Tracing and repairing escapes

When a tightness test fails, or someone reports a smell of gas, you need to find the escape, repair it and prove the repair, or make the installation safe if you can't.

Reported escapes: no allowance

Test the installation by the normal procedure in these situations:

• an installation that the emergency service provider or gas supplier has isolated after a reported escape or a suspected smell of gas
• the occupier or the engineer smells gas or suspects an escape.

But to pass, there must be no perceptible movement on the gauge and no smell of gas. The permitted drop for existing installations (see 6.4) doesn't apply.

Leak detection fluid

Use only a proprietary leak detection fluid (LDF) that complies with BS EN 14291 and suits the materials it goes on.

• Stainless steel: don't use a fluid containing more than 30 parts per million of halogens.
• Copper and brass: don't use a fluid containing ammonia. A pH of 7.0 or less shows there's no ammonia.
• Never use washing-up liquid or soap solution.

Some chemicals, such as ammonia and chlorides, can cause problems like stress corrosion cracking. Wipe the fluid off pipes and fittings after use so it doesn't cause corrosion later.

Gas detectors and electrical equipment

When you're looking for a known or suspected escape with a gas detector, the detector must be certified for use in a hazardous area. The same applies to any electronic test equipment used:

• where the air may contain a flammable mixture that uncertified equipment could ignite
• inside a designated hazardous zone
• where the equipment will be left unattended at any point during a test or purge
• wherever a risk assessment says certified equipment is essential.

If you're unsure about an uncertified electronic gauge, a water gauge can be used instead. Like gauges, detectors must be calibrated at least every 12 months (or as the manufacturer says), and checked, including the sample line, immediately before use.

After the repair

• Inspect the new joints by eye, then retest the installation.
• Don't paint or wrap the repaired joints until they've passed.
• Test any joint you disturbed with leak detection fluid.
• If the repair let air in, purge the installation (see 6.6).

Before using a flame on pipework

Where there's a risk that gas left in the pipework could be ignited, for example when using a blowlamp, take these long-standing precautions before you start:

1. Tightness test the installation or section, in particular to prove the isolating valve isn't letting by.
2. Disconnect the gas supply to it.
3. Remove the meter, where there is one.
4. Seal every exposed gas way straight away with an appropriate fitting.

If there could still be a danger after all that, you may choose to purge the gas out of the pipework first. Guidance on that is in IGE/UP/1 and IGE/UP/1A.

Sources: GSIUR 1998 reg. 22coating, retest IGEM/UP/1B Ed. 4 4.1.1, 4.1.4–4.1.5equipment, LDF IGEM/UP/1B Ed. 4 5.2.3joints IGEM/UP/1B Ed. 4 5.3.2.1(h)fail, make safe IGEM/UP/1B Ed. 4 5.5suspected escapes IGEM/UP/1B Ed. 4 6.4.1–6.4.2naked flame CCN1 Issue 16 §6aassessed

▸Tutor notes

• Ask learners to check the label of the leak detection fluid in their kit: does it state BS EN 14291, and is it safe on brass and stainless steel?
• Contrast the two cases: a routine test on an existing installation (allowance applies) and a test after a reported smell of gas (no allowance). Why the difference?
• CCN1 §6a performance criterion 2 assesses locating and repairing an escape. IGEM/UP/1B gives the tools and the pass criteria, but not a step-by-step method for finding the escape. A method section will be added once there's a source for it.