Sealing choices offer flexibility

When specifying piping systems for industrial plants, engineers have an important role in addressing and alleviating challenges for the contractor and the owner, both during project design and construction and throughout the facility's life cycle. Mechanical pipe joining is a method used on a variety of utility service and process piping applications in thousands of industrial manufacturing fac...

09/01/2009


When specifying piping systems for industrial plants, engineers have an important role in addressing and alleviating challenges for the contractor and the owner, both during project design and construction and throughout the facility's life cycle. Mechanical pipe joining is a method used on a variety of utility service and process piping applications in thousands of industrial manufacturing facilities worldwide.

When compared to welding, the ease and speed of installation and maintenance of mechanical piping methods, such as grooved pipe joining, provide multiple benefits including reduced total man hours on the job site, increased safety and the ability to meet or beat fast-tracked construction schedules.

Suitable applications for mechanical piping systems range from basic plant utility services such as cooling water and plant utility air lines to plant processes including, but not limited to, instrument air, lube oil feed lines, chemical cleaning, and inert gases such as nitrogen. Mechanical system manufacturers offer products for industry-specific specialty applications such as flue gas desulfurization, coal handing and pneumatic conveying.

Grooved, flanged and welded

Grooved and flanged mechanical joining systems eliminate the challenges and safety risks encountered when welding utility service and plant process piping.

The grooved mechanical system's design provides a simplified assembly. It is inherently easier to work with than other joining methods, and is comprised of three elements: the pipe groove, the gasket and coupling housings, and 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. Finally, the coupling is held in place with secured nuts and bolts.

While the grooved system is easy to install it also provides a durable union at every joint, offering maximum field flexibility and allowing for quick and safe system maintenance, reducing costly plant downtime.

Grooved piping systems are available with the rigid characteristics and similar support and guide requirements of a welded joint, as well as systems that offer flexibility to accommodate system movement, thermal expansion and contraction, or changes in direction that put stress on the joint.

The flame-free design of a flanged joint uses a series of bolts and nuts to compress a gasket between two flat-faced, flanged pipe ends. Prior to installation, flanges require a "make on" process where the flanged end is welded on to the pipe length. To install a flanged joint, workers must align the faces and bolt pattern, insert the gasket and insert the bolts and nuts. The bolts must then be tightened in sequence and, to ensure proper torque, all bolts must be touched at least three times in sequence. If tightened out of sequence, one side may loosen while the other is secured.

Instead of mechanical pipe joining systems, engineers may choose to install welded systems. To weld, first installers cut, bevel and prep the pipe lengths. Then installers must align and clamp the joint. Welding utilizes an electrode that creates an arc between itself and the grounded pipe ends and distributes material into the joint.

During the first pass, the filler bonds with the molten pipe ends at temperatures approaching 10,000 degrees F and creates a permanent welded joint. This process is then inspected and repeated two to three times per joint. If inspection is failed, fitters must cut out the joint, cut more pipe to length and repeat the entire weld process.

Faster, safer installations

The design of mechanical pipe joining methods leads to significant on-site man hours savings. On average, field fabrications of a flanged system is up to six times faster than welding. Furthermore, the simplified assembly and installation of the grooved piping method is up to 10 times faster than welding, leading to a reduction in project calendar days by as much as one half. The reduction in calendar days realized by installing a mechanical piping system gives owners the ability to meet, and even beat, compressed construction schedules and avoid liquidated damages.

By reducing on-site man hours and eliminating the risk of fire and release of noxious fumes , the installation of mechanical piping systems increases jobsite safety and decreases overall risk when compared with welding.

Most injuries on job sites occur via material handling, but the most significant risks — in terms of potential impact on people and businesses — are caused by fire and fume hazards. Mechanical pipe joining eliminates fire, open arcs, sparks, flames and toxic-fume hazards that are associated with welding, brazing, and soldering. Welding is associated with a number of potential health risks, as well as the risk of severe burns and explosion. By specifying a mechanical pipe joining system, an engineer reduces the owner's overall risks, especially those related to project schedule, costs and potential liability.

Depending on the type of project (e.g., new construction vs. plant expansion/retrofit), hazards may become a risk not only to construction workers, but also to the occupants of the structure and surrounding facilities. When someone is welding, to comply with mandatory safety regulations, all other work in the area must be postponed, leading to costly plant downtime and possible employee evacuation.

Benefits when the plant is up and running

Once the plant is operating, a piping system requires three types of maintenance: routine inspection, retrofit or expansion, and unscheduled repairs. By allowing access to the system, mechanical pipe joining makes maintenance and system access easy, fast, and safe, minimizing downtime. Because there is no need for flame and no risk of dangerous fumes, maintenance procedures are often performed while the majority, if not all, of the facility is operational.

A grooved mechanical pipe system offers, first and foremost, easy system access with a union at every joint. When pipes are welded together, the pipes become a single, extended piece of metal. A grooved coupling provides a union at every joint, which allows for easy system access — not to mention increased ease and flexibility for future system expansion.

To access the grooved system, a maintenance worker unscrews one or two nuts, and the pipe section is then easily removed. Furthermore, mechanical systems are more efficient than welded during both scheduled and unscheduled outages reducing downtime by an average of 25 percent. In many cases, during plant expansions and retrofits using grooved piping, existing piping systems are easily re-routed and kept in operation while new systems are put in place, increasing on-site safety and reducing overall plant downtime.

The elastomer gasket of a grooved joint does not require routine maintenance or replacement, as with point loaded flanged joints. Unlike the grooved method, the bolts and nuts of a flanged union absorb all force — not the gasket. Because of this force, the bolts and nuts loosen over time, causing gasket slippage and system leaks. Therefore, flanged systems require routine bolt and nut tightening, as well as gasket replacement.

Once maintenance is complete, a mechanical system can be up and running again quickly. With grooved systems in particular, the worker simply reinstalls the gasket, re-engages the coupling on the groove of a pipe, fitting, or valve, and tightens the bolts. Maintenance is not quite as easy with welded systems that require cutting out the damaged pipe section and welding it back together, which can be both unsafe and time-consuming in occupied spaces.

Since mechanical systems are easier to maintain than welded, facility managers are less likely to defer maintenance and in-house operations crews can perform necessary scheduled system maintenance. Furthermore, a well-maintained system will operate at optimal efficiency and will not put unnecessary strain on the equipment that it is connected to, such as boilers, compressors and water pumps.

In addition to making maintenance fast and safe, a grooved mechanical pipe joining system accommodates vibration within the piping system reducing the need for periodic product repair or replacement.

The engineer's impact

The plant engineer has a key role in choosing piping installations that are safe and efficient during every stage of a plant lifecycle. A mechanical system meets design challenges that are present in planning, fabrication, and construction—from gasket grade availability to the need for both flexible and rigid components to the use of tools for easily performing field maintenance without enlisting the help of outside shops.

The combined benefits of labor, material and man hour savings from utilizing mechanical joining methods for plant system piping translate to significant total installed cost savings.

Grooved piping systems provide a union at every joint for ease of maintenance and future retrofits (left). The flexibility of grooved-pipe couplings reduces the transmission of stresses through a piping system, while the gasket and ductile iron housing combine to dampen vibration. This reduces the wear and tear on systems and subsequently reduces the need for maintenance (right).

Maintaining pipe systems is a critical function in the plant, and sometimes gets overlooked or delayed in an effort to keep the facility running.


Author Information

Bill Lowar is the Industrial Divisional Manager with Victaulic, Easton, PA. For more information, go to




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