Many structures require some degree of piping-system maintenance. For example, strainers are changed monthly, weekly, or, in some systems, daily. Turbulence and strainer clogs, which can lead to floating debris in a system, can cause heavy wear on pumps and reduce the efficiency and life of equipment. Bearings and impellers also suffer from erosion over time and may need to be replaced. In addition, lines of pipe may become corrupt and require maintenance or replacement. All of these maintenance concerns are addressed in mechanical pipe joining systems.
Three types of maintenance are performed on piping systems: routine periodic inspections, physical changes or expansions to a piping system, and unscheduled repairs. Routine periodic inspections are performed to ensure that a system is intact and operating at peak efficiency. Physical changes or expansions to a piping system are performed to adjust existing installations, add to an existing system, or replace old piping. Unscheduled repairs are the most pressing and time sensitive type of maintenance because they are unplanned and, in most cases, require immediate action. Causes of these repairs can include erosion; corrosion; cracks; leaks; weld failure, such as pinholes and incomplete fusion; and material failure, such as pipe defects.
This article will focus on the role of mechanical pipe-joining systems in effective maintenance of piping systems. Their ease of installation, disassembly, and reinstallation make mechanical pipe-joining systems a simple way to enter piping systems frequently to perform routine and irregular maintenance.
ANATOMY OF A MECHANICAL JOINT
A mechanical pipe joint, or coupling, is easy to work with during maintenance. A mechanical joint is comprised of three elements: a pipe groove, a gasket, and coupling housings, nuts, and bolts. A pipe groove is created by cold-forming or machining a groove into an end of a pipe. A coupling housing's key section engages the groove. Within the housing is a resilient, pressure-responsive, C-shaped elastomer gasket that helps provide a triple seal.
Ethylene-propylene-diene-monomer (EPDM) gaskets, which are used in most water applications, are resistant to aging, heat, and oxidation. These modern, high-performance gaskets are injection-molded to precise tolerances, providing more uniform cross-sectional density than transfer or compression molding. After molding, gaskets are post-cured with an organic peroxide that enhances their structural integrity. Compared with other curing agents, such as sulfur, peroxide provides superior cross-linking of an elastomer's molecular chains, improving its resistance to deterioration and aging.
The next element in a grooved piping system is the coupling housing, which encases the gasket and locks into the groove around a pipe's circumference to create a unified joint. The coupling housing fully encloses the gasket, reinforcing it and securing it in position. Holding the housing section together are bolts and nuts that are tightened with a socket or wrench.
A mechanical joint creates a triple seal because of the pipe groove, gasket, and housings. This seal is enhanced when a piping system is pressurized.
A mechanical joint's design offers benefits to a user over the life of a system by reducing the need for maintenance, allowing quick and easy system access for repair work and system expansion, and affording a safe environment for workers and building occupants.
Reducing unscheduled maintenance
With a mechanical coupling, the compressive loads on a gasket are different than those on a flange. A gasket has a durable C-shaped cross-section seal that can handle significant compressive and cyclical loading. Workers can pressurize and depressurize a system repeatedly for many years without fatiguing a gasket's rubber. In a traditional flanged system, torque on bolts exerts a high compressive load on an internal gasket, which sticks to one or both flanges. When bolts are removed and flanges disassembled, the gasket often will tear, and fail upon reinstallation.
A mechanical pipe-joining system accommodates vibration within a system without the need for periodic repair or replacement. Traditional welded or flanged piping systems have rubber bellows or braided flexible hose to accommodate vibration. However, these materials wear out over time, requiring costly and time-consuming replacement. Flexible mechanical systems allow a pipe to move and vibrate within a coupling, localizing vibration generated by equipment and reducing the amount of noise transmitted down a pipeline. A mechanical joint's design allows this movement without the gasket wearing out.
Simplifying system access
Mechanical systems allow quick and easy access to piping systems for routine equipment maintenance, system expansion, and pipeline repair.
A coupling provides a union at every joint, allowing easy access to a piping system and flexibility for future system expansion. To access a system via a mechanical coupling, a worker unscrews two bolts and drops out the piping section without the need for a torch, saw, or welding machine. Required maintenance, such as replacing strainers or corrupt pipe sections or slipping in a tee to expand or join piping systems, then can be accomplished easily. To complete the job, the gasket is reinstalled, the coupling is placed back on the pipe or fitting, and the bolts are tightened. Welded systems do not have unions. To repair a welded piping system, workers have to cut out the damaged pipe section, causing operational concerns and safety hazards, particularly in existing facilities and occupied spaces.
Because mechanical pipe-joining systems are easier to assemble and disassemble, they require less labor and time to install. A traditional welded system requires highly skilled labor and is labor-intensive. Welded-system projects take up to 45-percent more man-hours to complete than grooved-system projects. In a traditional flanged system, multiple bolts are needed to create a seal. Removing these bolts is a time-consuming process. For example, with a 12-in. flanged system, 12 bolts need to be removed before the system can be accessible. This becomes a lengthy and complicated process in systems requiring regular routine maintenance. With mechanical piping systems, only two bolts need to be removed to access the system, allowing for time-efficient maintenance procedures. Additionally, unlike a flanged joint, a two-bolt coupling can be “free-floated” around a pipe for quick alignment adjustment and easy access.
Over the years, large chiller companies have transitioned away from flanged inlets and outlets to grooved inlets and outlets on chiller systems and condenser equipment. This migration has occurred for several reasons. Most important is the difficulty associated with aligning a flanged system's multiple bolt holes. With a grooved system, these companies quickly can plug in a chiller to run tests. If something goes wrong, a crane simply transports the unit out for maintenance. Mechanical couplings allow chiller manufacturers to assemble a product rapidly and test it before it is sold to a client.
In all facilities, but particularly in hospitals, schools, and airports, it is essential to provide a flame-free piping method. The dangers associated with welding decrease worker safety and increase project man hours, downtime, and costs.
The grooved method eliminates the potential for a fire because it is a flame-free method. Welding requires entire piping systems to be drained of liquid and dried prior to the performance of maintenance because pipes could burst from pressure caused by heat from a flame. If a welder opens the wrong pipe or a system is not drained properly, the welder can suffer from molten metal splatter when the liquid mixes with welding materials.
Further hampering productivity is the need for a fire watch during welding procedures. A fire watch is required when welding or cutting is performed in locations in which a fire might develop or combustible materials are present. Suitable fire-extinguishing equipment must be maintained and ready during welding, cutting, and burning activities. In addition, barriers and proper signs must be posted to notify traffic of a hot work area. Also, shields must be set up to prevent exposure to sparks and flashes. Finally, a clear path to an exit of at least 44 in. must be maintained during the entire procedure. By law, a fire watch also must remain for a minimum of 30 min after maintenance is complete for any smoldering flames to be detected and extinguished, further increasing a project's total man hours.
A grooved system does not require any additional man-hours or job-site preparation, unlike the extensive preparation necessary for welding. Mechanical pipe-joining systems eliminate the possibility of fire during maintenance because use of a flame is not necessary to join mechanical couplings. While welding creates sparks and the potential for fire, securing nuts and bolts to fasten a mechanical coupling does not involve heat at all. This decreases liability issues. Further, fire departments do not need to be on alert.
Because grooved systems are flame-free, they eliminate the need for complete system shutdown. As a result, buildings quickly can return to full operating capacity. Building occupants are not disrupted during maintenance because the building remains fully operable.
Another safety benefit associated with a grooved system: The potential for pipe fitters to develop short- and long-term health problems associated with exposure to fumes released during the cutting and welding of metal piping is eliminated. The cold-forming process of grooving a pipe and nut-and-bolt installation does not emit any harmful fumes, avoiding additional insurance costs.
Mechanical piping systems offer a reduced need for maintenance, while providing speed and ease in accessibility and a safe environment for workers and building occupants. Allowing workers to perform maintenance procedures quickly, easily, and safely makes mechanical piping a valuable option for projects that require regular maintenance procedures or when productivity cannot be interrupted for maintenance work.
Larry Thau is vice president of engineering for Victaulic Company Inc. A practicing mechanical engineer for 35 years, he holds more than 35 patents and lectures on piping technology around the world.
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