DN-16-b – Foam Plugging on LP Metallic Mains from 3”/80mm to 10”/250mm Diameter

Title Page

Site conducted
Conducted on
Prepared by
Location
Operative being assessed

Tools and equipment

Bag stop drilling machines/bases
Drilling base drills
Metallic vent stacks, flame traps and earthing straps
DI/CI pipe cutters & steel cutters
Continuity bond
Expanding pipe stoppers
Foam off kits (including spares)
Pressure gauges

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

Foam plug preparatory work – General:

Confirm the mains pressure by drilling and tapping the main and installing a pressure point.
Inform the Operational Manger if the pressure is above 75mbar.
Confirm with the Operational Manger the direction of flow as detailed in the written procedures.
Confirm size of riders to be installed across the section to be cut out as detailed in the written procedure.
Confirm with the Operational Manger that the main is one-way fed.
The upstream side of the operation is the where the gas has come from, whilst the downstream side is where the gas is going.
Manufactures instructions on the storage of the foam kits must be adhered to.

Preparatory work – Mains preparation work

A position on the main must be selected where there is no large corrosion defects or hard encrustations and the main cleaned by scraping and wire brushing. If necessary, wash the main with clean water to ensure secure seal at machine saddle. For ductile mains ensure that the plastic wrapping is removed. Ensure that the plastic coating is removed when encountered on steel mains.
The underside of the main must be excavated at points for access to the drilling machines and where the cut is going to be undertaken. Ensure the underside of the main is supported throughout the operation; wood blocks should be used to support it. Ensure sufficient room is made to operate the cutters to achieve a full circumferential cut.
A machine saddle and seal must be selected according to the main size, its condition checked, and fitted to the machine or main as appropriate. The fixing chain nuts should be tightened evenly to a moderate hand torque while ensuring that the machine is level.
The drill tap must be inspected and lubricated with oil or grease.
A parallel threaded drill tap must be fitted to the chuck and inserted in the machine.
An air test at a pressure of 350 mbar must be applied with the gate valve in the OPEN position and the machine seal checked with an approved leak detection fluid solution. No leakage must be visible during the test duration of 5 minutes.
If leakage is observed the machine must be inspected for the leakage path if the seal cannot be achieved without tightening the fixing chains beyond a moderate hand torque the base must be removed and the main cleaned further, or the equipment exchanged.
The pressure gauge used for this test must be left connected and monitored whilst the main is being drilled. The pressure gauge used must be suitable to operate within the pressure regime of the main.
Drill and tap the main in preparation for the installation of the foam bags using an approved under pressure-drilling machine and the tapping hole sizes as detailed in Table 37, (SGN/WI/ML/2)
Drill the main using a hand ratchet or air motor. Preferably the main should be tapped using a hand ratchet. If excessive force is needed this should be investigated. The drill tap should be withdrawn and for single spindle machines, the valve closed. The coupon should be retained for inspection.
This process must be repeated at each of the drillings to be made.
Complete all drillings.
Ensure an electrical continuity bond is installed across the full section of the main to be isolated and cut out.
Note: (Minimum dimensions from foam plugs)
Dimension between foam plug 1 and bypass point V1 = 800mm
Dimension between foam plug 1 and vent point V3 = 300mm
Dimension between foam plug 2 and bypass point V8 = 800mm
Dimension between foam plug 2 and vent point V5 = 300mm
The distance of 800mm allows for an additional foam plug to be installed if the first one fails.

Equipment set-up

Metallic vent stacks with flame traps must be installed, all protruding above the top of the excavation by a minimum of 2.5m. All valves must be in the closed position and the vent stacks must be adequately supported.
The foam bag must be loaded into the foam bag injection standpipe, following manufacturer’s instructions.
Once the foam bag has been inserted into the injection standpipe, the assembly must be inserted in to main via the drilling machine base, ensuring that the non-return valve in the neck of the foam bag prevents gas escaping through the injection tube.
Should gas start to pass through the injection tube the procedure must be stopped immediately, the injection tube withdrawn, and the under-pressure valve closed off.
The faulty tube must be inspected for damage and replaced. The procedure from b. above must then be repeated.
Fit cartridge to gun and attach to installed foam plug tube.

Assemble and Commission bypass:

The bypass must be protected from any risk from vandalism or mechanical damage and this must include the burying or sleeving of PE materials, using a flexible steel bypass or using all welded steel for constructing the bypass.
A PE bypass must not be left unattended overnight.
- Yes
- No
- N/A
The bypass should be fabricated with a minimum number of joints and maximum of six bends.
- Yes
- No
- N/A
Prior to installing around the main, the bypass must be pressure tested to 350mbar for 15 minutes. No pressure loss is allowed. On successful completion of this test the bypass can now be installed.
Ensure that the pressure gauges or recorders P1 and P4 are working and fitted correctly, showing current pressure in the main
Ensure all valves on the bypass and vents are closed.
Open the vent valve V6 and valve V7 on the downstream side of the bypass.
Slowly open the valve V1 on the upstream side of the bypass and allow gas to vent out of the bypass at the downstream vent position V6.
Confirm Two consecutive reading of greater than 90% G.I.A. from the vent and close the downstream vent valve V6 and valve V7.
Close the upstream bypass valve, V1, open the downstream bypass vent, V8 and open the upstream vent valve V4 and valve V2.
Confirm Two consecutive readings of greater than 90% G.I.A. from the vent and close the upstream vent valve V4 and valve V2.
Re-open the upstream rider valve, V1.
The bypass is now commissioned.

Foam plug main

Mix the resin and hardener according to the manufacturer’s instructions and pour the contents into the cartridge gun and dispense the foam into the bag number 1.
Mains pressures at P1 and P4 must be monitored to ensure that there is no drop-in pressure.
Repeat the process for bag position number 2.
The surplus foam left within the mixing container must be monitored to confirm the foam in the bag has cured.
Once the foam has cured the vent stack valves V3 & V4 on the upstream and V5 & V6 on the downstream can be opened to ensure an adequate seal. This can be confirmed by attaching a pressure gauge P2 & P3 onto the vent stacks below the vent valve position, closing the vent valves V4 & V6 and checking for let by through the foam bag.
Should a foam bag fail to seal a second stopping off operation using an additional foam bag via an additional tapping must be carried out before continuing with the operation.

Cutting operation

Verify that there is no back feed into the section to be abandoned or consumers still connected to the main by first closing off the downstream valve, V8 on the bypass. Pressure gauge, P4 on the main to be abandoned must be observed and checked for signs that the pressure within the main is falling.
Should the pressure within the main to be abandoned start to fall the bypass must be re-opened and the Operational Manager informed before the cause of the pressure drop is investigated.
Should the pressure remain constant the pressure in the main to be abandoned must be reduced by 5mbar by venting the gas through the vent valves V9 and V10. The pressure in the main must be allowed to stabilise and the pressure gauge on the main to be abandoned observed for a rise in pressure.
Should the pressure start to rise the Operational Manager must be informed immediately and the cause of the back feed investigated.
Only once the Operational Manager is satisfied that the abandonment is safe to continue the operative can proceed as below.
Ensure that the section of main to be cut is accurately marked.
The method of cutting will be determined by the material and diameter of the main and detailed in the work documentation.
Ensure the underside of the main is supported throughout the operation; wood blocks should be used to support it. Ensure sufficient room is available to operate the cutters to achieve a full circumferential cut.
Whilst cutting the main avoid unnecessary vibration that may cause the foam bags to pass.
Additional cuts should be made to ensure that the section of pipe is removed with the minimum of effort.
The open ends of the pipe must be fitted with expanding stoppers if the main is not to be capped immediately after cutting.
If an expanding stopper has been installed, remove the stopper and install the cap onto the end of the main.
Anchorage of the cap must be carried out as per (SGN/PR/DIS/4.2.2)

Test end caps

The end caps must now be tested for gas tightness as detailed below: Using the vent arrangement as shown, allow gas to pass to the other side of the foam bag and cap ends, by opening valves V2 & V3 on the upstream side and valves V5 & V7 on the downstream side ensuring that valves V4 & V6 are closed, so that live gas is now acting against the newly installed cap ends
Test the cap ends for soundness with leak detection fluid
Should the cap(s) show leakage, Valve V2 and/or V7 must be closed, the section between the cap and foam bag vented by opening valve V4 and/or V6, and the cap re-tightened.
Close valves V4 and/or V6 and open valves V2 and/or V7 and retest the cap end(s) for soundness with leak detection fluid.
Remove the foam injection tubes and test with leak detection fluid.
Once caps and plugs have been deemed satisfactory close valves V2 and V7 and open valves V4 and V6 to vent between the cap ends. Close valves V3 and V5.

Removal of equipment

Close bypass valves V1 and V8.
Vent the bypass to zero pressure by opening valves V2 & V7 Disconnect V2 and attach an air supply and direct purge the bypass with air at no more than 1/3 rd. of the main operating pressure.
Dismantle the bypass and using the drilling machine plug off under no gas conditions the connection points for the bypass and vents.
Remove the pressure gauges as per c. above and check the plugged off holes with leak detection solution.
Remove the continuity bond.
The applicator, foam cartridge and containers must be disposed of according to the manufacturer’ instructions, COSHH and as per Risk Assessment.
To ensure that the plugs screwed into the foam bag injection points are not leaking, leak detection fluid must be applied to them at least 24 hours after the foam off operation.
Should the plugs show leakage the plugs must be tightened and tested with leak detection fluid.