TPi September 2014

Unlike a flange that puts variable stress on the gasket and nuts and bolts, a coupling holds the gasket in precise compression from the outside of the pipe joint. Additionally, coupling gaskets do not need to be replaced on a regular maintenance schedule, while flange gaskets need to be replaced when the system is disassembled for maintenance. Better vibrations Over the life of a system, flanging can require quite a bit more work to maintain joint integrity. Pumps and other equipment frequently create vibration and noise in a piping system. For example, oscillatory forces can be generated due to the lack of balance of rotating components such as from pump vanes. Although field balancing can reduce this, it requires specialised equipment, which can become difficult, expensive and impractical. System vibration and other forces can lead to joint problems in a flanged system. Flanging employs a series of bolts and nuts to compress a gasket between two flat-faced, flanged pipe ends. The torque on the bolts employs a high compressive load on the internal gasket, which can cause the gasket to adhere to one or both of the flanges. When the joint is disassembled, the gasket can tear, resulting in failure upon reinstallation if not replaced. In order to accommodate system vibration and reduce noise, flanged systems employ specialised and expensive rubber bellows or braided flexible hoses to accommodate this vibration.

The mechanical grooved joint is comprised of four elements: grooved pipe, gasket, coupling housings, and nuts and bolts

These time savings increase with larger diameter piping systems. For example, a 900mm (36") flange joint on standard wall (9.7mm, or 3 / 8 ") carbon steel pipe would require 32 nuts and bolts and around 10 man-hours to complete, but only four nuts and bolts and around two hours with a grooved coupling. In addition, flanges require time-consuming star pattern tightening with specialised wrenches to measure and ensure that correct torque ratings are achieved. Grooved technology allows couplings to be assembled by simple hand tools, and the joint is properly installed once bolt pads of the coupling housings meet metal-to-metal. Victaulic grooved systems are designed for visual inspection to ensure complete assembly. When the bolt pads are metal- to-metal this indicates a properly installed coupling. Flanges, on the other hand, do not provide visual confirmation, and the only measure to ensure proper assembly is to fill and pressurise the system and check for leaks. Maintainability The same characteristics of grooved systems that accelerate installation – fewer bolts and no torque requirements – also make system maintenance a quick and simple task. When piping needs to be moved, rotated, changed or added, the two or four bolts of a coupling make these maintenance tasks much more efficient than a flange, which can have up to eight times as many bolts. 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. Couplings eliminate a lot of the regular maintenance associated with flanges, decreasing maintenance downtime, because they do not require regular retightening.

Mechanical couplings are quick and easy to install, and are flexible and strong

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Tube Products International September 2014

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