DN09-Live service insertion

Question - Name four factors which should be identified that will determine the suitability for using this technique?

Domestic service, minimum 2m from building line, 2in or below, operating at 75mbar or below (LP), the service length is within the guidelines as stated by the manufacturer, pressure loss along the length of the service, pipe corrosion

Accurately trace out the line of the service from the main to the meter?

Identify and investigate any change of direction including elbows?

Carry out an initial barhole leakage survey along the line of the service?

Excavate 2m from the property on the line of the service?

Use the Voltstick prior to undertaking any work on any exposed metalwork to ensure it is safe to continue and repeats when necessary?

Visually check the condition and size of the service to ensure it is suitable to live insert?

Check the approximate length to be live inserted from service insertion point to main and refers to manufacturer's instructions for maximum allowable length?

Close ECV?

Disconnect meter inlet if suitably trained and competent?

Apply correct temporary electrical cross bonding in accordance with current SGN procedure (EL/15)?

Prepare valved gland assembly to accommodate the flexible stopper?

Cut out section of live gas service pipe in accordance with current SGN procedures?

Installs valved gland assembly over the flexible stopper rod and takes care not to disturb the stopper and secures to the steel service pipe

Withdraws the flexible stopper into the valved gland assembly, closes the valve and removes the flexible stopper

Inserts semi-rigid flexible rod complete with correctly sized elbow tester into valved gland assembly as far as the closed valve, ensures the leading 150mm is as straight as practicable. Marks with tape as an indicator on withdrawal

Installs pressure gauge, opens gland assembly valve and checks district mains pressure

Inserts flexible rod as far as possible along the service in order to establish the length of service to be inserted

Marks indicated service length on flexible rod and withdraws through valve

Closes gland assembly valve

Confirms that the marked length is comparable to the indicated mains position carried out earlier. If necessary, carries out further investigations if indicated length is considered inaccurate

Measures and marks PE service pipe against the marked flexible rod length and records the measurement value in order for the correct quantity of sealant to be selected

Adds 1m of pipe to allow for the pushing machine and fittings, cuts and temporarily seals to avoid contamination

Fits the pipe cleaning wire brush to the end of the semi-rigid flexible rod and fits into valved gland assembly

Opens valve and pushes semi-rigid flexible rod with wire brush into the pipe to the marked service length position

Withdraws the wire brush into valved gland assembly

Re-checks mains pressure to ensure no blockage has occurred during the pipe cleaning process

Closes valve, removes flexible rod sealing fittings from the valved gland assembly

Feeds PE pipe through pushing machine and fits appropriate gland to Pipe Pushing Machine

Fits nose cone following manufacturer’s instructions

Carries out 100mb integrity test for 5 minutes (no drop allowed) on PE pipe

Pulls PE pipe and nose cone back into the pushing machine

Connects the pipe pushing machine to the valved gland assembly. Uses a swept bend to ease of application

Installs pressure gauge and connects purge hose to the vent on the valved gland assembly

Question - What is the minimum distance a purge stack must terminate above an excavation and the minimum distance downwind from any ignition source?

Answer - Must be positioned at least 2.5m above the excavation and 5m downwind of any source of ignition

Slowly opens gland assembly valve and records district mains pressure

Inserts PE pipe for approx. 300mm by using the pipe pushing machine

Fully opens the vent on the valved gland assembly, purges the 300mm of annulus to zero pressure and leaves vent open

Slowly continues inserting PE pipe into the carrier pipe using the pipe-pushing machine, observes the pressure gauge continuously

Pushes the PE pipe through the carrier pipe to the service tee or bend in the main

Question - How will it be known that the nose cone has entered the service tee or main?

Answer - The gauge pressure should rise to full district pressure

Checks that the tape mark on the PE pipe is close to the entry point on the carrier pipe, usually the marked position of the PE pipe will be within 150-300mm of the entry point

Reverses the pushing machine and slowly retracts the PE pipe by 50mm steps into the carrier pipe, shuts the purge valve and checks the pressure gauge for effectiveness of seal. Checks the pressure gauge remains at zero and ensures no significant build-up of pressure

Pulls back pipe by a further 50mm to lock nose cone into final position. Re-checks for good seal from the nose cone by ensuring the pressure gauge remains at zero. Ensures no significant build-up of pressure

Question - What would it mean if the gauge pressure starts to rise to the district pressure within 5 seconds and what action can be taken?

Answer - There is not an effective seal and the PE should be pulled back a further 50mm to form the seal

Question - What action should be taken if the seal is still not achieved?

Answer - Push the PE forward and try to re-establish the seal as before. If this fails, remove and replace the nose cone and repeat the operation to establish the seal. Ultimately, it may be necessary to abandon the operation and dead insert

Closes vent and removes the pressure gauge once an acceptable seal has been formed

Carefully removes pipe pushing machine and valved gland assembly and ensures PE pipe and nose cone are not disturbed

Fits appropriate mini end-seal to the carrier pipe and the inserted PE pipe, following manufacturer’s instructions

Carries out 100mb soundness test for 5 mins ensuring there is no drop in pressure

Fills annulus between PE pipe and carrier pipe in accordance with manufacturer’s instructions

Completes the service relay to the property by the most appropriate method, e.g. dead insertion, open cut, moling etc.

Connects to live inserted section using approved fitting and tests the complete service in accordance with current SGN procedures

Installs meter control gland assembly complete with pressure gauge onto the ECV

Opens ECV and inserts flexible rod into PE pipe to knock out nose cone plug. Pushes rod forward / backwards a few times to ensure a clear gas path is achieved resulting in the pressure gauge showing district mains pressure