Metallic Expansion Joints >>

Single Metallic Expansion Joints

This expansion joint is simply a bellows element with end connections. Regardless of accessories, such as liners and covers, it will deflect in any direction or plane that the bellows will. It is the least expensive type, but requires that the piping be controlled as to the direction of the movements required of the unit. 

The expansion joint should not be expected to control the movement of the pipe. If the piping analysis shows that the expansion joint must accept axial compression, then the piping must be guided and constrained so that only that movement will occur. 

This expansion joint will not resist any deflections with any force other than the resistance of the bellows, which is a function of the spring rate times the deflection amount. It is incapable of resisting the pressure thrust along its axis, which is the product of the pressure times the effective, or cross sectional, area of the bellows. Large diameter units, even with low pressures, can generate very large axial pressure thrust forces, which must be reacted by main and directional anchors. Otherwise the expansion joint will extend with disastrous results.

Multi-ply Stainless Steel Bellows
50 PSIG 85 PSIG 150 PSIG 300 PSIG

CYCLE LIFE AND RATED MOVEMENT

PT&P's single expansion joints are designed for 3000 cycles for any one tabulated movement shown. Cycle life may be increased, or movement may be increased (decreasing the cycle life) by utilizing the graph located on this page. The graph may also be used for superimposing more than one movement condition on the bellows at one time. It is important to remember that the movements shown in the bellows data pages do not allow for any installation misalignment. A proper specification for a bellows expansion joint should reflect what the actual system movements will be. To insure the highest quality bellows for the least cost, all movement conditions must be taken into account. Refer to the HOW TO ORDER section on page 43 for an example of the proper analysis and selection of a expansion joint.

Examples of movement conditions that typically occur in a piping system are:

• Installation Allow one cycle installation misalignment.

• Start Up/Shut-Down Movements produced between the minimum ambient temperature and the maximum start-up temperature. This is normally a very low number of cycles.

• Operating Movements produced due to temperature fluctuations during system operation. This is typically a very small movement for a very large number of cycles.

• Excursion Movement resulting from a worst case/ upset scenario, occurring during system operation. This is normally a very low number of cycles.

How To Use Graph

• Enter the graph horizontally at the number of anticipated cycles or the movement condition being considered.
• Move vertically until the graph is intercepted.
• Move horizontally and read conversion factor.

Example: Enter graph at 1,000 cycles; read C. F. of 1.

• Note: Maximum increase in movements for combined movement conditions shall not exceed 110% of catalog rated movements
• Note: Please reference the print version of Piping Technology & Products' Expansion Joint Catalog for reference tables containing technical data on Expansion Joints.

    HOW TO SELECT AND ORDER

    The first step in selecting the proper expansion joint assembly is to collect and organize as much information regarding the design and operating parameters of the system as possible. As a minimum the following information should be provided:

• Size of the line.

• Design pressure.

• Design temperature.

• Design movements and required cycle life.

• Overall length requirement, if any.

• Type of end connections.

• Bellows material.

• Pipe material.

• Flange specification and material.

• Type of expansion joint.

• Accessories.

Please refer to the data sheet on page 28.

Thick Wall Flanged and Flued Head Expansion Joint

EXAMPLE

1. Assume the following expansion joint design criteria:

a) Line size: 16-inch nominal diameter.

b) Design/operating pressure: 160 psig.

c) Design/operating temperature: 450° F.

d) Movements/cycle life:

Installation: 0.25-inch compression; 0.125-inch extension; 0.0625-inch lateral; 0° angulation. Start-up/shut down: 1.0-inch compression; 0.25-inch lateral; 0°angulation; 300 cycles. Operating: 0.25-inch compression; 0.063-inch lateral; 1.0° angulation; 10,000 cycles.

e) End connections: 150 lb ANSI raised face slip-on flanges; ASTM A l05 (carbon steel).

f) Bellows material: A-240-T316.

g) Type: Single; unrestrained (i.e. no tie rods, hinge, or gimbal hardware).

h) Accessories: Liner and cover.

2. Turn to the Conversion Factor Graph and calculate equivalent catalog movements.

    Total = 1.13 0.27 1.3

3. Refer to page 54, 16-inch nominal diameter single expansion joints, and go to the lowest pressure rating that is equal to or greater than specified design pressure (160 psig). Compare the total equivalent catalog movements to those shown in the catalog, keeping in mind that the tabulated movements in the catalog are for 3000 cycles for one movement only.

4. Select the shortest overall length that by inspection would appear to meet the movement criteria. Use the following formula to determine if the selected overall length is acceptable.

EQUIV. AXIAL EQUIV. LATERAL EQUIV. ANGULAR

RATED AXIAL RATED LATERAL RATED ANGULAR

200 psig rating/l 8-inch O.A.L.

1.13 0.27 1.30

2.75 0.69 10.0

5. Since 0.93 is less than 1.0, the 200 psig/l8-inch O.A.L. will meet the criteria for all the movement conditions specified in Step 1.

6. Include the designations for the type (S for single), and liner (L), and cover (C) in the part number. All of the actual movements must be specified when combination ends or covers are specified.

7. On combination end units, the direction of flow must be specified.

8. The resulting PT&P part number would then be as follows:

Part Number Example

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