Metal Expansion Joints Overview
This website outlines selection and installation of our Metal Bellows type Expansion Joints and pump connectors for use in pipe lines and process vessels to absorb motion in the system. Our products incorporate the latest recommendations of the Expansion joint Manufacturers Association.
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Construction Details
Bellows Profile
Unaflex® “MATCHLESS” Expansion Joint Bellows are produced from fully annealed type 321 stainless steel sheet stock rolled into a tube and seam welded. The latest technology in forming the corrugations of our bellows is employed. Other alloys such as Inconel®, Monel®, Titanium and 316 stainless steel may be provided from our extensive inventory or raw materials.
Fixed Flanges Type 44 
Ends are plate steel flanges conforming to ANSI dimensions welded directly to the integral ends of the bellows. Stainless steel and other alloys are available when specified.
Floating Flanges Type 66 
Ends are flat face plate flanges conforming to ANSI dimensions secured to the integral end of the bellows flared (Vanstoned) to retain the flanges. This allows the use of carbon steel flanges when the only wetted parts will be stainless steel of the bellows. Also permits easy bolt hole alignment.
Welding Nipples Type 22
Ends are carbon steel welding nipples with ANSI standard bevel. Schedule 40 pipe size is used through 12” diameters. 1/4” wall thickness for sizes over 12” unless otherwise specified.
Applications
- Diesel Engine Exhaust
- Diesel Generator Exit and Boiler Flue
- High and Low-Pressure Turbine Piping
- Main Feed Pump Suction
- Propeller Shaft Air System
- Condensate Pump Suction
- Saturated and Superheated Steam
Definition of Movement |
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| Axial Compression is the dimensional shortening of an Expansion Joint along its longitudinal axis while axial extension is the dimensional lengthening of the expansion joint. | Lateral Deflection is the relative displacement of the two ends of an Expansion Joint perpendicular to its longitudinal axis. | Angular Rotation is the displacement of the longitudinal axis of the Expansion Joint from its initial straight line position into a circular arc. |
Anchoring and Guiding
To assure satisfactory performance of an expansion joint in a piping system, it is imperative that the system be properly anchored and guided. Anchors must be designed to withstand the thrust forces, spring forces and guiding frictional forces of an expansion joint. Pressure thrust must be calculated by using the highest internal line pressure which the system will experience. This is frequently the test pressure. Spring force can be calculated from the expansion joint design data in our catalog.
Cycle Life
The cycle life of an expansion joint is the number of stress cycles endured, at operating conditions. A stress cycle is defined as one complete movement of the expansion Joint from initial to extreme position and return. "Matchless" Expansion joints are rated for 7000 cycles of life at maximum operating pressure and temperature if properly installed. For higher cycle life requirements, consult Unaflex Engineering Dept. Elevated temperatures reduce both rated movement for a given cycle life and pressure capabilities. To compensate multiply both rated movement and maximum pressure by the temperature compensating factor in the chart to the right.
| Temperature °F | Temperature Compensating Factor |
Room Temp. |
1.00 .86 .80 |
| 400 500 600 |
.78 .77 .74 |
| 700 800 900 |
.70 .66 .62 |
| 1000 1100 1200 |
.60 .58 .55 |
| 1200 1400 1500 |
.46 .35 .26 |
| *All information subject to change without notice | |