Two drawings, two moments
The PNGRB guidelines for multi-occupancy buildings ask for a design sketch before installation starts, and an as-built drawing before the gas distribution company commissions the system.
The design sketch
It shows what is going to be built: the route of the riser, pipe sizes, the position of valves, loops, supports and the shaft, and the points where the riser meets the building services. It is the drawing that the contractor works to and that the stress analysis supports.
The as-built drawing
It shows what was actually built. Any change made on site, such as a loop moved because of a beam or a support shifted because of a duct, is recorded. If the change affects the movement of the pipe, it should be checked against the stress analysis.
Why the difference matters
A riser that was analysed in one layout and built in another has not been analysed. Keeping the two drawings consistent is how the design remains valid.
Useful habits
Number the drawings and keep revisions. Mark changes clearly. Record the pipe material, size and thickness actually used, and keep the test records with the drawings.
Who uses them later
The gas company at commissioning, the building operator for maintenance, and any engineer who has to modify the riser in the years afterwards.
For design review or help preparing riser drawings, send us your project details. See our PNG riser stress analysis service.