Ideal Pipe Joining [Mar 2012]

March 22, 2012 5:52 am

During the World War I, mechanical pipe joining was invented by the company now known as Victaulic. Since being made commercially available in 1925, it has become a preferred joining method on many piping applications.  Yet many myths and misunderstandings still exist.  In this article, Pankaj Soni, Victaulic Country Manager – India assesses the technology and its durability
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 United States, and the All England Lawn Tennis Club centre court at Wimbledon, where the state-of-the-art retractable roof over the centre court used grooved technology for the heating and chilled water piping systems in the first project of its type in the world.
Recent work in India, where Victaulic has been operating for nearly five years, includes the fashionable Park Hotel Hyderabad, the Delhi Airport Metro Express, Mumbai Airport and the ICC Marriott in Pune.
Grooved mechanical pipe joining provides an attractive alternative to welding and flanging for engineers, owners and OEMs.  It allows quick, easy, safe installation and maintenance to meet compressed project schedules and reduce labour costs, along with maximum operating efficiency and built-in sustainability.  Above all, the benefits combine to give a lower total installed cost over the life of the system. 
For these reasons more and more OEMs are beginning to manufacture products with grooved ends, as they realise the considerable advantages this gives their own equipment.
For instance, manufacturers of pumps and other related types of equipment have come to realise the advantages of grooved technology, and many now offer a grooved outlet as a standard option. Not only does it make for easier product testing in the factory, but manufacturers know that having a grooved connection reduces the likelihood of additional forces on the equipment that could damage it.
The groove in actionMechanical pipe joining systems comprise of bolted couplings and a gasket seal which engage into grooved pipe without the need for hotworks. Whilst the technique may be relatively new in India, elsewhere this is not the case. Victaulic invented the system over 85 years ago and has continuously made pipe joining faster, easier and more economical with its unflagging focus on quality, research and development, and product innovation.
In addition to increasing installation speed, reducing the need for hotworks brings greater onsite safety, slashing risks, delays and the need for catch up, and also cutting energy consumption and harmful onsite emissions. Victaulic products are manufactured from 90 per cent recycled parts and install rapidly using only hand tools, whilst mechanical couplings enable more convenient maintenance, greater efficiency and lower operational energy requirements.    
The grooved system delivers numerous benefits – the system provides a union at every joint for ease of system maintenance and expansion – plus enhanced design versatility of the joint allows rigidity and flexibility throughout a system. A mechanical joint also provides noise and vibration attenuation, seismic relief, and accommodates thermal expansion and contraction.
A mechanical joint consists of four elements in total: grooved pipe, the coupling housings, a pair of nuts and bolts and the rubber gasket ring. This gasket is pressure responsive and is encased by the coupling housing when it engages in the groove around the circumference of the pipe. The gasket then creates a seal unified joint that is enhanced when the system is pressurised.
The flexibility of Victaulic flexible grooved-pipe couplings reduces the transmission of stresses through a piping system, while the gasket damps vibration. When flexibility is not desired, rigid couplings can be used. Both flexible and rigid couplings provide discontinuity at each joint, which helps minimise pipeline stresses.
Roll grooving The preparation method most commonly used today in mechanical piping systems is cold forming a roll groove onto the end of a pipe.
This method – known as roll grooving – was invented by Victaulic in the 1950s and is used on 90 per cent of grooving applications. Fast and clean, it is suitable for a wide variety of pipe sizes and standard wall thicknesses. Roll grooving is suitable for carbon steel, stainless steel, copper and aluminium pipe or tubing.
The latest development in grooving technology for medium to large-diameter pipes is the Advanced Groove System (AGS) from Victaulic. Suitable for sizes between 350mm and 1525mm (14 – 60”), AGS offers enhanced strength and reliability through a more robust coupling housing and a patented wedge-shaped roll groove, which results in a 40 percent increase in end-load carrying capabilities compared with previous joining methods.
Does grooving weaken the pipe end? Grooved system behaviour is very similar to welded or flanged systems, with all piping remaining in strict alignment and not subject to deflections during operation. This makes grooved systems ideal for use with pumps and valves, or where rigid pipe runs are critical. In addition, the availability of flexible mechanical couplings in the Victaulic product line provide a natural solution to noise and vibration attenuation, removing the need for additional flexible connections around pump sets.
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. When under pressure, two basic stresses occur: longitudinal and hoop. Longitudinal stress is often described as ‘tensile’ stress in material, the force pushing 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.
Flow dynamicsThe inside protrusion of a roll groove is small and smooth at its entry and exit and has been proven to have negligible effect on both flow and or line pressure. Published ratings take into account the groove and, through testing on the performance of a joint, pressure ratings with a three to one safety factor are evaluated. Recent flow testing was conducted on joints grooved with Victaulic roll grooving tools, and these tests confirmed excellent flow characteristics, with an insignificant contribution to system pressure loss. In fact, the amount was negligible in comparison with more common points of flow loss, such as pipe friction, valves, bends and branches.
Victaulic in-house testing on grooved and plain end pipe using 104.8mm Type “K” copper tubing and 50mm and 200mm Schedule 10 and Schedule 40 carbon steel pipe saw pressure drops measured with velocities between 4-20 metres per second at ambient water temperature.
The results proved that pressure loss was negligible. These findings are also supported through rigorous independent testing by Factory Mutual Research Corporation, further attesting to the low flow loss characteristics of grooved joints.
Proven reliabilityWhen it comes to specifying systems, reliability is a top priority for engineers. Mechanical grooved pipe joining has been a reliable and rugged component of a wide range of mission-critical applications, including data centres and flammable chemical cleaning.  It has also met the rigorous system demands required for high pressure performance in power applications and in hydraulic elevators.
The method has not only stood the test of time but has been used in some of the most innovative engineering projects in recent years, among them the Alexandria Library in Egypt and the Burj Khalifa in Dubai. Grooved systems are verified by independent approval agencies worldwide including Factory Mutual Approvals (FM), Lloyd’s Register of Shipping, Loss Prevention Certification Board Ltd. (LPCB), Underwriters Laboratories Inc. (UL), American Society of Mechanical Engineers (ASME), and many more. These are the same agencies that recognise welded, flanged and threaded systems.
Confidence in grooved mechanical piping systems comes from more than 85 years of research and development, exhaustive field observations, and extensive independent and manufacturer testing. Correctly used and installed, the products are safe and effective.
Engineers can be assured that grooved technology has been robustly tested in the laboratory as well as in the field to demonstrate its consistent strength and reliability. Details about the grooving process, the strength of grooved pipe, and flow characteristics are further explained in published reports from independent agencies as well as by manufacturers like Victaulic.For more information, visit: www.victaulic.com
 Country Manager for India with Victaulic, the world leader in mechanical pipe joining systems, Pankaj Soni is 41-years-old and has worked for a wide range of respected international engineering firms. Pankaj holds both a BE in Mechanical Engineering and an MBA, and has more than 18-years of professional industry experience.