Optimising maintenance: Larry Thau*, takes a look the maintainability of mechanical piping systems.
There are three types of maintenance that are performed on piping systems; routine periodic inspection, physical changes or expansion to the piping system and unscheduled repair. Routine periodic inspection is performed to ensure that the system is still intact and operating at peak efficiency. Physical changes or expansion to the piping system is performed to adjust existing installations, replace old piping or alter the existing system by adding to it. Unscheduled repair is the most pressing and time sensitive type of maintenance because it is unplanned and, in most cases, necessary immediately. It can include the repair of erosion and corrosion, cracks, leaks, weld failure, such as pinholes and incomplete fusion, and material failure, such as defects in the pipe itself.
This article will focus on mechanical pipe joining systems as an optimal way to effectively maintain piping systems in structures. Their ease of installation, disassembly and reinstallation make mechanical pipe joining systems a simple way to frequently enter piping systems to perform both routine and irregular maintenance.
Anatomy of a mechanical joint
The design of a mechanical pipe joint is inherently easier to work with during maintenance activities. The mechanical joint, or coupling, is comprised of three elements: the pipe groove, the gasket and coupling housings, nuts and bolts. The pipe groove is formed by cold forming or machining a groove into the end of a pipe. The key section of the coupling housing engages the groove. Within the housings is a resilient, pressure-responsive, C-shaped elastomer gasket that provides a triple seal. The coupling housing fully encloses the gasket, reinforcing it and securing it in position.
The EPDM (ethylene propylene diene monomer) gasket, which is used in most water applications, is resistant to aging, heat and oxidation. These modern high-performance gaskets are injection-molded to precise tolerances, which provide more uniform cross-sectional density than transfer or compression molding. After molding, the gaskets are post-cured with an organic peroxide that further enhances their structural integrity. Compared with other curing agents such as sulfur, peroxide provides superior cross-linking of the elastomer's molecular chains, thereby improving its resistance to deterioration and aging.
The third element in the grooved piping system is the coupling housing, which encases the gasket and engages into the groove around the circumference of the pipe to create a unified joint. Holding the housing section together are bolts and nuts that are tightened with a socket or wrench.
The mechanical joint creates a triple seal due to the pipe groove, gasket and housings. This seal is enhanced when the system is pressurized.
The maintainability benefit of mechanical piping systems:
The design of the mechanical joint offers benefits to the user over the life of the system by reducing need for maintenance, providing for quick and easy system access during routine or repair work, as well as system expansion and affording a safe environment for workers and building occupants.
Reduction in unscheduled maintenance
With a mechanical coupling, the compressive loads on the gasket are different than on the flange. The gasket has a C-shaped cross section seal that is very durable and can handle significant compressive and cyclical loading. Workers can pressurize and depressurize a system repeatedly for many years without fatiguing the rubber. In a traditional flanged system the torque on the bolts employs a high compressive load on the internal gasket, which makes it stick to one or both of the flanges. When the multiple bolts are removed and the flanges are disassembled, often the gasket will tear causing the gasket to fail upon reinstallation.
In addition to providing a robust product that is good for the life of the system, a mechanical pipe joining system accommodates vibration within the system without the need for periodic product repair or replacement. Traditional welded or flanged piping systems have rubber bellows or braided flexible hose to accommodate these vibrations; however these materials tend to wear out over time requiring costly and time consuming replacement. Flexible mechanical systems allow the pipe to move and vibrate within the coupling, therefore localizing vibrations generated by equipment and reducing the amount of noise transmitted down the pipe line. The design of the mechanical joint allows for this movement without wearing out the gasket.
The speed and ease of maintenance with a mechanical system
While mechanical systems reduce the need for maintenance to the piping system they also allow for quick and easy access to the system for routine equipment maintenance, system expansion or pipe line repair.
A coupling provides a union at every joint allowing easy access to the system and flexibility for future system expansion. To access the system via a mechanical coupling, a worker simply unscrews two nuts and drops the section out 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, is then easily accomplished. To complete the job the gasket is reinstalled, the coupling is placed back on the pipe or fitting and the two bolts are tightened. Welded systems don't have unions; to repair the piping system, workers actually have to cut out the damaged pipe section, which causes operational concerns and safety hazard particularly in existing facilities and occupied spaces.
Since mechanical pipe joining systems provide for an easier assembly and disassembly process they require less labor and a higher speed of installation. A traditional welded system requires highly skilled labor and is labor intensive; projects take up to 45% more man hours to complete than in grooved systems. In a traditional flanged system, multiple bolts are needed to create the seal and removing these bolts is a time-consuming process. For example, when working with a twelve inch flanged system, twelve bolts need to be removed before gaining access to the system. This becomes lengthy and complicated in systems requiring regular routine maintenance. With mechanical piping systems, only two bolts need to be removed to access the system, allowing for much more time-efficient maintenance procedures. Additionally, unlike a flanged joint a two-bolt coupling can be "free floated" around the pipe for quick alignment adjustment and easy access.
Over the years, large chiller companies have transitioned away from flanged inlets and outlets on chiller systems and condenser equipment and have switched to grooved inlets and outlets. This migration occurred for several reasons, with the most important reason being the difficulty associated with aligning multiple bolt holes in flanged systems. With a grooved system these companies can quickly 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 rapidly assemble a product and test it before it is sold to a client.
The grooved system eliminates the need for complete system shutdowns since there is no need to completely drain the system and torches are not used. As a result, buildings can return to full operating capacity very quickly. In addition, the work of building occupants is not disrupted during maintenance because the building remains fully operable, meaning productivity will not decline during the maintenance procedures.
In all facilities it is essential to provide a flame-free piping method for safety reasons. The dangers associated with welding increase project man-hours, down time, worker safety and cost.
The grooved method eliminates the potential for a fire since it is a flame-free method. Welding requires that entire systems be drained and dried prior to performing maintenance work since the pipe could burst when flame comes in contact with the liquid. For example, if a welder accidentally opens the wrong pipe or if the system is not fully drained, the worker can suffer from molten metal splatter.
Further hampering productivity, is the need for a fire watch during welding procedures. A fire watch is required whenever welding or cutting is performed in locations where a fire might develop, or where 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 notifying traffic of the hot work area. Shields must also be set up and are used to prevent exposure to sparks and flashes. Lastly, a clear path to an exit must be maintained during the entire procedure. The fire watch must remain after the maintenance is complete to detect and extinguish any smoldering flames, further increasing the total man-hours of the project.
The grooved system does not require any additional man hours or job site preparation, unlike the extensive preparation necessary during 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 presents the potential for fire, securing the nuts and bolts to fasten the mechanical coupling does not involve any heat at all. This significantly decreases insurance liability issues because there is no flame involved, and fire departments do not need to be put on alert.
Another safety benefit associated with a grooved system is that the potential for short and long term health problems due to pipe fitters' exposure to fumes from cutting and welding metal piping is eliminated. The cold-forming process of grooving the pipe and nut and bolt installation does not emit any harmful fumes making any added insurance and liability costs due to workers' health problems nonexistent.
Mechanical piping systems offer a reduced need for maintenance, 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.
The net result is that mechanical piping systems' eighty years of installed history along with improved performance, productivity and predictability have established the method as a viable alternative to other traditional systems particularly in today's world where labour, risk and compressed schedules loom larger each day.
For further information please visit: www.victaulic.com
*Larry Thau is Executive vice president and chief technicaln officer for Victaulic.
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|Title Annotation:||MAINTENANCE MATTERS|
|Publication:||Plant & Works Engineering|
|Date:||Jul 1, 2010|
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