Victaulic OEM and Marine Services Vice President Didier Vassal compared flange and grooved pipe joint methods and explained the advantages of grooved pipe joints over flanges. Efficient piping systems are essential for a range of services required on ships, including secondary systems such as bilge and ballast systems, sea and fresh water cooling, lubricating oil, fire protection and deck cleaning. For these systems, where the pipeline grade allows, an effective pipe connection alternative to welding/flanging is the use of slotted mechanical joints, which provide a series of technical, economic and practical advantages. These include enhanced performance; faster and simpler installation and maintenance and reduced weight on board. Performance issues In flanged pipe joints, two mating flanges are bolted together and the gasket is compressed to form a seal. As the bolts and nuts of the flange joint absorb and compensate the system force, over time, the bolts and nuts will stretch and lose their original tightness due to pressure fluctuations, system working 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 risks. The gasket needs to be replaced when disassembling the joint, because over time, the gasket will adhere to the flange surface. When disassembling the joint, the gaskets need to be scraped off the two flange surfaces, and these surfaces need to be cleaned before replacing the gaskets, again increasing maintenance downtime. Due to the bolt connection force and the expansion and contraction of the system, the flange gasket will also produce compression “deformation” over time, which is another cause of leakage. The design of slotted mechanical pipe joints overcomes these performance problems. First, a groove is formed at the end of the pipe, and the pipe connection is fixed by a joint, and an elastic, pressure-responsive elastomer gasket is installed in the joint. The coupling housing completely surrounds the gasket, strengthening the seal and holding it in place, because the coupling engages and forms a reliable interlock in the pipe groove. The latest coupling technology allows pipes up to 24 inches (600 mm) in diameter to be fully assembled with only two nuts and bolts to secure self-constraining joints. Due to the design relationship between pipes, gaskets, and housing, the mechanical joints form a triple seal. This relationship will be strengthened when the system is pressurized. Rigid and flexible joints are available in two forms: rigid and flexible. Groove mechanical pipe joints have passed the classification society type certification and can replace welding/flange connection methods in 30 systems, depending on the installation standards set by each certification body . For example, use rigid couplings around areas such as manifolds and valves, where they are easier to access and replace than flanges. Due to the nature of its design, rigid couplings also provide axial and radial stiffness comparable to flanges or welded joints. In addition to pipe movement caused by thermal expansion or vibration, flexible joints have advantages in applications where relative movement between the pipe and the supporting structure is expected. Expansion and contraction put pressure on flanges and pipes, which over time can damage the gasket. When this happens, there is a risk of leakage in the joints. The groove-type flexible coupling can adapt to pipe displacement in the form of axial movement or angular deflection. For this reason, they are very suitable for installing long pipelines, especially between blocks. The high seas can cause flanges to loosen over time, leading to the risk of leakage and pipeline separation. Rigid and flexible couplings also have the advantages of noise reduction and vibration reduction, without the need for special noise reduction components and perishable rubber bellows or similar items. The use of mechanical grooved piping systems can speed up and simplify installation and maintenance, and improve the efficiency of the ship’s piping system. Easy to install When installing for the first time, the bolt holes of the flange must be precisely aligned, and then tightened to fix 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 on the flange determines one of many fixed positions, only the fitting or valve can be rotated to match the bolt holes. In addition, the other end of the flange pipe must also be aligned with its mating flange, which further increases the difficulty of assembly and the risk of misalignment. The grooved piping system does not have this problem, and the installation is more convenient. The piping and mating parts can be rotated completely 360 degrees. There is no bolt hole pattern to align, and the coupling can be positioned anywhere around the joint. The coupling can be rotated around the pipe for easy access to the bolts and simplified access to the equipment. In addition to eliminating misalignment during installation, the 360-degree orientation function of the coupling and its smaller profile compared with flanges make the installation of the groove system very suitable for narrow spaces. In addition, the installer can position all the assembly bolts on each joint in the same position to facilitate system inspection and maintenance. The flanges are approximately twice the outer diameter of the pipe to which they are connected. On average, grooved joints are only half of this size. The size advantage of the smaller design makes the groove system ideal for space-constrained operations, such as deck and wall penetration-a fact that was recognized as early as the 1930s, when Victaulic joints were first used in British shipyards. Assembly speed Because the coupling has fewer bolts and does not have a torque requirement of up to 12” (300mm), grooved pipes can be installed much faster than flanges. Unlike flanges that must be welded to the pipe ends, grooved valve assemblies No welding is required, which further shortens installation time and eliminates potential thermal damage to the valve, while reducing safety risks by eliminating thermal processing. Comparison of DIN 150 ballast line installed with Victaulic grooved products and traditional connection methods Shows that the total installation time required has been reduced by 66% (150.47 man-hours and 443.16 man-hours). Compared with 60 rigid couplings, the time required to install 52 sliding sleeve flanges and welded elbows and tees shows The biggest time difference. The coupling requires only two bolts, and the pipe diameter can reach 24 inches (600 mm). In contrast, in the larger size range, the flange requires at least 20 sets of nuts and bolts. In addition, the method Lan needs to use special wrenches for time-consuming star pattern tightening to measure and ensure that the correct torque specifications are reached. The grooved tube technology allows the use of standard hand tools to assemble the coupling, once the mating bolt pads of the coupling housing meet the metal pair Fittings can be installed correctly if required by metal. Simple visual inspection can confirm correct assembly. On the other hand, flanges do not provide visual confirmation: the only way to ensure correct assembly is to fill and pressurize the system, check for leaks and rebuild as needed Tighten the joints. The same feature of the maintainability grooved piping system is that it speeds up installation-fewer bolts and no torque requirements-and also makes system maintenance or modification a quick and simple task. For example, for access to pumps or For valves, loosen the two bolts of the coupling, and remove the housing and gasket from the joint. In the flange system, multiple bolts need to be removed. When reassembling the flange, the same time-consuming initial installation is required. The bolt tightening sequence. Because they do not need to be re-tightened, couplings eliminate most of the daily maintenance related to flanges. Unlike flanges that apply variable stress on washers, nuts, and bolts, couplings change washers from Accurate external compression of the pipe joint. In addition, because the coupling gasket is not affected by high compressive force, it does not need to be replaced regularly, while the flange gasket needs to be replaced during system disassembly and maintenance. In order to reduce system noise and vibration, the flange system Requires rubber bellows or braided flexible hoses. These components may fail due to excessive stretching, and under normal wear and tear, they need to be replaced every 10 years on average, resulting in costs and system downtime. However, mechanical grooved pipes Joints can extend the life of the system. Their ability to adapt to system vibration reduces the risk of joint failure without the need for special products that require regular maintenance or replacement. The elastic spring washers included in the flexible and rigid couplings are very durable and can withstand huge The working pressure and cyclic load. The system can be repeatedly pressurized and decompressed without fatigue of the elastomer gasket. The weight reduction valve assembly is usually composed of flange components. However, this connection method will add unnecessary to the piping system Weight. A 6 inch (150 mm) flange valve assembly consists of a lug butterfly valve It is constructed, connected to a welded neck flange, with eight bolts and nuts on each side of the valve, weighing approximately 85 pounds. A 6-inch (150 mm) valve assembly uses a grooved end butterfly valve, grooved end pipe, and two rigid couplings to connect the assembly. It weighs about 35 pounds, which is 58% less weight than the flange assembly. Therefore, the grooved valve assembly is an ideal substitute for the shipbuilding industry. A comparison of the DIN 150 ballast pipelines installed above shows that when Victaulic grooved products are used instead of the traditional connection method, the weight is reduced by 30% (2,164 lbs vs. 3,115 lbs). Compared to 60 rigid couplings, 52 sliding sleeve flanges, bolt sets and washers result in an increase in the weight of the welding/flange system. The use of grooved pipe joints instead of flanges can reduce weight and is suitable for pipes of various sizes. The magnitude of the reduction depends on the pipe diameter and the type of joints used. In a test using a Victaulic 77 coupling (the heaviest coupling in the series) to connect the pipe, the total installation weight of the grooved component was much lower than that of two lightweight PN10 sliding sleeve flanges. The weight loss is recorded as follows: 4” (100mm) – 67%; 12” (300mm) – 54%; 20 inches (500 mm) – 60.5%. The use of lighter flexible type 75 or rigid type 07 couplings and/or heavier flange types can easily achieve a 70% weight reduction. For example, the 24-inch (600 mm) flange set used in the TG2 system weighs 507 pounds, but similar components using Victaulic fittings weigh only 88 pounds. Shipyards that preferentially use grooved couplings instead of flanges on selected systems have recorded that offshore support ships have reduced weight by 12 tons and cruise ships have reduced weight by 44 tons. The economic benefits brought by trough technology to shipowners are obvious: the lighter weight means more cargo or passengers and less fuel consumption. It also makes handling of the ship’s piping system easier. Development trend Due to the fast installation speed, strong maintainability and light weight, trough pipe systems can provide more significant advantages than similar flange products. These features, coupled with additional advantages such as reliability, ease of alignment and lower safety risks, have prompted shipowners, engineers and shipyards to choose grooved mechanical systems instead of flanges. This growing trend of using 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 products with grooved end connections. The range of services that can use grooved pipe joints is steadily increasing. Building on its successful application in water systems, Victaulic continues its long history of innovation to develop fire-resistant gaskets and obtain type approval for offshore fuel services.
(Published in the April 2014 edition of Maritime Reporter and Engineering News-http://magazines.marinelink.com/Magazines/MaritimeReporter)
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Post time: Nov-10-2021
