DN-15c - Dead mains insertion by pushing

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
Electrofusion control unit
Re-rounding clamps, scraper and marker pen
Stoppers
PE pipe cutter

General requirements: Insertion

Dead mains insertion is an integrated process for flow stopping, decommissioning, PE main insertion, testing and commissioning followed by service transfer as applicable. In some cases, the Operational Manager may decide to test individual, pipe strings or coils before insertion. Where required the pipe string must be anchored temporarily because then pipe may straighten or snake when pressurised. Warning signs advising the pressure testing is in progress must be placed at either end of the site. An air test of not greater than 50mbr must be applied, all joint(s) must be tested immediately using an approved leak detection fluid, which must be washed off with clean water. Following successful testing, the air test should be slowly released.
A number of excavations launch and receive pits and main to service connection excavations have to be completed prior to commencing insertion
The main must be pushed in using a pushing machine
During the insertion process the PE main is to be inspected for visible damage
For pipe string, the free end must be controlled to prevent injury/damage as a result of whipping
For pipe coils the lead end must be mechanically restrained until it is securely fastened in the push machine.
Insert flow stop equipment on section to be inserted as per Section B2, (SGN/WI/ML/2). use twin sets of equipment at either end e.g. 8 bags in total.
Carry out the Decay test as per Section H5, (SGN/WI/ML/2) if satisfactory decommission main to be inserted. If unsatisfactory the Operational Manager consulted to determine course of action to be taken.
Cut out section of main at either end ensuring the pipe is cut square, fit cap ends as appropriate with anchorage on the remaining live end(s).

Gauging of existing main

Confirm that the parent metallic main is clear of obstructions a proving length of the main should be inserted, pulled through and inspected for damage at each intermediate excavation.
The launch/receive excavation should be kept to a minimum. Figure 4, (SGN/WI/ML/2) provides guidance on sizes of excavation of launch pits but an assessment of site conditions must be undertaken.
- Yes
- No
- N/A
Intermediate excavation at bends refer to Figure 5, (SGN/WI/ML/2) siphons, valves or other intermediate points must be long enough to enable the fitting to be cut out and for the inspection pipe to go through.
Surface damage must not exceed 10% of the pipe wall thickness. Where this occurs, the pipe must not be used. If deep scratching of the pipe has occurred, further investigation of the parent main must be undertaken before continuing with the operation.
Typical insertion layouts are shown in Figures 4 and 5, (SGN/WI/ML/2).

Preparation for insertion of first pipe string

The PE pipe to be inserted must be protected from sharp edges of the existing parent main at each point of entry.
Fit a nose cone to the leading end of the pipe.
Rollers or other suitable packing must be adequately positioned at road level and in the launch excavation to guide the PE pipe into the metallic parent main.
- Yes
- No
- N/A
The position and adequacy of guide rollers to assist to negotiate any bends must be checked at this stage.

Insertion general

The preferred method of PE insertion is to push the pipe under controlled conditions from the launch pit.
Each pipe/coil must be marked at appropriate intervals as it is inserted to indicate the remaining length to be inserted, this will ensure the PE insertion head can be located, should there be an obstruction.
For each added pipe string the new butt fused joint must be allowed to cool and the bead removed. The bead must be inspected as per Appendix E, (SGN/WI/ML/2) and passed to the Operational Manager
- Yes
- No
- N/A
During the insertion process the passage of the pipe should be checked at the intermediate excavations for damage
Where the inserted PE pipe is required to change direction pipe rollers should be adequately positioned and the lead end of the PE pipe should slowly and carefully guide into the main opening.
During the and on completion of the insertion process, the surface of the lead pipe should be examined for damage.

System integrity test

Sufficient surplice pipe must be available left at either end for final connection.
The ends of the inserted main must be capped using PE end caps fused onto the main.
A pressure test must be applied to the new main in accordance with Section G1, (SGN/WI/ML/2)