Spring Hanger/Spring Support :When the piping system moves up or down due to thermal expansion, conventional rigid support is not feasible, as it may not take load at all or it may act as a pivot. Under such condition, it is recommended to use flexible support such as spring hangers. These spring hangers sustain the primary load by their resistance against compression while allowing for free thermal expansion. This is used to support the piping subjected to vertical movement where constant supports are not required. The inherent characteristic of a variable spring hanger is that its supporting force varies with the spring deflection as explained here.
The pipe weight is balanced by the spring resistance which is equal to the spring rate multiplied by the amount of compression the spring undergoes due to the pipe weight. During thermal expansion, the vertical movement of the pipe tends to reduce the compression on spring, thereby reducing its supporting force on the pipe also. Since the pipe weight is same during any condition, cold or operating, the variation in supporting force results in pipe weight transfer to the adjacent supports and / or equipment nozzles and consequently additional stresses in the system. When variable spring hangers are used, the effect of this variation must be considered. To quantify this variation, a factor called Variability Factor is introduced which is defined as,



Variability = (Spring Rate x Movement / Hot Load) X 100%
= {( Hot Load - Cold Load) / Hot Load} X 100 % (Downward Case)
= {(Cold Load - Hot Load) / Hot Load} X 100% (Upward Case)
Hot Load = Dead Weight + Lower Component Weight
Cold Load = Up : Hot Load + (Spring Rate x Movement)
Down : Hot Load - (Spring Rate x Movement)