These duct construction standards are intended for use by contractors, fabricators, and designers of air pollution control, pneumatic conveyance, and industrial ventilation systems.

Changes in the Third Edition –

The changes in this edition are relatively minor; generally reflecting clarifications based on contractors’ technical inquiries, and three main changes as described below:

• In the Duct Materials chapter, Aluminized Steel was added including a description of its unique corrosion and heat resistant characteristics, available thicknesses, and common uses.
• In the Duct Selection Tables for Carbon and Galvanized chapter, it was assumed that the yield strength and modulus of elasticity of carbon steel remains relatively constant from ambient to the maximum recommended design temperature of 650° F (345° C). However, the reality is that both strength characteristics drop a few percent, and while this effect is more signifi cant in the design of rectangular duct, it was decided that for the sake of consistency, the temperature correction factors established for rectangular industrial duct be adopted for round industrial as well. An analysis of the impact of this strength reduction reveals that in the overwhelming majority of cases there is no change in selected gage thickness from the previous edition. The reason for this is that when selecting duct material, we compare the calculated metal thickness to the equivalent decimal thickness of the selected gage, and since the selected gage must exceed the required thickness, the excess thickness offsets the increase required by the drop in metal strength. In the data of all the duct selection tables, only one case out of hundreds, required change to a heavier gage over the previous edition. 
• The other significant change is in the duct selection tables for Aluminum. Whereas aluminum sheet thickness has traditionally been based on the Brown and Sharp gage; for a number of years now, both manufacturers and users of aluminum identify sheet thickness by the decimal equivalent of the same Brown and Sharp gage. To simplify ordering material the aluminum tables have been updated from gage number to its decimal equivalent (nominal thickness), while calculations are still based on the minimum decimal thickness from the Brown and Sharp gage (See Table 3–7).
• Users of this standard should note that, as with the use of the term "duct", the term “pipe” can be used when indicating conveyance of air between two points. The term “pipe” originated in foundries and pneumatic conveying applications for industrial environments, and historically the terminology of “pipe” and “duct” have been used interchangeably. Likewise, theses terms have been used interchangeably within the scope of the SMACNA Round Industrial Duct Construction Standard.

Changes in the Second Edition –

The 1977 edition of these standards was the fi rst publication dealing with the selection of duct gage and reinforcing systems for industrial duct applications. While the fi rst edition served industry very well for many years, technology has continued to move forward, and the Industrial Task Force of SMACNA has responded to our membership’s request to expand and update the original text. We are taking their request one step further by restructuring the manual and providing supportive software to make the design process more “user friendly.” One of the main considerations in the development of the new standards is the opportunity to create a software program for personal computers that can greatly expand the computational capability of the user and permits an almost unlimited examination of different construction details and design solutions. A comprehensive review of the old procedures was completed and modifi cations implemented to update the technology and make the design procedures compatible with the computerization effort.

While the new procedures include many of the same assumptions as the original work, a number of new features have been added: 

• Microsoft™ Windows® based calculation software to expedite selection of construction details (software sold separately)
• Four different types of carbon steel and two different types of galvanized steel
• Seven different types of stainless steel alloys
• Four different types of aluminum alloys
• Design capability for high temperature systems up to 800°F (427°C), and higher with design review by a specialized professional
• Consideration of wind, snow, ice, and maintenance loads
• Expanded tables to include ducts to 96 in. (2440 mm)
• Expanded tables to include material up to ½ in. (12.7 mm) thickness
• All data presented in both English (Inch–Pound) and Metric (SI) units
• Expanded data for the selection of duct supports
• Chapter on the use of spiral lockseam pipe in industrial applications
• Accepted industry practice for round industrial ducts
• New Duct Class 5 for systems handling corrosives
• New chapter on welding
• New guide specification for the fabrication and installation of industrial duct systems
• Chapter of practical examples with step-by-step calculation instructions
• Chapter of flow charts to guide the user in design process

The Industrial Task Force is greatly indebted to Dr. Michael C. Soteriades, who did the original work for the first edition and also provided the professional consultation and analysis necessary for the development of this new and expanded publication.