The use of grooved mechanical piping has become the generally accepted method for joining pipe in the mining industry, particularly in underground mines.

This, says developer and producer of mechanical pipe joining systems Victaulic regional manager Barry van Jaarsveld would be the reason why bright-orange V-couplings, adorning piping systems, are a common sight in underground mines in South Africa.

He notes that grooved mechanical piping, the pipe-joining system that makes use of these couplings, is the preferred method for joining underground and plant piping systems in the mining industry owing to the ease and speed of installation and maintenance.

“There are many applications for such systems, but they have traditionally excluded high-pressure systems. Most couplings have moderate working-pressure limitations, so high-pressure systems require the use of alternative joining methods, typically heavy-duty flanges.

“However, the introduction of Victaulic high-pressure couplings which go up to 275 bar, has made the grooved joining method viable, and even preferable, for backfill, deep- mine chilled water and dewatering lines, and other high-pressure piping applications,” he says.

Grooved Mechanical Piping Basics

“By saving time during installation and maintenance and offering system flexibility, simplifying system alteration and pipe and fitting replacement, while improving safety, grooved piping helps owners reduce risk and ultimately save money.”

The mechanical joint comprises four elements; grooved-end pipe, a gasket, coupling housings, and nuts and bolts. The gasket is wrapped around two abutted pipe ends and enclosed in coupling housings.

“The key sections of the coupling housings engage the grooves, and the bolts and nuts are tightened to hold the housings together. In the installed state, the coupling housings encase the gasket and engage the groove around the circumference of the pipe to create a triple seal unified joint that is enhanced when the system is pressurised,” he says.

Van Jaarsveld adds that the primary benefit of grooved mechanical piping is that the systems are three to five times faster to install than other common methods of pipe joining.

“Assembly of the grooved pipe joint, placing the gasket and securing the coupling housings, can take anywhere from several minutes for a 50 mm joint to about half an hour for a 200 mm which is up to three times faster than assembling flanged pipe joints.

“Victaulic installation-ready couplings further reduce installation time to about half that of standard couplings. This type of coupling does not require disassembly prior to installation as it can be pushed onto the pipe ends and secured using standard tools. Factoring in materials and labour, grooved piping systems can result in total-installed cost savings of up to 30%,” he says.

He continues that with a union at every joint, piping system maintenance such as replacement of fittings in abrasive services and valve maintenance is also expedited.

“With a coupling on each end of a fitting, only four bolts – two on each coupling – need to be loosened to remove the couplings and drop the fitting out. A typical flanged connection would require the removal of 16 bolts. By allowing these maintenance tasks to be completed quicker and easier, couplings reduce downtime and costs. They can also reduce the labour needed to complete maintenance tasks.

“Another benefit of grooved piping is ease in rerouting and expanding piping systems. As work progresses underground, piping systems need to be repositioned and reach greater depths. With the ability to quickly and easily disassemble and reassemble piping components, system retrofits and expansions can be completed twice as fast as other joining methods.

“Grooved piping is also a safer joining method. No open flame or joint compounds are required to join pipe with couplings, and unlike flanged joints, the gasket does not need to be scraped off during maintenance. Victaulic installation-ready couplings further reduce risk of injury because the couplings remain assembled, eliminating loose parts that can be dropped,” notes Van Jaarsveld.

He states that deflection capabilities of flexible couplings allow the pipe to be deployed over uneven surfaces while maintaining the integrity of the system.

“The pipe joint can also accommodate thermal expansion and contraction, as well as seismic movement. Flanges require expansion joints to provide this type of flexibility.

“These benefits combine to make grooved piping the ideal method for moderate pressure piping services such as air and water supply in mines,” he says.

High-Pressure Piping Applications

Van Jaarsveld says the most common high-pressure piping applications in a mine are backfill, deep underground chilled water and dewatering lines.

“Piping paste and sand backfill solids requires very high pressures because the system is transporting a mixture of solid materials into the mine. In fact, backfill is one of the highest pressure piping applications within a mine.

“Chilled water lines in deep mines face a similar challenge. The deeper the mine, the more difficult ventilation and air-cooling become. Chilled water lines are used to overcome the natural heat of the rock, allowing personnel to comfortably work at depth. However, there is a lot of head pressure when pumping water to such depths, and as a result, the piping system must be capable of handling the significant pressure produced in such an installation,” he states.

He continues that almost every underground mine deals with the challenge of transporting mine water to the surface.

“High-pressure pumps have given mines the ability to pump water from very deep levels directly to the surface. These pumps are capable of reaching incredibly high pressures and the piping system must be able to handle the load.

“One of the traditional methods for joining these high-pressure piping systems is the use of heavy-duty flanges. However, flanges are not advantageous in these situations because they have high costs, are inefficient in installation and maintenance, and are not flexible.

“In terms of installation and maintenance, flanges are inefficient. They require more time to install and assembly involves aligning the faces, inserting the gasket, inserting eight or more bolts and tightening in sequence, and ensuring proper torque requirements are met. They are also more difficult to work with in pipe maintenance and alteration. Backfill lines, for example, can get clogged and require replacement of the pipe,” he states.

He adds that in addition, once the pipe wall thickness wears to a certain point, the system must be replaced. In both of these circumstances, flanges cannot be reused so replacement costs are higher. Dropping out the section of pipe to be replaced is also more time consuming. The nature of backfill systems also requires that they be rerouted as work progresses. Flanges can slow this process.

“Flanges are not a flexible pipe joint. When using flanges to join a system in which flexibility is required, such as chilled water lines, expansion joints must be used, which increases material costs,” he states.

Grooved Piping in High-Pressure Applications

In response to the difficulties associated with flanged pipe joints, mines are increasingly specifying high-pressure mechanical coup- lings for use on applications such as backfill, chilled water and dewatering lines.

“These couplings provide greater efficiencies in terms of labour and maintenance, flexibility to accommodate expansion and contraction, and have a lower total-installed cost than flanges,” he says.

He continues that with the ability to withstand working pressures of up to 275 bar, high-pressure couplings provide many of the benefits of standard couplings used on air and water lines. The design and specifications of the couplings, however, differ from standard couplings. There are two types of high-pressure couplings currently utilised in mines, EndSeal couplings and double-groove couplings.

EndSeal Couplings

EndSeal couplings, such as the HP-70ES from Victaulic, are available in two to 12 inch sizes. EndSeal describes the gasket that is used within the coupling. Rather than a standard C-shaped gasket, the gasket features a centre lip that positions between the pipe ends when the coupling is engaged. This provides a smoother flow path that reduces wear on the pipe ends.

The heavy-duty housings in combination with the EndSeal gasket allow EndSeal coup- lings to meet pressures of up to 172 bar.

“The groove profile for the EndSeal coupling also differs from that of standard couplings. Compared to a standard cut groove, the EndSeal groove has a shorter A-dimension, which is the length from the pipe end to the beginning of the groove, and is deeper and narrower.

“EndSeal couplings must be used on schedule 40 or heavier pipe, and for high-pressure applications, the pipe should be cut grooved,” states Van Jaarsveld.

Double-Groove Couplings

Double-groove couplings, such as the Style 808 from Victaulic, are available in 168.3 mm to 323.9 mm sizes and withstand pressures of up to 275 bar, the highest pressure rating available for any grooved mechanical pipe joining system.

“As the name implies, double-groove technology features two grooves on each pipe-end that engage key sections on the coupling housings. This double-groove engagement of mating coupling keys provides superior joint integrity at high pressures by distributing pipe end-loads.

“The housing design provides increased strength at points of high stress for high- pressure security. Double bolting on each side of the coupling reinforces the double-groove positioning for positive high-pressure reliability,” he says.

Double-groove couplings contain a standard C-shaped gasket. “The groove profile is the same as that of a standard cut groove, with the exception that there are two grooves on each pipe-end instead of one. Double-groove couplings must be used on cut-grooved schedule 80 or heavier pipe. These couplings do not require special weld-on nipples or collars, eliminating additional fabrication needs.

“Further, these couplings have an extremely high end-load rating. In fact, it is the only mechanical joint that accommodates pressures of up to 275 bar as well as end-loads in excess of 300 000 lbs.”

This means that, although the flexibility of the double-grooved joint allows the coupling to move within the groove to accommodate expansion, contraction and deflection, the joint will not pull apart if the end load is within specifications. The restrained joints create a system that does not require additional pipe supports.

Van Jaarsveld adds that Victaulic EndSeal and double-groove couplings are specified for backfill, chilled water and dewatering lines, depending on the pressure of the system.

“For systems with working pressures below 172 bar, EndSeal couplings are recommended. For systems with working pressures between 172 bar and 275 bar, double-groove couplings are used.

“When installed properly, testing proves that these couplings and their gaskets withstand the published working pressure for the life of the system. Like standard couplings, Victaulic high-pressure couplings have built-in safeguards to ensure correct assembly, metal-to-metal bolt pad contact provides visual confirmation of proper assembly,” he says.

He states that properly installed mecha- nical couplings are able to withstand the extreme pressures of backfill, chilled water and dewatering applications, and provide additional benefits that flanged systems cannot match.

“All of the benefits of standard couplings apply to high-pressure couplings. Decreased downtime owing to faster and easier installation and maintenance, lower total-installed costs, no need for specially skilled labour, ease in altering, rerouting and replacing piping, deflection capabilities that aid in routing the pipe over uneven surfaces and improved safety,” he concludes.