Distance from All Thread Rod to Sprinkler Pipe?

6/9/2022

When using loop hangers in fire sprinkler systems, is there a distance (minimum or maximum) that the end of the all-thread rod needs to be from the top of the steel pipe?

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11 Comments

6/9/2022 08:10:49 am

Our state (South Carolina) requires the all thread rod touches the top of the steel pipe. I feel this is a common requirement, I just can't speak for other areas. We are also in a seismic zone, so if we hang the pipe with rod lengths less than 6" we get to eliminate most of the seismic bracing too.

Dave L.

6/9/2022 10:32:31 am

It should be noted that the 6" length for eliminating lateral bracing is measured from the top of pipe to the point of attachment, so a 6" long rod would pretty much have to touch the top of the pipe.
Starting with the 2016 edition of NFPA #13 this allowance is no longer allowed when the seismic coefficient (Cp) exceeds 0.5 (although so far it can still get you out of branch line restraint)

Anthony

6/9/2022 08:12:15 am

TLDR: No, mostly.

Its important to have the rod in full contact with the whole of the nurl threads. It should be easy to see a full rotation of thread past the nurl apx 1/8'' to 1/4'' down. In seismic zones where restraint or surge clips are needed the clip with require something to hold on to. With some of these products the rod will need to be extended past the nurl.

There may be some specifics from Hilti/PHD specific to their hangers. I haven't looked at one of their cut sheets recently.

David G Kendrick

6/9/2022 08:12:49 am

Depends.

Threaded connections need full engagement to perform correctly. I have seen and worked under specifications where it was required to have a "full" thread penetration of the connector. Connector being the knurled nut or hex nuts as the case may be on clevis rings.

There was (or is) a point to using the threaded rod extended through to within 1/16" of the top of the pipe where the sprinkler head is in the pendant position and the water pressure supplying the head is at or over 100 psi. This is a surge restraint.

There are now products that clip into the pipe hanger that perform the same function without needing the extra threaded rod.

Seems a lot of this type of connection has been minimized with the use of flexible hose connections attached directly to the ceiling grid.

Alex

6/9/2022 08:15:05 am

Hi,

I don't believe there is anything within NFPA 13 Chapter 9 that outlines minimum or maximum distances between the rod and the top of the pipe.

I hate this type of answer because it tends to be the easy way out, but here, I think its the only answer: install per the manufacture cut sheet. Some loop hangers require the rod to extend into the loop a certain distance.

Thanks,
Alex

James Phifer

6/9/2022 08:15:43 am

Figure A.9.2.3.4.4(b) NFPA 13: 20116 ed shows the rod touching the top of the pipe as a way to prevent upward movement of the pipe.

6/9/2022 08:16:35 am

A minimum of one thread exposed would make sense. Many stud specifications I have seen call for a minimum of one to three threads exposed. As long as the threads are fully engaged into the swivel nut I would consider it acceptable.

Maximum would be touching the pipe as in Figure A.9.2.3.4.4(b).

Ryan Hinson

6/9/2022 08:51:02 am

Agree with the other posts above. Keep in mind that, if pushing piping through a hanger that is already installed, the tip of the ATR (likely cut quickly deburred with a chop-saw) may have a sharp tip in contact with the the pipe which can potentially scratch the pipe longitudinally. While not a big deal on black steel; this can be a big no-no on other types of pipe where external coatings need to remain intact for longevity of corrosion-resistance or for listed-installation requirements such as for CPVC where scratches are detrimental to the pipe's integrity.

Julie

6/15/2022 10:40:33 am

AHJ inspector here, when working at a major city in California, we required the thread to be in contact with the pipe. Here in Nevada, I have never seen another inspector enforce this or even mention it. I never see the threads touching the pipe here. I have tended to do what the others in my area are enforcing so we are consistent. I suppose that just means it depends on your AHJ if it’s not in code.

Chris

6/15/2022 05:34:03 pm

AHJ here for a fire dept (part time job) also licensed in the state of Ohio (full time job) for sprinklers, eletric fire pumps, diesel fire pumps, fire alarms, portable extinguishers, pre-engineered systems.
My personal take is the rod should come within 1/8” and 1/4” whether you live in a earthquake zone or not. Whether it’s uprights or pendants when I’m running a job I always make that a common practice

Chris

6/22/2022 12:47:39 pm

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Distance from All Thread Rod to Sprinkler Pipe?

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