Guidelines for Duct Hangers & Supports
Installing Fibreglass Ducting
Corrosion resistant and light weight fibreglass ducting is widely used for ducting corrosive gases at industrial sites and in corrosive atmospheres. The table below offers generalised information on hangers and supports when installing fibreglass ducting. The information is guideline only. Design for each installation needs to take into account site specific factors.
Source of Information
The information given is taken from the Australian Standard 2634-1983 "Chemical Plant Equipment - Made from Glass-Fibre Reinforced Plastics (GRP) Based on Thermosetting Resins". This standard was withdrawn in 2003 but is still used as it provides an excellent collection of user friendly design information.
The information in the table above is based on contact moulded manufacturing, a design factor of 5 to 1, pressure and vacuum limitations, ambient temperatures, and that there is no need for a corrosion barrier.
General Hanger/Support Spacings
The recommended maximum hanger/support spacings for specific duct wall thicknesses are given below.
Detailed Fibreglass Ducting Design
For the detailed design of fibreglass ducting, specific factors that need to be taken into account include:
- Chemicals and temperature to be handled
- Duct pressure, often partial vacuum
- Expansion and contraction
- Wind and seismic loads
- Other loads such as dampers and equipment
- Personnel and other loads during eg clean out
- Loads from any solids deposition
- Positions hangers and supports can be placed.
The general figures for hangers and supports given in the table opposite are not always able to be used. Also a network analysis of the pressure drops is usually done to ensure the correct sized ducting is selected and where dampers need to be placed so the airflows can be balanced.
Hanger and Support Design
In general ducts up to 600mm in diameter and not subject to vacuum service should be placed on saddles or in hangers providing 120 degrees minimum bottom support and full bearing over the supported area. For ducts of 600mm nominal diameter and above, 180 degrees bottom support should be provided. Any clamps or "U" bolts used in conjunction with the bottom supporting structure should provide a snug fit and not exert clamp pressure. Duct supports should have a minimum width of 50mm. Ducting should be supported and anchored to prevent undue loads on the duct itself and on connected equipment, and to permit controlled thermal expansion and contraction between fixed points and changes in direction.