Tightness testing and direct purging – What installers need to know

Following significant revisions to IGE/UP/1B, Peter Mason assesses how the changes will impact on the procedures for tightness testing and direct purging of certain types of installations.

IGEM/UP/1B Edition 3 – Tightness testing and direct purging of small Liquefied Petroleum Gas/Air, Natural Gas and Liquefied Petroleum Gas installations has been published.

As the title suggests, the standard now additionally includes tightness testing and direct purging procedures for Liquefied Petroleum Gas/Air (LPG/ Air) and Liquefied Petroleum Gas (LPG) installations. The tightness testing procedure for Natural Gas (NG) is slightly altered and the purging procedure for NG remains essentially as that described in IGE/UP/1B Edition 2.

LPG/Air is in use on Guernsey and Jersey. The Isle of Man (Manx Gas) is currently undertaking a gas conversion operation from LPG/Air (town gas) to Natural Gas (NG).

LPG/Air is a manufactured or derived 1st family Gas and is heavier than air. NG is a 2nd family gas and is lighter than air. LPG is a 3rd family gas and is heavier than air. The characteristics of the fuels need to be considered when releasing gas as part of any purging process.

IGEM/UP/1B Edition 3 supersedes IGE/UP/1B Edition 2, which covered small NG installations and changes the soundness testing and direct purging procedures within BS 5482-1 – Code of Practice for domestic butane and propane gas burning installations – Part 1: Installations at permanent dwellings, residential park homes and commercial premises, with installation pipework sizes not exceeding DN25 for steel and DN28 for corrugated stainless steel and copper.

There were previously no formal national standards for the soundness testing and direct purging of LPG/Air installations. The greatly extended scope of IGEM/UP/1B Edition 3 is best explained in terms of which type
of installation it is concerned with against each fuel type.

Natural Gas and LPG/Air

• Maximum Operating Pressure (MOP) at the Emergency Control Valve (ECV) outlet not exceeding 2 bar.
• Pipework size not exceeding 35mm copper, 32mm or 1¼” steel.
• Primary meter size not exceeding U16 (G10),
• Maximum installation volume (IV) of 0.035m3 (supplying a dwelling or non-domestic premises).
• Operating pressure at the meter outlet not greater than 21 mbar.

The standard covers small installations, which includes most domestic and small commercial customers. The maximum installation volume of 0.035m3 would be approached on an installation using a U6 meter with 25m of 35mm copper pipe or an installation using a U16 meter with 5m of 32mm steel pipe.

LPG

Pipework size not exceeding 35mm copper, 32mm or 1¼” steel.
• Primary meter size not exceeding U16 (G10).
• Maximum installation volume (IV) of 0.035m3 (supplying a dwelling or non-domestic premises).
• Operating pressure at the outlet of the final stage regulator not greater than 37mbar.

LPG installations in small commercial premises, permanent dwellings, residential park homes, Leisure Accommodation Vehicles including touring and motor caravans, and caravan holiday homes may be tested and direct purged using the procedures in the standard.

LPG installations in boats and other vessels are within the scope of PD 5482–3 and BS EN ISO 10239.

Tightness testing

The significant changes to tightness testing procedures may be divided as follows:

Test equipment

Test equipment needs to be well maintained – electronic gauges are to be calibrated as per manufacturer’s instructions and a certificate of calibration available.

Electronic gauges that are intrinsically safe need to be used when a test location may be within a flammable atmosphere.

Intrinsically-safe electronic gauges need to be used when the equipment is to be left unattended and whenever a risk assessment dictates that certified intrinsically safe equipment is necessary.

High specific gravity gauges are no longer considered to be suitable for tightness tests to IGEM/UP/1B Edition 3.

Leak detector fluids complying with BS EN 14291 must be used and must be wiped from pipework and components following testing.

Test criteria

Tightness testing procedures now vary within IGEM/UP/1B Edition 3 according to the fuel in use and whether the installation is new or existing.

Test criteria remain unchanged for new installations at ‘no perceptible movement’ – for example, 0.25 mbar or less on a fluid gauge or 0.2 mbar or less on an electronic gauge.

Tightness testing

The standard applies to tightness testing following any work that may have affected the gas tightness of any installation. The standard recommends that if a new installation is connected to a fuel supply, it is pressurised and tested with fuel.

Air tests may be carried out if desired on new installations.

The relevant test pressures for differing fuels and operating pressures are detailed within Appendix 3.

A tightness test using fuel must be performed before the installation is purged with fuel. A further tightness test using fuel on LPG installations must be carried out following an air-to-fuel purge.

Natural Gas

The installation now needs to be visually inspected to ensure that all sections of the installation to be tested are connected, joints made and open ends sealed appropriately. Automatic Isolation Valves (AIV), where fitted, must be open.

Tightness testing procedures for new and existing installations are now carried out using a common procedure. Let-by tests of ECVs and Meter inlet valves (MIV) are now carried out at a pressure between 7 and
10 mbar.

If the ECV is deemed to be letting by, the Gas Emergency Call Centre must be notified. If the MIV is letting by, the Meter Asset Manager (MAM) must be notified. Installations without a MIV may be tested according to Appendix 4 which is not within the scope of the standard and is deemed to be ‘advice’.

The stabilisation period for NG remains at one minute. The tightness test cannot proceed until a stable gauge reading is obtained and further stabilisation time may be necessary.

The tightness test pressure is now changed to between 20 and 21 mbar for two minutes.

On a new installation, or on an existing installation with no appliances connected, the criteria for a successful tightness test is ‘no perceptible gauge movement’ and no smell of gas.

On an existing installation with appliances connected, allowable pressure drops remain unchanged, with the exception of an ultrasonic meter or no meter connected to pipework with a diameter greater than 28mm and not exceeding 35mm.

The allowable pressure drop is reduced from 4.5 mbar to 4 mbar.

If the installation is new, or any gasways are exposed to air, the installation needs to be purged. LPG/air mixtures Procedures are broadly similar to NG installations with the following exceptions:

• If fitted, the UPSO on the outlet of the supply control valve will close at let-by test pressure (7– 10 mbar) and will require the reset mechanism to be operated to release any trapped pressure. The mechanism may
require resetting several times in order to achieve a let-by test pressure of between 7 and 10 mbar.
• If the ECV or MIV is letting-by, the gas supplier needs to be notified.
• For an operating pressure of 14 mbar, the tightness test pressure is between 13 and 14 mbar. If the pressure rises above 16 mbar, the pressure must be reduced to 7–10 mbar to release the locked-up regulator.
• For an operating pressure of 21 mbar, the tightness test pressure is between 20 and 21 mbar. If the pressure rises above 23 mbar, the pressure must be reduced to 7–10 mbar to release the locked-up regulator.
The stabilisation period is one minute. The tightness test cannot proceed until a stable gauge reading is obtained and further stabilisation time may be necessary.

On a new installation, or on an existing installation with no appliances connected, the criteria for a successful tightness test is ‘no perceptible gauge movement’ and no smell of gas.

On an existing installation with appliances connected, allowable pressure drops are given in Table 1.

If the installation is new, or any gasways are exposed to air, the installation needs to be purged.

Table 1
Meter Pipework diameter
Maximum pressure drop
No meter – pipework only with ECV/AECV <35mm 15 mbar
Diaphragm – U6/G4 <35mm 15 mbar
Diaphragm – U16/G10 <35mm 0.5 mbar

LPG

Tightness testing (previously soundness testing) procedures for LPG cylinder and small bulk tank installations have been significantly altered.

• The pressure gauge is connected to a pressure test point in the pipework downstream of the final stage regulator.
• The valve used to admit fuel into the installation needs to be tested for let-by at a pressure of 7 to 10mbar.
• Any regulator upstream of this valve (supply control valve) needs to be activated.
• If fitted, the UPSO on the outlet of the supply control valve will close at let-by test pressure (7 to 10 mbar) and will require the reset mechanism to be operated to release any trapped pressure. The mechanism may
require resetting several times in order to achieve a let-by test pressure of 7 to 10 mbar.
• Let-by is now tested at 7 to 10 mbar for one minute.
• Should the let-by test fail it may be necessary to test the cylinder supply control valve with LDF. If the valve is satisfactory, additional time should be allowed until a stable reading is obtained. It may be difficult to achieve a stable reading on an installation with a small pipework volume or if the pipework is exposed to direct sunlight.
• No attempt should be made to dismantle pipework on a bulk storage tank to check a supply control valve for let-by. If the operation of any valve is suspect, the gas supplier needs to be notified.
• The pressure needs to be raised to the tightness test pressure for a stabilisation period of 1 minute. Tightness test pressures are given in Table 2.
• The tightness test duration is two minutes.
• On a new installation, or on an existing installation with no appliances connected, the criteria for a successful tightness test is ‘no perceptible gauge movement’ and no smell of gas.
• On an existing installation with appliances connected, allowable pressure drops are given in Table 3.
Installation volumes may be estimated using the methods previously detailed in IGE/UP/1B Edition 2 and now in IGEM/UP/1B Edition 3 Appendix 7.

Table 2
Installation type Operating pressure Propane Butane
Regulator in the test section 28 mbar 20 to 21 mbar
30 mbar 28 to 29 mbar 28 to 29 mbar
37 mbar 30 to 31 mbar
No regulator in the test section 28 mbar 27 to 28 mbar
30 mbar 29 to 30 mbar 2 29 to 30 mbar
37 mbar 36 to 37 mbar

Following a successful tightness test, all pipework and control connections that have been tightness tested between the supply control valve and the final stage regulator need to be tested with LDF or a suitable gas
detector (properly calibrated for the fuel).

The connections to be tested operate at pressures up to 10 bar and any escape may only be detected when the installation operates at elevated pressures.

Table 3
Installation volume Permissible pressure drop Permissible pressure drop
< 0.0025m3 2.0 mbar
> 0.0025m3 and < 0.005m3 1.0 mbar
> 0.005m3 and < 0.01m3 0.5 mbar
> 0.01m3 and < 0.035m3 No perceptible movement

Direct purging

There are minor safety detail changes to purge procedures for NG. Purge criteria for LPG/Air and LPG are revised to fall in line with NG procedures; however, the characteristics of the various fuels need to be considered.

Natural Gas Installations with an IV of 0.02 m3 or under may be purged to atmosphere. Any accumulation of gas within confined spaces needs to be avoided. The area in which the purge is taking place must not be left unattended.

Installations with an IV over 0.02 m3 and not more than 0.035 m3 need to be purged through a cooking appliance burner or a temporary burner connected to the installation.

Installation volumes may be estimated using the methods previously detailed in IGE/UP/1B edition 2 and now in IGEM/UP/1B Edition 3 Appendix 7. Purge volumes are given in Table 4.

LPG/air mixtures The purge procedure is identical to that of NG except that any purge gas must be ignited as soon as possible.

Under no circumstances can LPG/Air mixtures be vented to atmosphere as the heavier-than air nature of this fuel causes the gas to accumulate at low levels.

Table 4 – Purge Volumes
Meter Pipework diameter PV
U6, G4, E6 <28mm 0.01m3
U6, G4, E6, U16 and G10 > 28mm <35mm 1.5 3 IV

LPG

The purge procedure is identical to that of NG except that any purge gas must be ignited as soon as possible. Under no circumstances can LPG be vented to atmosphere as the heavier-than-air nature of this fuel causes the gas to accumulate at low levels.

Safety precautions

A new sub-section has been added to the purging section detailing some of the risks involved in working on pipework that contains fuel gas.

If a blowlamp is to be used – or there is a danger that the fuel may be ignited on the section – it is important to test for tightness to ensure that there is no let-by into the installation. The gas supply needs to be disconnected and any meter needs to be removed. Any open end needs to be sealed with an appropriate fitting. If necessary, the installation may be purged of fuel gas to air by means of the procedures detailed in IGE/UP/1 or IGE/UP/1A.

If an installation is to be decommissioned, purging the pipework to air may be considered. A U6, G4 or E6
meter need not be purged to air but needs to be capped on permanent removal. Any meter with a capacity larger than that will require to be purged of fuel when permanently removed.

To Sum Up

In view of the significant changes to the procedures, it is suggested that before attempting tightness testing and direct purging procedures in accordance with IGEM/UP/1B Edition 3 that guidance is sought from the standard.

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