Tightness testing and direct purging – What installers need to know

The testing procedure IGEM/UP/1B edition 3 was launched in October 2012 and incorporated natural gas, LPG and LPG/air as well as a number of additional changes. Mike Heads re-examines this procedure as there still seems to be some confusion on its implementation.

This recent edition Tightness testing and direct purging of small Liquefied Petroleum Gas/Air, Natural Gas and Liquefied Petroleum Gas Installations replaces Edition 2, and the low pressure LPG testing in BS 5482-1
Code of practice for domestic butane and propane gas burning installations – Part 1.

NOTE
Boats will continue to use BS 5482-1 or BS EN ISO 10239.

Edition 2 was introduced to allow testing of larger volumes following the introduction of 35mm copper pipe and 32mm (1¼”) steel used in domestic installations, much of this is retained in this edition.

Tightness testing

The tightness testing is broken up into three sections: LPG/air mix, natural gas and LPG.

When candidates reference this document, a large number find themselves in the wrong section.

It could have been better if the LPG/air mix was in the appendix because it only constitutes a small number of installations so this would have reduced the confusion.

What is LPG/air mixture?

During conversion in the 1970s, there were a number of areas that were not thought to be financially viable for a costly natural gas network, so an alternative costeffective gas supply was produced in the form of LPG/air mixture.

It had similar properties to manufactured gas but was safer than manufactured gas because it doesn’t contain CO, although it is heavier than air. Over the years, more areas have been converted and now only the Channel Islands continue to use this gas.

The letby test procedure

Prior to performing a letby test, pipework should be inspected to ensure there are no open ends, and any burner control taps and pilots should be turned off.

All isolation valves are turned on, and any cooker lids with SSOVs should be raised. The letby test procedure has been simplified to a common pressure for all three gases of between 7mbar and 10mbar for one
minute. For natural gas, there is very little change from Edition 2, but for LPG this is a substantial change from BS 5482-1.

Perceptible movement

In common with other testing procedures, the concept of perceptible movement is incorporated. This is 0.25mbar for water gauge and digital manometer to two decimal places, and 0.2mbar to one decimal place.

LPG and medium pressure natural gas installations may have an UPSO – Under Pressure Shut Off valve – which needs to be operated after the test to ensure pressure has not built up between the valve and the UPSO (see Figure 1). There will be some movement of the gauge due to inflation of the diaphragm, but this check is to look for a large increase in pressure.

If the pressure increases by more than the ‘perceptible movement’, it may be caused by an internal leak within the test valve – ‘letby’. This can be tested by disconnecting the outlet of the valve and spraying inside with leak detection fluid while maintaining electrical continuity.

If it is shown to be leaking, it should be made safe. The emergency service provider should be contacted if natural gas is being tested or the supplier in the case of LPG.

If the valve appears satisfactory, but there is still an increase in the pressure reading on the gauge during this period, the pressure or temperature may be stabilising. Additional time would then be needed before a stable reading can be obtained.

A major decrease in pressure would probably be due to an escape on the installation.

Test pressure

The test pressure will vary depending on the gas and whether the test is against a valve or through a regulator. ‘Lock-up’ within the regulator would prevent the inlet being tested so the test is normally carried out at – or below – the operating pressure.

The test pressure for natural gas would be 20–21 mbar for low pressure installations (see Figure 2) and 18–19mbar for medium pressure installations.

The test pressure for LPG is a little more complicated because of the variation of installations covered and is dependent on whether the test is against a valve or through a regulator. On a standard propane installation tank or bottle – if the test is from a valve – the test should be 36–37mbar whereas if the test is through a regulator, the test should be 30–31mbar. Touring caravans would be tested at 28–29mbar.

There are various pressure settings for butane depending on the regulator used (see Table 1).

LPG/air would depend upon operating pressure and would be either 14 or 21mbar.

Stabilisation

Once the pressure has been raised to the test pressure, the valve is turned off and gas now needs to stabilise. The stabilisation for all the gases is one minute, which is usually sufficient for natural gas.
With LPG, if the pressure does not stabilise within one minute, extra time should be allowed.

Where a mixture of air and gas exists within the LPG installation, it may not be possible to stabilise the pressure. In this case, once it has been proved there is no major escape, the installation should be purged and retested.

After the stabilisation period, the pressure is re-adjusted to the test pressure. The testing time for all three gases is two minutes. Once the test is complete, remove the gauge reseal the test point and turn on the gas supply. Test the pressure test point, and supply control valve outlet connections and regulator
connections with LDF.

For pipework and new installations, no pressure drop is allowed more than the ‘perceptible movement’. Where
existing appliances are installed, there are maximum permissible pressure drops providing there is no smell of gas. For natural gas, there is virtually no difference (see Table 2), LPG is considerably different to BS5482-1 and TM 83 (see Table 3).

Volume less than 0.0025m3 would include touring caravans and motor homes, volumes up to 0.005m3 would cover static caravans/holiday homes, and volumes up to 0.01m3 would cover static caravans/holiday homes that include a meter Calculating installation volumes IGEM/UP/1B is the tightness test procedure for individual dwellings or non-domestic premises of up to 0.035m3. Therefore, if the installation is installed in 35mm or
the meter is a U16, there may be a need to calculate the volume to ensure it falls within the scope of the document. There are volume tables and a number of worked examples in Appendix 7 of the document for guidance.

Direct purging

Natural Gas

Purging of natural gas is very similar to the method described in Edition 2, providing the meter is a U6. The volume remains 0.01m3/0.35ft3 for an imperial meter – five times the badged capacity per revolution (later called the cyclic volume) of 0.002m3/0.071ft3.

If the volume of the installation is below 0.02m3 it may be purged to atmosphere providing safety precautions are taken to ensure the gas can be vented safely. If the installation volume is 0.02m3 or more, the gas must be ignited immediately through an open burner because this is too dangerous to release internally.

The calculation for purge volume differs from the methods used in the other IGEM tightness testing documents and is 1.5 times the total installation volume – see the example and Table 4.

Example:

Installation Volume = Meter + (pipework + 10% for fittings)

U6 meter 0.008m3 + 20m of (35mm) 0.0168m3 + fittings 0.001,68m3 = Installation Volume of 0.0265m3

Purge volume = IV 3 1.5 0.0265m3 3 1.5 = 0.03975m3

This would be rounded up to give a purge volume of 0.040m3.

In this example, the total installation volume is less than the 0.035m3 limit, but as it is greater than 0.02m3 it would have to be purged through an open burner, which may mean connecting a temporary burner
and igniting it during the purge.

LPG and LPG/air

The calculations of volumes is the same as for natural gas when it comes to purging. The gas must be ignited immediately from an open burner because heavierthan-air gases do not disperse easily and have a much lower
flammability limit.

The document covers safety precautions in detail when commissioning and decommissioning meters and pipework.

Appendix 3 also covers air testing of LPG pipework prior to connecting a live gas installation for LPG this would be 45–46mbar.

For natural gas this is 20–21mbar. The air testing of touring caravans and motor homes is still covered by BS EN 1949: 2011 + A1: 2013 and gas testing by IGEM/UP/1B Edition 3.

To Sum Up

• IGEM/UP/1B edition 3 now incorporates the testing of natural gas LPG and LPG/air.
• The changes for natural gas have only been minor, but for LPG has involved a considerable change – especially for letby and tightness testing.
• The idea of this recent IGEM document is to simplify the testing process. Once operatives become more familiar with this procedure, it will be more straightforward but hange is always difficult.