In one of the companies where I worked, non-criticality (and hence no flexibility analysis was further required) is assigned to a piping system which:
- Duplicates, or replaces without significant changes, a system operating with a successful service records;
- Can readily be judged adequate by comparison with previously analyzed systems;
- Is of uniform size, has no more than two points of fixation, no intermediate restraints.
The non-critical lines usually are:
[ol 1]
[li]Non-hydrocarbon lines such as air and utility water[/li]
[li]All lines which discharge to atmosphere including fire case relief and vent lines (excluding other relief and vent scenarios)[/li]
[li]All lines within skid mounted packages (which are the responsibility of package vendors)[/li]
[li]All small diameter piping (40mm and below) unless subjected to surging such as relief and blowdown[/li]
[li]All piping connected to open drains[/li]
[li]All piping connected to closed drains[/li]
[li]Lines that have similar configuration or mirror image to those that have been analyzed and satisfy the pipe flexibility.[/li]
[/ol]
Classification of the remaining piping systems considers: service conditions, size, and temperature range - into Class I and Class II of critical piping. But, as others have said, the term "critical" can be applied based on many different criteria.
Dejan IVANOVIC
Process Engineer, MSChE
