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Methods of Connecting Fire Sprinkler Pipe

7/18/2018

 
One of the popular aspects of fire sprinkler installations that is overwhelmingly familiar to fitters in the field yet something I hardly understood back as a new graduate is pipe connections. Today I'm breaking out some of the popular methods of joining steel pipe in fire sprinkler systems.

Steel Pipe
While copper, CPVC and PEX are listed for use in fire sprinkler systems (PEX is only for NFPA 13D systems), black steel pipe remains the most popular pipe material for commercial fire sprinkler applications, at least within the United States.

For steel pipe, the primary means of connecting the pipe include threaded fittings, grooved fittings, plain-end compression fittings, flanged connections, and welding.

Plain End Pipe
Steel pipe when initially formed has flat cut, unpolished ends. This is generally referred to as plain end pipe. 

Plain end pipe can be connected by compression fittings or push-on fittings, which bite into the pipe to prevent separation. While popular for other building systems, use of plain end pipe and compression or push-on fittings are not used in sprinkler systems due to the relatively high pressures sprinkler systems experience.
Black Steel Plain End Pipe
Threaded Pipe
​Perhaps the most common current method of joining fire sprinkler pipe for smaller pipe diameters, threaded pipe makes use of helical crests that screw into a female threaded fitting.

To create threaded pipe, a plain-end pipe is cut with a threaded machine decreasing the thickness of the pipe wall. As a result, the areas remaining below and adjacent to the thread become weaker and more susceptible to corrosion breakthroughs with the thinner wall of pipe.
Threaded Fire Sprinkler Pipe

​As compared to grooving or welding pipe, the pipe wall thickness must be thicker to accommodate the cut-in threads (ASME B1.20.1) for threaded pipe. NFPA 13 6.5.1.2 (2002-2016 Editions) addresses minimum pipe thicknesses for threaded pipe up to 300 psi, unless the pipe is separately listed for fire sprinkler use:
Pipe Diameter
Minimum Pipe Thickness for Threaded Pipe
Basis
6-inch and smaller
Schedule 40
NFPA 13 2002-2016 6.3.3
8-inch and greater
Schedule 30
NFPA 13 2002-2016 6.3.3
When connecting threaded pipe, joint compound or pipe tape is applied to the male thread to avoid water leakage. 

While threading larger pipe was common throughout the early to mid twentieth century, the weight of Schedule 40 pipe and difficulty of turning large diameter threaded pipe makes threading an uncommon choice for larger diameter sprinkler pipe today.

Grooved Pipe
Grooved pipe is a popular method of pipe joining invented by Victaulic with roots in both World Wars to deliver water and petroleum with faster, more reliable method of pipe connection. 
Grooved Fire Sprinkler Pipe

Grooved pipe is formed by either cutting into the pipe (cut groove) or by pressing an indentation into the pipe (roll groove).

Cut groove pipe results in a lesser pipe thickness, weakening the pipe and also offering less protection against corrosion.

Roll grooving, while keeping the pipe wall thickness, also poses issues in low-sloped dry and pre-action systems as the rolls on the interior side of the pipe create areas to trap water and create an air-water interface for corrosion to occur.
​
Roll vs Cut Groove Fire Sprinkler Pipe

Grooved pipe has a number of inherent advantages. Smaller pipe thicknesses are permitted for grooved pipe, resulting in thinner pipe which makes transporting, carrying, and lifting into place easier. Minimum thicknesses for Grooved Pipe: 
Pipe Diameter
Minimum Pipe Thickness
​for Cut Grooved Pipe
Basis
6-inch and smaller
Schedule 40
NFPA 13 2002-2016 6.3.3
8-inch and larger
Schedule 30
NFPA 13 2002-2016 6.3.3
Pipe Diameter
Minimum Pipe Thickness
​for Roll Grooved Pipe
Basis
5-inch and smaller
Schedule 10
NFPA 13 2002-2016 6.3.2
6-inch
0.134 in.
NFPA 13 2002-2016 6.3.2
8-inch and 10-inch
​0.188 in.
NFPA 13 2002-2016 6.3.2
12-inch
0.330 in.
NFPA 13 2002-2016 6.3.2

With thinner, lighter pipe and easy grooved coupling options, labor can be less difficult and significantly quicker.

Welded & Flanged Pipe
A less common but additional option for restraining pipe is welding. Pipe can be welded as an outlet - where a welding equipment cuts a hole in one pipe whereafter another pipe segment is held in place and the two are welded together.
Welded Fire Sprinkler Pipe

Welding has a few advantages - it can be (and often is) performed in a fabrication shop, does not require any additional fittings, and can allow for more custom pipe arrangements.

For instance: a 4-inch x 4-inch x 1/2-inch outlet for a pressure gauge connection might be a special order reducing tee (ie: costly); as a welded outlet, it could be quickly and easily welded into place with the outlet easily threaded or grooved.

Welding is not limited to outlets, however. "Slip-on flanges" can be welded to the hub side of the flange to a piece of pipe, allowing two flanged fittings to be bolted together with a gasket in-between.
​
Flanged Fire Sprinkler Pipe

Flanged pipe and fittings are common around fire pump assemblies, as NFPA 20 annex material even notes that "flanges welded to pipe are preferred" despite screwed, flanged mechanical joints or other approved fittings are allowable (NFPA 20 2003-2007 5.13.2.1, 2010-2013 4.13.2, 2016 4.14.2, 2019 4.15.2).
Pipe Diameter
Minimum Pipe Thickness
​for Welded Pipe
Basis
5-inch and smaller
Schedule 10
NFPA 13 2002-2016 6.3.2
6-inch
0.134 in.
NFPA 13 2002-2016 6.3.2
8-inch and 10-inch
​0.188 in.
NFPA 13 2002-2016 6.3.2
12-inch
0.330 in.
NFPA 13 2002-2016 6.3.2

Different installing contractors often have different preferences on fabricating pipe. Personally I've worked with some who prefer to have welded outlets along 21-foot lengths of pipe and groove as much as allowed for a job to use lighter, thinner pipe, including through branch piping. Others prefer some flexibility of threaded pipe to make quick changes in the field and provide a more traditional, tightly-connected threaded system.

What do you commonly see? Does your team have preferences for fabrication methods? Discuss this here.

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Nimal Tissa Wijetunga
8/1/2018 12:46:29 am

Dear Sir,

I would like to download this article. How could I do that.

Pls. advise.

Sincerely,
Nimal.

Joe Meyer
8/5/2018 06:35:45 am

Hi Nimal,

If you're already subscribed to these articles, you can just print any email to a PDF. Otherwise if you click on any of the articles you can right click > print and also print it to a PDF.

If you're looking for something more formal, please email me at [email protected] and we'll see what we can come up with. Thanks Nimal!

Joe

Michael J. Agri Jr.
8/5/2018 02:21:11 pm

Nice, clear, concise piece.

However, one has to wonder what group of geniuses decided that it was a good idea to use Schedule 10 with rolled groove joints, in sprinkler applications. I would expect such installations to mechanically fail, early and often.

Chuck U Farly
8/5/2018 09:11:19 pm

You do realize that schedule 10 grooved in 2 1/2” and larger sizes has been used for many years right?

Schedule 40 threaded pipe has a lower CRR than 10 grooved so which is early and when is often?

Jasmine Paulos link
10/15/2018 07:05:44 am

This is something interesting.I found this article very informative . I am glad that I came across such an article.You have very nicely explained about it in a detailed manner.Keep posting such article.

Thomas Dietrich link
3/4/2019 01:00:50 pm

I ask this only to satisfy my own curious nature.
I've observed sprinkler system pipes that appear to be joined with what appears to be a two piece clamp which is itself joined by nuts and bolts. How does this method function? An illustration would be helpful.
Regards, Thomas Dietrich
New Milford NJ.

USHA SARASWATHI link
5/28/2019 05:17:31 am

Dear Sir,

Please send offer for below enquiry with technical sheet .

For Tender Participation

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STANDARD/SPECIFICATION:ASTM;
7041 / 80 MM
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FLANGE,FIRE WATER SYSTEM,100 MM,DUCTILE
PARENT EQUIPMENT/FUNCTION:FIRE WATER SYSTEM;
SIZE:100 MM;
MATERIAL:DUCTILE IRON;
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7041 / 100 MM
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FLANGE,FIRE WATER SYSTEM,150 MM,DUCTILE
PARENT EQUIPMENT/FUNCTION:FIRE WATER SYSTEM;
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FLANGE,FIRE WATER SYSTEM,200 MM,DUCTILE
PARENT EQUIPMENT/FUNCTION:FIRE WATER SYSTEM;
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STANDARD/SPECIFICATION:ASTM;
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FLANGE,FIRE WATER SYSTEM,250 MM,DUCTILE
PARENT EQUIPMENT/FUNCTION:FIRE WATER SYSTEM;
SIZE:250 MM;
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STANDARD/SPECIFICATION:ASTM;
7041 / 250 MM
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FLANGE,FIRE WATER SYSTEM,300 MM,DUCTILE
PARENT EQUIPMENT/FUNCTION:FIRE WATER SYSTEM;
SIZE:300 MM;
MATERIAL:DUCTILE IRON;
STANDARD/SPECIFICATION:ASTM;
7041 / 300 MM
QTY : 4 NOS


FLANGE,FIRE WATER SYSTEM,400 MM,DUCTILE
PARENT EQUIPMENT/FUNCTION:FIRE WATER SYSTEM;
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QTY : 4 NOS


Thomas Jameson link
6/11/2019 01:38:38 pm

It's good to know that grooved pipe is formed by cutting into the pipe. My brother has been wondering how groove pipe is made for a while now. I'll pass this information along to him so that he's aware of how it's made.


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