Threaded Over Grooved Branch Pipe?

7/29/2019

Lately I have seen a couple specifications require branch lines to have threaded connections and they specifically do not allow grooved, even when Schedule 40 pipe is used and even when most of the armover connections are welded pipe outlets.

These could just be old/outdated specs, but is there a reason/theory that suggests threaded connections are better than grooved? They can be cheaper but also can increase labor costs on large jobs. Just curious if there's a perspective I'm not considering here, thanks in advance.

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6 Comments

Thomas Jones III

7/29/2019 10:04:18 am

Thread pipes are more expensive to install, more prone to leak, and harder to replace on service work. I would recommend grooving anything over 1". Sometimes it makes sense to thread when you are trying to work with the hydraulics.

David link

7/29/2019 10:18:54 am

Thomas Jones III,
I have to ask. Where do you see the hydraulics advantage of threaded pipe and fittings compared to grooved pipe and fittings when the pipe is schedule 40 for both types of connections?

Dominic

7/29/2019 10:19:23 am

I think a lot of times those specs are outdated, but I will say threaded pipe gives a more cleaner look than grooved pipe. You can notice when you weld 1 1/4 and 1 1/2 pipe it can deform the pipe, making it hard to keep the lines straight and to pitch the lines for proper drainage.

Ivonn link

7/29/2019 11:47:00 am

It can be a bad experience with a coupling, some leakage that damages the product and they consider that a threaded accessory is safer.
A coupling that is damaged the metal part or the gasket could not fail until long after unlike a leak in a thread fitting thats it shows immediately or at least is that I have heard from customers.

In my opinion both are reliable if they are installed correctly

Rusty Scott

7/29/2019 02:58:24 pm

I've been on both the contractor and engineering side. My old contractor company liked to use threaded in certain cases and grooved in others, all about the $. It just depended on the floorplan layout size. I will say a lot of the time on tree systems we used threaded branch outlets. Also our labor force is from GA and SC where labor costs are significantly less than lets say TX or CA for example.

On the engineering side, our specifications use to read that 2" and smaller be schedule 40 because threading branch piping was just the way the world worked back in the day. Our specs now have options that allow Schedule 10 for 1 1/4" and larger when grooved.

In my experience I have never had a thread leak after the 200 psi pressure test has been approved. I have however had grooved couplings leak after the fact. This is typically on main piping where there were a lot of fittings or on the riser where it's harder to brace.

Another comparison to think about, (when there is a fire pump involved) we allow threaded reducer fittings but do not allow grooved reducer couplings. We've had cases on the contractor side where the reducer coupling failed and water dumped on a tissue paper manufacturer's storage facility. The blowout of the grooved coupling tends to be much greater than that of a threaded fitting.

Ben O'Regan link

7/30/2019 10:09:39 am

I can't imagine a contractor being happy about installing pipe over 2" diameter threaded. It's hard work doing up those larger connections compared to one bolt for a grooved coupling. Even though the materials might be cheaper the contractor is going to charge more for their trouble.

Another difference is rigidity - grooved couplings flex, threaded joints are stiffer, but that's usually not an issue at all.

Both systems are quite reliable. I have seen threaded connections rust out if they have been in service for a very long time (like 50 years). I don't know about grooved couplings, maybe they can deteriorate if they get old enough.

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