What Is a Spring Hanger? Variable Support
Quick Answer: A spring hanger (also called a variable spring hanger or variable support) is a pipe support that uses a helical coil spring to carry the weight of a pipe while allowing vertical thermal movement. As the pipe moves up or down due to temperature changes, the spring compresses or extends, and the supporting load changes proportionally. Spring hangers are the standard solution for suspended hot pipes on pipe racks and equipment connections in refineries, power plants, and petrochemical facilities.
How It Works
A spring hanger consists of a coil spring housed inside a cylindrical or box-type casing, with a load-indicating scale and a travel-indicating pointer. The hanger is installed between the overhead structural steel and a pipe attachment (rod, clamp, or clevis). During operation, the pipe moves vertically due to thermal expansion; the spring accommodates this movement while continuing to support the pipe weight.
Because the spring force varies with displacement (F = k x d, where k is the spring rate), the support load at the operating position differs from the load at the cold (installed) position. This variation is expressed as a percentage.
Selection Specifications
| Parameter | Typical Range | Notes |
|---|---|---|
| Load range | 0.1 kN to 250 kN (25 lbf to 56,000 lbf) | Per manufacturer catalog (sizes 0 through 30+) |
| Travel range | 5 mm to 250 mm (0.2 in to 10 in) | Per spring size and type |
| Load variation | Max 25% (per MSS SP-58) | Difference between cold and hot load |
| Spring rate (k) | Fixed per spring size and type | Published in manufacturer tables |
| Operating temperature | Up to 550 C (1,020 F) for standard springs | Higher with special materials |
| Design standard | MSS SP-58 / MSS SP-69 | Materials, design, selection, application |
Selection Procedure
- The pipe stress engineer runs a thermal flexibility analysis and identifies support points with vertical movement.
- At each spring location, the software outputs the hot load (operating weight), cold load (installed weight), and vertical travel (movement from cold to hot).
- The engineer selects a spring size from the manufacturer catalog where the operating load falls within the spring’s working range and the travel does not exceed the spring’s capacity.
- The load variation (%) is checked: (hot load - cold load) / hot load x 100. If this exceeds 25%, a constant spring is used.
- The cold load setting (pre-load) is specified so the spring is set at the factory and locked with a travel stop for installation.
Variable Spring vs. Rigid Support
| Feature | Rigid Support (rod hanger) | Variable Spring Hanger |
|---|---|---|
| Vertical movement | None allowed | 5-250 mm |
| Load variation | Zero (constant dead weight) | Up to 25% |
| Cost | Low | Moderate |
| Application | Ambient-temperature pipes, minimal movement | Hot or cold pipes with thermal displacement |
| Pipe stress impact | Can create high stresses if pipe moves | Absorbs movement, reduces nozzle loads |
Spring hangers are required for maintaining acceptable nozzle loads on equipment such as pumps, compressors, and heat exchangers. Overloaded nozzles from improperly supported pipes are a leading cause of flange leaks and equipment misalignment during plant operation.
Mounting Configurations
Spring hangers can be installed as overhead (suspended) or base-mounted (seated) units:
- Top-mounted: Hanger attached to structural steel above the pipe; rod and clevis connect to a pipe clamp or lug. This is the most common arrangement on pipe bridges and rack top tiers.
- Base-mounted: Spring can assembly sits on the support steel, with the pipe resting on top via a pipe shoe. Used where overhead steel is not available.
Both configurations follow MSS SP-58 for materials and MSS SP-69 for application guidelines.
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