If I had high confidence of all the following, I wouldn't see the need for
new calcs:
- Strictly pipe replacement (no added offsets, elbows, riser
nipples, etc)
- The original calcs were accurate (done properly and reflect 'as
built' conditions)
- Water supply hasn't deteriorated.
A bit of a side note - if the attic has a roof with slope greater than 2/12,
the design area very likely didn't include a 30% increase for the slope.
That requirement didn't appear in 13 until 1996. But since the pipe
replacement is legitimately a repair, you probably don't need to meet any
standard other than what was in effect 17 years ago.
Ed Kramer
Littleton, CO
> I walked through an attic this afternoon where all of the existing
> mains need to be replaced. The piping is 3" schedule 10 black steel,
> that is developing leaks after 17 years (we found another one on our
> tour). The proposal is out there to replace the existing with 3"
> schedule 40 galvanized (and provide proper pitch). I did a couple of
> quick calculations and at 250 gpm, the friction loss per foot for the
> two pipes is very close to the same. (.077 for the sch 10 black v.
> .075 for the sch 40 galv). My guess is that the difference in
> pressure would be about 0.75 psi. The calc has about 12 psi
> remaining. If this was strictly a pipe replacement (no other
> modifications), would you recommend new hydraulic calculations?
>
> Todd G. Williams, PE
> Fire Protection Design/Consulting
> Stonington, Connecticut
> www.fpdc.com
> 860.535.2080
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