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Groove goes on for jointing

Mechanical grooved pipe joining has been proven through research, testing and extensive evaluation.

During its 85-year history, it has stood the test of time in some of the most impressive engineering feats including the Hoover Dam in the US, the Grand Arche de la Defence in France, the Alexandria Library in Egypt and the Burj Al Arab Hotel in Dubai.

For engineers, the benefits of the grooved system are many. The design versatility of the joint allows rigidity and flexibility throughout a system; a mechanical joint provides noise and vibration attenuation, seismic relief, and accommodates thermal expansion and contraction. The system also provides a union at every joint for ease of system maintenance and expansion.

The most common preparation method used today in mechanical piping systems is cold forming a roll groove onto the end of the pipe. Roll grooving was invented in the 1950s and is used on 90 per cent of grooving applications. Fast and clean, it is used on a wide variety of pipe sizes and standard wall thicknesses.

Roll grooving can be used on carbon steel, stainless steel, copper and aluminium pipe or tubing as well as PVC pipe. Most coupling manufacturers provide roll-grooving equipment based on customers’ requirements.

The latest development in grooving technology is the Advanced Groove System (AGS) for medium- to large-diameter pipes between 350 mm and 1,524 mm. AGS offers enhanced strength and reliability through a more robust coupling housing and a patented wedge-shaped roll groove, which results in a 40 per cent increase in end-load carrying capabilities compared with previous joining methods.

A question that is often asked regarding a grooved joint concerns the reliability of the groove under stress.

When examining the stress on pipes created by internal pressure and the typical ‘overstress’ failure mode, the cut groove has proved not to be the weakest link. Under pressure, two basic stresses occur: longitudinal and hoop. Longitudinal stress is often described as ‘tensile’ stress in material, the force pushing the pipe apart in the axial direction.

A failure due to longitudinal stress would cause a circumferential fracture around a pipe. Hoop stress can be described as ballooning or expansion of a pipe diameter in a radial manner. A failure due to hoop stress would cause the pipe to split lengthwise along its axis.

With pipe that is roll grooved, any potential increase in pipe hardness, reduction in tensile strength or reduction in elongation has no effect on the integrity of the joint. Pipe material changes are comparable to any other cold-forming manufacturing operations.

Fred Matyiku is regional director - Northern Europe at Victaulic