Duct Design Experts, How do I de

[ctmecheng]

Duct Design Experts,

How do I determine if my circular duct design needs stiffening rings? And, if it does need them, how do I determine the correct member size for the stiffener?

After reading "The Structural Design of Air and Gas Ducts for Power Stations and Industrial Boiler Applications," I used their determination of D/t, distance between supports over the thickness of the duct, as less than 10 will produce minimal meridional stresses. From this I determined for my duct design I get a value of 3.9 for my largest span between supports. I am assuming that since this value is less than 10 that I will not need any stiffening rings. The pressure for this duct, in history, has reached a maximum of 15 in of H2O, ~0.5 psi. Since this pressure is minimal my hoop stresses are minimal. Is my method behind this correct or am I off in the wrong direction.

Also, the duct design it needs to be relatively modular for installation. How do I determine what member size I should use for my mating face? My duct size is 11'-6" OD and I was considering rolled channel but I do not know how to best determine the size. Along with the mating condition how do I determine the best choice for gasket material?

Thank you in advanced for all of your help,
CTmecheng

 

[lilliput1]

You have to get SMACNA Industrial Duct Design. They would have tables for duct reinforcing requirements depending on pressure duty and gauge of ductwork. Also they have details on ductwork connections.