Use 100 or 120 C-Factor for Dry-Pipe to Wet-Pipe?

10/7/2022

We are converting an existing dry system to a wet-pipe system. The entire non-conditioned area where the system was located in is being converted to fully-conditioned.

When running the new hydraulic calculations, would you keep the 100 C-Factor or would you increase it to 120 for wet pipe?

For reference the dry system has been in place for approximately 30 years.

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8 Comments

Anthony

10/7/2022 08:07:43 am

I don't believe the code speaks to this as a hard "shall" but best practice would be to use 100 c as the existing piping will have a rougher interior from the years of existence as a dry system as compared to a wet system.

I would strongly recommend checking out a few low spots on the system to makes sure the piping is in good enough shape to be reused.

Jesse

10/7/2022 08:12:29 am

C=100 would be the more conservative calc. I'd check with the AHJ and see what they want to see.

radhakrishnan duraikkannu

10/9/2022 02:15:31 am

100 C-factor shall be used, as the system is 30 years old.

Dan Wilder

10/7/2022 08:48:43 am

What does the last 5 year internal say about the condition of the pipe? Is there any indication of debris in the system (drops, low points, end of mains, top of clapper at the riser) after that long of an in-service record? Have a good look at coupling rubbers, those dry out and have caused us a lot of issues in previous conversions.

Conservative approach would be to keep the C of 100 and then utilize the standard remote area vs the previous 30% increase or even start with small room allowances as needed (no mention of occupancy). If the pipe looks good (systems that old typically look decent when properly installed), maybe the C of 120 could be used pending inspection results.

I would definitely propose N2 wet inerting as an option.

Brian Cockburn

10/7/2022 09:23:49 am

I tend to think using C=100 would be the better choice as the pipe interior would be rougher, as mentioned above. That being said, scoping the inside of the pipe would tell you what condition it's in and you can use that to inform your decision.

Aside: Most AHJs know little to nothing about hydraulic calculations. They rely on engineers to ensure they get done properly. They would likely just tell you to use the more conservative assumption since it would reduce their liability.

Glenn Berger

10/7/2022 09:53:46 am

I agree with Dan's comment above. My question is how much of the existing system is being changed out? Are you just swapping out the control valve or something more invasive?

Don Thomas link

10/7/2022 10:06:14 am

I would definitely do an extensive internal pipe check and a thorough 5 year prior to doing anything to a dry system that has been in place for 30+ years.

After that if all is still well, I think I would keep the 100 C to be conservative.

Alex

10/7/2022 10:47:34 am

Hi,

I agree with others that using the C-100 would be best. Although, based on the age of the system, I highly recommend additional internal piping review to ensure the pipe is still in good condition.

Thanks,
Alex

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Use 100 or 120 C-Factor for Dry-Pipe to Wet-Pipe?

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