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Swaging a war on piping system leaks

Safe, sound, secure—swaged fittings provide leakproof alternative to conventional connection methods

A man, a plan, a canal—Panama! Perhaps the longest and most well-known palindrome ever devised, it describes one of the biggest and most well-known construction projects ever undertaken: the canal that cuts across Central America from the Gulf of Panama (near Panama City) on the Pacific side to Limon Bay (near Colón) on the Atlantic side.

Although Theodore Roosevelt was president when the U.S. got involved, he wasn’t the man with the plan. That man was Charles V, king of Spain and Holy Roman Emperor, who conceived the idea in 1534 when looking for a way to cut down the sailing time between Spain and Peru. Plans came and went for nearly 350 years but never got much past the concept stage until the late 19th century, when two successive groups of private investors tried and failed to create a viable waterway. Taken over by the U.S. government in 1904 and completed in 1914, the canal system originally comprised two lanes with lock chambers that measured 110 feet wide and 1,050 ft. long.

That was enough for a century, but international commerce and ship sizes have grown in the meantime. The canal expansion project involves a third lane to accommodate larger vessels. The lock chambers are much larger: 180 ft. wide and 1,400 ft. long. The largest of the gates weighs more than 4,000 tons.

The number of hydraulic lines that run the gates is mind-boggling, and the number of connections is an order of magnitude greater. The company that had the contract for the hydraulic power units, controls, and piping, Bosch Rexroth Germany, decided not to use threaded fittings or welded flanges, but opted for two types of mechanical connectors: nonwelded 37-degree flare flanges and PYPLOK® fittings, which are 360-degree radially swaged connectors. According to the manufacturer, Tube-Mac® Piping Technologies Ltd., installation is faster and connections are more reliable than when using conventional fittings.

Flared pipe is nothing new—it has been in use since the 1800s—but the swaged connector concept was devised for an aircraft application.

The Aircraft Angle

The year was 1968. The aircraft designated F-4 (fighter, model 4) had been rolling out of the McDonnell Douglas plant in St. Louis for a decade. Originally designed for the U.S. Navy, it had to withstand the stresses of combat maneuvers and carrier takeoffs and landings. The aircraft’s hydraulic system relied on threaded connectors, and leaks were inevitable. The company’s engineers addressed this problem by developing a 360-degree radial compression swaged fitting. It worked, and following a common defense industry practice, McDonnell Douglas licensed the manufacture of the connector to a company that specialized in making aerospace fittings.

“Deutsch Metal Components received the license, and over time it expanded the concept to go beyond aerospace,” said Chris Peitchinis, vice president of global business development for Tube-Mac Piping Technologies Ltd. “It developed the industrial version, PYPLOK.”

This allowed the company to cater to two distinct markets: hydraulic systems, which use components with SAE designations, and fluid processing systems, which use components that carry ANSI designations. Both markets use pipe

systems that convey fluid under pressure, but they are different domains and overseen by different standards-setting bodies.

Tube-Mac took an interest in it as soon as it discovered the connector.

Figure 1
Flare flange units contain cones and O-rings; tightening the bolts brings the flared pipe and cones together, and the O-rings seal everything up, making a sturdy connection.

“One of our sales managers saw PYPLOK connectors in a steel mill and asked about it, and eventually Tube-Mac was Deutsch’s biggest PYPLOK customer,” Peitchinis said.

Specializing in piping systems installation and repair, Tube-Mac sells everything needed to install an engineered piping system, including pipe, connectors, clamps, valves, hoses, and any necessary fabrication and installation equipment. The new connector was an ideal complement to its existing product line.

In 2007, Deutsch sold the product line to Tube-Mac.

Connections Overview

For some pipe connections, especially diameters larger than 10 inches, welding is the only way to go for a strong, robust connection. However, welding is a capital-intensive process that requires a skilled welder and, depending on the application, an X-ray to determine the weld’s soundness. If flammable vapors are present, it requires additional precautions, a hot-work permit, fire-suppression equipment, and someone to stand fire watch. Threading likewise requires a machine and an operator who knows how to use it. Depending on the pipe size and pressure rating, a mechanical connection can be faster and less expensive.

Tube-Mac’s nonwelded 37-degree flare flange connection uses two flange units (see Figure 1). The user slips one flange unit onto each pipe, flares both pipe ends to 37 degrees, places cone inserts inside each flared pipe end, and uses bolts to draw the flanges together, making a sealed connection. Tube-Mac’s flare flange connectors are available in pipe sizes from ½ to 8 in. They come in SAE Code 61, SAE Code 62, and ISO 6164 styles and can withstand pressure up to 5,800 pounds per square inch (PSI).

A second method, one used for heavy-wall pipe, also uses two flange units but requires machining the pipe face flat and cutting a groove into the outside diameter (OD) to accept a retaining ring. Like the flare flange connections, bolts do the heavy work, drawing the flanges together to create the seal. Tube-Mac makes these connectors in pipe sizes from 1.5 to 10 in. They are available in the same styles and pressure rating as the flare flange units.

“The main drawback is that flange connections require periodic checks,” Peitchinis said. “These need to be inspected at least annually and the bolts tightened if necessary.” Other associated costs are the capital investment for a flaring or grooving machine and the expense involved in training.

PYPLOK is the third nonwelded connector, compatible with NPS pipe (¼ to 3 in.) and OD tube (imperial sizes from ½ to 2 in. and metric sizes from 6 to 60 mm). It withstands pressure up to 9,000 PSI depending on size and material.

It is an alternative for small diameters, providing connections for tube ODs from ½ to 2 in., pipe sizes from ¼ to 3 in., and metric sizes from 6 to 60 mm. It withstands pressure up to 9,000 PSI.

“It’s easy to use, but this doesn’t mean it’s foolproof,” Peitchinis said. The three main steps are deburring the pipe, inserting the pipe to the proper depth, and swaging the connector to the proper diameter.

Figure 2
The PYPLOK connection has two O-rings at each end. The inner O-rings seal fluids in; the outer O-rings form backup seals that keep contaminants out.

“The first concern is deburring, which is necessary to prevent nicking the O-rings,” he said. Each connector has two O-rings on each end, presenting several opportunities for damage from burrs (see Figure 2).

“Second, the kit comes with a tool for marking the insertion depth on the pipe,” Peitchinis said. “The user has to insert the pipe to the mark so it engages both O-rings,” he said.

After cutting, deburring, and marking the tube, the user inserts both tubes to the mark, then uses the hydraulic tool to swage the connector.

“When he’s done, he uses the go/no-go gauge to verify that the connector was swaged successfully,” Peitchinis said.

The O-rings are available in two compounds: Viton® for temperatures from -15 to 400 degrees F, and EPDM E0962-90, created by Parker Hannifin, to seal against hostile chemical, pressure, and high-temperature steam applications.

The connectors conform to standard end connections (SAE, NPT, and DIN) and flange patterns in accordance with SAE Code 61/ISO 6162-1, SAE Code 62/ISO 6162-2, ISO 6164, and ANSI Class. They are available in straight, T, 45-degree and 90-degree elbows, and reducers. The company also makes custom connectors.

Swaging is a cold-work process that doesn’t require any special skill and, according to Peitchinis, cuts the installation time to as little as 10 percent of the time needed for welded fittings. Tube-Mac provides the training—less than half an hour—or it can provide onsite project management and installation technicians.

In addition to reducing the time needed for installation, PYPLOK connectors save time in another way: they don’t require a periodic inspection.

“Once a PYPLOK connection is installed, it’s permanent,” Peitchinis said.

Tube-Mac Piping Technologies Ltd., 853 Arvin Ave., Stoney Creek, ON L8E 5N8, Canada, 905-643-8823, www.tube-mac.com

Sidebar: PYPLOK’s Origins

Fighter capability? Check! Bombing missions? Check! Carrier takeoffs and landings? Check! Wild Weasels? Check! Blue Angels? Check! Thunderbirds? Check! The longest-serving U.S. military aircraft ever built? A big check on that last one.

First flown in 1958, the venerable F-4 Phantom II filled a number of roles: air superiority, ground attack, reconnaissance, and electronic warfare. Its longevity and adaptability are testament to the aircraft’s design. Initially developed for the U.S. Navy and intended for carrier service, it quickly caught the attention of the U.S. Air Force and, in time, became one of the most fearsome weapons in both branches.

However, just as a chain is only as strong as its weakest link, a complex system comprising innumerable parts is only as reliable as its least reliable component. Catapult takeoffs, combat maneuvers, and arrested landings put a lot of stress on every component in an airplane. Thermal expansions and contractions make matters worse. For the F-4, the ambient temperature on a single mission could vary from 60 degrees F on the deck to -70 degrees F at the aircraft’s service ceiling (60,000 feet). Under such conditions, the threaded couplers used on the aircraft’s hydraulic system would loosen and leak.

In 1968, engineers at McDonnell Douglas addressed this problem by developing a 360-degree radial compression swaged fitting. Intended to be robust, leakproof, and permanent, the connector worked as intended and has an important role in aircraft construction to this day.

About the Author
FMA Communications Inc.

Eric Lundin

2135 Point Blvd

Elgin, IL 60123

815-227-8262

Eric Lundin worked on The Tube & Pipe Journal from 2000 to 2022.