Resources
There are several references for process duct work. These references are worked together to review duct design processes. Other references are often used for duct design, but they give similar results. Finite element design of process duct work is possible, but a requirement of design theory and allowable stresses is required to properly interpret the finite element model.
- ASCE - Structural Design of Air & Gas Ducts for Power Stations and Industrial Boiler Applications
- Roark & Young. Formulas for stress & Strain, various editions
- US Steel Plate, Plate Structures, Volume I & II
- US Steel Plate, Steels for Elevated Service Temperatures 1974
- AISC, On Line steel temperature versus Yield, and steel temperature versus Young's modulus charts.
- Lincoln Arc Welding, Design of Welded Structures, Omar Blodgett, chapter 6, Section 6.6
- Lincoln Arc Welding, Tubular Steel Structures, by Troitsky
- Cold Formed Steel Structures
- ASHRE, for the design of pressure drop, elbows and fans
- API 560, contains references to minimize wind ovaling
- SMNACA can also be use as a reference
Cement, lime and lead industry accepted dust loads (for structural loading) are: Process ductwork is intended to convey large volumes of dust. some of this dust will settle to the bottom of the duct during power outages and normal operation.
The percentage of duct cross section filled with dust is often assumed to be as follows:
- Duct slopes level to 30 degrees, 40% of cross section.
- Duct slopes, 30 degrees to 45 degrees, 25% of cross section
- Duct Slopes, 45 degrees to 85 Degrees, 15%
- Above 85 degrees, a 2 in (50 mm) interior coating of dust.
- These loads are always confirmed with the client, before use, but the above in US common practice
To minimize the build up of dust, each material has a minimum carrying velocity, lime = about 2800 fpm., cement about 3200 fpm, and lead dust about 4200 fpm.
Dust density depends on industry, Normally these are: cement dust density = 94 pcf, lime industry = 50 pcf, lead oxide dust = 200 pcf.
Duct Wear: High temperature ductwork often caries large volumns of hot abrasive dust. Often the design temperature of the duct, or the abrasiveness of the dust, prevents the use of abrasive resisting steels. In these cases refractory can be anchored inside the duct, or abrasive resisting tiles, with weld nuts, are welded to the inside of the ductwork.
Duct Thermal Movement Duct steels expand with temperature. Each type of steel may have a different coefficient of thermal expansion.
Read more about this topic: Process Duct Work
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