Pipe Inert Purge Volume and Time
Inert (nitrogen) purge volume and time for a pipe run while brazing or purging a gas / process line.
Example
You enter
- Pipe inside diameter (in) 2.067
- Run length (ft) 100
- Volume changes to sweep 5
- Purge gas flow (scfh) 60
You get
- Pipe volume 2.33 ft^3
- Purge volume 11.65 ft^3
- Purge time 11.7 min
Details, formula, and sources
Pipe volume = pi/4 x ID^2 x length; purge volume = pipe volume x air changes; time = purge volume / flow. 100 ft of 2 in pipe holds 2.33 ft^3, so five volume changes is 11.65 ft^3 and about 12 minutes at 60 scfh; a 4 in line holds 8.84 ft^3 and takes 44 min. The volume changes and the acceptable oxygen or dew point come from the spec; a meter confirms the endpoint. Distinct from purging a confined space.
pipe_volume_ft3 = (PI/4) x (pipe_id_in/12)^2 x length_ft; purge_volume_ft3 = pipe_volume_ft3 x air_changes; purge_min = purge_volume_ft3 / flow_scfh x 60.
Inert-purge identity by name (pipe volume from the bore; purge volume over the air changes; time over the flow); first-principles arithmetic.
The volume and time arithmetic is public first-principles; the volume changes and endpoint come from the spec or manufacturer.
Estimate. AHJ and licensed professional govern.
Field names used by the API: pipe_id_in, length_ft, air_changes, flow_scfh, pipe_volume_ft3, purge_volume_ft3, purge_min
- Volume changes ~5 to 7 to reach a low oxygen level (default 5); the spec governsbrazing / process spec
- Purge flow ~60 scfh default; a meter confirms the endpointfield practice