by Bill Lowar, Victaulic
May 24, 2012

How pipe-joining methods affect system operation

 

Equipment—such as pumps and chillers—is increasingly being designed with grooved inlets and outlets. Although the standard has been flanged in the past, manufacturers are recognizing the benefits of grooved pipe joining, not just for pre-sale equipment testing, but also for the performance and maintenance benefits that end users will realize. The grooved-pipe-joining method is a good choice for equipment connections and for utility and process piping systems within commercial and industrial facilities.

 

Grooved Basics

Grooved pipe joining employs a mechanical coupling—consisting of housings, an elastomeric gasket and nuts and bolts—to join grooved-end pipe, valves, fittings, equipment and accessories. 

The pipe groove is made by cold forming (roll grooving) or machining (cut grooving) a groove into the ends of a pipe. To assemble the joint, two grooved pipe ends—or a pipe end and a valve or fitting, etc.—are abutted. The gasket is positioned around the joint. The housings are placed over the gasket, and finally, the bolts and nuts are tightened to secure the housings together. In the installed state, the coupling housings encase the gasket and engage the grooves around the circumference of the pipe to create a leak-tight seal in a self-restrained pipe joint.

Rigid couplings provide a mechanical and frictional interlock onto the pipe ends sufficient to result in a rigid joint with characteristics similar to those of welded or flanged joints, because all the piping remains in strict alignment and is not subject to deflection during operation. Flexible couplings permit controlled linear and angular movement, which can accommodate thermal expansion and contraction, deflection, seismic movement and vibration. 

 

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The anatomy of grooved pipe joining

 

Quick Installation

When testing equipment, manufacturers need a joining method capable of connecting the unit to a test loop that is quick but secure. Grooved couplings enable the quick connection of equipment to run these tests. With just two bolts to secure each coupling—as opposed to the multiple bolts that are required for each flange—manufacturers can rapidly assemble the product and test it before it is sold to a client. With fewer bolts and typically no torque requirements, grooved piping is up to six times faster to install than flanging. This time savings is also beneficial when connecting the equipment and associated piping systems at the end user’s facility. 

Once connected, many grooved systems are designed for visual inspection to ensure complete assembly. The joint is properly installed when the bolt pads meet metal-to-metal. Flanges, on the other hand, do not provide visual confirmation. The only measure to ensure proper assembly is to fill and pressurize the system and check for leaks.

 

Ease of Maintenance

The same characteristics of grooved systems that speed installation—fewer bolts and no torque requirements—also make system maintenance a quick task. To gain access to a pump or valve, for example, the two bolts of the coupling are loosened, and the housings and gasket are removed from the joint. In a flanged system, multiple bolts need to be removed. The same time-consuming bolt-tightening sequence required upon initial installation is also required upon reassembly of the flange.

Throughout the life of the system, flanging requires significant maintenance to sustain joint integrity. Pumps and other equipment frequently vibrate and are subject to noise in the piping system. For example, oscillatory forces can be generated due to the lack of balance of rotating components, such as in pump vanes. Although field balancing can reduce this, it requires specialized equipment, which can become difficult, expensive and impractical.

 

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Piping connected to a pump using the grooved-pipe method

 

Flanged systems employ rubber bellows or braided flexible hoses to accommodate vibration. With time or overextension, these products can wear or fail, requiring replacement. 

 

Vibration Dampening

Grooved couplings accommodate vibration without the need for specialty products that require periodic repair or replacement. The resilient elastomeric gasket contained within both flexible and rigid couplings aids in the dampening of noise and vibration. The design of the coupling enables the gasket to seal against the pipe, while the housing provides both space for the elastomeric material to flex and containment to prevent overstretching. 

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