July 29, 2021

How to Choose Variable Spring Supports

Choosing spring supports can be a confusing and time consuming task, we are here to help!

How To Choose Variable Spring Supports

Retaining the appropriate pipe orientations is vital for permitting sufficient fluid flow throughout a process. It requires hangers (rigid or flexible) that provide supports at critical points of the piping system. These systems experience thermal expansions or vibrations that lead to slight vertical displacements. Using rigid hangers under such conditions tends to exacerbate safety risks as they restrict vertical movements, increasing the internal pipe stresses. Spring supports compensate for the vertical displacements by corresponding elastically to thermal expansions, vibrations and load variation. By design, variable spring supports exert varying supporting loads on pipes over a specified displacement range per the spring’s stiffness. The hangers’ compression springs have an initial load setting and extend or retract in response to changes in pipe load quantities. The variation limits extend by approximately 25% of the usual loading based on the sensitivity of the piping. The rate of change in spring load compared to the final load setting defines the variability factor of the hanger.

Selection Criteria

1. Size of load to be supported by the hanger
The travel series (maximum vertical displacement) is a function of the hot load and must fall within the variability range of the support. Undersizing the hanger leads to the accumulation of undesirable external loads that dissipate through connections, other supports or pipeline equipment leading to system instabilities. Maximum deflection should correspond to the spring rate. A certain amount of load will give a definite extension or retraction distance of the compression spring. Using hangers with extra-long springs tends to increase pipe instability. Ideally, the hanger needs to support the total piping loads without deforming or impeding thermal expansion.

2. The physical arrangement of hangers
Pipe supports can be top hanging or base mounted depending on the strength and physical characteristics of the attachment structures for the hangers. The physical arrangement of supports needs to provide sufficient headroom and limit interference. In practice, pipes could be suspended vertically from beam weldments or upwards from the floor.

3. Allowable piping load deviation

Load deviation represents the difference between the hot load (actual operating conditions) and the cold load (initial or installed setting). These values are vital for determining the variability of hangers. When choosing a hanger, consider the actual stress levels that the system generates over the hot and cold operating conditions. The variability of standard hangers is limited to 25% per the Manufacturers Standardization Society (MSS) specifications.

The Selection Procedure

Choosing a variable spring hanger shouldn’t be a daunting task. Standard MSS charts provide essential recommendations for typical hanger types. The following is a simple procedure for selecting the proper size and series of a hanger.

Determine the permissible hot load for the piping system and the Accompanying Vertical displacement.
Estimate the travel range based on the hanger’s spring rate
Select the tiniest spring that satisfies hot load displacements ( Maximum Displacement at hot load should lie within the spring’s deflection range).
Verify if the cold load lies within the spring’s operating range.
Should the cold load lie beyond the selected spring parameters, select the next one with a higher travel range.
If the spring satisfies hot and cold load requirements, verify if the variability lies within the acceptable limits.