Figure
9, (SGN/WI/ML/2)
During insertion, the PE pipe should be carefully measured to enable the live head to be easily located in the event of an obstruction.
In all cases the main must be ‘pushed’ in, using an approved pushing machine.
The pushing machine should, for safety reasons, be located in the launch excavation.
Prior to anchoring the pushing machine the area below must be confirmed free of other utilities by checking plans and the use of an approved pipe and cable locator.
Rollers or other suitable packing should be set up both at road level and in the launch excavation to guide the inserted main into the existing main.
Prior to insertion an integrity pressure test of 40mbar must be undertaken on the pipe string/coil. The pressure test duration must be derived from Table 43, (SGN/WI/ML/2). A stabilisation period of 1 hour is required and no pressure loss is allowed. To mitigate against the effect of temperature, e.g. direct sunlight, the pipe string/coil should be tested when the temperature will remain constant or protected by shrouding the pipe with a suitable cover. If a pressure loss is observed the pipe/fittings must be checked to locate the source of leak. Once the source of the leak has been found and rectified the pressure test must be repeated.
The use of pipe coils is the preferred method for live insertion up to and including 180mm PE.
Prior to the insertion process the pipe must be visually checked for damage.
For pipe coils the lead end must be mechanically restrained until it is securely fastened into the PE pipe-pushing machine.
The main to be inserted may be one or two-way fed. For two way fed mains the launch excavation should be utilised for insertion in both directions by installing a gland box on either side of the cut out main.

Insertion - Commission

Install, purge and commission bypass as stated in Section B, (SGN/WI/ML/2). It is important that the bypass is positioned on the main to be inserted so that the foaming off operations to be carried out later does not affect the bypass.
Insert flow stop equipment, e.g. bags, pressure points, etc., in accordance with Section B, ( SGN/WI/ML/2) ensuring that the exposed main is supported at all times.
- Yes
- No
- N/A
Cut out section of main between bags ensuring that the cut-out section will facilitate the positioning of the gland box, PE pushing machine and room for the PE to snake out of the excavation without exceeding the PE bend radius. Reference must be made to Section B1, (SGN/WI/ML/2). for PE bends radius.
Fit approved end cap onto the existing metallic main not to be inserted and provide temporary anchorage. See Figure 9, (SGN/WI/ML/2)
The installation of live mains insertion component part, i.e. gland box and PE pushing machine must be undertaken in accordance with the manufacturer’s instructions.
Fit gland box assembly onto main to be inserted.
A retrievable gland box incorporating a valve may be installed, or alternatively, a gland box incorporating a plastic seal, which acts as a valve until the PE is inserted through it...
Remove bagging off equipment on side not to be inserted as per Section B, (SGN/WI/ML/2)
Install live head onto the end of the PE main.
Install pushing machine into excavation ensuring that the ground below the machine has been checked for other utilities prior to installing the pins.
Push live head until in contact with valve V1 or plastic seal.
Install 32mm/1” purge rider over the bags and a 1” vent pipe to end of PE coil in accordance with Section H1, (SGN/WI/ML/2)
Direct purge by pushing the PE through the plastic seal or valve in the gland box. Open the vent pipe at the end of the PE coil.
Commission the rider across the bags and purge out PE pipe in accordance with Section H, (SGN/WI/ML/2). Purge must commence from the live head to the vent pipe located at the end of the PE main.
Check for two readings of greater than 90% G.I.A at the vent pipe connected onto the end of the PE coil or pipe string. When a full purge has been achieved, close the vent pipe, deflate and remove the bags in the main to be inserted as per Section B, (SGN/WI/ML/2)
On one-way systems attach a pressure gauge to the far end of the main to be inserted to check if pressures are lost during insertion process due to blockages caused by debris or water. A tested system of communication must be set up between the operatives at the launch excavation and at the far end of the main to be inserted.
Start pushing PE main into the host main, monitoring pressures in the host main. Carefully record the length of new pipe pushed in as it passes into the gland box, in order that the position of the live head is known

Insertion - Completion

When the new PE pipe has been ‘pushed’ in to the required length, either inject foam into the annulus using the hole drilled for the flow stop bags nearest the gland box assembly to facilitate its subsequent removal or alternatively, if gland box is to be left in place, there is no requirement to foam off. The main would only require to be squeezed off. The distance and location of the live head must be determined and recorded on the job documentation.
Squeeze off PE pipe, this should be a minimum of 6x pipe diameters from insertion seal if fitted.
Cut PE pipe at a suitable point (upstream of gland box assembly) to allow for installation onto exiting host main.
Re-apply the flow stopping equipment on the existing main, and connect new PE main to existing main. Purge mains connection as per Section B, (SGN/WI/ML/2) Remove flow-stopping equipment.
Test all new joints with approved leak detection solution, washing off the solution with clean water on the PE main.
Where the gland box has been removed, an end seal must be fitted immediately to the inserted main as per the manufacturer’s instructions
Close bypass and monitor pressures before dismantling.
Plug all holes and test with approved leak detection solution.
Reinstate excavation in accordance with the reinstatement manual.
Procedure for transfer of service connections + Transfer of services must begin from the gland box towards the live head. The number of services to be transferred in one transaction will be dependent upon site conditions and available resources. + Installation of foam and muff end seals must be undertaken in accordance with the manufacturer’s instructions.

Decommissioning of host main

Identify number of services to be transferred and excavate.
Identify foam injection position. Note: Foam must be injected at the service location nearest to the live head.
Pressure monitoring should be established using the emergency control valve on the service furthest from the foam off position.
- Yes
- No
- N/A
A service connection position may be used for the foam insertion point. Alternatively, drill and tap the main using a specially designed drill, care being taking not to damage the inserted PE.
Install foam injection equipment.
Select and check the correct size of foam kit suitable for the combination the old main and the replacement PE main size being used as per manufacturer’s tables.
Mix and inject foam according to the manufacturer’s instructions.
Isolation of the annulus containing the services to be transferred must be monitored to ensure gas isolation (seal). This can be confirmed by carrying out a decay test at the isolated section, by monitoring the pressure. Should the pressure rise on the gauge a second foam kit at a second location must be used
If gas seal is satisfactory, vent the annular section of the host main to be abandoned by removing the service connections in the intervening space. Prior to removing the section of main around the service connections, carry out an atmosphere check using an approved gas detection instrument ensuring there is no more than 20% LEL in the vicinity of the proposed breakout. If the seal is not satisfactory the Operations Manager must be informed.

Service transfers

Reference must be made to the Work Procedures for Service Laying for the renewal/reconnection of the service onto the PE main.
On completion of service transfer, fit the end seal kit as per manufacturer’s instructions.

Live head recovery

On completion of the service transfers, the live head assembly should be removed. Location of the live head is determined by accurate measurement during the insertion process and can be confirmed by the use of view inspection caps fitted onto the host main
Installation of live mains insertion component part must be undertaken in accordance with the manufacturer’s instructions

Recovery of live head

Ensure you have located the position of the live head.
Excavate ensuring you have an adequate work area.
Inject foam into the annular space adjacent to the last service transfer position or near to the live head assembly, ensuring that foam travel will not exceed the distance between the point of injection and the position of the live head. Refer to manufacturer’s recommendation on insertion foam kits.
Break out section of existing main upstream of the foam.
Install a bypass from the new PE main to a position downstream of the proposed flow stop position to ensure continuity of supply.
As per Section H1, (SGN/WI/ML/2) purge and commission the bypass
Insert flow stop equipment between live head and the downstream by-pass connection.
Squeeze off new PE main.
Slowly vent the annular space (the pressure should fall to zero). Turn off the vent, no pressure build up should occur. A pressure increase would indicate a failure of the flow stop equipment; check equipment and re-apply flow stopping equipment as necessary.
If no pressure builds up, fit continuity bond and break out the host pipe between the flow stop equipment and the foam off kit.
Recover the live head and either connect the new PE pipe to the existing main and remove flow stopping and by-pass equipment or if the insertion is to continue, temporarily cap off PE main, fit the gland box assembly to existing main ready for the next insertion.
Install end seal at foam off position.