This post gives some brief details about spring supports used in pipe supports.
What is a purpose of Spring Supports?
- In general Spring supports are installed when vertical movement of the pipe causes large stresses in the line and/or high loadings developed on equipment nozzles due to:
Lifting of the pipe from the support
Restraint for the downward movement of the pipe - Spring supports are used to ensure effective supporting in cases where there is a significant temperature difference between installed and operating conditions.
- More common in vertical piping and pipe supports near equipment’s with sensitive nozzles.
What is spring support design objectives?
- Should provide support load necessary to balance the piping system after the pipe has moved from its installed position.
- Permit total movement of pipe from its cold to hot position.
- Does not cause an excessive expansion stress range in the pipe as the spring load ranges from its cold to hot position.
What are the types of spring supports?
Main classification is based on the operating Principle, with having below main types of spring supprots.
- Variable support spring
- Constant effort spring
These types selected for use depends on the % load variation.
Mostly variable springs are selected for load variations less than 25%
Parameters used in spring supports:
What is Cold load in Spring Supports?
Load on the pipe supports under installed conditions (N) (Ambient temperature)
What is Hot load?
Load on the pipe supports under operating conditions (N)
What is Spring Rate in Spring Supports?
Spring constant of the variable spring used (N/mm)
Variable Effort Supports:
Variable Effort Spring is a device, having a single spring coil which supports the gravity loads of piping systems, that are subjected to vertical thermal movements. This device produces a varying load when the pipe moves from cold to hot position.
Variable springs are preferred to constant on economic grounds, being cheaper by a factor of between 2 and 3 than an equivalent constant unit. Generally, variability at spring adjacent to strain sensitive equipment such as pumps, compressor and turbines is limited to 20%.
Maximum variation in load is 25%.
Constant Effort Springs:
Constant Effort springs are a device having a single spring coil working in conjunction with counter balancing mechanisms to support gravity load of piping systems that are subjected to vertical thermal movements. This support produces a constant load when the pipe moves from cold position to hot position.
Construction of Spring Supports:
- Both types of spring are pre-compressed so that they exert a specified upward force on the pipe.
- This force is equal to the weight of the pipe (plus contents) the spring is intended to support, thus imposing minimum weight loading on adjacent supports or equipment.
- As the pipe moves from installed to operating position the force exerted by a variable spring alters as the compression on the coils is either increased or reduced where as that of constant unit remains virtually unaltered
- Springs are not designed for Hydro-test loads. However, support members shall be designed to take hydro-test loads.
Spring Selection Chart:
Variable & Constant Supports Comparison:
| Details | Variable Spring Support | Constant Spring Support |
| Design | Simple design with Helical spring | Sophisticated design with Spring & Bell Crank Lever |
| Application | Non critical applications Eg:-. Heat Exchangers, Vessel, ordinary piping etc. | Critical applications Eg:. Steam piping near steam turbines , Steam Headers, Boilers, etc. |
| Movement | Applicable for Low thermal movements (upto 50 mm) | Applicable for large thermal movements (above 50 mm) |
| Space | Less space for installation | Large space for installation |
| Cost | Low cost | High cost |
Applicable Standards:
MSS SP 58 – Pipe Hangers and Supports – Materials, Design and Manufacture
MSS SP 69 – Pipe Hangers and Supports – Selection and Application
MSS SP 77 – Guidelines for Pipe Support Contractual Relationships
MSS SP 89 – Pipe Hangers and Supports – Fabrication and Installation Practices
MSS SP 90 – Guidelines on Terminology for Pipe Hangers and Supports
