C-Factor for a 55-Year Old System with Debris?

10/22/2024

Hydraulic Upgrade to old wet and dry systems and determine "C" factors to be used. Question:

We plan to upgrade a fire sprinkler system from a Pipe Schedule Ordinary Hazard system with k-5.6 standard response heads to 0.25/2000 sqft with k-8 sprinklers, what "C" factor should be used?

The system is 55 years old and has a good water supply that would easily work for a new system using a C=120; however, debris has built up in the pipe, and if we were to do a hydro-pneumatic flush, the roughness would be much worse than that of new pipe.

The AHJ has no answers other than to do what we feel is best, and the insurance company just wants to see the density increased and "proven" to work at 0.25/2000. Furthermore, there are 2 dry systems that are 55 years old, and they want these upgraded, too. Even if we add a pump, it's just going to slam the sludge to the end of the lines and plug up any new heads that are installed.

Do you have any thoughts?

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11 Comments

Pete H

10/22/2024 06:52:09 am

There's no outright code requirement for "Old black steel that just had debris flushed out and is now significantly rougher inside." so I can see why the AHJ told you to do what you think is best. Because technically, you could submit this as a C=120 on the wet system (the dry systems would be C of 100).

Is the density increase because of storage/commodity or is that the AHJ's thought to how to handle the impediments within the pipe?

You sound like you want safety for piece of mind, so flush the system, and if you want, arbitrarily calculate it for C of 100 on the wet, and C of 90 on the dry, while hitting the AHJ's .25/2000 density (and .25/2600 on the dry). But you're already in a grey area and it sounds like the client isn't looking to replace the old piping/system. If the potential debris based impairments cause relevant issues, let it come up on the annual inspection (obstruction investigation as per chapter 14 of NFPA 25 2017 Edition), and resolve it accordingly. But right now you're just proving the water in the system for the design works.

Alan Kavanaugh

10/23/2024 10:30:49 am

Howdy Folks,

C Factors are based on pipe materials, type of materials and interior finish of pipe. Assuming brand new pipe installed or after flush why would you give an Alarm System (Wet System) a higher C factor than a Dry system?

10/23/2024 10:55:02 am

Because a wet system always has a higher C factor than a dry system.

Check Table 23.4.4.8.1 (NFPA 13 2016 edition).

Black steel (wet systems including deluge) C = 120

Black steel (dry systems including preaction) C = 100.

A lower C factor means rougher pipe / increased friction loss.

Dry systems have rougher pipe coefficients because the lack of constantly being filled with water actually causes more impairments or unexpected materials within the pipe to develop and cause greater friction loss.

So if the OP wants to feel safer, as they outlined, they calculate their systems with lower C factors than required just based on the expected additional friction loss from the age of the pipe developing a greater amount of impairments.

10/23/2024 10:57:58 am

And to be fair, not always, a nitrogen based dry system can attain a C factor of 120 in newer editions of NFPA 13.

10/23/2024 11:38:54 am

Thanks Pete for that clarification. Still doesn't make sense to me based on new installs? As you described roughness is based on the type of pipe not the sprinkler system factors? Interesting.

Jesse

10/22/2024 08:16:06 am

I think Pete is on the right track, and I also am curious as to the driver for the density increase.

The AHJ saying "do what you feel best" is akin to them saying we dond't want this albatros around our collective necks. I'm concerend about the debris and sludge in the system.

I got to wondering what I would do if this project came through my office and I'm not too sure I'd want my stamp on it... J

Glenn Berger

10/22/2024 08:31:11 am

I experienced this situation in the past and I wanted an invasive piping inspection conducted.

In the end, the entire piping system was replaced because of the build-up discovered in the piping system.

This is a designer beware scenario. Your question does indicate that debris was discovered in the pipe . This situation must be remediated.

10/22/2024 09:02:13 am

Yeah Glenn that's kind of where I was going in my comment.

We had a hotel remodel. The hotel was changed to low income housing. Understand that the number of calls I was involved in as a FF / Medic to this particular place was incredible. It was a rat hole, and tdhat's being nice. We were modifying existing AS and adding a standpidpe system and fire pump. We recommended replacing all existing piping and they wouldn't.

Until the hydro test.....

Franck

10/22/2024 09:19:36 am

I would recommend at least to replace the entire dry sprinkler system.
I had an experience in the past where we tested a quite old dry pipe system from the ITC, and the water pushed all the debris and sediment to the far end where it blocked the sprinkler orifice with absolutely no water coming out.
This is definitely not what you want on a fire event.
And we had to replace the entire system.

For the wet pipe system, if sprinklers are pendent, you will probably need to replace all of them as sediment will have accumulated over time on the orifices.
A careful flushing is necessary and you will have to flush all dead ends… This might be a painful operation and with an unknown result.
If I was the AHJ, I would definitely recommend to replace it all.
It is 55 years old, it has made its time !

franck

10/22/2024 09:24:24 am

In addition, when you will restore the entire system and remove sediment and scale, corrosion will certainly starts with new fresh water and you will experience leakage and other maintenance issues.
Not to speak about the ability of your system to sustain pressure on the mid-ling term with no degradation on the piping system.

I would not be the one Responsible for accepting this situation.

Jack G

10/22/2024 11:36:45 am

There is a formula in the haven Williams/ equations where you can measure the flow and pressure between 2 points and calculate the c- factor.
Since you were flushing the system, you could have done this in several locations, come up with a c factor.
In the 60 s Kemper used to figure the age of the system was the drop in the c factor. 55 years = 65 c factor. I like testing and calculate c s for the branches and cross mains and supply mains better. Use those c factors in your hydraulic program.

C-Factor for a 55-Year Old System with Debris?

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