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High-Temp / Steam Unions

HART High-Temp Union

Fail Safe Leakproof Reliability

At any pressure, HART O-Rings actually strengthen the seal rather than loosen it.

VViton® Florocarbon A (FKM-A)
EEthylene Propylene (EPDM)
TTeflon® Tetrafluoroethylene (FEP)
BNitrile / Buna N (NBR))
NNeoprene® Polycloroprene (CR)
KKalrez® Perfluoroelastomer (FFKM)
HNHydrogenated Nitrile (HNBR)
EPNSF Approved EPDM (Ethylene Propylene)
GMetalic Graphite Spiral Wound Seal
SHigh-Temp Steam (up to 550*F max) EPDM
INo O-Ring (Integral Seat "Bail to Cone")
Teflon®, Viton®, Kalrez® are
Registered Trademarks from DuPont


The O-ring is fitted into a machined groove between the two halves of the union. When the halves are drawn together the O-ring compresses to an ovalized cross-section, forming a positive, resilient seal which serves to block the fluid, thus sealing even at low or no pressure.

Under Load

As pressure is increased the O-ring is forced to flow and is "squeezed " into the downstream side causing the O-ring to conform to the shape of the end, blocking the groove gap. The more the system pressure increases, the more effective the seal.

Stright-Away Breakout

The flat faced construction allows for slipping the component in and out without disturbing the surrounding tube or pipe sections. Pipe alignment is much easier with Hart Unions since it is unnecessary yo spring the line during make-up or disassembly.

Specialty Orders

Specialty O-Rings also available. Inquire within.


The charts below contain all the information necessary to place an order. Use the appropriate codes in the manner shown below. Example: a Class 3000 Female Threaded 1" Union with Viton O-ring and 316 Stainless Steel Ends is coded as follows:

When a size reduction or change in material is needed, simply enter the Tailpiece code and then the Threadpiece code separated by a slash as shown below. A Dielectric Class 3000 Union with a Dielectric Coated A105 Carbon Steel Tailpiece that is 3/4" Female NPT, with a 304 Stainless 1/2" Male NPT Threadpiece, Teflon O-Ring, is coded as follows:

To order, call 800-769-0503

FNPT 3,000 lb, Pipe 31 31 0  (1/8")
1  (1/4")
2  (3/8")
3  (1/2")
4  (3/4")
5  (1")
6  (1 1/4")
7  (1 1/2")
8  (2")
9  (2 1/2")
10 (3")
11 (3 1/2")
12 (4")

V Viton® Florocarbon A (FKM-A)
E Ethylene Propylene (EPDM)
T Teflon® Tetrafluroethylene (PTFE)
N Neoprene® Polychloroprene (CR)
K Kalrez® Perfluogenated Nitrile (FFKM)
HN Hydrogenated Nitrile (HNBR)
EP NSF Approved Ethylene Propylene (EPDM)
ES Parker Steam EPDM O-Ring (500*F)
G Metallic Spiral Wound Graphite Seal
I No O-Ring (Integral Seat "Ball and Cone")
Teflon®, Viton®, Kalrez® are
Registered Trademarks from DuPont
MNPT 3,000 lb, Pipe 32 32
SW 3,000 lb, Pipe 33 33
SW 3,000 lb, Tube 34 34
BW 3,000 lb, Pipe 35 35
Sweat Copper Tube 36 36
FNPT 6,000 lb. Pipe 61 61
MNPT 6,000 lb, Pipe 62 62
SW 6,000 lb, Pipe 63 63
SW 6,000 lb, Tube< 64 64
BW 6,000 lb, Pipe 65 65
A Aluminum
B Brass 464 or 360
CS A105 Carbon Steel
304 A182F304 Stainless
304L A182F304L (low carbon) Stainless
316 316 A182F316 Stainless
316L A182F316L (low carbon) Stainless
A20 Allloy 20 (formally known as carpenter steel C20)
73 70/30 Copper Nickel
91 90/10 Copper Nickel
H Hastelloy
I Inconel
M Monel 400
T Titanium


O Orifice
D Dielectric (Insulating)
H Hammer Lug


Call to Order: 800-769-0503

High-Temp / Steam Unions

Extreme Environment, Class 3000 Service

HART Industrial spiral wound gasket unions are engineered to provide Class 3000 Service in extreme temperature and environmental conditions. Operational conditions such as temperature, pressure, and media will dictate selection of the proper spiral wound gasket for your application.

Unions containing spiral wound gaskets can be supplied to meet national standards such as MSS-SP-83 and ASME B16.20. The pipe union design is similar in principle to flange joints but outperforms the difficulties associated with standard “ground-joint” pipe unions. This is accomplished by forming the seal with replaceable spiral wound gasket without the need of a ground joint (ball & cone) finish. Our flat face design provides turbulence-free fit across seats. This design is ideal where piping requirements dictate the necessity of having a flat face seal to make and break the pipe line.

All HART Unions are Made in the USA!


  • Standard graphite spiral wound gasket union.
    • Resistant to 850*F (450C) for hydrocarbon and superheated steam service!

  • Higher Temperature Options Available!
    • Engineered solutions for 1400F (760C) and higher including turbine and energy.

Configuration Description
Standard 316 Stainless Steel with Flexible Graphite Filler
Optional 316 Stainless Steel with Silicate Filler
Custom Materials Monel 400, Inconel 600, Hastalloy, 347 Stainless, and more!

Standard O-Ring Union Features:

  • Turbulence Free: All unions provide a turbulence-free fit across the seats
  • O-Ring Isolation: The O-Ring seal is strategically located in the thread piece face reducing O-Ring media contact and added protection against abrasives and erosion.
  • Precision Machined components: All unions are precision machined to provide high quality and fail-safe leak proof reliability.
  • Interchangeable End Connections: Threaded, socket weld, and butt-weld ends are interchangeable. This feature reduces overall costs by eliminating unnecessary nipples, bushings, couplings and inserts.
  • Material Versatility: Unions can be provided in all standard metals or combination of metals. This includes 304 Stainless, 316 Stainless, A 105 Carbon Steel, Brass, Monel 400, Hastalloy, and Titanium.
  • Excellent vibration resistance: Seals will not loosen, even under extreme pressure and pressure surges.

3D Animations

HART High-Temp Union Exploded View


Order with O-Ring / Gasket Code "G" for HART High-Temp Unions!

HART High-Temp Union 3/4 View