PetroStreet

Load:
In Constant Spring hanger the load remains constant throughout its travel range. But In variable spring hanger the load varies with displacement.
Thermal displacement - defining role
Spring hangers are used when thermal displacements are upwards and piping system is lifted off from the support position. Variable spring hanger is preferable as this is less costly.
Constant springs are used:
When thermal displacement exceeds 50 mm When variability exceeds 25%
Sometimes when piping is connected to strain sensitive equipment like steam turbines, centrifugal compressors etc and it becomes very difficult to qualify nozzle loads by variable spring hangers, constant spring hangers can be used.
More to follow, colleagues.

Industry approved variability
Variability= (Hot Load-Cold load)/Hot load = (Spring Constant × displacement)/Hot load.
Limit for variability for variable spring hangers is 25%.

Spring Datasheet
Major parameters are: Spring TAG, Cold load/Installed load, Vertical and horizontal movement, Piping design temperature, Piping Material, Insulation thickness, Hydro-test load, Line number etc.

Calculating the height of variable spring hanger
Select the height from vendor catalog based on spring size and stiffness class.
For base mounted variable spring hanger the height is mentioned directly. It is the spring height.
For top mounted variable spring hanger’s ass spring height with turnbuckle length, clamp/lug length and rod length.