In the Groove

Coupling options and quick installation give grooved pipe a flexible advantage for many projects.
In the Groove
Sections of grooved pipe are joined with a coupling system. A gasket is positioned between two abutted pipe ends, then enclosed in the coupling housing, the key sections of which engage the grooves. The bolts and nuts are tightened with a socket wrench or impact wrench, which holds the housing segments together.

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Unpredictable conditions can make the outdoor installation of pipework more difficult than in enclosed construction sites. Grooved piping systems offer advantages in laying pipework that can make them a superior choice over other joining techniques, and as a result, are increasingly being selected for the transport of water in municipal and hydroelectric applications.

The challenges of outdoor pipe installation

Installing piping systems outdoors can create numerous challenges, mainly weather and site conditions. Inclement weather, difficult or uneven terrain, ground swell and landslides can create a variety of problems for installation crews, which engineers should account for when specifying the pipe-joining method.

Both wet and dry weather extremes can affect welding activities. In dry conditions, particularly when the risk of forest or brush fires is high, welding may be limited or even prohibited. In wet or cold conditions, welding can suffer from delays because the pipes may need to be covered and/or preheated before work can begin.

Weather conditions may be unpredictable, but site conditions are predictable and should be factored into the system design. Welding on steep or rough terrain is difficult, and the quality of work could suffer as a result. In some situations, access to basic amenities can also be an issue, and power generation equipment may need to be brought in.

When designing a water transport piping system, there are a lot of details to take into consideration, some predictable, some unpredictable, and attention to these factors can affect project schedule and cost.

Solving environmental challenges

Grooved mechanical piping systems help alleviate many of the environmental issues, as well as the disadvantages associated with welding or flanging piping systems.

A grooved mechanical joint consists of four elements: grooved pipe, gasket, coupling housing, and bolts and nuts. The pipe groove is made by cold forming or machining a groove into a pipe-end. A gasket is positioned between two abutted pipe-ends, then enclosed in the coupling housing, the key sections of which engage the grooves. The bolts and nuts are tightened with a socket wrench or impact wrench, which holds the housing segments together. In the installed state, the coupling housing encases the gasket and engages the groove around the circumference of the pipe to create a leak-tight seal in a self-restrained pipe joint. Only the gasket is exposed to the media inside the pipeline.

Two-piece mechanical couplings are available in sizes up to 60 inches in diameter, and are offered in a rigid or flexible style. The rigid style forms a completely rigid pipe joint similar to that of a welded joint, whereas the flexible style allows limited linear and angular movement to accommodate expansion, contraction, deflection, seismic movement and settling.

Unlike welding, which requires dry pipe, grooved couplings are ideal for outdoor, remote use because they can be assembled in any weather condition without the need for power tools. Installation is as simple as aligning the pipe ends, positioning the gasket and coupling housing segments on the joint, and tightening the nuts and bolts. Once installed, many grooved couplings offer visual confirmation of proper installation, eliminating the need for X-ray testing.

A typical large-diameter joint will require several hours to weld, while a grooved mechanical coupling can be installed in less than an hour. In fact, joining pipe with grooved couplings is up to six times faster than welding and three times faster than flanging. In harsh climatic conditions, the difference is even more dramatic.

The speed and simplicity of installation dramatically cuts labor time, resulting in reduced total costs. Reduced labor and added flexibility with work crews significantly impacts installation time on projects. There are also indirect cost savings associated with grooved piping, including the elimination or reduction of rework, X-ray/non-destructive testing, purge gases, generators, and excavation required for welding. Additionally, the faster the job is completed, the less money that is needed for on-site insurance, equipment rentals and other indirect costs.

A trench carrying a flanged or welded pipe must be nearly twice the width of a trench carrying a grooved line, so the use of grooved technology can reduce a project’s environmental impact. At a recent penstock installation in British Columbia, the use of a grooved system successfully narrowed the piping trench from 42.5 feet to 19.5 feet for the 2.5-mile length of the line.

Grooved mechanical piping systems are flame-free assemblies, which reduces the risk of fire as well as other hazards during installation, and also eliminates any work stoppages due to weather or environmental conditions.

Design advantages

With a union at every joint and 360 degrees of rotational movement, grooved piping systems provide optimal field flexibility and are easily adjusted as needed.

Pipe misalignments during installation are easier to resolve as angles can be changed with less difficulty, and with their deflection capabilities, flexible couplings can accommodate for minor misalignments. For major misalignments, pipe sections can be added to or removed from a grooved system in the field much faster than adding or removing pipe from a welded or flanged system.

Maintenance is also simpler with grooved joints, which can be disassembled and reassembled quickly. A coupling can be removed by loosening the nuts and removing the housing segments and gasket — a process that takes just a few minutes. Once the maintenance is complete, the coupling can be reassembled on the pipe at the same speed as initial installation. No new parts are required. This characteristic also simplifies system modification and expansion.

Welding converts individual pipe sections into a single unit, making it difficult to access a specific point in the system. If not accessing a welded system at a union, the pipe would need to be cut to provide access. Although flanges provide system access, maintenance can be time consuming because each of the bolts needs to be loosened and removed, and in some cases, the gasket needs to be scraped off and replaced following completion of the work. Re-assembly requires the same star-pattern tightening sequence as initial installation.

Grooved piping systems are a good option for a variety of water transport applications, but they may not be appropriate for all circumstances. Grooved mechanical couplings, like all joining methods and materials, have limitations. These limitations include excessively high and low temperature extremes, excessively high pressures and chemical compatibility with various chemical services. It is recommended to consult the manufacturer’s website, technical support or published literature when questions arise about specific services and product performance.

Many benefits

There is potential for significant financial savings when using mechanical grooved piping systems. Faster field installation, elimination of hotworks and reduced need for expansion joints are all advantages that are particularly important when choosing a pipe-joining method for cost-conscious projects.

Choosing a grooved piping system is an attractive option for owners, engineers and system designers alike in a sector where margins are increasingly tight.

About the Author

Steve Morrison is Global Water Systems Technology Market Manager with Victaulic, a leading producer of mechanical pipe-joining systems. For more information, visit www.victaulic.com.



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