DYNASTA
Introduction
Pipe stress analysis is a critical aspect of piping system design, ensuring that pipelines can withstand various forces such as thermal expansion, weight, pressure, and external loads. One of the essential elements in stress analysis is the selection and placement of supports. Proper support selection helps prevent excessive stresses, displacements, and failures in the piping system. This article explores the different types of pipe supports used in stress analysis and their functions.
1. Normal Supports
a) Anchor Supports
• Completely restrict movement in all six degrees of freedom (three translational and three rotational).
• Typically used at equipment nozzles, fixed points, or near expansion joints.
• Example: Welded supports on a structural beam.
b) Rest Supports
• Allow movement in the horizontal plane but prevent downward movement due to gravity.
• Commonly used for supporting long horizontal pipes.
• A sliding plate (Teflon, …) may be used to reduce friction forces and facilitate thermal expansion
• Example: A pipe resting on a steel beam.
c) Hold down Supports
• Restrict upward movement of the pipe while allowing horizontal movement.
• Used where uplift forces are expected due to internal pressure or thermal effects.
• Example: Pipe clamps with hold-down restraints on elevated pipe racks, flare, bridge
d) Axial Stops
• Restrict axial movement but allow lateral movement.
• Control axial displacements.
• Example: Pipe shoe/ Pipe clamps with axial stops.
e) Guides
• Allow axial movement but restrict lateral displacement.
• Used in pipelines subjected to thermal expansion or dynamic forces.
• Example: Guides along a straight pipe run.
2. Special Supports
Special supports shall be used in specific cases as per stress analysis.
a) Spring Hangers
• Absorb vertical movement due to thermal expansion or load variations.
• Two types:
o Variable Spring Hangers – Allow variable deflection and load absorption.
o Constant Spring Hangers – Maintain a constant supporting force regardless of displacement.
• Commonly used in high-temperature systems, steam and hot fluid lines to reduce stress concentration.
b) Rigid Hangers
• Provide support in vertical to prevent downward movement due to gravity.
• Used as a alternative design to normal rest supports without friction.
• Commonly used in onshore plant
c) Rigid Struts
• Work as compression as well as tension element.
• Restrict movement in specific directions while allowing controlled flexibility in others.
• Be a good alternative to the normal piping guide supports in piping systems subjected to dynamic loads.
• Example: Steel struts installed to prevent excessive movement in high-vibration environments.
d) Snubbers
• Absorb sudden forces and limit excessive movement during dynamic events like water hammer, or seismic activities.
• Types:
o Hydraulic Snubbers – Use hydraulic fluid to dampen shock loads.
o Mechanical Snubbers – Utilize mechanical springs for energy absorption.
• Commonly used in nuclear plants and high-energy piping systems.
e) Dampers
• Reduce oscillations and vibrations in piping due to rotating equipment or external loads.
• Example: Tuned mass dampers installed near vibrating machinery.
Conclusion
Proper selection of pipe supports is crucial in stress analysis to ensure structural integrity, minimize excessive loads on equipment, and maintain operational safety. Engineers must consider factors such as thermal expansion, external forces, and system constraints when choosing support types. By strategically implementing a combination of rigid, flexible, guided, and vibration-absorbing supports, piping systems can be optimized for durability and performance.
