Everything You Need To Know To Find The Best Grooved Fittings

We previously have introduced different types and combinations of threaded fittings - which have been around for more than a century.

Here we're introducing another common way to join pipe; using grooved fittings. 
An attic sprinkler system using a grooved elbow with couplings.  Use of "mechanical" couplings that could allow faster joining of pipe came to life in by Lieutenant Ernest Tribe. Just a few years later the Victory Pipe Joint Company renamed itself to Victaulic (a combination of "victory" and "hydraulic"), and grew to expand the technology worldwide. 

Today, Victaulic and other manufacturing leaders provide grooved fittings that are often used for pipes in fire sprinkler systems. It is not uncommon for both mains and branch lines to be grooved today.

What are common grooved fittings, and how do they work? Let's introduce them.  An in-rack sprinkler with a branch line using (starting with the sprinkler) a groove x thread reducing elbow
​with a grooved coupling, a grooved piece of pipe, and a grooved tee (connection not shown). PIPE
Let's start with the pipe. In order to give grooved fittings an opportunity to "grip" the pipe and remain in place, they need an opportunity to resist the pressure of the water that is trying to "pull away" the pipe from the fittings which join them together. A grooved coupling about to connect two grooved-end pipes. Note the loose nut and bolt on the right-hand side, allowing the coupling to be expanded and "slip" over the pipe on the left. In order to create a groove in the pipe, steel can either be "roll groove" or "cut groove". Roll groove pipe involves pressing an indentation into the pipe near the end of the pipe. This allows a grooved fitting to slip over the end of the pipe and fit into the groove. Roll groove pipe has the advantage of not reducing the pipe thickness, so it can have more tolerance for corrosion than thinner pipe, similar pipe with threads, or pipe with cut grooves.

Pipe which is cut groove involves cutting into the pipe rather than pressing it. This cutting removes a portion of the pipe wall, making a thinner but smooth interior pipe wall. This thinner wall makes it more susceptible to corrosion, however, for pipe systems with a minor slope, the smooth inside of the pipe does not create a ridge where water can sit and corrode the pipe. Roll Grooved Pipe (top) and Cut Grooved Pipe (bottom). Note the ridge on the inside of the pipe wall for roll groove pipe, and the thinner pipe wall along the cut groove pipe. A tape measure with a "go" or "no-go" measurement to determine if the groove is within manufacturer tolerances. ELBOWS & TEES
Let's start with the basics. Elbows allow bends of 90-degrees (most common), 45-degrees, 22-1/2 degrees, and 11-1/4 degrees.

Why not every possible angle? What if I need to have a 60-degree bend because of my building?

First, it wouldn't be economical to make a fitting of every bend. Second, is that using just two 90-degree elbows back-to-back we're able to create a "swing joint" and make any angle we could want, just by changing the elevation of the pipe that's being joined. Victaulic "FireLock" Grooved Fittings; 
90-Degree Elbow #001 (left), 45-Degree Elbow #003 (center), and Standard Tee #002 (right) One notable specialty with the grooved elbow is a "Drain Elbow", which has the elbow except it includes a drain outlet at the bend of the elbow. This is used all the time with fire department connections which come down a wall and need to be capable of being drained (to avoid having water-charged pipe freeze and burst). This is also called a "Drain-El" or is a Victaulic #10-DR. A wall-mounted fire department connection that is away from the riser, here showing the "Drain Elbow" with a ball drip below. The portion upstream of the check valve is intended to be dry unless the FDC is actively being used in order to avoid freezing water inside. COUPLINGS
Nice sketches, Joe, but that's not how things look in the field!

That's because unlike threaded fittings, the actual pipe joining is by a grooved coupling. The coupling has malleable iron bumps that grip the indent of one groove (pipe/fitting) and connect it to the second groove (the other pipe/fitting).  A grooved coupling (here a Victaulic #009N shown). OTHER FITTINGS
There are a host of other fitting types. Grooved Reducing Tees? Yep. Less common. Less common can equate to more expensive, or at least that's what I hear from contractors familiar with all the pricing nuances.

What other grooved fittings do I often see? 

Reducing fittings, which is a concentric, single-cast piece of metal that has a large groove on one end and tapers down to a smaller groove on another end. One note of caution is using these in the vertical orientation; I've heard it is much better, more stable, and stronger to use a reducing-fitting as opposed to a reducing-coupling when in a vertical orientation. One of my clients goes so far to say to not use reducing couplings at all (where the coupling itself has two different groove sizes). I wouldn't have the expertise to gauge that myself. A flange x groove reducer (left) and a grooved cap (right). There are also reducing adapters, than can accept a flange connection and convert it to a reduced groove connection. 

Crosses are also available, as are caps (like the Victaulic #006 shown above on the right) which can terminate the end of a branch line. These caps even have 1-inch threaded opening options for easy auxiliary drains. 
Many manufacturers have equipment and components with grooved ends that can readily attach to pipe and fittings.

They offer a compact, simple design that streamlines the process of connecting pipes, valves, and fittings

Well-designed and assembled networks of pipe provide a safe and efficient way to move materials from one location to another. And piping systems as varied as indoor plumbing, petroleum pipelines, and fire sprinkler systems rely on countless leak-free joints to ensure that nothing’s lost along the way. Grooved couplings have made this reliable connection much easier.

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In this article, we look at grooved couplings, explaining how they deliver on the characteristics of flanged or welded joints while significantly reducing the labor hours required for installation and maintenance. We also talk briefly about their history, how they compare to other joint types, the installation process, and other important features impacting contractors’ bottom lines.

If you’ve stumbled across this page while searching for grooved pipe couplings and other fittings, you can view our selection here.

Two world wars propelled the development of grooved pipe couplings

World War I saw the introduction of the flamethrower, a weapon designed to flush enemy troops out of trenches with burning liquid. As a lieutenant in the British Army, Ernest Tribe—later the co-founder of the global piping titan Victaulic—trained soldiers in their use. While they could be deadly to their targets, early flamethrowers could also backfire. Fuel tubes often detached, spraying flame at operators and other nearby soldiers.

In response, Tribe developed and later patented what he saw as a reliable way to join pipes together: mechanical couplings. His ambitious invention sought to make leakproof connections between pipes possible without flanges, allowing pipes to be connected end-to-end. A leak-preventing ring, held in place by a metal housing, wrapped around the circumference of two adjacent pipes, preventing liquid from escaping even under pressure.

Tribe’s invention improved over the decades to come—particularly with the introduction of synthetic rubber gaskets capable of withstanding exposure to petroleum products. By World War II, couplings manufactured by The Victaulic Company became the go-to device for military engineers laying 4-inch pipes, known as “invasion tubing,” to deliver petroleum to military installations.

Today, mechanical grooved couplings based on Tribe’s design are used in piping systems of all kinds. They’re a popular choice in commercial HVAC and fire protection systems, an increasingly common joining method in commercial plumbing and piping systems, and even an integral part of more than 25 Olympic stadiums.

Grooved couplings, one of many joining options available to pipefitters, provide a seal using indentations and simple components

To hold pipes, fittings, and valves together, grooved couplings rely on indentations—or grooves—near inlets and outlets. In roll-grooved pipes, these indentations are formed using a machine that rotates the end of the pipe while pressing in, leaving a ring-shaped impression in the pipe. As this short video shows, roll grooving displaces the metal, forming a small bulge inside the pipe:

Cut grooving, on the other hand, forms a groove in pipe by removing metal from the outer surface. This grooving method, typically used on Schedule 30 and heavier pipe, reduces the thickness of the pipe wall. Both cut-grooved and roll-grooved pipe can meet manufacturing requirements for grooved and shouldered joints—codified in the standard ANSI/AWWA C-606—without failures or a noticeable loss in pressure.

To join roll- or cut-grooved pipe, grooved couplings use a flexible gasket along with metal housings, nuts, and bolts. The gasket wraps around both pipe ends, preventing liquid from escaping, while the housing, nuts, and bolts secure it in place, creating a seal that can withstand vacuum or pressure conditions.

Grooved couplings aren’t the only option available to pipefitters. Pipes may be bonded together with adhesives, joined by flanges, soldered, welded, or even brazed. Most often, though, grooved couplings are compared with two of these methods: flanging and welding.

In flanging, a series of bolts connect two plates or rings, called flanges, together. These flanges connect to pipes, valves, and fittings through welding or threading, and are largely used where rapid assembly and disassembly are desired. Welding joins components to one another directly using heat—and sometimes pressure and/or metal additives—to form a chemical and mechanical bond.

They can drastically reduce installation times over flanged or welded joining methods

Grooved couplings are often favored over flanged and welded methods of joining pipes because they’re easier and significantly faster to install. One of the most detailed estimates of the labor hours involved in the installation of piping systems comes from the Seabee Planner’s and Estimator’s Handbook, a guide for planning and estimating construction projects undertaken for the United States Navy.

Suggested reading:
Stainless Steel Pipes vs. PVC: Which is More Durable?

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According to the Handbook, installing copper pipe couplings takes anywhere from 24 minutes for pipe smaller than 1/2″ and more than three hours for a single 4″ pipe coupling. Flanged steel pipes can reduce the time required significantly at larger diameters, ranging from just under a half-hour for 1/2″ pipe and just under one hour for flanges installed to 6″ pipe. Grooved couplings take far less time across the board, installing in about less than six minutes for 1″ pipe, less than 20 minutes for 6″ pipe, and under an hour for 18″ pipe.

In terms of installation time, these estimates suggest that welded pipe can’t begin to compete with grooved couplings—an idea reinforced by Victaulic in their estimates for grooved and welded pipe installations. Using data from the Mechanical Contractors Association of America, Victaulic also found a significant reduction in the labor-hours required for coupling grooved pipes instead of welding pipes together. In an HVAC project using more than 120 couplings, grooved piping systems reduced the overall installation time by nearly two thirds, cutting the total man-hours required from just over 2,000 hours to only 740.

While the exact figures vary, it’s clear that grooved couplings can offer significant benefits to installers. Particularly when labor rates are high, these improved installation speeds can create a sizable reduction in cost for contractors and their customers.

A simple process makes for fast installation of grooved couplings

At the core of these labor savings is a fundamentally simple installation process. With a grooved coupling and only two more items—gasket lubricant and a tool to tighten the nuts—installers can quickly secure these couplings to pipe and fittings. While approaches to installation vary with each manufacturer, a typical installation process might look like this:

1. Inspect and clean the pipe ends, ensuring that they’re free of deformations, loose paint, dirt, grease, or other contaminants.
2. Ensure that the gasket is correct for the application. Some gaskets are designed only for water service, while others are made for petroleum service—and still others are made from materials specially formulated for more specific applications.
3. Apply a thin layer of lubricant to the sealing lips and exterior of the gasket.
4. Place the gasket over one end of one pipe, leaving the pipe end exposed.
5. Align and abut the two pipes to be joined and center the gasket between the grooves of the pipes to be joined.
6. Place the coupling housing in position over the gasket, ensuring that the coupling keys—the long outer edges—are engaged in the grooves.
7. Insert bolts and nuts, making them hand-tight.
8. Tighten the nuts, alternating frequently to ensure that pressure is evenly distributed over the gasket.

Notably, these couplings can be oriented at any angle around the joint. By rotating the coupling around the pipe, installers can tighten nuts and bolts wherever it’s most convenient. Flanged couplings can’t offer this simplicity: the bolt holes on each flange must align perfectly, restricting the number of possible angles.

Grooved couplings offer additional time savings in inspection, maintenance, and error reduction

Ease of installation may be the single-most-important contributor to grooved couplings’ low installation times. However, they also reduce labor hours in less obvious ways. Many grooved systems can be visually inspected after installation: to confirm that they’re properly tightened, installers can simply look at the bolt pads. If the two halves of the metal housing make contact, the mechanical coupling has been properly secured. This contrasts with welds—which may require x-ray inspections or ultrasonic testing—and flanged joints, which can’t be checked without filling and pressurizing the piping system.

The same mechanism that makes grooved couplings so easy to install also facilitates their quick removal during maintenance operations. To detach a section of pipe for replacement—or remove system components for repair—maintenance technicians only need to drain the system and undo the two bolts holding the housing together.

And while all types of piping joints require proper training and expertise to install, the simplicity of grooved couplings reduces the specialized knowledge needed—and decreases the margin for error with it. The American Society of Civil Engineers’ list of installation pitfalls for flanged joints underscores this point. Misalignment, flawed bolt-tightening practices, errors in bolt selection, and other issues can turn a sound design into flawed execution in flanged piping systems. That compares poorly with most grooved couplings, which are easy to realign and simply won’t fully tighten if they’re not properly seated.

Grooved fittings make rapid installation possible

For any consumer in any industry, most purchases involve choices between cost and quality—but grooved couplings are the rare example of a product that’s easier to use, cheaper to install, and just as effective as the alternatives. If you’re looking for a better way to join pipes, valves, and fittings, take a look at our selection of grooved couplings.

Available in sizes from 1/4″ to 8″, each coupling features a ductile iron body conforming to ASTM A536 Grade 65-42-12 and offers the strength and straight lays typical of welded or flanged joining methods. With a waterproof EPDM rubber seal, these UL-listed and FM-approved grooved couplings are suitable for installation in fire sprinkler systems, standpipe systems, and a wide variety of other piping systems.

Click here to view our selection of grooved pipe fittings, including grooved pipe couplings.

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