Non-Domestic Gas Pipework Design, Sizing, Materials and Installation
This domain tests pipework from the meter or regulator outlet to the appliance isolation valve: pressure tier, sizing, materials, jointing, protection and bonding.
Design rules
I.S. 820 and I.S. EN 1775 govern building pipework, normally up to 5 bar MOP. Commercial meters may deliver low pressure (around 21 mbar) or medium pressure (for example 300 mbar or 2 bar) with a site regulator. Size pipework so the pressure at the appliance inlet stays within the appliance's stated range at full load.
Sizing method:
- Calculate the gas rate of every appliance and allow for diversity only where the standard permits.
- Measure the run and add equivalent lengths for bends, tees and valves (commonly 10–20%).
- Select a diameter from the sizing table so the total drop is within the allowance; for low pressure this is often about 1 mbar.
- Correct for gas density when sizing LPG or medium-pressure sections.
Materials and installation
Carbon steel to EN 10255, copper to EN 1057, stainless steel and PE (EN 1555) for buried sections are typical. Threads to EN 10226, welded and flanged joints are accepted; press-fit must be approved for gas. Support at intervals, sleeve wall and floor penetrations, seal the annulus, protect against corrosion, and fit isolation valves at each appliance. Main equipotential bonding connects to the installation pipe close to the meter outlet, before any branch.
Worked example
A 15 m run with 20% allowance becomes 18 m equivalent. At 8 m³/h the 22 mm table entry gives 1.6 mbar - too high for a 1 mbar allowance. Upsizing to 28 mm reduces drop roughly by (22/28)⁵ ≈ 0.30, giving about 0.48 mbar, which is acceptable.
Traps
Ignoring equivalent length; sizing on nominal diameter rather than bore; using a domestic 1 mbar rule on medium pressure; burying joints; omitting sleeving or bonding.
Exam focus
Pressure tiers, equivalent length, density correction, material limits and bonding position.