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V E S S E L

D E S I G N

- d

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LLOYD E. BROWNELL

Professor of Chemical and Nuclear Engineering University of Michigan

EDWIN H. YOUNG

Associate Professor of Chemical and Metallurgical Engineering

Reg. pu’o...@.

1. . ACC.

No..

357

University of Michigan

Lib. Asstt . . . r/C . . . .

JOHN WILEY & SONS

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20 19 18 17 16 15 14

Copyright @ 1959 by John Wiley 8 S o n s , I n c . .411 rights reserved.

Reproduction or translation of any part of thi\ work beyond that permitted by Sections 107 or 108 of the 1976 Unlted States

Copy-rtght Act without the permisbton of the copyright owner is unlaw-ful. Requests for perm!sston or further tnformatton should be addressed to the Permissions Department, John Wiley&Sons, Inc.

library of Congress Catalog Card Number: 5?--5882 Printed in the United States of America

ISBN 0 4 7 1 1 1 3 1 9 0

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-PREFACE

This book was prepared primarily for se~io-and students in

engineer-ing. The needs of design engineers and consultants as well as those of students

were considered in selecting the topics and methods of presentation. The book is based upon our experiences gained in industrial design offices and in 16 years of

teaching courses in equipment design at the University of Michigan. We both

have supervised research and development of process equipment, and have acted as consultants in this field.

The book was originally prepared as class notes, which have been used for about ten years in teaching courses in process equipment design at the senior and graduate levels in the Chemical and Metallurgical Engineering Department of the University of Michigan. Typical problems have involved the design of fraction@ingto w e r s , trm vacu>m cry&all&m, condensers, heat exch-rs, high-pres?re reactors, and other types of process equipment.

The design of process equipment requires a thorough knowledge of the func-tional process, the materials involved, and the methods of fabrication. The___- ._.... design factors to be considered are many and varied and, in most cases, so inter-woven that exact methods of attack are often impossible to formulate. Com-promises are necessary and the design engineer often has only experience in similar or related fields to guide him in his choice. Thus, the engineer must realize that considerable engineering judgment is required in applying all recom-mended specific methods of design.

One purpose of this book is to consolidate the basic concepts, industrial prac-tices, and theoretical relationships useful in the design of processing equipment. Many of these considerations and much of this vital information are widely scattered throughout the technical literature, industrial bulletins, appropriate codes, and handbooks. It is not intended that this book should cover all the ramifications of design problems, but it will serve as a guide to the student and the practicing engineer for efficient and economical design of equipment for the processing industries. vii ya __ -I \ 7 ~.‘T-.- .-_ _ ._- --_--- ---

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c--. c--. c--.

VIII Preface

The organization is based on the premise t)hut t,he vessel is the basic part of most types of processing equipment.

For example, a heat exchanger or evaporator is a vessel with tube bundles and a fractionating tower is a vessel with trays. The first 12 chapters are concerned in part with the development of fundamental relationships on which many of the code specifications are based. Chapter 13 is concertled entirely with code prac-tice and covers selected code specifications not covered in the earlier chapters. Chapters 14 and 15 are concerned with the design of vessels beyond the scope of the ASME code.

The sequence of chapters was selected to permit the introduction of a briet review of elementary theories of mechanics and strength of materials early in the book. More advanced theory is developed as needed in subsequent chapters. The integration of theory with practice in design eliminates the necessity of a separate section on erigineeritlg mechanics. The sequence of presentation allows for an orderly development of theoretical relatiotlships when the book is being used as a textbook in teaching design. The material presented covers the rauge from simple vessels for low-pressure service to thick-walled vessels for high-pressure applications. Tl~tf rxperierlced designer will find the book useful as a reference in a design office.

In all but a few cases derivations of equations and the method of analysis have been given so that the etlgirleer will utlderstaltd the assumptions and limitations involved. Also, example calculations and designs have been included to illustrate the use of the relationships and recommended procedures.

We wish to acknowledge the assistance given by a large number of individuals and companies in providing subject material and illustrations on process equip-ment, design and in making reviews and suggestions. We are particularly iudebted to the following: C. E. Freese, Mechanical Consultant, and B. B. Kuist, The Fluor Corporation; W. H. Burrows, Chief Engineer, Manufacturing Depart-ment, Standard Oil Company of Indiana; A. E. Pickford, Department Head, .dpparatus Design, C. F. Braun and Company; H. B. Boardman, Director of ltesearch, L. P. Zick, Research Engineer, and E. N. Zimmerman, Chicago Bridge and Iron Company; W. T. Gurm and Walter Samans, American Petroleurn Institute; J. M. Evans, Chief Engineer, and F. L. Maker, Standard Oil Company of California; R. S. Justice, Chief Engineer, Gulf Oil Corporation; F. L. Plummer, Director of Engineering, Hamrnond Iron Works; W. D. Kinsell, Manager, Con-struction, Engineering Department, The Pure Oil Company; G. E. Fratcher, Director of Engineering, A. 0. Smith Company; F. E. Wolosewick, Sargeut and Lundy Engineers; P. E. Franks, Chief Engineer, Sinclair Refining Cornpany; D. W. Carswell and H. B. Peters, Chief Engineer, The Texas Company; W. T. Brown, Manager, Mechanical Division, and Harry Wearne, Construction Man-ager, Shell Oil Cornpany ; F. J. Feeley, Jr., Assistant Director, Engineering Design Division, Esso Hesearch aud Engineering Company; J. H. Faupel, E. I. du Pont de Nemours and Company; W. H. Funk, Lukens Steel Company; and the follow-ing additional companies and organizat3ons: Horton Steel Works, Ltd.; Blaw-Knox Company; Graver Tank and Manufacturing Company; American Cyanamid Cornpany; Inland Steel Company; Ryerson Steel Company; Taylor Forge and Pipe Works; Aluminum Company of America; M. W. Kellogg Company; Amer-ican Standard Association, Inc.; The Girdler Company, Inc.; Baldwiu-Lima-Hamilton Corporation; Bethlehem Steel Compally, Inc.; ITnited States Depart-ment of Interior, Bureau of Miues; Great Lakes Steel Corporation; McGraw-Hill

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Book Company, Inc.; I‘uivrrsal-Cyclops Steel Corporatiorr: at~d the United States Steel Corporation.

We also wish to express our appreciation to the Amrricau Society of Mechanical

Engineers and the American Petroleum Institute for permissiou to use selected

material from the 1956 edition of the Unfired Pressure L‘essel Code and the API Specification for Welded Oil Storage Tanks and Production Tanks, respectivei). We are also indebted to Dr. J. McKetta, Mr. F. L. Standiford, Dr. H. H. Yang, and Dr. M. D. S. Lay, who assisted in the preparation of the course notes while enrolled in the Graduate School of the University of Michigan, and to Professor Donald L. Katz, Chairman, Department of Chemical and Metallurgical Engi-neering, University of Michigan, for encouragement and advice in the preparation of this book. Many individuals have given valuable suggestions, comments, and assistance in the preparation of this book and ally omissions irr ackuowledgment are not iutended.

Ann Arbor, Michigm! April, 1959

LLOYD E. BROWNELL EDMIK i-z. YOUNG

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CONTENTS

. . c Chapter 1 2 3 4 5 6 7 8 9 1 0 11 12 13 14 15 References Appendix A. B.

Factors Influencing the Design of Vessels Criteria in Vessel Design

Design of Shells for Flat-Bottomed Cylindrical Vessels

Design of Bottoms and Roofs for Flat-Bottomed Cylindrical Vessels

Proportioning and Head Selection for Cylindrical Vessels with Formed Closures

Stress Considerations in the Selection of Flat-Plate and Conical Closures for Cylindrical Vessels

Stress Considerations in the Selection of Elliptical, Torispheri-cal, and Hemispherical Dished Closures for Cylindrical Vessels Design of Cylindrical Vessels with Formed Closures Operating under External Pressure

Design of Tall Vertical Vessels Design of Supports for Vertical Vessels

Design of Horizontal Vessels with Saddle Supports De&n of Flanges

Design of Pressure Vessels to Code Specifications High-Pressure Monobloc Vessels

Multilayer Vessels Design Conventions Welding Conventions xi 1 1 9 3 6 5 8 76 98 1 2 0 141 1 5 5 183 2 0 3 2 1 9 249 2 6 8 296 317 3 2 3 327

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xii Contents C . D. E. F. G. H. I. J . K. 1. Author Index Subject Index

Pricing of Steel Plate Allowable Stresses

Typical Tank Sizes and Capacities Shell Accessories

Properties of Selected Rolled Structural Members Values of Constant C of Eq. 13.27

Charts for Determining Shell Thickness of Cylindrical and Spherical Vessels under External Pressure

Properties of Various Sections and Beam Formulas Properties of Pipe Strength of Materials 330 335 3 4 6 349 3 5 3 3 6 2 364 381 3 8 6 3 9 2 3 9 5 399

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C H A P T E R

0

1

FACTORS INFLUENCING

THE DESIGN OF VESSELS

e

hemical engineering involves the application of the sciences to the process industries which”‘&e primarily con-cerned with the conversion of one material into another dy chemical or physical means. These processes require the

handling and storing of large quantities of materials in con-tainers of varied construction, depending upon the existing state of the material, its physical and chemical properties, and the required operations which are to be performed.

For handling such liquids and gases a container, or “vessel,” is used. Thzyessel is the basic part of most types of proc-essing equipment. Most process equipment units may be considered to be vessels with various modifications neces-sary to e

tions. xor example, an a_utoclave may be considered to beble the units to perform certain required func-a high-pressure vessel equipped with func-agitfunc-ation func-and hefunc-ating sources; a distillation or absorption column may be consid-ered to be a vessel containing a series of vapor-liquid con-tactors; a heat exchanger may be considered to be a vessel d--containing a suitable provision for the transfer of heat through tube walls; and an evaporator may be considered to be a vessel containing a heat exchanger in combination with a vapor-disengaging space.

Regardless of the nature of the application of the vessel, a number of factors usually must be considered in designing the unit. The most important consideration often is the selection of the type of vessel that performs the required service in the most satisfactory manner. In developing the design a number of other criteria must be considered, such as the properties of the material used, the induced stresses, the elastic stability, and the aesthetic appearance of the unit. The cost of the fabricated vessel is also important in relation to its service and useful life.

1.1 SELECTION OF THE TYPE OF VESSEL

Usually the first step in the design of any vessel is the selection of the type best suited for the particular service ipquestio~.- The primary factors influencing this choice are: the function and location of the vessel, the nature of the fluid, the operating temperature and’pressure, and the neces-sary volume for storage or capacity for processing. Vessels

may be classified according to service,

tempera-ture and pressure service, matkrials of construction, or geometry of the vessel.

The most common types of vessels may be classified according to their geometry as:

‘1. Open tanks.

23. Vertical cylindrical and horizontal vessels with formed. Flat-bottomed, vertical cylindrical tanks. ends.

4. Spherical or modified spherical vessels.

Vessels in each of these classifications are widely used as s~o%& vessels and as processing vessels for fluids. The range of service for the various types of vessels overlaps, and it is difficult to make distinct classifications for all applications.

It is possible to indicate some generalities in the existing

uses of lhe common types of vessels. Large volumes of

nonhazardous liquids, such as brine and other aqueous solu-tions, may be stored in ponds if of very low value, or in open steel, wooden, or concrete tanks if of greater value. If the fluid is toxic, combustible, or gaseous in the storage condi-tion, or if the pressure is greater than atmospheric, a closed system is required. For storage of fluids at atmospheric pressure, cylindrical tanks with flat bottoms and coni-cal roofs are commonly used. Spheres or spheroids are 1

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--:,t

I-

lo’-0”

Inside diameter

I

lo’-0” UnAred Pressure Vessel 150 Ib.sq in. at 85O’F

Fig. 1.1. Example of a cylindrical vessel with formed ends designed to the original API-AWE code. (Courtesy of Amer. Pet. Inst.!

__----employed for pressure storage where the volume required is large. For smaller volumes under pressure, cylindrical tanks with formed heads are ,more economical.

l.la Open Vessels. Open vessels are commonly used

as surge tanks between operations, as vats for batch opera-tions where materials may be mixed and blended, as settling tanks, decanters, chemical reactors, reservoirs, and so on. Obviously, this type of vessel is cheaper than covered or closed vessels of the same capacity and construction. The decision as to whether or not open vessels may be used depends upon the fluid to be handled and the operation.

Very large quantities of aqueous liquids of low value may be stored in ponds. It is doubtful if ponds may be correctly referred to as vessels. They are, however, the simplest

containers made from the cheapest of materials, rolled earth. Not all types of earth can be used for storage ponds; a clay which will form an almost watertight bottom is essential. An example of the use of ponds of rolled earth is found in the process whereby salt is crystallized from sea water by solar evaporation (1). When more valuable fluids are handled, more reliable but more expensive containers are required. Large circular tanks of steel (2) or reinforced (or prestressed) concrete (3), (4) are often used for settling ponds in which a slowly rotating rake removes sediment from a slightly inclined conical bottom. Vessels of this type, as exemplified by the Dorr classifier, may have diameters ranging from 100 to 200 ft and a depth of several feet.

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are constructed of mild carbon steel, concrete, and some-times of wood (5). Other materials find limited use where serious corrosion or contamination problems are encount-ered. However, in the process industries in general, the major portion of existing vessels are constructed of steel because of its low initial cost and ease of fabrication. In many cases such vessels are lined with lead, rubber, glass, or plastic to improve resistance to corrosion. In the food industry fir is commonly used for pickle and kraut tanks, whereas quarter-sawed white oak is employed for wine and spirits. Redwood or Cyprus tanks are often employed for water storage reservoirs. Wood is also used in place of steel for handling dilute solutions of hydrochloric, lactic, and acetic acids and salt solutions and is indispensable as a low-cost tank in the tanning, brewing, and pickling industries (6).

In the food and pharmaceutical industries it is often neces-sary to add materials to open vessels in the preparation of mixtures. Small open tanks or kettles are usually employed for such purposes. Glass-lined steel, copper, Monel, and stainless steel tanks are widely used in these applications to resist corrosion and prevent contamination of the process materials.

1 .l b Closed Vessels. Combustible fluids, fluids

emit-ting toxic or obnoxious fumes, and gases must be stored in closed vessels (7). Dangerous chemicals, such as acid or caustic, are less hazardous if stored in closed vessels. The combustible nature of petroleum and its products necessi-tates the use of closed vessels and tanks throughout the petroleum and petrochemical industries. The extensive use of tanks in this field has resulted in considerable effort on the part of the American Petroleum Institute to

stand-Selection of the Type of Vessel 3

ardize design for purposes of safety and economy. Tanks used for the storage of crude oils and petroleum products are generally designed and constructed in accordance with API Standard 12 C, API Specification for Welded

Oil-Storage Tanks. This is the standard reference used in

designing tanks for the petroleum industry, but it is also a useful guide for other applications.

CYLINDRICAL VESSELS WITH FLAT BOTTOMS AND CONICAL OR DOMED ROOFS. The most economical design for a closed vessel operating at atmospheric pressure is the verti-cal cylindriverti-cal tank with a coniverti-cal roof and a flat bottom resting directly on the bearing soil of a foundation com-posed of sand, gravel, or crushed rock. In cases where it is desirable to use a gravity feed, the tank is raised above the ground, and the flat bottom may be supported by columns and wooden joists or steel beams. Cylindrical, flat-bot-tomed, cone-roofed tanks are provided with “breathers” or vents which permit expansion and contraction of the fluids as a result of temperature and volume fluctuations. Tanks up to 24 ft in diameter may be covered with a self-supporting roof; tanks with larger diameters, up to 48 ft, usually require at least one central column for support. Tanks larger than 48 ft in diameter are frequently designed with multiple-column supports or with a floating or pontoon roof which rises and falls with the level of liquid in the vessel. In general, tanks with conical roofs are limited to essentially atmospheric pressure. If domed roofs are used, pressures from 244 to 15 lb per sq in. gage may be permitted. These vessels are normally smaller in diameter and of greater height for a given capacity than tanks with conical roofs (8, 9).

Fig. 1.2. Oil refinery installation. (Courtesy of C. F. Braun & Company.)

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4 Factors Influencing the Design of Vessels

CY L I N D R I C A L VESSELS W I T H FORMED ENDS. Closed cylindrical vessels with formed heads on both ends are used where the vapor pressure of the stored liquid may dictate a stronger design. Codes have been developed through the efforts of the American Petroleum Institute (10) and the American Society of Mechanical Engineers (11) to govern the design of such vessels. These vessels are usu$ly less than 12 ft in diameter if they are to be shipped by rail. However, field-erected vessels may exceed 35 ft in diameter and 200 ft in length. If a large quantity of liquid is to be stored, a batt,ery of vessels may be used.

A variety of formed heads arca used for closing I hta ends of cylindrical vessels. The formed heads include the hemi-spherical, elliptical-dished, torihemi-spherical, standard-dished,

one type or another. Figure 1.2 shows a wide variety of such items in a petroleum refinery. Note that nearly all of the processing equipment shown consists of cylindrical vessels with formed ends.

SPHERWAL AND MODIFIED SPHERICAL VESSELS. Storage containers for large volumes under moderate pressure are usually fabricated in the shape of a sphere or spheroid. Capacities and pressures used in this type of vessel vary greatly. Capacity ranges from 1000 t.o 25,000 bbl, and pressures range from 10 lb per sq in. gage for the larger vessels to 200 lb per sq in. gage for the smaller ones. Figure

1.3 shows a battery of horizont.al cylindrical vessels and spherical vessels for storing petroleum products at pressures up to 100 lb per sq in. gage.

Fig. 1.3. Spherical and horizonial storage tanks at Crown Central Petroleum Plant near Houston, Texas. (Courtesy of Hammond Iron Works.)

conical, and toriconical shapes. For special purposes flat plates are used to close a vessel opening. However, flat he;ids are rarely ustd for large vessels. For pressures uot covered by the ASME code, the vessels are often equipped with standard dished heads, whereas vessels that require code construction are usually equipped with either the ASME-dished or elliptical-dished heads. The most common shape for the closure of “pressure vessels” is the elliptical dish. Figure 1.1 shows a drawing of a vertical cylindrical vessel with formed ends designed to the original API-ASME code.

Most chemical and petrochemical processing equipment such as distilling columns, desorbers, absorbers, scrubbers, heat exchangers, pressure-surge tanks, and separators are essentially cylindrical closed vessels with formed ends of

Where a given mass of gas is to be stored under pressure, it is obvious that the required storage volume will be inversely proportional to the storage pressure. In general, for a given mass the spherical type of tank is more economi cal for large-volume, low-pressure storage operation. At higher storage pressures, the volume of gas is reduced, and therefore the cylindrical type of storage vessel becomes more economical. If allowance is made for the cost of compression and cooling of the gas, some of this apparent saving is lost. When handling small masses of gas, there is an advantage in the use of cylindrical storage vessels because the cost of fabrication becomes the controlling factor and small cylindrical vessels are more economical than small spherical vessels.

Further economy can sometimes be realized by using

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Methods of Fabrication 5 and greater reliability as compared with cast iron, it i s more suitable for high-pressure service where metal porosity is not a problem. The vessel diameter is still limiting because of problems in casting. Alloy cast-steel vessels can be used for high-temperature and high-pressure installations.

Form is a method of shaping metal that is commonly usedfor certain vessel parts such as closures, flanges, and fittings. Vessels with wall thicknesses greater than 4 in. are often forged. Ot$her special methods of shaping metal, such as pressing, spinning, and rolling of plates, are used for forming closures for vessel shells and are discussed later in the text. Sheet-metal forming is similar to pressing in that metal is shaped by means of presses and dies, but this method is limited to relatively thin stock. The process of sheet-metal forming as a method of vessel fabrication finds its greatest application in the field of nonferrous metals such as copper, Monel, and stainless steel, where cost con-siderations often preclude the use of heavier stock.

Riveting was widely used, prior to the improvement of modernwelding techniques, for many different kinds of vessels, such as storage tanks, boilers, and a variety of pres-sure vessels (12). It is still used for fabrication of

nonfer-rous vessels such as copper and aluminum. However,

welding techniques have become so advanced that even these materials are often welded today. Because of the trends away from riveted construction, the designs based upon riveting as a method of fabrication will not be dis-cussed in this text.

M_achining is the only method other than cold forming that can be used to secure exact tolerances. Close toler-ances are required for the mating parts of equipment.. Flange faces, bushings, and bearing surfaces are usually --.-machined in order to provide satisfactory alignment. Lab-oratory and pilot plant equipment for very-high-pressure service is sometimes machined from solid stock, pierced ingots, and forgings. Multilayer vessels for high-pressure Fig. 1.4. Two multispheres for storage of nitrogen under 400 lb per sq in.

gage. (Courtesy of Chicago Bridge & Iron Company.)

modified spherical vessels such as the two multispheres shown in Fig. 1.4. These storage vessels were designed to handle nitrogen at 400 lb per sq in. gage working pressure. Modified spherical vessels are also used for storage of large volumes under moderate pressures. Large ellipsoidal ves-sels have been built to hold 55,000 bbl at a pressure of 75 lb per sq in. gage. The largest vessels for storage under pressure are the semi-ellipsoidal tanks, which have been made to hold as much as 120,000 bbl at a pressure of 235 lb per sq in. gage. As the capacity of an individual vessel is increased, the pressure that the vessel can safely maintain h (wit,hout very heavy construction) c!ecreases. A

hemi-spheroid with a capacit,y of 20,000 hhl of natural gasoline at a working pressure of 2 35 lb per sq in. gage is shown in Fig. 1.5.

1 . 2 M E T H G C S O F F A B R I C A T I O N

,

Process equipment is fabricatel b”y a _ num$er.o&r&_____ - . . ^_-estam’methods such as fusion welding, casting, forging, machining, brazing and soldering, and sheet-metal forming.__. . Each method has certain advantages for particular types of equipment. However, fusion welding is the most important method. The size, shape, service, and material properties of t.he equipment all may influence the selection ‘of the fabrication method.

GLet-irqn castings have been widely used for the mass production of small pipe fittings and are used to a consider-able extent for larger items such as cast-iron pipe, heat-exchanger shells, and evaporator bodies because of the superior corrosion resistance of cast iron as compared with steel. Large-diameter vessels cannot be easily cast, and the strength of gray iron is not reliable for pressure-vessel service. C& steel may be used for small-diameter thick-walled vessels. Furthermore, because of its higher strength

Fig. 1.5. A 20,030-bbl hemispheroid gasoline-storage tank 64 ft in diameter by 35 ft high. Designed for 2% lb per $9 in. gage woridng pressure. (Courtesy of Chicago Bridge & Iron Company.)

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----Fig. 1 . 6 . W e l d i n g e x t e r n a l circum-fere ntiol seam of shell of large vessel with automatic welder. (Courtesy of C. F.Braun 8 C o m p a n y . )

services may be fabricated by machining a series of con-centric shells and shrink fitting for producing desirable pre-stress conditions. This method of vessel fabrication is dis-cussed in a later section of the text. In general, machining is an expensive operation and is limited to small vessels and parts in which the cost can be justified.

1.2a Fusion Wejam. Fusion welding is the most

widely used method of fabrication for the construction of steel vessels (12). This method of construction is virtually unlimited with regard to size and is extensively used for the fabrication and erection of large-size process equipment in the field. Often such equipment is fabricated by the method of subassembly. In this process, sections of the unit are shop welded and then assembled in the field. Equipment having a size sufficiently small to permit transportation by trucks, rail, or barge is usually completely shop welded beta

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se of the lower cost and greater control of the welding p cedure in the shop.

There are two tvpes of fusion welding t-hat are exte.nsively used for the fabrrqation of vessels. These are: (1) the gas welding ‘&ocess, in which a combustible mixture of acetylene and oxygen supply the necessary heat for fusion, and (2) the electric-arc welding process, in which the heat of fusion is ‘supplied by an electric current (13, 14, 15, 16). Arc welding is the preferred process because of the reduction of heat in the material being welded, the reduction of oxidation, and better control of the deposited weld metal. A wide range of arc-welding equipment is available, from the small portable welding units to the large automatic welding machines. Small arc-welding machines are widely used in welding shops that fabricate small equipment whereas the

automatic machines are better suited for the welding of heavy sections involving the deposition of a large quantity of weld metal. Figure 1.6 illustrates the use of an auto-matic welding machine in fabricating a large-diameter vessel.

Gas welding is the preferred type of welding for light gages of metal (20 gage or less), which are difficult to weld by the arc-welding process. Gas welding equipment is extremely useful in flame cutting either in the field or in the shop.

One of the most recent and successful developments in the field of arc welding of vessels is the submerged-arc welding process (17). This process was virtually unknown at the beginning of World War II. The necessity of expediting production of welded equipment during the war years resulted in the realization of the advantages of this tech-nique. The process involves submerging of the arc beneath a blanket of granulated mineral flux. The, arc beneath the blanket generates heat to melt the electrode and deposits weld metal. A portion of the granulated flux melts, forming a protective layer on the weld metal, and solidifies with the weld metal. In addition to completely protecting the weld metal from the atmosphere, this process makes the weld metal virtually free of hydrogen. As the arc is covered, there is no arc flash, and also a lesser quantity of smoke and obnoxious fumes is produced as compared with the earlier welding processes. As the weld can not be observed by the operator, mechanical attachments are used to control the dimensions of the weld. Several inches of weld metal can be deposited in one pass, a fact which greatly decreases the welding time involved. However, the greatest advantage

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-Methods of Fabrication 7 of the submerged-arc process is t.he elimination of the

opera-tyble.

1

‘w, 1.2b Welding Standards. The success of fabrication by welding is dependent upon the control of the welding variables such as exFrience and training of the welder, the use of proper materials, and welding procedures. An inex-perienced welder or a welder using inferior materials or incor-rect procedures can fabricate a vessel that has good appear-ance but has unsound joints which may fail in service. Thus it is absolutely essential that the welding variables be controlled in order to produce sound joints in the equip-m e n t . A nuequip-mber of codes and standards have been estab-lished for this purpose. Some of these standards are:

“ASME Code Welding Qualifications” (Section IX of the

ASME Boiler Code)

ASA Code for Pressure Piping (B 131.1, Section 6 and’ Appendices I and II)

Standard Qualijication Procedures of the American

Weld-< ing Society

API Standard 12 C, API Speci$cation for Welded Oil

Storage Tanks (Sections 7 and 8)

The American Welding Society (AWS) established the basic standards for qualifying operators and procedures. These standards of qualification form the basis for most of the standards in the various codes. For practical purposes, therefore the rules for qualifying welders and welding procedures are essentially the same in the various codes and standards. Regardless of whether or not the welded vessel is intended to meet one of the codes or standards, it is advis-able that the welding conform to one of the minimum standards.

Each fabrication shop should establish welding procedures best suited to its need and its equipment. To meet the welding standards previously mentioned, it is not necessary that welding procedures be the same in all shops. But it is necessary that, regardless of the procedures used, the welded joints pass the qualification tests for welding proce-dures and that the welding operators be qualified in using these ,wrne procedures. To meet welding standards, welds made by the shop proced&es must be tested to determine tensile strength, ductility, and soundness of the welded joints. The req&ed tests for the welding procedures speci-fied by APmndard 12 C involve the following:

A. For groove welds:

1. Reduced-section-tension test (for tensile strength).

2. Free-bend test (for ductility). 3. Root-bend test (for soundness).

4. Face-bend test (for soundness). 5. Side-bend test (for soundness).

B. For fillet welds:

1. Transverse-shear test (for sbear strength). 2. Free-bend test (for ductility).

3. Fillet-weld-soundness test.

,

,-The minimum results required by tests such as those listed above are described in detail in the various codes. A few representative requirements are:

1. The tensile strength in the reduced-section-tension test

Double-welded butt joint Double-welded butt joint

(V-type groove) (U-type groove)

rover Q In. Y

Single-welded butt joint T Smgle-welded butt joint with backing strip wlthout backing strip (may be V-or U-type groove) (may be V-or U-type groove)

Single-welded butt joint

with backing strip wlthout backing strip

Double full-fillet lap joint Single full-fillet lap joint with plug welds Fig. 1.7. Examples of welded joints. (Note: The two types of lap welds shown may be used only for circumferential joints and for shell plates not over 36 in. thick, and for attachment of nozzles and reinforcements without thickness limitation.) (From the API-ASME code [lo].)

shall not be less than 95 y0 of the minimum tensile strength of the material being welded.

2. The minimum permissible elongation in the free-bend test is 20%.

3. The shearing strength of the welds in the transverse-shear test shall not be less than 87 y0 of the minimum tensile strength of the material being welded.

4. In the various soundness tests, the convex surface of the specimen is examined for the appearance of cracks or

other defects. If any crack exceeds $6 in. in any direction, the joint is considered to have failed.

The individual welders, as well as the shop procedures,

must meet certain standard qualifications. The individual welders must qualify under the established procedure according to the test previously described. This is

impor-tant because a welder may qualify when using one procedure but may be unable to qualify when using another procedure. For example, an operator of an automatic welding machine may produce satisfactory welds with that machine but may not qualify when using manual equipment.

1.2~ Types of Welded Joints. A variety oi types of welded joints are used in the fabrication of vessels. The selection of the type of joint depends upon the service, the thickness of the metal, fabrication procedures, and code requirements. Figure 1.7 is a diagram from the API-ASME code for unfired pressure vessels which illustrates some of the types of welded joints used in the welding of steel plates for the fabrication of pressure vessels. Other types of weld joints and details for the preparation of such joints are given in Appendix B. Instead of drawing weld details to specify the type of weld desired, most engineering of&es now use standard symbols for ,welding conventions (16). Typical welding symbols are shown in Fig. 1.8.

(17)

8

Factors Influencing the Design of Vessels Type of weld Groove Bead Fillet Plug and Feld weld Weld all around F l u s h Location of welds

Arrow (or near) side of joint

1. The side of the joint to which the arrow points is the arrow side, and the opposite side of the joint is the other side.

2. Arrow-side and other-side welds are some size unless otherwise shown. 3. Symbols apply between abrupt changes in the direction of welding, or to the extent of hatching or dimension lines, except where the all-around symbol is used.

4. All welds are continuous and of user’s standard proportions unless otherwise shown.

5. Tail of arrow used for specification process or other reference. (Tail may be omitted when reference not used.)

6. When a bevel- or J-groove weld symbol is used, the arrow shall point with a definite break toward the member which-is to be chamfered. (In cases where the member to be chamfered is obvious, the break in the orrow may be omitted.)

7. Dimensions of weld sizes, increment lengths, and spacing, in inches. 8. For more detailed instruction in the use of these symbols refer to Stondord

Welding Symbols, published by American Welding Society.

I

1.

I--Fig. 1.8. Welding symbols recommended by API Standard 12 C. (Courtesy of American Petroleum Institute.)

I.3 TYPES OF CRITERIA IN VESSEL DESIGN

The selection of the. type of vessel is based primarily upon the ?&&Z&l-s&vice required of the vessel. The func-I &al requirements impose certain operating conditions in respect to such things as temperature, pressure, dimensional limitations, and various loads. If the vessel is not designed properly, so as t,o accommodate these requirements, the /

ve el may fail in service.

Failure may occur in one or more manners, such as by plasticformation resulting from excessive stress, by rup-ture without plastic deformation, or by elastic instabilit,y. I:aiJuz-may also result from corrosion, wear, or fat,igue. Design of the vessel to prot,ect against such failures involves the considerat,ion of these factors and the physical

proper-I ies of the mat.eriuls. Various types of possible vessel failure and criteria in vessel design are discussed in the following chapter.

1 . 4 E C O N O M I C C O N S I D E R A T I O N S

.ilthough the chemical-process requirements generally limit the choice of materials of fabrication, the final selection is frequently dictated by economic considerations. Fo1 purposes of comparison the relative costs of lO,OOO-gal tanks fabricated from various materials are tabulated in Table 1.1 (w&h steel as the unit reference) (18). An examination of t.his table indicates t,hat the cheapest const&&~materials,._. provided they can be used, are wood, concrete, and steel. These materials can frequently be lined with a thin protec-tive layer this eliminates the necessity of fablicat.ing the

vessels from more expensive metals or alloys. As the size of the tank is increased to handle larger volumes, the rela-tive costs of using alloys and nonferrous metals increases. Prestressed or reinforced concrete may sometimes be used to advantage for the construction of large vessels.

1.4a Steel Pricing. The bulk of chemical and petro-chemical process equipment is fabricated from plain carbon steel. -1 knowledge of the method of pricing steel is

essen-Table 1.1. Relative Costs of Materials of Construction for Tanks

/ Cost Relative to Steel

~.~______-. J 10,000 gal 100,000 gal WOOd Concret y’(reinforced) 0.40.6 0:; St,eel’ 1.0 1.0 Lithcotr-lined steel 1.2 1.2 Rubber-lined steel 1.8 2.0 Lead-lined steel 1.8 2 .o coppe:L 2.0 2.6 Aluminum 2.4 3.0 Glass-lined st.eel 2.7 3.0 Xi-Clad steel 2.7 3.0 Stain-clad steel 2.7 3.0

Stainless steel, type 304 3 4 3.5

,Mon&clad steel 3.4 3.5

Incouel-clad steel 3.4 3.5

Stainless steel, type 316 4.4 4.8

&lone1 metal 4.4 4.8

(18)

Economic Considerations 9

mill price to compensate for t.he handling, storage, and delivery of the steel st.ock. Therefore, the difference between warehouse prices and mill prices is essentially :I service charge.

The relative amount of “millproduction” that was shipped to warehouses for warehouse distribution for the ten-yea1 period 1944-1954 is indicat.ed in Fig. 1.9. This figure indi-cates that for the seven-year period 1945-1952 about 18yc of the total steel-mill production on the average was shipped to the warehouses. For the year 1951 the stezl mills produced 78,928,950 tons of steel products and shipped

14,399,432 tons (18.50’%) to the warehouses.

In the design of equipment for large process plants, it is not unusual to place vessel orders with the vessel fabricator from 6 to 12 months before the required shipping dates I,O enable t)he vessel manufacturer t.o order t,he steel plate from the mill rather than from a warehouse.

M I L L P R I C I N G . In general, steel is purchased from the

mill or warehouse in the “hot-rolled” or “cold-rolled” condi-tion. The steel is further classified as sheet, strip, plates, or bars. Alloy steels and &ructural steels are classified sepa-rately. “Hot-rolled, plate steel,” or “cold-rolled strip steel,” or “alloy steel bars,” and so on are combined classi-ficat,ions of types of available steel. Table 1.2 shows the grade classification, by size, of flat, cold-rolled carbon steel by a typical steel mill. Table 1.3 shows t.he corresponding grade classification by size of flat, hot-rolled carbon steel. The steel mills and the warehouses quote “base prices” for each class of steel product. Table 1.4 shows a section of a typical mill base-price list as of January, 1956. The prices are all F.O.B. cars or trucks at the mill works (Indiana

Harbor, Indiana.) The prices quoted in Table 1.4 apply to an order of 10,000 lb or more of the size ordered at one time (one thickness and one width is considered one size), of one grade or analysis, released for shipment to one destina-tion at one time. For weights of less than 10,000 lb, “item-quantity extras” apply. Item la, of Appendix C lists the quantity extras charged by a typical steel mill (Inland St.eel Company, as of May 13, 1953) for carbon-steel plates.

:(

Table 1.2. Grade Classification by Size of Flat, Cold-rolled Carbon Steel

(Courtesy of Great Lakes Steel Corporation, Division of National Steel Corporation, Detroit, Michigan)

Thickness. inches

0.250 or 0.249.9 to

Width, inches t,hicker 0.0142

up to 12 Bar Strip (1)

Over 12 to 24 Strip (2) Strip (2) Over 12 to 24 Sheet (3) Sheet (3)

Over 24 to 32 Sheet Sheet

Over 32 Sheet Sheet

Notes: (1) Up to 35 in. wide and less than 0.225 in. in thickness, and not to exceed 0.05 sq in. in cross section, having rolled or prepared edges is “flat-wire.” (2) If special edge, finish, or definite t,emper, as defined by ASTM Specification A-109. (3) If no special edge, finish, or temper is specified or required.

tial in order to arrive at economical designs for equipmenL fabricated of steel.

Steel may be purchased from t,wo sources-a steel mill or a st,eel warehouse. The prices paid for the steel from the two sources are very different, the warehouse prices being appreciably higher. The reason for these price differences is found in the methods used by steel mills to obtain maxi-mum-volume production in order to minimize unit costs. It is the present practice of the steel mills to accumulate orders until they have sufficient tonnage to permit economi-cal rolling. Therefore, the steel mills usually serve cus-tomers who require material in reasonably large quantit,ies and- who can anticipate their requirements well in advance. It is apparent that this mode of operation is not conducive to quick delivery; three or four months, or more, depending upon the rolling schedule, may elapse before delivery.

This situation makes necessary another means of furnish-ing steel to customers who require material quickly and in quantities too small for mill production schedules. The steel warehouse fills this distribution need, supplying steel immediately from large warehouse stocks. The steel ware-house secures steels from many rolling mills, in a full range of qualities, finishes, shapes, and sizes, and stores these steels. Thus fabricators using steel may purchase any particular product immediat,ely from stock or combine orders for various pr0durt.s and buy all at one time from one convenient source.

Obviously the warehouse must. be paid an increase over

Table 1.3. Grade Classification of Flat, Hot-rolled Carbon Steel

(Courtesy of Great Lakes Steel Corporation) Width, inches

Thickness, To 3% Over Over Over Over inches incl. 355 to 6 6 to 12 12 to 48 48 0.2300 and thicker Bar Bar Plate Plate Plate 0.2299 to 0.2031 Bar Bar Strip Sheet Plate

0.2030 to 0.1800 Strip Strip Strip Sheet Plate

0.1799 to 0.0568 Strip Strip Strip Sheet Sheet

Year

Fig. 1.9. Percentage of total millproduction of steal products shipped to warehouses.

.,_ _ .-.-- _._~____~__ - -.-~-

-/ I \ -i---‘ - \I 7

(19)

.T-1 0

Table 1.4. Mill Price List

(Courtesy of Inland Steel Company, Chicago, Illinois,

January, 1956)

Base Price per 100 lb Hot-rolled sheets (18-gage and heavier) $4.325

Hot-rolled strip 4.325

Cold-rolled sheets 5.325

Hot-rolled carbon-steel bars (merchant quality) 4.65

Hot-rolled alloy-steel bars 5.575

Reinforcing bars 4.65

Carbon-steel plates 4.50

Carbon-steel structural shapes 4.60

Carbon-steel plates fall into three classifications: (1) those furnished to chemical requirements, (2) those fur-nished to physical requirements, and (3) those furfur-nished to both chemical and physical requirements. Item lb of Appendix C lists the “classification extras.”

Other mill-price extras of primary interest are given in item 1, Appendix C and are classified as: quality extras, length extras, width-and-thickness extras and killed-steel extras.

Circular- and sketch-plate extras are involved when items such as blanks for formed heads are purchased. As these plates are usually flame cut, gas-cutting extras also apply. Gas-cutting extras are also charged for rectangular plates when the thickness limits for shearing are exceeded. Item 2 of Appendix C lists the gas-cutting extras per linear foot of cutting.

The previously mentioned extras such as quality,

thick-Fig. 1 .lO. Base price of steel plates in Pittsburgh.

ness, and width are calculated on a dollar-per-loo-lb basis, whereas the extras for circular and sketch plates are calcu-lated on a percentage basis, as listed in item 3 of Appendix C. The percentage is calculated on the net-per-loo-lb price of the smallest rectangular plates from which each circular or sketch plate is obtained exclusive of freight and extras for gas cutting a quantity. The outside dimension of each circular or sketch plate determines the size of the smallest rectangular plate from which the circular or sketch plate is obtained.

A wide variety of other “mill extras” are quoted by the various steel mills. The reader is referred to company price lists for complete quotations on these other extras, among which are:

1. Heat-treatment extras 2. Surface-finish extras 3. Testing extras 4. Chemical-requirements extras 5. Specification extras 6. Special-requirements extras

7. Dimensional and workmanship extras 8. Extras for special-shipment requirements 9. Special-marking-of-plates extras

10. Loading extras

11. Bundling-of-plates extras.

Each extra is usually separate and distinct. The indi-vidual items are combined to form a “full extra” applicable to the order.

The steel-mill base prices given in Table 1.4 and the steel-mill extras given in Appendix C are quoted as of January 31, 1956.. It must be emphasized that these prices are representative of the prices quoted by steel mills at that time. As economic conditions vary, prices charged for manufactured products fluctuate, and the base and extra prices are subject to change. Figure 1.10 illustrates the changes in the base price of steel plate in Pittsburgh from July, 1938 to January, 1956 (19). The horizontal line to April, 1945 is for the period during which government con-trols were maintained on steel prices because of the national emergency of World War II. The curve indicates that the price of steel plate at the mill doubled between 1945’ and 1956. Reference should always be made to the most-recent available price lists for estimation purposes.

WAREHOUSE PRICING. Steel warehouses are strategically located throughout the country to provide a convenient source of supply for steel products. Whereas the steel mills produce steel products of standard length and width, the warehouse will supply steel cut to the customer’s require-ments. Typical operations in the warehouse include shear-ing, sawshear-ing, slittshear-ing, and flame cutting. Some warehouses will supply steel plates rolled to cylindrical shapes and bar shapes, bar stock rolled to rings or bent to other shapes, and plates with drilled or punched holes. Figure 1.11 shows typical stocks of steel in a warehouse.

Prices vary somewhat from warehouse to warehouse, depending upon the location of the warehouse, the distance from the mill, and the service performed. Item 4 of Appen-dix C gives typical warehouse prices from one warehouse

(20).

(20)

!

E c o n o m i c C o n s i d e r a t i o n s 1 1

Fig. 1.11. Interior view of warehouse showing typical stocks of steel. (Courtesy of Joseph T. Ryerson 8 Son, Inc.)

>’ . 1.4b Fabrication Costs. The direct costs of producing \ a piece of process equipment include the cost of materials b and the cost of labor. Material costs consist of the shop

material used in the fabrication plus the parts purchased from an outside source. The cost of steel plate, which has been discussed in the previous section, usually comprises a major portion of the material costs for vessels. The labor costs involved in the actual fabrication of the equipment I are often difficult to estimate accurately in advance. How has reported methods of short-cut estimations of welded I process vessels (21).

FABRICATION PR O C E D U R E.

I One of the first steps in the

fabrication of the vessel is usually the preparation of the shell for rolling. The edges of the individual plates for the shell require machining to true the edges and, in the case of code welding, to prepare the edge for welding. Figure 1.12 shows a 40-ft planer machining a double “U” edge on a lx-in. plate 29 ft long for a vessel shell. The next step is i usually crimping the edges of the plate which will be joined

by a longitudinal weld. The crimping step is required because the rolls cannot be used to form the two ends to the desired curvature. Figure 1.13 shows a 350-ton hydraulic press in the foreground, crimping the edge of a plate before rolling. In the background plates are shown being rolled into a cylindrical shape on pyramid rolls.

MAN-HOURS AND MATERIALS. After the shell has been

given edge preparation and rolled into shape, the vessel components must be fitted and assembled by welding. i Figure 1.14 gives curves according to How (21) for estimat-ing the man-hours involved in the various stages through

assembly of the shell and closures. The upper curve of

Fig. 1.14~ gives the cutting time in hours per linear foot for flame cutting the shell plate as a function of plate thickness. This curve may be used when the shell is cut from standard plate kept in stock, such as mill plate. If the plate is pur-chased from a warehouse, it may be obtained, cut to size, and the cutting cost included in the purchase price. In addition to the man-hours involved in flame cutting, a machine rate burden which includes the cost of machine time and gas consumed is also involved in flame cutting. The curve for cutting-machine rate burden is shown in the lower part of Fig. 1.14~~.

The number of man-hours involved in edge preparation prior to crimping and rolling are given in Fig. 1.14d. The combined number of man-hours involved in crimping the longitudinal seam ends and rolling the plate into a cylindrical form are given as parameters in Fig. 1.14b; the man-hours are treated as a function of plate lengths and thicknesses. The parameters given in Fig. 1.14b are based upon the rolling and crimping of a few plates; the figure therefore gives a liberal allowance for these operations when more than a few plates are rolled and crimped at one time.

The man-hours required for the fitting and assembling of the shell and closures for the vessel are given by the solid lines in Fig. 1.14~ as a function of the plate thickness and with three parameters for different degrees of complexity of the vessel. Also included in this figure are three curves having nearly the same shape as the parameters and indi-cated by the dotted lines that may be used as a rough check on the total man-hours involved in fabrication. These latter three curves are intended to be used only as a check to disclose any gross errors in the total estimation. In

(21)

addi-Fig. 1.12. Machining a double U edge on a plate 1 yh in. thick and 29 ft long for a vessel shell by means of o 40-ft planer. (Court+sy o f C, F. Broun g Company.)

(22)

4 % k i%il 1 I%12 I3 4 5 6 % % 1% 1% 2% P l a t e t h i c k n e s s , i n . (4 3.5 I /+I I 1 4 -9 I I I\ I I I I I 8 I A v e r a g e s t e e l t h i c k n e s s , i n . Cd I Economic Considerations 13 Plate thickness. i n . (b) 0.6 01111111/1(( % b % % % % 1 I?$ 1% 1% 1%

Plate thickness, in. (4

F i g . 1 . 1 4 . C u r v e s o f H o w (21) fsr e s t i m a t i n g s h o p t i m e f o r v e s s e l f a b r i c a t i o n . ( a ) C u t t i n g t i m e a n d m a c h i n e r o t e b u r d e n f o r tlgme c u t t i n g w i t h a u t o m a t i c i machines. (b) T i m e f o r r o l l i n g plates 6 0 t o 7 2 i n . i n w i d t h a n d o f v a r i o u s l e n g t h s a n d t h i c k n e s s e s . (d F i t t i n g a n d a s s e m b l y , a n d total f a b r i c a t i o n t i m e ( f o r r o u g h c h e c k ) , f o r s t e e l t a n k s a n d weldments. (d) W e l d i n g a n d e d g e - p r e p a r a t i o n t i m e a n d w e l d i n g - r o d w e i g h t f o r c o d e b u t t w e l d s i n c a r b o n s t e e l . (Cow-t e s y o f M c G r a w - H i l l P u b l i s h i n g C o . )

t ion to giving the number of man-hours for edge preparation, Fig. 1.14d also gives the welding time and quantity of weld-ing rod per linear foot, involved in assembly of the vessel ends and shell.

Most vessels contain two or more nozzles for charging and discharging operations. The man-hours and welding-rod requirements for attaching different types of nozzles are given in Fig. 1.15.

Formed closures such as dished heads can be purchased from fabricators with the edges beveled for welding. Costs for this preparation are given in a later section describing formed heads. However, if it is practical to machine the heads in the shop that fabricates the vessel, the man-hours required for this operation may be estimated from Fig. 1.16~ and b. Bolting flanges for nozzles may be shop fabri-cated from flat plates. The machining time for t.his opera.

1

(23)

-14 Factors Influencing the Design of Vessels 1.6 1.4 1 . 2 -B l.O-e $CL p 0.8 -a g 0.6 0.4 0.2 -

O-1.61

1 . 4I

-l.2t-,

2 1.0 // m / / Tii / / .E / / $ 0 . 8 I I I I/ I/ I 2 Labor. hr

LO.6 Weld rod. II

I I I

0 I

% 1 1 % 1% 2 2 % 3 3% 4

Nominal nozzle size, in. (4

J ! slip-on flange

I

2 2%33%4 5 6 8 1 0 1 2 1 4 1 6 1 8

Nominal nozzle size, in. (d

o0.5 1.0 2 1 . 5 -# e $ 2.0 -12 $ 2.5 -% 3 3.0 3.5 4.0 4.5 -4.5 4.0 p 3.5 =lox .E 3.0 f$ “r 2.5 &cl 2 2.0 1 . 5 1.0 (1.5 2 2% 3 3354 5 6 8

Nominal nozzle size, in. (b)

o-- 30 5 -- 25 25 -5 30 -0 2 2%33%4 5 6 8 1 0 1 2 1 4 1 6 1 8

Nominal nozzle size, in. UJ

Fig. 1.15. Curves of How (21) for estimating welding-time in hours and welding-rod requirements for nozzle attachments to vessels. (a) Welding time and welding rod for installing XH steel couplings in unfired pressure vessels. (b) Welding time and welding rod for installing long-welding-neck forged-steel nozzles. (c) Welding time and welding rod for fabricating 150-psi nozzles in unfired pressure vessels. (d) Welding time and welding rod for fabricating 300-psi r,ozzles in untired pressure vessels. (Courtesy of McGraw-Hill Publishing Co.)

(24)

Economic Considerations 15 6 5 t E 0 E 4 2m 4I 3 I u-z AZk 2 1.8 ’ E 1.6 -0 1.4 1.2 / 0.9 / 0.8 1 5 20 25 30 35 40 50 60 70 80 100 120 2 ..8 ..6 ..4 I- 0.8 ’ ,+’ n I 1 5 20 25 30 35 40 50

Outside diameter of head, in. Outside diameter of head, in.

(4 (6) 6.5 6.0 5.0 8 ; 3.0 8 i 2.5 2 8 2.0 5 1.8 0.6 k 1.6 L ; 1 . 4

8 1 . 2 flanges up to 6 ips inclusiv

1.1 1.0 0.9 0.8 c 1 2 3 4 5 6 8 10 12 14 16 18 20 22 24 26 4 % k % t J6 1 1%

Nominal flange size, in. Size of weld, in.

(cl (4

Fig. 1.16. Curves of How (21) for estimating man-hours of machining time and welding-rod requirements for miscellaneous operations in vessel fabrication, (a) Machining time, flanged and dished heads, grooved face, carbon-and-nickel- or stainless-clad steel. (b) Machining time, flanged and dished heads. beveled face, carbon-and-nickel- or stainless-clad steel. (c) Machining time for carbon-steel plate flanges, 1 to 26 ipr, >/4 to 2% in. thick. (d) Welding time and weight of welding rod for fillet welds in carbon steel. (Courtesy of McGraw-Hill Publishing Co.)

(25)

-1 6 Factors lnftuencing the Design of Vessels Table 1.5. Engineering News-Record Construction

Cost Index

(Courtesy of McGraw-Hill Publishing Co.) Year 1913 1915 1920 1925 1926 1930 1932 1935 1940 1945 Index 100 94 235 206 208 202 157 195 242 308 Year 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 Index 346 413 461 477 510 543 569 600 628 660 (July)

i.ion is given in Fig. 1.16~. Various attachments such as skirts, saddles, and lugs may be added to the vessel, usually by fillet welding. The man-hours per foot and the welding required for fillet welding is given in Fig. 1.16d. Addi-tional curves for some alloy and rumferrous metals are giver1 Iry How (21).

1.5 ESTIMATING CURRENT COSTS

COST INDICES. Because of the constant change of costs

for material, labor, taxes, and plant overhead, available COSI data rapidly become obsolete. Thus some method of bringing cost data up to date is required. The procedure normally followed is t,he application of available “cost. indices.” The cost indices are relative numbers giving the variation in a group of costs with reference to a base year. To use a cost index the estimator simply multiplies t.he known cost at a given date by the ratio of the current index value to the index applicable a.t the date of the known cost.

Index A Cost A = Cost B ___

Index B

(1.1)

A number of indices are in wide use; they differ somewhat because of the basis used in their preparation and the refer-ence year. Three widely used indices are the Engineering ‘Vews-Record (ENR) construction-cost index (22), the

Table 1.6. Marshall and Stevens Equipment-Cost Index

(Average for All Industries)

(Courtesy of McGraw-Hill Publishing Co. [235])

Year lndex Year Index

1913 57.9 1947 150.6 1915 55.9 1948 162.8 1920 153.3 1949 161.2 1925 105.3 1950 167.9 1926 100 .o 1951 180.3 1930 87.0 1952 180.5 1932 66.1 1953 182.5 1935 78.0 1954 184.6 1940 86.1 1955 190.6 1945 103.4 1956 208 .a 1946 123.2 1957 (June) 224.1

Table 1.7. Twenty-City Average of Hourly Rates for

Skilled Labor

(From Engineering News-Record) (Courtesy of McGraw-Hill Publishing Co.) Year Rate, dollars/hr Year Rate, dollars/hr

1926 1.27 1950 2.52 1932 1.03 1952 2.84 1939 1.44 1953 3.01 1945 1.66 1954 3.14 1946 1.80 1955 (July) 3.25 1949 2.41

Marshall and Stevens eyuipment-cost index (23), and the Nelson refinery index (24).

The ENR construction-cost, index (22) reflects labor-wage-rate and material-price trends. The index consists of the cost of a hypothetical block of construction requiring 6 bbl of cement, 1.088 M fbm of lumber, 2500 lb of steel, and 200 hours of common labor. This cost was $100 in the year 1913, which is taken as the reference year. Although this index is intended to reflect average construction costs and has no particular relation to the cost of equipment, it has proved extremely useful in estimating changes in costs for complete plant,s. Because of its wide use it has often been the basis of estimating changes in equipment costs. Table 1.5 lists some values of this index as a function of time.

The Marshall and Stevens equipment-cost index reflects the comparative costs of equipment (23). It is based upon t.he costs of machinery and major equipment, installation labor, plant furniture and fixtures, tools and minor equip-ment, and oflice furniture. These costs are estimated quarterly for 47 different industries, with a separate formula for each industry and with the year 1926 as a reference of 100. The petroleum-industry index contains the following component percentages: process machinery, 25; installation labor, 19; power, 12; maintenance equipment, 2; and admin-istration, 6. Other process industries for which indices are prepared are: the cement industry, the chemical industry, the clay-products industry, the glass industry, the paint

Table 1.8. Average Boilermaker Wages in July, 1954, as a Function of Locale

(U. S. Bureau of Labor Statistics)

dollars+

U. S. Average 3.11

New England (Me., Vt.., Mass., Conn., R. I.,

N. H.) 3.00

Mid-Atlantic (N. Y., Pa., N. J.) 3.44

Border States (Del., Md., Ky., W. Va., Va.) 3.01

Southeast (Tenn., S. C., N. C., Ala., Ga., Miss.,

Fla.) 2.90

Great Lakes (Minn., Wis., Mich., Ill., Ind., Ohio) 3.13 Midwest (N. Dak., S. Dak., Kans., Nebr., MO.,

Iowa) 2.96

Southwest (Tex., Okla., La.) 2.90

Mountain (Mont., Idaho, Wyo., Utah, Ariz.,

N. Mex., Colo.) 3.01

References

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