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What Is a Constant Spring Hanger? | Process Engineering Glossary
What Is a Constant Spring Hanger?
A constant spring hanger is a pipe support device that provides an essentially constant support force throughout its full range of vertical travel, regardless of how far the spring deflects as the pipe moves due to thermal expansion or contraction. This constant-force characteristic is achieved through an internal mechanism, typically a helical spring combined with a lever or cam arrangement, that compensates for the spring’s natural tendency to change force with deflection, maintaining a nearly uniform support load across the entire travel range.
Constant spring hangers are used at critical locations where the load variation inherent in a variable spring hanger would cause unacceptable pipe stress or equipment nozzle loading, providing more consistent support at the cost of greater mechanical complexity and higher initial expense.
Applications of Constant Spring Hanger
Critical Equipment Nozzle Locations
Locations near sensitive equipment nozzles where load variation from a variable spring would cause nozzle forces to exceed manufacturer allowables in either the cold or hot condition often require constant spring hangers.
Large Thermal Movement Locations
Piping locations with very large vertical thermal movement produce excessive load variation in variable springs, making constant springs necessary to keep load variation within acceptable limits.
High-Temperature and Cryogenic Piping
High-temperature piping and cryogenic piping both experience large thermal movements from ambient to operating temperature, frequently requiring constant spring hangers at multiple support locations.
Benefits of Knowing Constant Spring Hanger
Provides consistent support across the full travel range. The essentially constant support force eliminates the load variation concern that limits variable spring hanger applicability at critical locations.
Reduces equipment nozzle load variation. Constant support force at spring locations near equipment nozzles keeps nozzle loads more consistent between cold and hot conditions, simplifying nozzle load compliance.
Supports larger travel ranges than variable springs. Constant spring hangers are available in larger travel ranges than variable springs, accommodating the movement at locations where variable spring travel capacity would be insufficient.
Limitations to Consider
Higher cost and mechanical complexity. The internal cam or lever mechanism that provides constant force adds significant cost and mechanical complexity compared to a simple variable spring hanger.
Internal mechanism requires periodic inspection. The cam or lever mechanism can wear, bind, or corrode over time, requiring periodic inspection to confirm continued proper operation during plant turnaround activities.
Overspecification wastes money. Using constant springs where variable springs would be adequate wastes the cost premium, making correct identification of truly critical locations important to avoid unnecessary expenditure.
Constant Spring Hanger FAQ
How does load variability determine when a constant spring is needed?
Piping stress analysis calculates the load variability at each spring support location, and when that variability exceeds the acceptable limit, typically 25 percent, a constant spring hanger replaces the variable spring.
How does cold load relate to constant spring hanger installation?
Like variable springs, constant spring hangers are preset to their cold load position with travel stops for installation, with stops removed when the system reaches operating conditions.
How does constant spring hanger selection relate to primary stress and support spacing?
The spring must carry the load determined by support spacing and primary stress analysis while accommodating the predicted vertical movement at that location.
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