This was not brought up in project specs or plans. Nor was it brought
up in plan review. This was a project that had an existing 4" ductile
supply line. It is supplying some paint booths and some exhaust ducts
in an otherwise unsprinklered building. When the guys did the forward
flow test of the new backflow preventer, there was an issue that they
weren't getting as much water as they thought it should have. So, the
EOR for the project comes back and says something about the calcs.
According to my customer, the EOR says per a "chart" the C-Factor should
have been 60 instead of 140. For 3 of the 4 paint booths, it is not a
problem. They are small and plenty of margin. For the 4th, we end up
with a problem. But, if there is nothing in the specs or criteria to
cause the modification of that pipe, I am not sure where it will go.
The good thing is that we still have a margin on the system, but it is
less than the 10% required.
I have just never heard of having to do this modification. I wanted to
make sure it was something I have not been missing.
Travis Mack, SET
MFP Design, LLC
2508 E Lodgepole Drive
Gilbert, AZ 85298
480-505-9271
fax: 866-430-6107
email:[email protected]
On 8/29/2014 2:20 PM, Mark A. Sornsin, P.E. wrote:
Travis,
Off-hand I can offer no help.
But I am curious to see the responses. Had the engineer denoted the requirement
in the project drawings or specs, I'd definitely side with them. If not, then
I want to know if he has a leg to stand on (i.e. code reference).
This CAN be a significant issue and is another example of a potentially serious
'miss' by engineers who don't do their jobs with regards to sprinkler system
drawings/specs. E.g., take a 200 ft. run of existing 6 in. pipe - 50 years old.
They tell you to use it to modify the existing pipe schedule sprinkler system to
meet the new occupancy. Most often, a contractor can get away with simply assuming
it is 6" ductile with a c-factor of 140. But what if in reality it is unlined
cast iron? What C-factor are you to use?
FM taught me that it depended on the water corrosiveness. Who determines that?
I don't know if the FM data is acquired from anything that could be cited by
code. Their tables say 50 yr old cast iron in mildly corrosive ware should have
a C-factor of 75; if corrosiveness is severe, it should be 40. At an extra
Hazard, Group I demand of 750 gpm, the friction though 100 feet of pipe can
vary from 1.5 psi at C=140; to 4.6 psi at C=75; to 14.9 psi at C=40. Pretty
significant variance and not something that should be blown off by the engineer
or designer.
Ideally you'd do a water test THOUGH that pipe to verify actual friction losses
- but that is almost never a viable option. Then again, if you were able to do
so, you may be able to get a change order when you prove that the engineer
overlooked a serious issue.
Mark A. Sornsin, P.E. | Karges-Faulconbridge, Inc. | Fire Protection Engineer |
Fargo, ND | direct: 701.552.9905 | mobile: 701.371.5759 |
http://www.kfiengineers.com
-----Original Message-----
From: Sprinklerforum [mailto:[email protected]] On
Behalf Of Travis Mack
Sent: Friday, August 29, 2014 3:52 PM
To: [email protected]
Subject: Modifications to C-Factor due to age of pipe
Does anyone know if there is any requirement in NFPA or Uniform Facilities
Criteria to modify the C-Factor of existing underground piping based on the age
of the pipe? If so, do you have a section reference so I can look it up. An
engineer is requiring us to do it, but won't provide the reference. Yeah..It
is one of those days.
--
Travis Mack, SET
MFP Design, LLC
2508 E Lodgepole Drive
Gilbert, AZ 85298
480-505-9271
fax: 866-430-6107
email:[email protected]
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