Steel Pipe— A Guide for Design and Installation
AWWA MANUAL M11 Fourth Edition
Science and Technology AWWA unites the drinking water community by developing and distributing authoritative scientific and technological knowledge. Through its members, AWWA develops industry standards for products and processes that advance public health and safety. AWWA also provides quality improvement programs for water and wastewater utilities.
Copyright © 2004 American Water Works Association, All Rights Reserved.
MANUAL OF WATER SUPPLY PRACTICES—M11, Fourth Edition
Steel Pipe—A Guide for Design and Installation
Copyright © 1964, 1985, 1989, 2004 American Water Works Association All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information or retrieval system, except in the form of brief excerpts or quotations for review purposes, without the written permission of the publisher. Project Manager and Technical Editor: Melissa Christensen Copy Editor: Mart Kelle Production Editor: Carol Stearns
Library of Congress Cataloging-in-Publication Data Steep pipe : a guide for design and installation.-- 4th ed. p. cm. -- (AWWA manual ; M11) Includes bibliographical references and index. ISBN 1-58321-274-4 1. Water pipes--Design and construction--Handbooks, manuals, etc. 2. Pipe, Steel--Design and construction--Handbooks, manuals etc. I. American Water Works Association. II. Series. TD491.A49 S74 628.1'5--dc22 2004043748
Printed in the United States of America American Water Works Association 6666 West Quincy Avenue Denver, CO 80235-3098 ISBN 1-58321-274-4
Printed on recycled paper
Copyright © 2004 American Water Works Association, All Rights Reserved.
Contents List of Figures, vii List of Tables, xi Foreword, xiii Acknowledgments, xv Chapter 1 History, Uses, and Physical Characteristics of Steel Pipe . . . . . . . . . . . . . . . .
.
.
.
.
.
.
1
History, 1 Uses, 2 Chemistry, Casting, and Heat Treatment, 3 Physical Characteristics, 6 Ductility and Yield Strength, 6 Stress and Strain, 7 Strain in Design, 9 Analysis Based on Strain, 11 Ductility in Design, 12 Effects of Cold Working on Strength and Ductility, 13 Brittle Fracture Considerations in Structural Design, 13 Good Practice, 17 Evaluation of Stresses in Spiral-Welded Pipe, 18 References, 18 Chapter 2 Manufacture and Testing
.
.
.
.
.
.
.
.
.
.
.
.
.
21
.
.
.
.
.
.
.
.
.
.
.
.
.
27
.
.
.
.
.
.
.
.
45
Manufacture, 21 Testing, 24 References, 25 Chapter 3 Hydraulics of Pipelines
.
Formulas, 27 Calculations, 31 Economical Diameter of Pipe, 42 Distribution Systems, 43 Air Entrainment and Release, 43 Good Practice, 43 References, 43 Chapter 4 Determination of Pipe Wall Thickness Internal Pressure, 45 Allowable Tension Stress in Steel, 46 Corrosion Allowance, 48 External Fluid Pressure—Uniform and Radial, 48 Minimum Wall Thickness, 50 Good Practice, 50 References, 50
iii Copyright © 2004 American Water Works Association, All Rights Reserved.
Chapter 5 Water Hammer and Pressure Surge
.
.
.
.
.
.
.
.
.
51
Basic Relationships, 51 Checklist for Pumping Mains, 54 General Studies for Water Hammer Control, 55 Allowance for Water Hammer, 56 Pressure Rise Calculations, 56 References, 56 Chapter 6 External Loads
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
59
.
.
.
.
.
.
.
.
.
.
.
69
Load Determination, 59 Deflection Determination, 60 Buckling, 63 Extreme External Loading Conditions, 65 Computer Programs, 68 References, 68 Chapter 7 Supports for Pipe
.
.
.
.
.
Saddle Supports, 69 Pipe Deflection as Beam, 73 Methods of Calculation, 75 Gradient of Supported Pipelines to Prevent Pocketing, 76 Span Lengths and Stresses, 76 Ring Girders, 79 Ring-Girder Construction for Low-Pressure Pipe, 100 Installation of Ring Girder Spans, 101 References, 109 Chapter 8 Pipe Joints
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
111
.
.
.
.
.
.
.
.
.
121
Bell-and-Spigot Joint With Rubber Gasket, 111 Welded Joints, 112 Bolted Sleeve-Type Couplings, 113 Flanges, 113 Grooved-and-Shouldered Couplings, 115 Expansion and Contraction—General, 116 Ground Friction and Line Tension, 117 Good Practice, 118 References, 119 Chapter 9 Fittings and Appurtenances
.
.
.
Designation of Fittings, 121 Elbows and Miter End Cuts, 122 Reducers, 131 Bolt Hole Position, 131 Design of Wye Branches, Laterals, Tees, and Crosses, 131 Testing of Fittings, 132 Unbalanced Thrust Forces, 132 Frictional Resistance Between Soil and Pipe, 132 Anchor Rings, 132 Nozzle Outlets, 132
iv Copyright © 2004 American Water Works Association, All Rights Reserved.
Connection to Other Pipe Material, 133 Flanged Connections, 133 Valve Connections, 133 Blowoff Connections, 133 Manholes, 134 Insulating Joints, 134 Air-Release Valves and Air/Vacuum Valves, 135 Casing Spacers, 135 Good Practice, 136 References, 137 Chapter 10 Principles of Corrosion and Corrosion Control
.
.
.
.
139
.
.
.
.
.
153
General Theory, 139 Internal Corrosion of Steel Pipe, 148 Atmospheric Corrosion, 149 Methods of Corrosion Control, 149 Cathodic Protection, 149 References, 151 Chapter 11 Protective Coatings and Linings
.
.
.
.
.
Requirements for Good Pipeline Coatings and Linings, 153 Selection of the Proper Coating and Lining, 153 Recommended Coatings and Linings, 155 Epoxy-Based Polymer Concrete Coatings, 158 Coating Application, 158 Good Practice, 158 References, 159 Chapter 12 Transportation, Installation, and Testing
.
.
.
.
.
.
.
161
.
.
.
.
.
.
.
177
Transportation and Handling of Coated Steel Pipe, 161 Trenching, 162 Installation of Pipe, 165 Anchors and Thrust Blocks, 170 Field Coating of Joints, 173 Pipe-Zone Bedding and Backfill, 173 Hydrostatic Field Test, 174 References, 175 Chapter 13 Supplementary Design Data and Details
Layout of Pipelines, 177 Calculation of Angle of Fabricated Pipe Bend, 178 Reinforcement of Fittings, 178 Collar Plate Design, 182 Wrapper-Plate Design, 184 Crotch-Plate (Wye-Branch) Design, 185 Nomograph Use in Wye-Branch Design, 187 Thrust Restraint, 193 Anchor Rings, 199 Joint Harnesses, 199 Special and Valve Connections and Other Appurtenances, 204
v Copyright © 2004 American Water Works Association, All Rights Reserved.
Freezing in Pipelines, 204 Design of Circumferential Fillet Welds, 220 Submarine Pipelines, 222 References, 224 Appendix A Table of Working Pressures for Allowable Unit Stresses, 225 Index, 235 List of AWWA Manuals, 241
vi Copyright © 2004 American Water Works Association, All Rights Reserved.
Figures 1-1
Steel pipe in filtration plant gallery, 2
1-2
Stress–strain curve for steel, 8
1-3
True stress–strain for steel, 8
1-4
Stress–strain curves for carbon steel, 9
1-5
Plastic and elastic strains, 9
1-6
Actual and apparent stresses, 10
1-7
Determination of actual stress, 10
1-8
Experimental determination of strain characteristics, 12
1-9
Effects of strain hardening, 14
1-10
Effects of strain aging, 14
1-11
Transition curves obtained from Charpy V-notch impact tests, 17
1-12
Spiral pipe weld seams, 18
2-1
Schematic representation of the sequence of operations performed by a typical machine for making electric-resistance-welded tubes from steel strip, 22
2-2
Cross section through weld point, 22
2-3
Electric resistance welding using high-frequency welding current, 22
2-4
Electric resistance welding by induction using high-frequency welding current, 22
2-5
Sequence of operations in a typical double submerged arc weld process, 23
2-6
Schematic diagram of process for making spiral-seam pipe, 24
2-7
Schematic diagram for making plate pipe, 24
3-1
Solution of the Hazen-Williams formula, 28
3-2
Solution of Scobey flow formula for Ks = 0.36, 30
3-3
Solution of Manning flow formula for n = 0.011, 32
3-4
Moody diagram for friction in pipe, 40
3-5
Resistance coefficients of valves and fittings for fluid flows, 41
4-1
Relation of various heads or pressures for selection of design pressure (gravity flow), 46
4-2
Relation of various heads or pressures for selection of design pressure (pumped flow), 46
5-1
Surge wave velocity chart for water, 53
6-1
Position of area, 67
7-1
Details of concrete saddle, 70
7-2
Saddle supports for 78-in. pipe, 70
vii Copyright © 2004 American Water Works Association, All Rights Reserved.
7-3
Ring girders provide support for 54-in. diameter pipe, 71
7-4
Expansion joints between stiffener rings, 71
7-5
Anchor block, 71
7-6
Stiffener ring coefficients, 78
7-7
Equivalent stress diagram—Hencky–Mises theory, 80
7-8
Bending stress in pipe shell with ring restraint, 81
7-9
Stiffener ring coefficients, equal and opposite couples, 81
7-10
Stiffener ring stresses for partially filled pipe, 81
7-11
Stiffener ring coefficients, radial load supported by two reactions, 81
7-12
Stiffener ring coefficients—transverse earthquake, 81
7-13
Combination of solutions, 82
7-14
Stresses, moments, and plate thickness, 84
7-15
Detail of assumed ring section, 94
7-16
Long-span steel pipe for low pressures, 101
7-17
111-in. pipe on ring girders, 102
8-1
Welded and rubber-gasketed field joints, 112
8-2
Bolted sleeve-type couplings, 114
8-3
Grooved coupling, 116
8-4
Shouldered coupling, 116
8-5
Typical expansion joint with limit rods, 117
8-6
Typical expansion joint configurations, 118
9-1
Recommended dimensions for water pipe fittings (except elbows), 122
9-2
Recommended dimensions for water pipe elbows, 123
9-3
Tangent-type outlet (AWWA C208), 125
9-4
Lateral less than 30 degrees, 126
9-5
Reducing elbow, 126
9-6
Computation method and formulas for compound pipe elbows, 127
9-7
Sample pipeline profile illustrating air valve locations, 136
10-1
Galvanic cell—dissimilar metals, 140
10-2
Galvanic cell—dissimilar electrolytes, 142
10-3
Galvanic cell on embedded pipe without protective coating, 142
10-4
Galvanic cell—pitting action, 142
10-5
Corrosion caused by dissimilar metals in contact on buried pipe, 142
10-6
Corrosion caused by dissimilar metals, 143
10-7
Corrosion caused by cinders, 143
10-8
Corrosion caused by dissimilarity of surface conditions, 143
viii Copyright © 2004 American Water Works Association, All Rights Reserved.
10-9
Corrosion caused by dissimilar soils, 144
10-10
Corrosion caused by mixture of different soils, 144
10-11
Corrosion caused by differential aeration of soil, 144
10-12
Stray-current corrosion caused by electrified railway systems, 145
10-13
Control of stray-current corrosion, 146
10-14
Corrosion rate in various soils, 147
10-15
Cathodic protection—galvanic anode type, 150
10-16
Cathodic protection—rectifier type, 150
10-17
Bonding jumpers installed on sleeve-type coupling, 151
10-18
Bonding wire for bell-and-spigot rubber-gasketed joint, 151
12-1
Densified pipe zone bedding and backfill, 164
12-2
Special subgrade densification, 164
12-3
Bolt torque sequence, 168
13-1
Example of adequately detailed pipe special, 179
13-2
Plan and profile of bend in pipe on centerline of pipe, 179
13-3
Reinforcement of openings in welded steel pipe, 181
13-4
One-plate wye, 186
13-5
Three-plate wye, 186
13-6
Two-plate wye, 186
13-7
Nomograph for selecting reinforcement plate depths of equal-diameter pipes, 188
13-8
N factor curves, 189
13-9
Q factor curves, 189
13-10
Selection of top depth, 190
13-11
Wye branch plan and layout, 191
13-12
Thrust at branch or tee, thrust at bulkhead or dead end, 194
13-13
Resultant thrust at pipe elbow, 194
13-14
Typical thrust blocking of a horizontal bend, 194
13-15
Thrust blocking of vertical bends, 195
13-16
Force diagram, 197
13-17
Lap welded joint, single-butt weld joint, 198
13-18
Harnessed joint detail, 198
13-19
Anchor ring, 199
13-20
Harness lug detail, 207
13-21
Reinforcing pad for tapped opening, 208
13-22
Nipple with cap, 208
ix Copyright © 2004 American Water Works Association, All Rights Reserved.
13-23
Flanged connection for screw-joint pipe, 208
13-24
Wall connection using coupling, 208
13-25
Extra-heavy half coupling welded to pipe as threaded outlet, 208
13-26
Thredolets, 208
13-27
Casing and removable two-piece roof, 211
13-28
Section of casing giving access to gate valve gearing, 212
13-29
Access manhole, 212
13-30
Blowoff with riser for attaching pump section, 213
13-31
Blowoff connection, 213
13-32
Manifold layout of relief valves and pressure regulators, 213
13-33
Tapping main under pressure, 214
13-34
Maximum frost penetration and maximum freezing index, 214
13-35
Heat balance in exposed pipelines, 216
13-36
Fillet nomenclature, 220
13-37
Submarine pipeline—assembly and launching, 223
13-38
Submarine pipeline—positioning by barge, 223
13-39
Submarine pipeline—floating string positioning, 224
x Copyright © 2004 American Water Works Association, All Rights Reserved.
Tables 1-1
Effects of alloying elements, 3
1-2
Maximum strain in pipe wall developed in practice, 12
3-1
Multiplying factors corresponding to various values of C in Hazen-Williams formula, 28
3-2
Multiplying factors for friction coefficient values—Base Ks = 0.36, 30
3-3
Multiplying factors for friction coefficient values—Base n = 0.011, 32
3-4
Slope conversions, 34
3-5
Flow equivalents, 35
3-6
Pressure ( psi) for heads ( ft), 36
3-6M
Pressure (kPa) for heads (cm), 36
3-7
Head ( ft) for pressures ( psi), 37
3-7M
Head (cm) for pressures (kPa), 37
3-8
Pressures (kPa) for heads ft (m), 38
3-9
Pressure equivalents, 38
4-1
Grades of steel used in AWWA C200 as basis for working pressures in Table A-1, 47
5-1
Velocity of pressure wave for steel pipe, 53
6-1
Values of modulus of soil reaction, E′ (psi) based on depth of cover, type of soil, and relative compaction, 62
6-2
Unified soil classification, 62
6-3
Live-load effect, 63
6-4
Influence coefficients for rectangular areas, 66
7-1
Practical safe spans for simply supported pipe in 120° contact saddles, 74
7-2
Summary of moment calculations, 85
7-3
Stresses at support ring, 90
7-4
Summary of stresses for half-full condition, 100
7-5
Trigonometric data, 100
7-6
Values of moment of inertia and section modulus of steel pipe, 103
10-1
Galvanic series of metals and alloys, 141
10-2
Soils grouped in order of corrosive action on steel, 148
10-3
Relationship of soil corrosion to soil resistivity, 148
12-1
Comparison of standard density tests, 165
12-2
Torque requirements for AWWA C207 Class D ring flange bolts, 171
xi Copyright © 2004 American Water Works Association, All Rights Reserved.
12-3
Torque requirements for steel pipe flange bolts and studs, 172
13-1
Example of pipe-laying schedule, 180
13-2
Recommended reinforcement type, 181
13-3
Dimensions and bearing loads for anchor rings in concrete—maximum pipe pressure of 150 psi and 250 psi, 200
13-4
Tie bolt schedule for harnessed joints, 201
13-5
Dimensions of joint harness tie bolts and lugs for rubber-gasketed joints, 205
13-5A Maximum allowable load per tie bolt, 206 13-6
Plate dimensions and drill sizes for reinforced tapped openings, 209
13-7
Maximum size of threaded openings for given size pipe with reinforcing pads, 209
13-8
Dimensions of extra-heavy half-couplings, 210
13-9
Dimensions figures thredolets, 210
13-10
Heat balance factors, 217
13-11
Values of D and v, 218
13-12
Conduction heat-transfer values, 218
13-13
Emissivity factors, 219
13-14
Wind velocity factors, 219
A-1
Working pressures for allowable unit stresses, 226
xii Copyright © 2004 American Water Works Association, All Rights Reserved.
Foreword This manual was first authorized in 1943. In 1949, committee 8310D appointed one of its members, Russel E. Barnard, to act as editor in chief in charge of collecting and compiling the available data on steel pipe. The first draft of the report was completed by January 1957; the draft was reviewed by the committee and other authorities on steel pipe. The first edition of this manual was issued in 1964 with the title Steel PipeDesign and Installation. The second edition of this manual was approved in June 1984 and published in 1985 with the title Steel Pipe—A Guide for Design and Installation. The third edition of the manual was approved in June 1988 and published in 1989. This fourth edition of the manual was approved March 2003. Major revisions to the third edition included in this edition are (1) the manual was metricized and edited throughout; (2) a discussion of Chemistry, Casting and Heat Treatment (Sec. 1.3) and a discussion of stress evaluation in spiral-welded pipe (Sec. 1.12) were added to chapter 1; (3) Table 4-1 was revised to reflect new steel grades and Charpy test requirements for pipe with wall thicknesses greater than 1⁄ 2 in. (12.7 mm); (4) calculations for external fluid pressure (Sec. 4.4) was revised to include consideration of pipe stiffness added by the cement–mortar coating and lining; (5) in Table 6-1, values of E′ used for calculation of pipe deflection were revised to reflect increasing soil stiffness with increasing depth of cover; (6) in chapter 7, the discussion of ring girder design was revised, and a design example was added; (7) chapter 9, Fittings and Appurtenances, was revised to reflect the provisions of AWWA C208-96; (8) a new section on installation of flanged joints was added to chapter 12; and (9) thrust-restraint design calculations in chapter 13 were revised. This manual provides a review of experience and design theory regarding steel pipe used for conveying water, with appropriate references cited. Application of the principles and procedures discussed in this manual must be based on responsible judgment.
xiii Copyright © 2004 American Water Works Association, All Rights Reserved.
This page intentionally blank.
Copyright © 2004 American Water Works Association, All Rights Reserved.
Acknowledgments This revision of Manual M11 was made by the following members of the Steel Water Pipe Manufacturers Technical Advisory Committee (SWPMTAC). The Steel Water Pipe Manufacturers Technical Advisory Committeee Task Group on updating the manual M11 had the following personnel at the time of revision: Dennis Dechant, Task Group Chairman H.H. Bardakjian, American International, Rancho Cucamonga, Calif. R.J. Card, Victaulic Depend-O-Lok Inc., Atlanta, Ga. R.R. Collins, JCM Industries Inc., Nash, Texas D.H. Eaton, Romac Industries Inc., Bothell, Wash. B. Kane, Cascade Waterworks Manufacturing Company, Yorkville, Ill. B.D. Keil, Continental Pipe Manufacturing Company, Pleasant Grove, Utah M. Mintz, M-Square Associates Inc., Elmont, N.Y. R.N. Satyarthi, Baker Coupling Company, Inc., Los Angeles, Calif. K.L. Shaddix, Smith-Blair Inc., Texarkana, Texas B. Spotts, RTLC Piping Products Inc., Kosse, Texas J.C. Taylor, Piping Systems Inc., Fort Worth, Texas M. Topps, Glynwed Piping Systems, Hixson, Tenn. R. Warner, National Welding Corporation, Midvale, Utah This revision was reviewed and approved by the Standards Committee on Steel Pipe. The Standards Committee on Steel Pipe had the following personnel at the time of approval: George J. Tupac, Chairman John H. Bambei Jr., Vice Chairman Dennis Dechant, Secretary Consumer Members G.A. Andersen, NYC Bureau of Water Supply, Little Neck, N.Y. J.H. Bambei Jr., Denver Water Department, Denver, Colo. D.W. Coppes, Massachusetts Water Resources Authority, Southborough, Mass. R.V. Frisz, US Bureau of Reclamation, Denver, Colo. T.R. Jervis, Greater Vancouver Regional District, Burnaby, B.C. T.J. Jordan, Metropolitan Water District of Southern California, La Verne, Calif. T.A. Larson, Tacoma Public Utilities, Tacoma, Wash. G.P. Stine, San Diego County Water Authority, Escondido, Calif. Milad Taghavi, Los Angeles Department of Water & Power, Los Angeles, Calif. J.V. Young, City of Richmond, Richmond, B.C.
xv Copyright © 2004 American Water Works Association, All Rights Reserved.
General Interest Members W.R. Brunzell, Brunzell Associates Ltd, Skokie, Ill. R.L. Coffey, Kirkham Michael & Associates, Omaha, Neb. H.E. Dunham, MWH Americas Inc., Bellevue, Wash. K.G. Ferguson,* MWH Americas Inc., Parker, Ariz. S.N. Foellmi, Black & Veatch Corporation, Irvine, Calif. J.W. Green, Alvord Burdick & Howson, Lisle, Ill. K.D. Henrichsen, HDR Engineering Inc., St. Cloud, Minn. M.B. Horsley,* Black & Veatch Corporation, Overland Park, Kan. J.K. Jeyapalan, Pipeline Consultant, New Milford, Conn. Rafael Ortega, Lockwood Andrews and Newnam, Houston, Texas A.E. Romer, Boyle Engineering Corporation, Newport Beach, Calif H.R. Stoner, Consultant, North Plainfield, N.J. C.C. Sundberg, CH2M Hill Inc., Bellevue, Wash. G.J. Tupac, G.J. Tupac & Associates, Pittsburgh, Pa. J.S. Wailes,† Standards Engineer Liaison, AWWA, Denver, Colo. L.W. Warren, Seattle, Wash. W.R. Whidden, Post Buckley Schuh & Jernigan, Orlando, Fla. Producer Members H.H. Bardakjian, Ameron International, Rancho Cucamonga, Calif. Mike Bauer, Tnemec Company, Inc., North Kansas City, Mo. R.J. Card, Victaulic Depend-O-Lok Inc., Atlanta, Ga. R.R. Carpenter, American Cast Iron Pipe Company, Birmingham, Ala. Dennis Dechant, Northwest Pipe Company, Denver, Colo. J.E. Hagelskamp,† American Cast Iron Pipe Company, Birmingham, Ala. B.D. Keil, Continental Pipe Manufacturing Company, Pleasant Grove, Utah J.L. Luka,* American SpiralWeld Pipe Company, Columbia, S.C. B.F. Vanderploeg,* Northwest Pipe Company, Portland, Ore. J.A. Wise, Canus International Sales Inc., Langley, B.C.
*Alternate †Liaison
xvi Copyright © 2004 American Water Works Association, All Rights Reserved.
AWWA MANUAL
Chapter
M11
1 History, Uses, and Physical Characteristics of Steel Pipe
HISTORY ____________________________________________________________________________________ Steel pipe has been used for water lines in the United States since the early 1850s (Elliot 1922). The pipe was first manufactured by rolling steel sheets or plates into shape and riveting the seams. This method of fabrication continued with improvements into the 1930s. Pipe wall thicknesses could be readily varied to fit the different pressure heads of a pipeline profile. Because of the relatively low tensile strength of the early steels and the low efficiency of cold-riveted seams and riveted or drive stovepipe joints, engineers initially set a safe design stress at 10,000 psi (68.95 MPa). As riveted-pipe fabrication methods improved and higher strength steels were developed, design stresses progressed with a 4-to-l safety factor of tensile strength, increasing from 10,000 (68.95) to 12,500 (86.18), to 13,750 (94.8), and finally to 15,000 psi (103.42). Design stresses were adjusted as necessary to account for the efficiency of the riveted seam. The pipe was produced in diameters ranging from 4 in. (100 mm) through 144 in. (3,600 mm) and in thickness from 16 gauge to 1.5 in. (38 mm). Fabrication methods consisted of single-, double-, triple-, and quadruple-riveted seams, varying in efficiency from 45 percent to 90 percent, depending on the design. Lock-Bar pipe, introduced in 1905, had nearly supplanted riveted pipe by 1930. Fabrication involved planing 30-ft (9.1-m) long plates to a width approximately equal to half the intended circumference, upsetting the longitudinal edges, and rolling the plates into 30-ft (9.1-m) long half-circle troughs. H-shaped bars of special configuration were applied to the mating edges of two 30-ft (9.1-m) troughs and clamped into position to form a full-circle pipe section.
1 Copyright © 2004 American Water Works Association, All Rights Reserved.