Hiscox’s flanged expansion joint uses a pipe that slides inside an outer barrel through a packing gland. End flanges connect the two members to the pipeline. The illustration shows this sliding construction, while the calculator evaluates unconstrained one-dimensional thermal length change in the entered pipe length.
Flanged Expansion Joint Interactive Calculator
Enter a reference length, a material- and temperature-appropriate mean expansion coefficient, and reference/final temperatures to calculate free thermal length change. The result does not size or select an expansion joint.
Equation Used
- Uniform temperature change over the entered reference length.
- Entered mean coefficient is valid for the actual material and temperature interval.
- The length is free to change axially without restraint for this calculation.
- Pressure thrust, restraint forces, joint friction or stiffness, combined movements and cycle life require separate piping and joint calculations.
Free thermal growth is not required joint travel unless the real piping restraints and movement distribution establish that relationship.
Sliding tube, barrel and packing gland
The longitudinal section follows Hiscox item 416. The smaller tube slides through the gland into the outer barrel, maintaining an overlapping flow passage. Packing surrounds the moving tube. Repeated motion uses illustrative dimensions and travel; it does not represent a rated joint stroke.
Actual expansion-joint behavior depends on the selected construction, restraints and full piping system. Sliding packed joints and flexible metallic bellows are different constructions. The EJMA references below concern metallic bellows; they do not establish ratings or packing requirements for this historical sliding joint.
Use free growth as one input
Choose a mean coefficient appropriate to the actual pipe material and temperature interval. The result is the length change an idealized unrestrained uniform member would undergo. A qualified piping analysis must determine how much of that movement reaches a particular joint.
Linear thermal length change
For reference length L0, entered mean coefficient alpha and temperature change deltaT=T1-T0, free length change is deltaL=L0 alpha deltaT. With alpha entered in mm/(m·°C), L0 in metres and deltaT in °C, deltaL is in millimetres. Final length is L1=L0+deltaL/1000.
Joint selection requires the movement reaching that joint, the piping restraints and the selected joint ratings. Free pipe expansion alone does not determine a permitted travel fraction.
Example free expansion
For 20 m, an entered mean coefficient of 0.012 mm/(m·°C), and a change from 20°C to 180°C, free length change is 38.4 mm and calculated final length is 20.0384 m. That does not select a 38.4 mm joint.
From free expansion to joint selection
NIST defines linear thermal-expansion coefficient from length change per initial length and temperature change, and notes that the coefficient may vary with temperature. EJMA identifies its standards as covering selection and application of metallic-bellows expansion joints, including pressure, stresses and temperature effects.
This calculator omits pressure thrust, anchors and guides, joint spring force, stress, cycle life, installation temperature and offset, simultaneous axial/lateral/angular movement, tolerances, corrosion, vibration and manufacturer-rated limits. Use the applicable code, EJMA guidance and the selected manufacturer's certified data.
Questions
Is absolute free growth the minimum required joint travel?
No. System restraints and movement distribution must be analyzed.
Is the entered coefficient a universal material constant?
No. Use a value appropriate to the actual material and temperature interval.
Does this check pressure thrust or cycle life?
No.
References
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances (1901), page 113, item 416: flanged sliding expansion joint. The EJMA links below describe the separate metallic-bellows construction.
NIST, Thermal Expansion: definition of the linear thermal-expansion coefficient and its possible temperature dependence.
Expansion Joint Manufacturers Association, EJMA Standards: scope of metallic-bellows selection/application guidance and design factors including pressure, stresses and temperature effects.
EJMA, Bellows: axial movement, cycles and the role of restraints such as tie rods and anchors.
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