Pipework, Fittings, Jointing and Pressure Testing
What the exam tests
Pipework materials, fittings, jointing methods and pressure testing for domestic gas installations. The exam expects you to select suitable materials, reject prohibited joints and prove both strength and tightness before gas is introduced.
Core rules
- Domestic gas pipework is commonly copper or steel; the material and jointing method must suit the gas, location and standard. I.S. 813 restricts where certain joints may be used and requires protection against corrosion and mechanical damage.
- Joints must be accessible for inspection and testing unless the standard permits otherwise. Concealed compression or soldered joints in inaccessible voids are a recurring exam failure.
- New pipework is strength-tested and then tightness-tested. Test with air or inert gas, never with gas, and use a calibrated gauge.
- Before testing, isolate the meter/ECV and appliances, stabilise temperature, record the starting pressure and test duration, then compare any drop with the permitted value for the installation volume.
- After testing, purge and prove gas at each appliance before commissioning.
Worked example
A 15 m run of 15 mm copper feeds a 2 m³/h hob. The installer assembles compression joints, but one joint would sit inside a sealed wall cavity. He reroutes the pipe so the joint is accessible, then pressure-tests the new section with air. The gauge is allowed to stabilise, the test pressure and duration are recorded, and the observed drop is compared with the permitted drop for that volume. Only then is the pipe purged and connected. The reasoning is: compliant joint location first, then a valid test, then purge.
Marks-losing traps
Using a bubble test as the only tightness test; testing with natural gas; ignoring temperature change during a test; leaving an inaccessible joint because it never leaks; failing to record test pressure and duration.