Table Of ContentStructural Design of Air and
Gas Ducts for Power Stations
and Industrial Boiler
Applications
Second Edition
Prepared by the Air and Gas Duct Structural Design Committee
Published by the American Society of Civil Engineers
Library of Congress Cataloging-in-Publication Data
Names: American Society of Civil Engineers. Air and Gas Duct Structural Design
Committee.
Title: Structural design of air and gas ducts for power stations and industrial boiler
applications / Air and Gas Duct Structural Design Committee of the Energy Division
of the American Society of Civil Engineers.
Description:Secondedition.|Reston,Virginia:ASCE,AmericanSocietyofCivilEngineers,
2020.|Includesbibliographicalreferencesandindex.|Summary:“Thisreportwillassist
structural engineers in understanding the structural behavior of a duct system and in
analyzing and designing its many structural components”– Provided by publisher.
Identifiers:LCCN2020007322|ISBN9780784415580(paperback)|ISBN9780784483008
(adobe pdf)
Subjects:LCSH:Powerplants–Equipmentandsupplies.|Steam-boilers.|Airducts–Design
and construction. | Flue gases.
Classification: LCC TJ164 .S87 2020 | DDC 621.31/21–dc23
LC record available at https://lccn.loc.gov/2020007322
Published by the American Society of Civil Engineers
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Copyright © 2020 by the American Society of Civil Engineers.
All Rights Reserved.
ISBN 978-0-7844-1558-0 (print)
ISBN 978-0-7844-8300-8 (PDF)
Manufactured in the United States of America.
26 25 24 23 22 21 20 1 2 3 4 5
Acknowledgments
This publication never could have been completed without the hard work and
dedication of all the committee members. I thank all of them for donating their
time and sharing their knowledge for the betterment of our industry.
Air and Gas Duct Structural Design Committee
Matthew Rosecrans, Chair Sargent & Lundy
Kevin Como Burns & McDonnell
Jason Fifarek Sargent & Lundy
John Liu Kiewit
Paul Nystedt Babcock Power
Lucas Pachal Nederveld, Inc.
Douglas Polack American Electric Power
Dennis Richard Black & Veatch (retired)
Dan Sack Becht Engineering
David Six Babcock & Wilcox
Eric Skibbe Kiewit
Jeffrey Thompson Consulting Engineer
Original Air and Gas Duct Structural Design Committee
Ron Schneider* Gilbert/Commonwealth Engineers
Dan Blackwood Southern Company Services
Vic Bochicchio Zurn Balcke-Durr, Inc.
Bob Bucelwicz Boston Edison Co.
Joe Clark* ABB Combustion Engineering Systems
Roy Hogan* ABB Environmental Systems
Bill Jacks Tennessee Valley Authority
Ron Johnson* Babcock & Wilcox
Paul Kokosinski* Public Service Electric & Gas
Tim Laughlin* Sargent & Lundy
Tom Longlais Sargent & Lundy
Jim Newell Stone & Webster Engineering Corp.
Rod Simonetti* Gilbert/Commonwealth Engineers
Mike Stiefermann* Central Electric Company
Ken Tamms American Electric Power
Walt Van Dyke* Foster Wheeler Energy Corp.
Ray Warren* Warren Engineering
Heim Weinstein Public Service Electric & Gas
Jim Whitcraft* Bechtel Power Corp.
*Individuals of the original committee providing significant and time-
consuming contributions to author various sections of this publication.
ix
x ACKNOWLEDGMENTS
Otherengineersanddesignersinthecommitteemembers’organizationsalso
contributed to the development of this ASCE publication. Some significant
contributors are
(cid:129) Daniel Biss, David Wagner, Timothy Frymoyer, and Kenneth Bauer from
Gilbert/Commonwealth Engineers;
(cid:129) Kurt Wachholder and Edward Hanko from Sargent & Lundy; and
(cid:129) Suzana Rufener from Babcock & Wilcox.
Matthew R. Rosecrans, P.E., S.E., M.ASCE
PREFACE
This ASCE publication has been created by a select committee of structural and
mechanicalengineerswhoareextremelyexperiencedinthestructuralanalysisand
designofairandflue-gasductworkforpowerstationsandlargeindustrialboiler
applications.
TheneedforthisASCEpublicationwasidentifiedin1991bytheASCEFossil
Power Committee under the chairmanship of Thomas Longlais to capture
industry practices for the design of air and gas ducts because they were not
directlycoveredbybuildingcodesorotherpublicationsatthetime.Theoriginal
Air&GasDuctStructuralDesignCommitteewasformedunderRonSchneider,
andthiscommitteefinalizedtheoriginalASCEpublicationin1995.Over20years
later the original publication was useful, but had become dated because of new
industrypractices,codechanges,andadvancementsintechnology.TheAir&Gas
Duct Structural Design Committee was revived by the ASCE Energy Division in
February 2016 to update the publication. A group of industry experts was
assembled, and all 12 committee members were given the opportunity to review
andcommentonall13chaptersofthepublication.TheresultingASCEpublica-
tion was unanimously agreed to by the committee.
vii
Contents
Preface..............................................................................................................................................vii
Acknowledgments........................................................................................................................ix
Chapter 1 Introduction..................................................................................1
1.1 Statement of Intent and Expected Use of This Book.............................1
1.2 Limitations and Scope of This Book................................................................2
1.3 Ductwork Systems Descriptions.........................................................................4
1.4 Glossary/Definitions...............................................................................................11
1.5 Descriptions of Major Ductwork Equipment............................................19
1.6 Ductwork Accessories...........................................................................................21
References..............................................................................................................................22
Chapter 2 Ductwork Arrangement and Behavior...................................23
2.1 Overview.....................................................................................................................23
2.2 Interfaces with Equipment.................................................................................25
2.3 Thermal Expansion.................................................................................................32
2.4 Supports......................................................................................................................41
2.5 Duct Geometries.....................................................................................................51
2.6 Internal Trusses and Struts................................................................................54
2.7 Effects of the Arrangement on Loads..........................................................58
References..............................................................................................................................62
Chapter 3 Structural Material: Selection, Application,
and Properties............................................................................63
3.1 Introduction...............................................................................................................63
3.2 Availability of Materials........................................................................................63
3.3 Material Properties.................................................................................................64
3.4 Material Selection...................................................................................................75
3.5 Bolts...............................................................................................................................78
3.6 Welding Electrodes................................................................................................79
3.7 Ductwork Protection.............................................................................................80
3.8 Hanger Elements.....................................................................................................82
References..............................................................................................................................82
Chapter 4 Service Conditions and Design Loads...................................85
4.1 Service Conditions..................................................................................................85
4.2 Design Loads.............................................................................................................91
References............................................................................................................................100
iii
iv CONTENTS
Chapter 5 Load Combinations and Associated Design Strengths....101
5.1 Design Considerations........................................................................................101
5.2 Stress-Based versus Strength-Based Design...........................................101
5.3 Strength at Temperatures within the Creep Range...........................102
5.4 Load Definitions....................................................................................................103
5.5 Developing Load Combinations for Ductwork Design......................104
5.6 Load Combinations for Allowable-Strength Design............................107
5.7 Load Combinations for Load and Resistance Factor Design.........109
References............................................................................................................................111
Chapter 6 Ductwork Global Structural Analysis...................................113
6.1 Introduction.............................................................................................................113
6.2 Global Approach...................................................................................................114
6.3 Structural Model Considerations...................................................................120
References............................................................................................................................131
Chapter 7 Plate Design..............................................................................133
7.1 Introduction.............................................................................................................133
7.2 Rectangular Ductwork Plate Design............................................................135
7.3 Circular Ductwork Plate Design.....................................................................142
7.4 Other Considerations..........................................................................................147
References............................................................................................................................150
Chapter 8 Structural Element Design.....................................................151
8.1 General Considerations......................................................................................151
8.2 Rectangular Ducts.................................................................................................152
8.3 Circular Ducts..........................................................................................................164
8.4 Internal Trusses and Struts..............................................................................168
8.5 Duct Supports.........................................................................................................175
8.6 Lateral External Tie Elements.........................................................................178
8.7 Serviceability and Deflection Limits............................................................178
References............................................................................................................................179
Chapter 9 Structural Design of Flow Distribution Devices.................181
9.1 Function of Flow Distribution Devices......................................................181
9.2 Flow Devices for Process Equipment.........................................................182
9.3 Flow Layout and Structural Considerations............................................183
9.4 Support Considerations.....................................................................................184
9.5 Structural Analysis................................................................................................185
9.6 Structural Design...................................................................................................188
References............................................................................................................................190
CONTENTS v
Chapter 10 Drawing, Fabrication, and Construction:
Techniques and Considerations..........................................191
10.1 General Considerations...................................................................................191
10.2 Drawings and Specifications........................................................................198
10.3 Fabrication.............................................................................................................201
10.4 Welding...................................................................................................................203
10.5 Shop Inspection..................................................................................................205
10.6 Surface Preparation...........................................................................................206
10.7 Handling and Shipping...................................................................................207
10.8 Erection...................................................................................................................210
References............................................................................................................................211
Chapter 11 Insulation and Lagging.........................................................213
11.1 Introduction...........................................................................................................213
11.2 Purpose of Insulation and Lagging...........................................................213
11.3 Types of Insulation and Lagging...............................................................215
11.4 Effects of Insulation and Lagging on the Structural
Design of Ducts..................................................................................................217
11.5 Methods of Installation and Quality of the Work.............................218
11.6 Construction Details..........................................................................................222
References............................................................................................................................225
Chapter 12 Maintenance Examination of Existing Duct Systems.....227
12.1 Factors That Influence the Need for Structural Examinations....227
12.2 Field Examination Techniques.....................................................................231
12.3 Potential Damage Areas.................................................................................237
12.4 Examination Data, Evaluation, and Disposition..................................241
References............................................................................................................................244
Chapter 13 Reinforcement of Existing Ductwork.................................245
13.1 Introduction...........................................................................................................245
13.2 Evaluation of Existing Ductwork.................................................................246
13.3 Ductwork Walkdown........................................................................................246
13.4 Ductwork Modification....................................................................................247
13.5 Reinforcement......................................................................................................249
13.6 Other Considerations........................................................................................254
References............................................................................................................................256
Index.................................................................................................................257
CHAPTER 1
Introduction
1.1 STATEMENT OF INTENT AND EXPECTED USE OF THIS BOOK
This ASCE publication has been created to assist structural engineers in the
structural analysis and design of air and flue-gas ducts for power stations and
industrial boiler applications. It is not intended to be used to size or configure
ductwork for flow and pressure drop considerations.
Theinformationinthisbookwaswrittenspecificallyforstructuralengineers.
TheASCEcommitteeresponsibleforcreatingthisbookstronglyrecommendsthat
the structural analysis and design of ducts be performed by qualified structural
engineers, and not by technicians, designers, or drafters.
Thestructuralengineeriscautionedagainstreadingselectedsectionswithout
firstreadingandunderstandingtheentirepublication.Muchoftheinformationin
each section depends on information in other sections. The structural engineer
should read all the information presented in Chapters 1 through 13 and
understand how it is interrelated before proceeding with analysis and design
activities.
Air and gas ducts for power stations and industrial boiler applications are
uniquestructures.Thestructuralanalysisanddesignoftheseductsiscurrentlynot
referenced or governed by any national code or design standard, and few
published data on ductwork structural analysis and design procedures are
available. Ductwork structural analysis and design is complicated by the need
toaccommodatelargethermalmovementsandtoassessthebehaviorofmaterials
at high temperatures, sometimes in a corrosive or erosive environment. The
structuralbehaviorofsteelductworkcanbedifficulttounderstandforstructural
engineers inexperienced in ductwork analysis and design. Usually, ductwork is
initially routedand configured considering only flow and pressure drop require-
ments, but the final arrangement must also consider structural support and
structural behavior. In some organizations, ductwork design responsibility is
divided between the mechanical process engineering and structural engineering
disciplines. Often, problems that arise can be attributed to the failure to clearly
assign and accept responsibilities between the disciplines. Communication
between the disciplines and establishment of clear areas of responsibility are
vital to ensure successful ductwork performance.
1
2 AIRANDGASDUCTS
Ductwork arrangements have become more complex, and the design
pressureshaveincreasedsignificantly,becauseofprecipitators,fabricfilters,NO
x
removal systems (also known as selective catalytic reduction, or SCR), and
scrubbers being added to the boiler exhaust system as flue-gas emission require-
mentsbecamemorestringentovertheyears.Iftheexperiencedstructuralengineer
is not allowed input into the ductwork arrangement, a structural system could
evolvethatispronetostructuraldistress.Also,higherboileroutlettemperatures
andmorecorrosivescrubberoutletgaschemistryhaveincreasedtheimportance
of choosing the proper materials and the proper design strengths. There is a
history in the power industry of failures and major degradation of flue-gas
ductwork. There are many reasons for these failures or degradation, but many
of the problems might have been avoided by better initial designs or material
selection.
The information in this book may be used for international projects.
However, if the materials to be used are different from those referenced in this
book, special attention will be required from the structural engineer. Materials
referenced byotherinternationalstandardsmay beused andshouldbe carefully
assessed by the structural engineer, including mechanical properties, chemical
composition, and material properties at elevated temperatures. Materials
equivalentatambienttemperaturemaynothaveequivalentpropertiesatelevated
temperatures.
Withthisbook,ASCEhopestofillavoidinthestructuralengineeringfield.It
isexpectedtobeusedasaguideforstructuralengineersastheyparticipateinthe
routing and configuration of a ductwork system, including the duct and its
support structure. This book is also expected to be a valuable tool for structural
engineers in understanding the structural behavior of a duct system and in
analyzing and designing its many structural components.
1.2 LIMITATIONS AND SCOPE OF THIS BOOK
1.2.1 Scope
Thisbookpresentscurrentapproachestothestructuralanalysisanddesignofair
andflue-gasductwork.Includedaresectionsonmaterialselection,behavior,and
performance; design loads, loading combinations, and design strengths; thermal
considerations; vibration considerations; structural arrangement and behavior;
toggle duct behavior and expansion joint considerations; overall duct structural
analysisanddesignmethods;anddesignconsiderationsforlocalelementsofthe
structure,suchasstiffeners,internalbraces,connections,turningvanes,andother
flow distribution devices. It also discusses drawing and specification content,
fabrication and construction techniques and considerations, duct support
methods, and special considerations in the design of duct support structures. It
discusses field maintenance examinations and inspections for preventative
