For power and process piping in industrial plants, spring hangers or supports are often required to meet the design criteria of those piping. Spring hangers are not very complicated assembles. However, it is still important for an engineer to understand why they need to use spring hangers to piping, how they work in the field, and how to deal with field troubleshooting related to spring hangers. In this article, some fundamentals of spring hanger application will be introduced.
I. Function and Purpose of Spring Hanger
Spring Hangers are often regarded as special type pipe support with spring in the assembly. A characteristic of spring hanger which distinguishes it from other types of support is the lower stiffness (or spring rate). Having the lower stiffness than the other “rigid” pipe supports, spring hangers can accommodate the displacement of piping while it still provides some amount of reaction force to support the piping. As spring hangers are to be designed to sustain the desired piping load covering the displacement range of piping, computational piping stress analysis is highly recommended to determine the spring hanger design data such as load and travel capacity.
When there is vertical upward or downward displacement of piping occurs while there is still needs for supporting the pipe or equipment weight, a rigid support with low flexibility may not provide a good supporting capacity due to lift off of the piping, or may provide to high reaction force to piping. Spring hangers can provide much more stable supporting forces to piping while the springs are compressed or extended according to the pipe displacement.
Common cases which require spring hanger application are as follows:
- Lines connected to/from extremely high or low temperature pressure vessel (e.g. reactor, coke drum, LNG separator)
- Lines connected to/from extremely high or low temperature rotating equipment (e.g. power expander, gas compressor)
- Lines connected to fired heaters
- Lines connected to storage tanks subjected to high differential settlement
- Lines connected to high temperature air-cooled heat exchangers
- In-line shell and tube heat exchangers (reboilers) attached to column
Malfunction or omission of spring hanger at high required support locations can lead the following field troubles.
- Pipe support failure due to inappropriate load distribution
- Equipment nozzle or body failure due to excessive piping load to equipment nozzle
- Vibration of pump or compressor due to excessive piping load to equipment nozzle
- Piping component failure due to increased pipe bending stress at locations with higher stress intensity (e.g. pipe bends, tees)
- Leakage at flange connection due to excessive thermal expansion load
- Higher risk of vibration due to piping lift off from the support location
II. Types of Spring Hangers
Categorization by load types – Constant Spring Hanger
Constant spring hangers are designed with lever assembly to reduce the load variation from the pipe displacement. Conventional constant spring hangers are usually designed to meet 3~6% max. load variation. With the lever arm component in it, constant hangers can cover the pipe displacements as high as 750mm in maximum. Utilizing its characteristics, constant spring hangers are appropriate to support the piping connected to any load sensitive equipment such as a compressor. However, as the cost and the required installation space of constant spring hanger are much higher than those of variable spring hanger, the responsible engineer is recommended to optimize his or her design minimizing the number of constant spring hangers.
Categorization by load types – Variable Spring Hanger
Variable hangers with simpler assembly consist of one or more spring in side a shell are more economical and smaller than the constant spring hangers with same capacity. However, as the load variation is as high as 25%, it is not appropriate to use the variable spring hanger at locations with high pipe displacement.
Categorization by installation configuration – Hanger Type (or Suspension Type)
- Categorization by installation configuration
- Hanger Type (or Suspension Type)
Supports the piping with spring assembly consist of a clamp, hanger rod and clevis lug attached to a structure on top
Categorization by installation configuration – Pedestal Type (or Compression Type)
Supports the piping with spring assembly consist of spring can and load plate at the bottom of pipe. This spring assembly is normally installed on top of steel structure or foundation.
III. Installation of Spring Hangers
While spring hangers are not very complicated assembly, every manufacturer has its own installation and maintenance manual and provides it to the customer with the products. It is strongly required for field engineering and construction department are fully understanding the requirements and instructions in the manual. Common items to be checked during spring hanger installation are as follows:
- Primary parts and miscellaneous components of spring hanger assembly
- Name plate information
- Orientation of structural attachments such as clevis lug – considering the pipe displacement direction
- Bolting status of each component
- Welding quality of load sustaining parts
- Load indicator set as per spring datasheet