Pipe Couplings and Fittings

The Uniflex Coupling (SUA)

The Uniflex Pipe Coupling, known as the SUA, is a gasketed pipe union built to replace traditional ground joint unions in steam and process piping systems. Instead of relying on two precision-machined metal surfaces to form a seal, the SUA uses a spiral-wound gasket, similar in principle to a flange joint, to create a leak-tight connection rated to 3000 PSIG and temperatures up to 850°F.

Manufactured by Nicholson and supplied by Uniflex, the SUA is available as a forged carbon steel or Type 316L stainless steel union and is designed to solve the three problems that plague conventional ground joint unions: frequent leakage, heavy maintenance demands, and difficult stocking. The design meets MSS SP-83 standards for 3000 lb. unions.

How It Works: SUA vs. Ground Joint Unions

Traditional ground joint unions seal by forcing two machined metal surfaces together. That mating surface has to be manufactured with extremely tight tolerances, and once it wears, warps, or is damaged during disassembly, the union starts to leak. Repairing it typically means replacing the entire union housing, and reinstalling it often requires springing the pipe out of position, which adds stress to the surrounding piping.

The SUA design removes the ground joint surface from the equation entirely. A spiral wound gasket, held in place by a patented retainer, sits between the two halves of the union and forms the seal, the same basic principle used in flange joints. Because the gasket, not the metal surface, does the sealing, wear and tear on the union housing itself becomes far less of an issue, and the seal is fully protected from damage caused by overtorquing during installation.

Key Benefits

• No energy losses — A spiral-wound gasket ensures a long-life, leak-tight seal, preventing the energy loss that comes from steam and process fluid leaks at conventional unions.
• Lower maintenance and labor costs — Because only the gasket needs to be replaced rather than the entire union housing, and the pipe never has to be sprung during make-up or disassembly, reassembly time is reduced by more than 60% compared with conventional unions.
• Lower inventory costs — One Uniflex coupling satisfies all pressure series of flanges in its pipe size, so facilities only need to stock a few couplings and gasket kits per size rather than mated parts.
• Ease of installation — The gasket is held firmly in place by a patented retainer, eliminating the risk of damaging the seal during installation from overtorquing.
• No welding damage to seal — Because the gasket is installed after welding the coupling into the piping system, the risk of heat damage to the seal is eliminated.
• Component interchangeability — All components within a given size class are fully interchangeable, and end connections can be socket weld, threaded, or a combination of both.

Industrial Applications

The Uniflex SUA coupling is built for demanding steam and process piping applications, including:

• Steam systems, up to 1500 PSIG superheat
• Dowtherm systems
• Process fluids and gases to 3000 PSIG CWP, including acids, caustics, and nitrogen
• Steam trap, valve, pump, and compressor manifolds
• Nuclear power plants
• Hydraulic fluids and hot oils

Specifications

Pressure and temperature ratings: Up to 3000 PSIG at 100°F for carbon steel housings, and up to 2430 PSIG at 100°F for Type 316L stainless steel housings, rated for continuous service to 850°F. Pressure ratings decrease as operating temperature increases; consult the full temperature/pressure chart in our spec sheet before specifying for high-temperature service.

Materials of construction:

• Housing: Forged carbon steel (ASTM A105) or Type 316L stainless steel
• Gasket: Spiral wound Type 304 stainless steel with graphite filler
• Gasket retainer: Type 316 stainless steel

Design standard: Meets MSS SP-83 for 3000 lb. unions. Union design is straight-through with oppositely aligned connections, suitable for horizontal or vertical piping installations.

Available options: Teflon gasket filler, and gasket winding materials including Type 347 stainless steel, Type 316 stainless steel, Monel, Inconel 600, Hastalloy, and nickel. Additional materials available on request.

Uniflex Coupling Models

Model	End Connection	Material
SUA-T	Threaded (NPT)	Carbon Steel
SUA-SW	Socketweld	Carbon Steel
SUASS-T	Threaded (NPT)	Stainless Steel
SUASS-SW	Socketweld	Stainless Steel
SUG	Gasket kit (10 gaskets)	—
SUGR	Gasket kit (10 gaskets, 10 retaining rings)	—

Connections are available in 1/2″ to 2″ NPT or socketweld, and the two connection types can be combined on a single union to match your existing piping configuration. When ordering mixed connection types, specify the female end first (for example, SUA-T (SW/NPT) indicates a socketweld female end and NPT male end).

Dimensions and weight by pipe size:

Pipe Size	A (in)	B (in)	C (in)	Weight (lbs)
1/2″	2.0	1.8	0.9	0.8
3/4″	2.2	2.2	1.1	1.2
1″	2.4	2.6	1.1	1.6
1 1/4″	2.8	3.0	1.4	2.5
1 1/2″	3.0	3.4	1.5	3.3
2″	3.4	4.1	1.6	4.7

Full dimensional drawings and the complete temperature/pressure rating chart are available in our downloadable spec sheet.

Download the Spec Sheet (PDF)

Gasket Kits: When to Replace Just the Seal

Because the SUA’s sealing surface is the gasket rather than the union housing, most maintenance only requires a gasket change rather than a full union replacement. Uniflex offers two gasket kit options:

• SUG — Includes 10 replacement gaskets for facilities that need to restock the wear component without replacing hardware.
• SUGR — Includes 10 gaskets and 10 retaining rings for a complete internal refresh of the sealing components.

Installation Tip

Using the Uniflex coupling in all regulator and trap stations up to 2″ simplifies future changeouts, since components in each size class are fully interchangeable and end connections can be mixed as needed.

Partner with Uniflex for Reliable Pipe Couplings

Trust Uniflex for pipe couplings that reduce maintenance, simplify stocking, and hold up to the demands of high-pressure, high-temperature pipe fitting systems. Our team can help you specify the right model, material, and end connection for your application or plumbing systems.

Request a quote or contact us at 248-486-6000 to discuss your project.

Frequently Asked Questions

What is the Uniflex SUA pipe coupling?

The SUA is a gasketed pipe union manufactured by Nicholson and supplied by Uniflex. It replaces traditional ground joint unions by using a spiral-wound gasket to create a leak-tight seal rated to 3000 PSIG and 850°F, reducing the maintenance and stocking issues common with precision-machined ground joints.

What sizes does the Uniflex coupling come in?

The SUA coupling is available in 1/2″ to 2″ pipe sizes, in either NPT threaded pipes or socketweld connections.

What pressure and temperature can the SUA coupling handle?

Carbon steel housings are rated up to 3000 PSIG at 100°F, and Type 316L stainless steel housings are rated up to 2430 PSIG at 100°F, with service temperatures up to 850°F. Pressure ratings decrease as operating temperature rises, so consult the full rating chart for your specific application.

What end connections are available?

The SUA is available with threaded pipe connectors(NPT) or socket-weld end connections, and the two can be combined on a single union to match your existing piping setup.

What materials are the couplings made from?

The housing is available in forged carbon steel (ASTM A105) or Type 316L stainless steel. The gasket is spiral wound Type 304 stainless steel with a graphite filler, and the retainer is Type 316 stainless steel. Additional gasket materials, including Teflon filler, Monel, Inconel 600, and Hastalloy, are available as options.

Can I replace just the gasket instead of the whole coupling?

Yes. Because the gasket is the primary sealing component, most maintenance only requires replacing the gasket rather than the entire union. Gasket kits are available as SUG (gaskets only) or SUGR (gaskets with retaining rings).

How is the SUA different from a standard ground joint union?

A ground joint union relies on two precision-machined metal surfaces to form a seal, which can wear or warp over time and cause leaks. The SUA uses a spiral-wound gasket held by a patented retainer instead, so the seal does not depend on maintaining a perfect metal-to-metal fit, and reassembly time is typically reduced by more than 60%.

Is the SUA coupling safe to use during welding?

Yes. The gasket is installed after the coupling is welded into a piping system, protecting the sealing surface from heat damage during installation.