Grooved pipe couplings are some of the most important equipment in fire protection, allowing quick and water-tight connections without pipe threads, flanges, or welding. Instead, installers simply butt the ends of pipes together and seal them with a gasket and clamp.
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But there are also two kinds of grooved couplings that serve different purposes. Rigid grooved couplings don&#;t allow much movement and serve as a standard pipe joint. But for situations where some give is needed&#;specifically, seismic protection of fire sprinkler systems&#;flexible grooved couplings are the solution.
This article reviews the basics of grooved pipe couplings and details the differences between a rigid and flexible coupling. We also explain when and how NFPA 13: Standard for the Installation of Fire Sprinkler Systems ( edition) requires using flexible couplings for seismic protection.
Shop our selection of rigid grooved couplings and other fittings for your pipe-joining needs. Looking for flexible couplings? Contact QRFS today for a quote or to place a special order.
Grooved couplings are the fastest way to join pipes. And the technology is simple. Earnest Tribe, the founder of Victaulic, patented the grooved pipe joint in after developing the tech to meet wartime needs. Grooved couplings avoid the need for welding or other joint types. Instead, they use three components: 1) pipe with grooved ends, 2) synthetic rubber gaskets, and 3) c-shaped clamps.
To form a joint, installers butt two pipes with grooves cut in the ends together. A lubricated gasket slips over the pipe ends so that it overlaps the joint. And a c-shaped clamp or housing fits into the grooves of the pipe, compressing and stabilizing the gasket. This video from Victaulic shows how the joints are made:
But as we mentioned, there are two kinds of grooved joints. So, what&#;s the difference between a rigid and flexible coupling?
From the outside, you can&#;t look at a grooved coupling and know whether it&#;s rigid or flexible; they look the same. The difference is on the inside of the joint in the way that the gasket, groove, and clamp fit together. A rigid clamp permits next to no separation, rotation, or angular movement. But a flexible coupling permits some movement and space without compromising the seal or damaging the pipe. NFPA 13 officially describes how much flexibility is allowed:
3.3.83 Flexible Coupling. A listed coupling or fitting that allows axial displacement, rotation, and at least 1 degree of angular movement of the pipe without inducing harm on the pipe. For pipe diameters of 8 in. (200 mm) and larger, the angular movement is permitted to be less than 1 degree but not less than 0.5 degree.
Key to this definition is the term &#;listed.&#; A testing laboratory such as UL or FM Global must verify that a flexible grooved fitting meets specific flexibility, seal, and strength requirements before it can be used in a fire sprinkler system.
This diagram from Bentley Communities helps illustrate the physical difference between the two types of joints:
Almost all grooved couplings use rigid joints because rigid, unmoving joints are desired for most situations. But flexible couplings, while less common, do play essential roles in seismic protection for fire sprinkler systems that require an earthquake-resistant design.
Some fire sprinkler systems require design measures to protect them from earthquake damage. In our overview of the principles of seismic protection, we explain the two basic techniques for protecting pipes from damage: adding rigidity and adding flexibility. Rigidity, in the form of seismic bracing, ensures that pipe moves with a building in an earthquake instead of shaking violently and breaking loose.
Flexibility, on the other hand, prevents damage to pipes caused by differential movement. When an earthquake&#;s powerful p-waves shake a building, the whole structure can move&#;but not always all at the same time. For example, the ground floor moves first in tall buildings, and the top floors lag behind. This wave-like motion that resembles a slinky is called &#;story displacement.&#; And the differential movement it causes in various onsite equipment can snap fire sprinkler pipes.
The solution to this problem is flexibility, which designers can achieve with flexible grooved couplings. The modest &#;give&#; allowed by these devices can prevent pipes from being damaged in an earthquake.
NFPA 13 requires grooved flexible couplings for pipes that are 2 ½&#; or larger (Section 18.2.1) in certain buildings that fall into specific design categories (SDC). And because story displacement significantly affects risers, most of these rules involve risers (18.2.3.1):
Flexible couplings are also required at horizontal tie-ins to the riser (18.2.3.2) and the connection of drop-pipes (18.2.4).
Flexible couplings allow flexibility when two structures move independently. But don&#;t forget that bracing, which ensures pipe moves with a building, is the other core technique of seismic design. Flexible couplings can work against this objective by reducing rigidity. So, to compensate, NFPA 13 says that flexible couplings should only coincide with structural separations (18.2.2). And where they are used outside the explicit instructions, extra sway braces are needed (18.2.3).
In our previous blogs, you can learn more about the principles of sway bracing and how cable sway braces work.
Flexible couplings can also be used to construct seismic separation assemblies. These pipe assemblies are used where horizontal pipe must cross an engineered gap, called a seismic joint, between two structures.
The &#;structures&#; can be two independent buildings or two freestanding wings of the same building. When a pipe crosses a gap like this, NFPA 13 requires seismic separation assemblies (18.3.1) to keep it from breaking when the two structures move during an earthquake.
There are two ways to build a seismic separation assembly (18.3.2). One approach uses flexible pipe arranged in a u-bend. The other involves a zig-zag pattern of flexible grooved elbows. Either way, the assembly should accommodate a wide range of motion in three directions: the complete closing of the gap between the structures, a doubling of the gap, or lateral movement equal to the size of the gap.
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You need a stiff joint for the vast majority of sprinkler pipe connections. That&#;s why most grooved pipe joints use rigid couplings. But sometimes, flexibility is necessary for seismic design, and the extra range of motion provided by flexible couplings can prevent earthquake damage.
Be sure to check your local codes, including whether a building falls within a seismic design category (SDC) that requires special equipment to keep fire protection systems safe. A qualified system designer must make this determination. Regardless of what you need, QRFS can provide:
If you have questions or need help finding the part you need, call us at (888) 361- or .
This blog was originally posted at blog.qrfs.com. If this article helped you, check us out at Facebook.com/QuickResponseFireSupply or on Twitter @QuickResponseFS.
Posted on September 23,
Grooved mechanical coupling systems are the most versatile, economical, and reliable grooved pipe joining system available today. Benefits of grooved pipe connectors to contractors include safer job sites, reduced total installed costs, and ease and speed of installation.
A grooved pipe joint consists of four elements
A pipe groove can either be cold formed or machine formed. A gasket encompassed by the coupling housing is wrapped around the two pipe ends, and the coupling housing key sections engage the grooves. The pipe coupling&#;s bolts and nuts are tightened with a socket wrench or impact wrench. In the installed state, the mechanical pipe coupling housing encases the gasket and engages the grooves around the circumference of the pipe to create a leak-tight seal in a self-restrained pipe joint.
Grooved pipe couplings can employ one of two basic styles: flexible or rigid. There are benefits to both styles. To read more on the differences between flexible and rigid grooved pipe couplings and when to use them, check out this blog post.
Not only do benefits of grooved pipe couplings include being fast and easy to install, but it&#;s also safer than any other pipe joining method. Grooved mechanical coupling systems are installed without the need for flame, eliminating the fire hazards typically associated with welding/brazing or soldering. Welding is one of the most dangerous industrial activities; its hazards include fire risk, electric shock, compressed gases, and toxic fumes. As such, welding requires personal protection for the eyes, hands, feet, and body. Welding activities also require a fire watch during and following the work, which can slow the construction schedule and increase costs.
The safety of installers on the job site is of the utmost importance; however, it becomes even more critical during expansion and/or retrofit projects where buildings such as hospitals and schools may remain open and operational during construction. The benefits of grooved mechanical couplings can decrease the risks to workers and in the projects mentioned above, building tenants. The grooved pipe joining method is the hands-down winner in a side-by-side safety comparison to welding, one of the most dangerous industrial activities.
When accommodating thermal expansion and contraction in a piping system, the grooved pipe joining method conforms to industry practices. Simultaneously, it provides design flexibility, reduces stress on the mechanical piping system and provides a more compact, easy-to-inspect, and productive method of installation over other pipe joining methods.
Grooved mechanical couplings allow for movement of the pipe due to the design of their components. The dimensions of the pipe coupling housing key are narrower than the pipe groove allowing room for the pipe coupling housing key to move in the pipe groove. Additionally, the width of the pipe coupling housing allows for pipe end separation which in turn allows the grooved pipe joint to accommodate linear and angular movement. The mechanical coupling provides a self-restrained joint, and the unique pressure-responsive design of the pipe connector enables positive sealing even under deflection and linear pipe movement.
In retrofit projects, avoiding disruption to building occupants while minimizing cost overruns associated with night and weekend work can be a challenge. Grooved mechanical pipe joining systems can address these issues as a reliable alternative to welding and flanging. The widely-accepted flame-free technology is fast and easy to install and maintain, providing compatibility between new system design and existing systems.
In many cases, existing piping systems can be rerouted and kept in operation while work is performed on old systems or while new systems are installed. The grooved system eliminates the need for complete system shutdowns because there is no need to drain and dry the system, and an arc or flame is not required to disassemble or reassemble the joint. As a result, buildings can return to full operating capacity very quickly. The benefits of grooved in this situation are simple: avoid downtime. To access a piping system joined with grooved components, a worker simply disassembles two couplings to drop out a pipe section. To complete the job, the grooved couplings are easily placed back on the pipe, and the nuts are tightened.
Although there might be a higher upfront materials cost than with welding, the benefits of grooved are found in the reduction of labor time and labor costs. Based on the elimination of welding, and the need for highly skilled and relatively expensive labor, the assembly of mechanical coupling systems reduces labor man-hours as well as the labor rate. This contributes to an overall reduction in piping system costs, known as total installed costs. Victaulic estimates that jobs requiring welding applications demand up to 45 percent more man-hours on average over grooved piping solutions, and at a much higher labor rate.
Grooved mechanical piping is inherently faster to install than any other pipe joining method because the gasket and coupling housings simply need to be positioned onto the grooved pipe ends. The bolts and nuts are tightened with standard hand tools. Following installation, most grooved systems can be visually inspected. Metal-to-metal bolt pad contact confirms that the pipe coupling has been properly installed and secured into place. Welding, on the other hand, often requires X-ray inspections to ensure a sound joint. The benefits of grooved pipe couplings are demonstrated in the ease and speed of installation savings. Victaulic&#;s Installation-Ready&#; mechanical pipe couplings can be installed up to ten times faster than welding and six times faster than flanging.
It&#;s easy to see the benefits of grooved piping systems and how it is quickly becoming the standard on commercial building job sites. With the ability to improve job site safety, speed and simplify installation, reduce total installed costs, and ease maintenance and expansion, grooved mechanical piping will long hold a place in contractors&#; toolkits. When you add the engineering benefits to the mix&#;design versatility; accommodation of thermal expansion and contraction, deflection and seismic movement; and noise and vibration attenuation&#;grooved piping is in a class of its own.
Check out some of our case studies to see the benefits of grooved in action.
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