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What Is a Variable Spring Hanger? | Process Engineering Glossary
What Is a Variable Spring Hanger?
A variable spring hanger is a pipe support device that uses a helical coil spring to support a pipe’s weight while allowing the pipe to move vertically as it expands or contracts due to temperature changes during operation. The support force a variable spring provides changes as it deflects, increasing as the spring compresses and decreasing as it extends, following the linear relationship defined by the spring’s spring rate, which means the support load varies between the cold installed condition and the hot operating condition.
Variable spring hangers are the most common type of spring support in process piping, used at locations where thermal expansion causes vertical pipe movement that a rigid support cannot accommodate without creating excessive restraint forces on the piping system during thermal cycling.
Applications of Variable Spring Hanger
Hot Piping Vertical Movement Support
Variable spring hangers support pipe weight at locations where thermal expansion causes vertical movement, maintaining support while accommodating the movement that a rigid hanger would resist.
Equipment Nozzle Load Management
Spring hangers near equipment nozzle connections help manage the support loads during thermal movement, keeping nozzle forces within equipment manufacturer allowables across both cold and hot conditions.
Pipe Bridge and Rack Elevated Piping
Piping on pipe bridge structures that experiences significant vertical thermal movement uses variable spring hangers at locations where rigid supports would create unacceptable stress or nozzle loads.
Benefits of Knowing Variable Spring Hanger
Accommodates thermal movement while maintaining support. Variable springs provide continuous pipe weight support throughout the full range of thermal movement, preventing the pipe from becoming unsupported during operation.
Widely available and well-understood technology. Variable spring hangers are a mature, standardized product available from multiple manufacturers in a wide range of load and travel capacities.
Simpler and less expensive than constant-force alternatives. Where the load variability from a variable spring is acceptable, it provides a simpler and less costly solution than a constant spring hanger.
Limitations to Consider
Support force varies with position. The inherent load variation between cold and hot positions means the pipe experiences different support forces at different operating states, and this variation must be acceptable for the piping stress analysis to show satisfactory results.
Travel stops must be removed before operation. Travel stops that lock the spring during construction must be systematically removed before the system enters service, and forgotten travel stops create rigid support conditions where springs were intended.
Spring selection requires accurate load and travel data. Correct spring selection depends on accurate predicted loads and travel from piping stress analysis, and errors in these predictions result in springs operating outside their intended range.
Variable Spring Hanger FAQ
How does spring rate affect variable spring hanger performance?
Spring rate determines how much the support load changes per unit of travel, with lower spring rates producing less load variation but requiring physically larger springs for the same load capacity.
How does cold load relate to variable spring hanger installation?
Variable springs are preset to their cold load position for installation, with travel stops holding the spring at this preset until operating conditions are established and the stops are removed.
How does variable spring hanger selection relate to support spacing?
The load each spring must carry is determined by the pipe span established during support spacing design, with the vertical movement at each location determining the required spring travel capacity.
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