Northern Ireland: medium-pressure supply and tightness testing

The Northern Ireland gas network in the street is generally at 75 mbar to 4 bar. Although medium pressure on the mainland is usually up to 2 bar pressure, in Northern Ireland it reaches up to 4 bar feeding the regulators at the primary domestic meter installation and is then reduced to a low-pressure supply of 21 mbar (+/-2) for the gas installation.

For tightness testing and purging downstream of the meter, we recommend following the guidance in IGEM/UP/1B Edition 3 1; for meter installations up to 6m3/h, you should reference BS 6400-2:2018 2

Medium-pressure meter boxes must be installed to BS 64002:2018: if they are installed inappropriately or damaged, there is an increased risk of gas entering the cavity/property. Therefore, the location of the box and vent from the relief valve must conform to the separation distances guidance given in section 6 of that standard. Further guidance can be found in TB004 and TB100 from Gas Safe Register.

You should be aware that a medium-pressure meter installation is slightly different from a low-pressure type, with a regulator that has been selected to be suitable for the mediumpressure supply. It may be a single or two-stage regulator incorporating several safety features like a slam-shut device, UPSO, excess flow valve and relief valve.

The tightness test procedure that follows is guidance in relation to natural gas (NG) domestic installations commonly found in Northern Ireland and some other parts of the UK. Most of the procedure is already commonly used for low-pressure gas installations but an additional procedure is required to test the safe working of the regulator with a medium-pressure supply with low pressure downstream.

New installations will have a meter isolation valve (MIV) fitted between the regulator outlet and the meter; this is in addition to the Emergency Control Valve (ECV) fitted at the end of the service pipe before the meter installation.

These types of meter installation have a reset lever at the regulator to enable pressure to be released/equalised as part of the testing procedure. Depending on the regulator type, this lever is used to reset the UPSO or excess flow/slam-shut device.

Tightness test procedure of a domestic individual dwelling with a medium pressure service (where an MIV is fitted):

• With the ECV shut, ensure there are no open ends that will permit the escape of gas, and that all appliance isolation valves (AIV) are open and the MIV is closed. Attach your manometer to the test point after the MIV.

• Slowly open the ECV to pressurise the pipe up to the regulator, then open the UPSO reset lever on the regulator to pressurise up to the MIV. With the ECV open, slowly open the MIV until the manometer reads between 7 mbar and 10 mbar. When you have a suitable pressure reading, start your 60-second let-by test.

• If there is no perceptible movement of the manometer reading, the MIV has passed a let-by test. If it fails by giving a readable movement, then the MIV should be tested with leak detection fluid (LDF). Disconnect the outlet of the MIV and use a small amount of LDF on the closed ball of the valve to determine the passing of gas. If it is confirmed as a faulty valve, inform the local emergency service provider (ESP), which will attend the fault.

• A tightness test can only proceed following a successful let-by test.

Natural gas was first introduced in Northern Ireland in 1996 via a gas pipeline from Scotland. Initially, it was available to homes in Greater Belfast, the immediate surrounding area and Larne, where the gas distribution network was been developed by Phoenix Natural Gas. By last year, nearly a quarter-of-a-million customers had been connected.

In the following years, the network was extended to the North-west and Ballymena, Antrim, Banbridge, Craigavon, Portadown, Armagh and Newry, connecting a further 64,000 customers.

More recently, the Gas to the West project, completed in 2019, has brought natural gas to Dungannon, Coalisland, Cookstown, Magherafelt, Omagh, Enniskillen, Derrylin and Strabane and is expected to serve around 40,000 households and businesses. Similarly, Gas to East Down is providing new infrastructure to 13 towns and the majority of pipelines are now laid.

To do this, slowly open the MIV and raise the pressure to between 20 mbar and 21 mbar, closing the MIV once the correct pressure is reached.

• The temperature and pressure must now be allowed to stabilise for 60 seconds (stabilisation period). Adjustment to between 20 mbar to 21 mbar is allowed but you should wait until a stable reading is obtained.

• When you are satisfied that the gas is stable, the 120-second tightness test can begin. It is expected that for new installations a successful test/ pass will only be when there is no readable movement.

• For an installation with existing appliances connected and no smell of gas (with a installation volume (IV) not exceeding 0.035m3), the maximum permissible drops detailed in the table below are deemed as acceptable.

Tightness test procedure of a domestic individual dwelling with a medium-pressure service (where an MIV is NOT fitted):

• With the ECV shut, ensure there are no open ends that will permit the escape of gas, and that all appliance isolation valves (AIV) are open. Attach your manometer to the test point on the meter.

• Slowly open the ECV: this will pressurise the pipe up to the regulator, close the ECV. Open the reset lever to pressurise the whole installation and keep open: at this point, adjust the pressure to between 7 mbar and 10 mbar. You do this by allowing more pressure by slowly opening and closing the ECV, or purging gas from a purge valve to a safe area. When you have a suitable pressure reading between 7mbar and 10 mbar, start your

60-second let-by test. Keeping the reset lever open ensures you are testing from the ECV through the whole installation, however this can be difficult on some regulators. Alternatively, you can operate the reset lever and record the pressure reading determine the passing of gas. If it is confirmed as a faulty valve, inform the local emergency service provider (ESP), which will attend the fault.

• A tightness test can only proceed following a successful let-by test: to do this, slowly must now be allowed to stabilise for 60 seconds (stabilisation period). Adjustment to between 18 mbar and 19 mbar is allowed but wait until a stable reading is obtained.

• When you are satisfied that the gas is stable, the 120-second tightness test can begin. The pass criteria of the test is the same as that for an installation with an MIV fitted.

2) BS 6400-2:2018 Specification for installation, exchange, relocation, maintenance and removal of gas meters with a maximum capacity not exceeding 6m3/h. Medium pressure (2nd family gases)

Technical Bulletin 004: Managing risks from inappropriately installed medium-pressure-fed domestic-sized meter installations located in built-in or surface-mounted boxes at the start of the test, then operate it again at the end of the test (60 seconds). Record and compare the two readings to confirm no perceivable movement.

Technical Bulletin 100: Dealing with damaged pre-fabricated built-in domestic sized gas meter boxes.

• If there is no perceptible movement of the manometer reading, the ECV has passed a let-by test. If it fails by giving a readable movement, then the ECV should be tested with leak detection fluid (LDF). Disconnect the anaconda from the ECV and use a small amount of LDF on the closed ball of the valve to open the ECV, and raise the pressure to between 18 mbar and 19 mbar and close the ECV.

• If you have exceeded 19 mbar but not 21 mbar, you can drop this back to between 18 mbar and 19 mbar from a purge valve to a safe area. If you exceeded 21 mbar, then to ensure there has been no lock-up of the regulator you must drop to between 7 mbar and 10 mbar and raise the pressure slowly again.

• The temperature and pressure

Note: When carrying out a let-by on an ECV (where no MIV is fitted), you can operate the reset lever and record the pressure reading at the start of the test, then operate it again at the end of the test (60 seconds). Record and compare the two readings to confirm no perceivable movement. The other option is to hold the rest lever open throughout the 60-second test, but this will be difficult on some models of regulator. ■

Bibliography

1) IGEM/UP/1B Edition 3 (with Amendments October 2012): Tightness testing and direct purging of small Liquid Petroleum Gas/Air, Natural Gas and Liquid Petroleum Gas installations

You can find additional guidance in Technical Bulletin 004 (meter installations) and Technical Bulletin 100 (damaged meter boxes). These can be read and downloaded by logging into your Gas Safe Register online account at www.GasSafeRegister. co.uk/sign-in

For further guidance please contact the technical team by phone on 0800 408 5577 or email at: technical@ gassaferegister.co.uk