Didier Vassal, Vice President of OEM and Marine Services at Victaulic, compares flanged and grooved pipe connection methods and explains the advantages of grooved pipe fittings over flanges.Efficient piping systems are essential for the range of services required on board, including secondary systems such as bilge and ballast systems, seawater and freshwater cooling, lubricating oils, fire protection and deck cleaning.For these systems, where the pipe grade allows, an effective alternative to welding/flanging is the use of slotted mechanical joints that offer a range of technical, economic and practical advantages.These include enhanced performance; faster, simpler installation and maintenance and reduced onboard weight.Performance Issues In flanged fittings, two mating flanges are bolted together and compress gaskets to create a seal.Because the bolts and nuts of flanged joints absorb and compensate for system forces, they can stretch and lose their original tightness over time due to pressure fluctuations, system operating pressure, vibration, and thermal expansion and contraction.When these bolts experience torque relaxation, the gasket will lose its compression seal, which can lead to varying degrees of leakage.Depending on the location and function of the piping system, leaks can be costly and dangerous, leading to maintenance/repair downtime and risk.The gasket will need to be replaced when the joint is disassembled because over time the gasket will bond to the flange face.When disassembling the fitting, the gaskets need to be scraped off both flange faces, and these surfaces need to be cleaned before replacing the gaskets, again increasing maintenance downtime.Flange gaskets also experience compressive “deformation” over time due to bolting forces and system expansion and contraction, which is another cause of leaks.The design of grooved mechanical fittings overcomes these performance issues.A groove is first formed in the pipe end, and the pipe connection is secured by a connector that accommodates a resilient pressure-responsive elastomer gasket.The coupling housing completely surrounds the gasket, strengthening the seal and holding it in place when the coupling is engaged and creating a positive interlock in the tube groove.The latest joining technology allows pipes up to 24″ (600mm) diameter to be fully assembled with just two nuts and bolts to secure self-restraining joints.The mechanical joint creates a triple seal due to the design relationship between the pipe, gasket, and housing, which is enhanced when the system is pressurized.Rigid and Flexible Couplings Available in rigid and flexible, slotted mechanical couplings are Class Society Type Approved and can be used in place of the weld/flange method in 30 systems subject to installation standards established by each certifying agency.For example, use rigid couplings around areas like manifolds and valves, which are easier to access and replace than flanges.Depending on the nature of their design, rigid couplings also provide comparable axial and radial stiffness to flanged or welded joints.In addition to pipe movement due to thermal expansion or vibration, flexible couplings have advantages in applications where relative movement between the pipe and support structure is expected.Expansion and contraction can put pressure on flanges and pipes, damaging gaskets over time.When this happens, the joint is at risk of leaking.Slotted flexible couplings can accommodate pipe displacement in the form of axial movement or angular deflection.For this reason, they are ideal for installing long pipes, especially between blocks in the open sea where flanges can loosen over time, leading to the risk of leaks and pipe separation.Rigid and flexible couplings also offer the benefit of noise and vibration damping, eliminating the need for specialized noise-reducing components and perishable rubber bellows or similar.The use of mechanically grooved piping systems can speed up and simplify installation and maintenance, and increase the efficiency of piping systems onboard.Ease of installation On initial installation, the bolt holes of the flange must be precisely aligned and then tightened to secure the joint.The bolt hole indexes on the equipment inlet and outlet must also be perfectly aligned with the flanges on the pipes to be connected to the equipment.Since the number of holes in the flange only determines one of many fixing positions, only the fitting or valve can be rotated to match the bolt holes.In addition, the other end of the flanged pipe must also be aligned with its mating flange, which further increases the difficulty of assembly and the risk of misalignment.Grooved piping systems do not have this problem, and allow for easier installation, with 360-degree rotation of piping and mating components.With no bolt hole pattern to line up, the coupling can be positioned anywhere around the joint.Couplings can be rotated around the pipe to facilitate bolting and simplify access to equipment.In addition to eliminating misalignment during installation, the coupling’s 360-degree orientation capability, along with its smaller profile compared to flanges, makes grooved system installations ideal for tight spaces.Additionally, installers can locate all assembly bolts on each joint in the same location for easy system inspection and maintenance.Flanges are about twice the outside diameter of the pipes they connect to.On average, a slotted coupling is half this size.The size advantage of the smaller design makes the groove system ideal for jobs where space is limited, such as deck and wall penetrations – a fact that was recognised back in the 1930s when Victaulic couplings were first used in British shipyards.Assembly Speed Grooved pipe can be installed much faster than flanged because the coupling has fewer bolts and torque requirements do not exceed 12” (300mm). Unlike flanges that must be welded to the pipe ends, grooved pipes The valve assembly does not require welding, which further reduces installation time and eliminates potential thermal damage to the valve, while also reducing safety risks by eliminating hot work. DIN 150 ballast installed with Victaulic grooved products A comparison of wire and traditional connection methods showed a 66% reduction in total installation time required (150.47 man-hours vs. 443.16 man-hours). Installation of 52 slip flanges and welded elbows and tees compared to 60 rigid couplings The time required shows the greatest difference in time. Couplings require only two bolts up to 24″ (600 mm) pipe size. By contrast, flanges require at least 20 sets of nuts and Bolts. In addition, flanges require time-consuming star tightening with a specialized wrench to measure and ensure the correct torque specification is achieved. Grooved tube technology allows the coupling to be assembled using standard hand tools, once the coupling housing is mated The bolt pads are in metal-to-metal contact and the joint fits correctly. A simple visual inspection confirms correct assembly. Flanges, on the other hand, provide no visual confirmation: the only way to ensure correct assembly is the filling and pressurization system, check Leak and retighten joints as needed. Serviceability The same properties of grooved piping systems that speed installation—fewer bolts and no torque requirements—also make system maintenance or retrofit a quick and easy task. For example, To gain access to the pump or valve, loosen the two bolts of the coupling and remove the housing and gasket from the joint. In a flanged system, multiple bolts need to be removed. When reassembling the flange, it is also required at the initial installation The same time-consuming bolt-tightening procedure is performed at the The shaft coupling holds the gasket in precise compression from outside the fitting. Additionally, since the coupling gasket is not subject to high compressive forces, regular maintenance is not required, whereas the flange gasket needs to be replaced when the system is disassembled for maintenance. To attenuate system noise and vibration, flanged systems require rubber bellows or braided hose. These components can fail due to overstretching and, under normal wear and tear, require replacement on average every 10 years, resulting in cost and system downtime time. However, mechanical grooved pipe joints can extend the life of the system. Their ability to accommodate system vibration reduces the risk of joint failure without the need for special products that require regular repair or replacement. Included in flexible and rigid couplings Elastomeric gaskets are extremely durable and can withstand enormous operating pressures and cyclic loads. The system can be repeatedly pressurized and depressurized without fatigue to the elastomer gasket. Weight relief valve assemblies are often constructed from flanged components. However, this The connection method can add unnecessary weight to the piping system. A 6The inch (150 mm) flanged valve assembly consists of a lug butterfly valve connected by a butt weld flange and eight bolts and nuts on each side of the valve and weighs approximately 85 pounds.A 6″ (150 mm) valve assembly uses a grooved end butterfly valve, grooved end pipe and two rigid couplings to connect the assembly and weighs approximately 35 lbs, 58% lighter than a flanged assembly.Therefore, grooved valve assemblies are an ideal replacement for the shipbuilding industry.The above installed DIN 150 ballast wire comparison shows a 30% weight reduction (2,164 lbs vs. 3,115 lbs) when Victaulic grooved products are used instead of traditional connection methods.52 nested flanges, bolt sets and washers compared to 60 rigid couplings are the main reason for the increased weight of the welded/flanged system.Weight savings by using slotted fittings instead of flanges can be achieved in a wide range of pipe sizes.The magnitude of the reduction depends on the pipe diameter and the type of fitting used.In tests using one Victaulic Style 77 coupling, the heaviest coupling in the series, to connect the pipe, the total installed weight of the grooved assembly was significantly reduced compared to two light-duty PN10 slip flanges.Weight loss records are as follows: 4” (100mm) – 67%; 12” (300mm) – 54%; 20” (500mm) – 60.5%. Use lighter weight flexible Type 75 or Rigid Type 07 couplings and/or Heavier flange types that can easily achieve 70% weight savings. For example, a 24″ (600 mm) flange set for the TG2 system weighs 507 lbs, but a similar assembly using Victaulic fittings weighs only 88 lbs. Shipyards using grooved couplings instead of flanges on selected systems have recorded weight savings of 12 tonnes on offshore support vessels and 44 tonnes on cruise ships. The economic benefits of slotting technology for ship owners are clear : Lighter weight means more cargo or passengers and less fuel consumption. It also makes handling of piping systems onboard easier. Due to fast installation, maintainability and light weight, Growing Trend grooved piping systems are much easier to handle than Its flanged piping system offers significant advantages. These features, combined with the added benefits of reliability, ease of alignment and reduced safety risks, have motivated shipowners, engineers and shipyards to choose grooved mechanical systems over flanges. This This growing trend to use grooved technology is supported by equipment suppliers such as heat exchangers, box coolers, and coolers, as well as valve and compressor manufacturers, many of which now offer grooved terminations for their products. The range of services using grooved fittings is steadily increasing. Building on successful applications in water systems, Victaulic continues its long history of innovation by developing and type-approved refractory gaskets for marine fuel service.
(Published in the April 2014 edition of Maritime Reporter & Engineering News – http://magazines.marinelink.com/Magazines/MaritimeReporter)
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Post time: Jan-15-2022
