Surface Production Operations: Volume 5: Pressure Vessels, Heat Exchangers, and Aboveground Storage Tanks: Design, Construction, Inspection, and Testing

By Maurice Stewart

Covering both upstream and downstream oil and gas facilities, Surface Production Operations: Volume 5: Pressure Vessels, Heat Exchangers, and Aboveground Storage Tanks delivers a must-have reference guide to maximize efficiency, increase performance, prevent failures, and reduce costs. Every engineer and equipment manager in oil and gas must have complete knowledge of the systems and equipment involved for each project and facility, especially the checklist to keep up with maintenance and inspection--a topic just as critical as design and performance. Taking the guesswork out of searching through a variety of generalized standards and codes, Surface Production Operations: Volume 5: Pressure Vessels, Heat Exchangers, and Aboveground Storage Tanks furnishes all the critical regulatory information needed for oil and gas specific projects, saving time and money on maintaining the lifecycle of mechanical integrity of the oil and gas facility. Including troubleshooting techniques, calculations with examples, and several significant illustrations, this critical volume within the Surface Production Operations series is crucial on every oil and gas engineer’s bookshelf to solve day-to-day problems with common sense solutions.

• Provides practical checklists and case studies for selection, installation, and maintenance on pressure vessels, heat transfer equipment, and storage tanks for all types of oil and gas facilities
• Explains restoration techniques with detailed inspection and testing procedures, ensuring the equipment is revitalized to maximum life extension
• Supplies comprehensive coverage on oil and gas specific American and European standards, codes and recommended practices, saving the engineer time searching for various publications

• Language: English
• Publisher: Elsevier Science
• Release date: Jul 22, 2021
• ISBN: 9780128037447

Maurice Stewart

Dr. Maurice Stewart, PE, a Registered Professional Engineer with over 40 years international consulting experience in project management; designing, selecting, specifying, installing, operating, optimizing, retrofitting and troubleshooting oil, water and gas handling, conditioning and processing facilities; designing plant piping and pipeline systems, heat exchangers, pressure vessels, process equipment, and pumping and compression systems; and leading hazards analysis reviews and risk assessments.

Book preview

9780128037447_FC

Surface Production Operations

Pressure Vessels, Heat Exchangers, and Aboveground Storage Tanks: Design, Construction, Inspection, and Testing

First Edition

Maurice Stewart

Table of Contents

Cover image

Title page

Copyright

Dedication

Preface

Acknowledgments

1: Engineering principles

Abstract

1.1: General overview

1.2: Basic principles

1.3: Stress analysis

1.4: Discontinuity stresses

1.5: Fatigue analysis

1.6: Thermal stresses

2: History and organization of codes

Abstract

2.1: Overview and objectives

2.2: Pressure vessels and equipment

2.3: History of pressure vessel codes in the United States

2.4: Organization of the ASME Boiler and Pressure Vessel Code

2.5: Organization of Code Committee

2.6: Updating and interpreting the Code

2.7: ASME Code stamps

2.8: Organization of the ASME B31 Code for pressure piping

2.9: Some other pressure vessel codes and standards in the United States

2.10: Worldwide pressure vessel codes

2.11: ASME Code, Section VIII, Division 1 versus Division 2

2.12: Design criteria, ASME Code, Section VIII, Division 1

2.13: Design criteria, ASME Code, Section VIII, Division 2

2.14: ASME Code, Section IX: Welding

2.15: ASME Code, Section I, Power boilers

2.16: Additional requirements employed by users in critical service

3: Materials of construction

Abstract

3.1: Overview

3.2: Material selection

3.3: Nonferrous alloys

3.4: Ferrous alloys

3.5: Heat treatment of steels

3.6: Brittle factors

3.7: Hydrogen embrittlement

4: Materials selection for pressure vessels

Abstract

4.1: Overview

4.2: Selection of materials for service conditions

4.3: Selection of materials to prevent brittle fracture

4.4: Guidelines for preventing brittle fracture in existing equipment

5: Mechanical design of pressure vessels

Abstract

5.1: Overview and objectives

5.2: General considerations

5.3: Owner’s, user’s, and manufacturer’s responsibilities

5.4: Determining design conditions

5.5: Mechanical design

6: Fabrication, welding, and in-shop inspection

Abstract

6.1: Overview

6.2: Plate materials

6.3: Forming of shell and head components

6.4: Nozzles

6.5: Fabrication welds

6.6: Welding processes and procedures

6.7: In-shop inspection

7: In-service inspection by nondestructive examination (NDE)

Abstract

7.1: Overview

7.2: General considerations

7.3: Design for inspection

7.4: Code and jurisdiction requirements

7.5: Forms of deterioration

7.6: Analysis of in-service inspection data

7.7: Fitness-for-service analysis

7.8: Nondestructive examination techniques

8: Repair, alteration, and re-rating

Abstract

8.1: Overview

8.2: Code and jurisdiction requirements

8.3: Repairs

8.4: Alteration

8.5: Re-rating

9: Heat transfer theory

Abstract

9.1: Overview

9.2: Objectives

9.3: What is a heat exchanger?

9.4: Fouling

9.5: Process specification

9.6: Information needed for specifying work

9.7: Deliverables from the supplier

9.8: Evaluating designs

9.9: Economic pressure drop and velocity

9.10: Basic heat transfer theory

10: Heat exchanger configurations

Abstract

10.1: Overview

10.2: Shell-and-tube exchangers

10.3: Double pipe exchangers

10.4: Plate-fin exchangers

10.5: Plate-and-frame exchangers

10.6: Indirect-fired heaters

10.7: Direct-fired heaters

10.8: Air-cooled exchangers

10.9: Cooling towers

10.10: Other types of heat exchangers

10.11: Heat exchanger selection guidelines

11: Tubular heat exchanger inspection, maintenance, and repair

Abstract

11.1: Overview

11.2: Asian, European, and North American Nondestructive Testing Societies and related organizations

11.3: Evaluating and inspecting heat exchangers

11.4: Tubular exchanger inspections

11.5: Most likely locations of corrosion

11.6: Shop work

11.7: Shop inspection

11.8: Nondestruction examination

11.9: Minor repairs

11.10: Major repairs

11.11: Hydrostatic leak testing

11.12: Hydrostatic leak testing

11.13: Baffles and tube sheets

11.14: Heat exchanger bundle removal

11.15: Bundle removal procedures

11.16: Tube bundle removal

11.17: Shell repair

11.18: Heat treatment

11.19: Double-pipe exchangers

11.20: Inspection and repair of exchanger parts

11.21: Exchanger alteration

11.22: Quality control inspections

12: Heat exchanger materials considerations

Abstract

12.1: Component materials

12.2: Minimum pressurizing temperature

12.3: Sacrificial anodes

12.4: Insulation

13: Above ground storage tanks

Abstract

13.1: Objectives

13.2: Functions of an oil terminal

13.3: Storage tanks

13.4: Other storage facilities

13.5: Measurements of above ground storage tanks

13.6: Samples (Refer to Fig. 13.78)

13.7: Common tank problems and possible solutions

14: Selection of tank materials

Abstract

14.1: Overview

14.2: Selection of materials for service conditions

14.3: Typical tank materials considerations

15: Tank design

Abstract

15.1: Objectives

15.2: General design considerations

15.3: Basic data

15.4: Tank sizing

15.5: Safe oil height (SOH) and LPO determination

15.6: Bottom design

15.7: Shell design

15.8: Seismic and wind design

15.9: Roof design

16: Foundations

Abstract

16.1: Objectives

16.2: Soil considerations

16.3: Foundation design and secondary containment

17: Fabrication and construction

Abstract

17.1: General considerations

17.2: Foundation

17.3: Site construction

17.4: Erection considerations

17.5: Bottom construction

17.6: Shell construction

17.7: Roof considerations

17.8: Site construction

17.9: Erection sequence

17.10: General considerations

18: Inspection and testing

Abstract

18.1: Inspection philosophy

18.2: Inspection frequency

18.3: Inspection and testing techniques

18.4: Records

18.5: Tank inspection checklists

19: Fire protection

Abstract

19.1: General considerations

19.2: Common causes of fires

19.3: Design considerations for fire fighting

19.4: Location and spacing

19.5: Drainage and impounding

19.6: Fire suppression systems

19.7: Design requirements

20: Maintenance and repairs

Abstract

20.1: General considerations

20.2: Out-of-service replacement or repairs

20.3: In-service repairs

20.4: Specific considerations

Appendix A: Design calculations for an aboveground welded steel storage tank

A.1: Aboveground welded steel storage tank design

Appendix B: Design of a concrete ringwall foundation

B.1: Concrete ringwall foundation design example

Appendix C: Design of a crushed stone (gravel) ringwall foundation

C.1: Crushed stone ringwall foundation design

Appendix D: Design of a pile supported concrete slab foundation

D.1: Pile-supported concrete slab design

Index

Copyright

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Dedication

This book is dedicated to my wife, Eli, and son, Chad, for their enduring support, patience, and tolerance throughout the preparation of this book; and in memory of my parents Maurice and Bessie Stewart.

Maurice I. Stewart Jr., PE, PhD

Preface

Maurice I. Stewart, Jr., PE, PhD

I wrote this book with the intention of providing facility engineers, process engineers, petroleum engineers, senior field operations personnel, and managers with a starting point for addressing pressure vessel, heat exchanger, and aboveground storage tank selection, design, construction, testing, troubleshooting, and repair tasks.

Engineering curricula for mechanical and chemical engineers provide students with a basic understanding of the thermodynamics, thermal design, fluid mechanics, and stress analysis of surface production equipment. However, for the most part, the curricula doesn’t deal with the day-to-day needs of the practicing professional. This book is an attempt to bridge the knowledge gap by providing the necessary information for the day-to-day needs of the practicing engineer. This book begins by covering fundamental principles and then proceeds to address more advanced principles, such as the effects of wind and seismic loads in susceptible areas.

Practicing engineers responsible for selecting/designing surface production equipment frequently have information scattered among numerous books, periodicals, journals, and old notes. Then, when faced with a particular problem, they spend hours researching its solution only to discover the execution may have been rather simple. This book is an attempt to eliminate those hours of research by providing guidance as to the problems most frequently encountered in the selection, design, troubleshooting, testing and repair of pressure vessels, heat exchangers, and aboveground storage tanks.

This book makes no claim to originality other than that of the format. The material is organized in the most concise and functionally useful manner. Whenever possible, credit has been given to the original sources. Although every effort has been made to obtain the most accurate data and solutions, it is the nature of engineering that certain simplifying assumptions be made. Example problems should be viewed in this light, and where judgments are required, they should be made with due consideration.

Many experienced facility engineers will have already performed many of the calculations outlined in this book but will find the approach herein slightly different. All procedures have been developed and proven, using actual design problems. The procedures are easily repeatable to ensure consistency of execution. They also can be modified to incorporate changes in Codes, Standards, Recommended Practices, and requirements of the Authorities having Jurisdiction. Everything required for the solution of an individual problem is contained in the procedure.

This book may be used directly to solve problems, as a guideline, as a logical approach to problems, or as a check to alternative design methods. If more detailed solutions are required, the approach shown can be amplified where required. The user of this book should be advised that any code formulas or references should always be checked against the latest editions of Codes, that is, ASME Section VIII, Division 1 and Division 2, API 510, API 650, API 653, API 620, and API 2000. These codes are continually updated and revised to incorporate the latest available data.

1 am indebted to my many friends and colleagues for their help and advice to make this book possible and invite any suggestions readers may make concerning corrections or additions.

Acknowledgments

Maurice I. Stewart, Jr., PE, PhD, Stewart Training and Consulting (STC), LLC

This book is essentially a summary of the knowledge accumulated by the author with more than 45 years as a facility engineer practicing in the upstream and midstream oil and gas industry. I would like to take this opportunity to express my appreciation and gratitude to my many friends, colleagues, and mentors for providing invaluable learning opportunities.

In 2013 my good friend and colleague, O.T. Lewis, and I co-authored "Pressure Vessels Field Manual and Heat Exchanger Equipment Field Manual." The focus of both of the manuals was on common operating problems and practical solutions. I provided information covering engineering principles, application of the applicable codes, equipment design and materials selection. On the other hand, O.T. provided information covering fabrication, inspection, testing, and repair of both pressure vessels and heat exchangers. I have taken the information O.T. provided in the two Field Manuals and included it in this book. I have credited O.T. for the numerous photos he provided illustrating inspection, testing, and repair techniques. I am very thankful for O.T.’s contribution to this book.

A deep debt of gratitude goes to my good friend and colleague-Heri Wibowo, the graphic artist, illustrator and draftsman who not only prepared all illustrations, tables, photos, and figures but also took my poorly typed raw manuscript and transformed it into a format suitable to submit to the Elsevier. Heri took loosely drawn sketches or concepts, often poorly sketched on a sheet of paper or my iPad and transformed them into very detailed drawings illustrating the exact points I was trying to get across in the text. Without Heri’s contribution this book, or the other 12 books I’ve authored or co-authored, would certainly not have been possible.

I want to thank my international business partners and very close friends-Jamin Djuang, Managing Director of PT Loka Datamas Indah (LDI Training); Chang Choon Kiang "CK," Managing Director of Professional Training Southeast Asia (PTSEA); and Clement Clem Nwogbo, Managing Director of Resource Plus. Together, for over 30 years, we have provided training to over 35,000 professionals in every oil-producing region of the world.

I also want to thank my colleagues on the numerous API Committees, in which I served as a committee member, with whom I have had many interesting discussions, and the thousands of students in the courses I have taught that have, at times, presented me with difficult field scenarios or asked difficult questions, which in turn I’ve included as example problems or case studies in the book. Without their valuable input, none of the books I have authored would have been possible.

1: Engineering principles

Abstract

This chapter discusses the basic stresses effecting pressure vessels, heat exchangers and aboveground storage tanks. The chapter also illustrates how to analyze vessels and their component parts in an attempt to arrive at an economical and safe design. Pressure vessel failures are grouped into four categories and are further broken down into eight types of failures. The major general and local loads acting on pressure vessels are discussed. ASME Code, Section VIII, Division 1 based on design-by-rules and Division 2 design-by-analysis are covered. The maximum stress theory, maximum shear stress theory, comparison of the two theories, primary membrane, secondary, peak stresses and discontinuity stresses are also discussed.

Keywords

Design-by-rules; Design-by-analysis; Maximum stress theory; Maximum shear stress theory; Primary stresses; Membrane stresses; Secondary stresses; Peak stresses; Primary bending stress; Local primary membrane stress

1.1: General overview

Volume 1: Design of Oil-Handling Systems and Facilities and Volume 2: Design of Gas-Handling Systems and Facilities of the Surface Production Operations series present the basic concepts and design techniques necessary to select, specify, size, operate, and trouble-shoot oil, water and gas handling, conditioning and processing facilities. Volume 3: Facility Piping and Pipeline Systems and Volume 4: Pumps and Compressors build upon the information that is presented in Volumes 1 and 2. Volume 5: Pressure Vessels, Heat Exchangers and Aboveground Storage Tanks continue to build upon the information in Volumes 1 and 2.

Volume 5 discusses the applications, applicable design codes and standards, materials of construction, mechanical design, fabrication, welding, in-shop and in-service inspections, testing, maintenance and repair of pressure vessels, heat exchangers and aboveground storage tanks.

1.2: Basic principles

Pressure vessels, heat exchangers, and other process equipment operating at pressures greater than 15 psig (1 barg) must be designed to resist all modes of failure under all combinations of internal and external loads that the vessel will be subjected to under normal operating conditions. Pressure vessels are normally designed in accordance with the American Society of Mechanical Engineers (ASME) Code, Section VIII, Division 1; Design-by-Rules which does not require a detailed evaluation of all stresses. While the Code provides formulas for thickness and stress of components, it is up to the engineer to select the appropriate analytical procedures to determine stress due to other loadings and must select the appropriate combinations of loads so as to achieve an economical and safe design.

Section VIII, Division 1, Paragraph (UG-239c) states that the maximum general primary membrane stress must be less than allowable stresses provided in the material sections of the Code. The Code also requires that the maximum primary membrane stress plus the primary bending stress may not exceed 1.5 times the allowable stress provided in the material sections. The engineer should have a basic understanding of the various types of stresses and loadings so as to accurately apply the results of analysis. The following paragraphs provide the basic knowledge required for applying the results of analysis.

1.3: Stress analysis

1.3.1: ASME code, section VIII, division 1 vs division 2

Division 1 does not consider the effects of combined stress nor does it give detailed methods on how stresses are combined. On the other hand, Division 2 provides specific guidelines for stresses, how they are combined and allowable stresses for categories of combined stresses. Division 1 is design by rules whereas Division 2 is design by analysis. Although stress analysis as utilized by Division 2 is beyond the scope of this text, the use of stress categories, definitions of stress, and allowable stresses is applicable.

Division 2 stress analysis considers all stresses in a triaxial state combined in accordance with the maximum shear stress theory. Division 1 considers a biaxial state of stress combined in accordance with the maximum stress theory.

Before discussing stress analysis, it must be understood this book will not emphasize how to do stress analysis, but rather how to analyze vessels and their component parts in an attempt to arrive at an economical and safe design. The difference being that we analyze stresses where necessary to determine thickness of material and sizes of members. It is not necessary to find every stress but rather to know the governing stresses, and how they relate to the vessel or its attachments.

The shell thickness as computed by Code formulas for internal or external pressure alone is often not sufficient to withstand the combined effects of all loadings. Detailed calculations consider the effects of each loading separately and then must be combined to give the total state of stress in that part. The stresses that are present in pressure vessels are separated into various classes in accordance with the types of loads that produced them, and the hazard they represent to the vessel. Each class of stress must be maintained at an acceptable level and the combined total stress must be kept at another acceptable level. The combined stresses due to a combination of loads acting simultaneously are called stress categories.

1.3.2: Pressure vessel failures

Pressure vessel failures are grouped into the following four categories:

•Material

•Improper selection of material

•Defects in material.

•Design

•Incorrect design data

•Inaccurate or incorrect design methods

•Fabrication

•Poor quality control

•Improper or insufficient fabrication procedures including welding, heat treatment, or forming methods.

•Service

•Change of service condition by the user

•Inexperienced operations or maintenance personnel

•Upset conditions

•Some types of service require special attention for material selection and fabrication methods

Pressure vessel failures can also be broken into types of failures, which describe how the failure occurs. Each failure has a why it failed. For example, it may have failed due to corrosion fatigue because the wrong material was selected. The engineer be familiar with both the categories and types of failure as with categories and types of stress loadings.

The major types of failure are:

•Excessive plastic deformation

•Elastic instability or elastic buckling, vessel geometry, and stiffness as well as properties of materials are protection against buckling including creep or stress-rupture at high temperatures.

•The primary and secondary stress limits as specified in ASME Section VIII, Division 2, are intended to prevent excessive plastic deformation and incremental collapse.

•Brittle fracture

•Can occur at low or intermediate temperatures.

•Brittle fractures have occurred in vessels made of low carbon steel in the 40° to 50°F (5° to 10°C) range during hydrotest where minor flaws exist.

•Stress rupture

•Creep deformation as a result of fatigue or cyclic loading, that is, progressive fracture.

•Creep is a time dependent, whereas fatigue is cyclic dependent.

•Plastic instability

•Incremental collapse. Incremental collapse is cyclic strain accumulation or cumulative cyclic deformation.

•Cumulative damage leads to instability of vessel by plastic deformation.

•High strain

•Low cycle fatigue is strain governed and occurs mainly in lower-strength/high-ductile materials.

•Stress corrosion

•Chlorides cause stress corrosion cracking in stainless steels.

•Caustic service can cause stress corrosion cracking in carbon steels.

•Material selection is critical in these services.

•Corrosion fatigue

•Occurs when corrosive and fatigue effects occur simultaneously.

•Corrosion can reduce fatigue life by pitting the surface and propagating cracks.

•Material selection and fatigue properties are the major considerations.

1.3.3: Loadings

Loadings, or forces, cause the stress in pressure vessels. The loadings should be isolated so to determine where they apply and how when they apply to a vessel. Loadings can be applied over a large general area or over a smaller local area of the vessel. Both the general and local loadings can produce both membrane and bending stresses. The stresses are additive and will define the overall combined stress in the vessel or vessel component. Once the combined stresses are known then they are compared to an allowable stress.

Loading categories and types can be summarized as follows:

•Categories

•General loads—Applied continuously across a pressure vessel section

▪Pressure loads—Internal or external pressure (design, operating, hydrotest and hydrostatic head of liquid.

▪Moment loads—Due to wind, seismic, erection, transportation.

▪Compressive/tensile loads—Due to dead weight, installed equipment, ladders, platforms, piping and vessel contents.

▪Thermal loads—Hot box design of skirt-head attachment.

•Local loads—Due to reactions from supports, vessel internals, attached piping, attached equipment, that is, platforms, mixers, etc.

▪Radial load—Inward and outward.

▪Shear load—Longitudinal or circumferential.

▪Torsional load

▪Tangential load

▪Moment load—Longitudinal or circumferential.

▪Thermal load

•Types

•Steady loads—Long-term duration, continuous.

▪Internal/external pressure

▪Dead weight

▪Vessel contents

▪Loadings due to attached piping and equipment

▪Loadings to-and-from vessel supports

▪Thermal loads

▪Wind loads

•Nonsteady loads—Short-term duration; variable.

▪Shop and field hydrotests

▪Earthquake

▪Erection

▪Transportation

▪Upset, emergency

▪Thermal loads

▪Start-up, shutdown

To illustrate the effect of combined stresses let’s look at a pressurized, vertical pressure vessel bending due to wind, which causes an inward radial load applied locally. The effects of the general steady pressure load are longitudinal and circumference tension. The effects of the local nonsteady wind load are longitudinal tension on the windward side and longitudinal compression on the leeward side. The local nonsteady loads are both circumferential and longitudinal, tension on the inside surface, and compressive on the outside surface of the vessel. At any given point, the steel experiences a certain level of stress or the combined effect. It’s the engineer’s responsibility to combine the stresses from the various loadings to arrive at the worst probable combination of stresses, combine them using some failure theory and then compare the results to an acceptable stress level so as to obtain an economical and safe design.

The above example illustrates how categories and types of loadings are related to the stresses they produce. The stresses applied continuously and uniformly across the entire section of the vessel are defined as primary stresses. The stresses as a result of pressure and wind are primary membrane stresses. These stresses should be limited to the Code allowable. These stresses would cause bursting or collapse of the vessel, if allowed to reach an unacceptably high level.

The stresses from the inward radial load could be either a primary local stress or a secondary stress. It is a primary local stress if it is produced from a persistent load or by a yielding load. Either of the stresses could cause local deformation but would not, by itself, cause the vessel to fail. If the stress is a primary stress, the load would be redistributed; if it is a secondary stress, the load will relax once a slight deformation occurs. This is only true for ductile materials. In brittle materials, there would not be any difference between primary and secondary stresses. If a material cannot yield to reduce the load, then the definition of secondary stress does not apply. Thus, the type and category of loading will determine the type and category of stress. Each combination of stresses will have different allowable stresses, such as:

•Primary stress:

si1_e

•Primary membrane local (PL):

si2_esi3_e

•Primary membrane + secondary (Qm):

si4_e

where:

Pm = primary membrane stress.

Qm = membrane stresses from sustained loads.

S = allowable stress as per ASME Code, Section VIII, Division 1, at design temperature.

Sa = allowable stress for any given number of cycles from design fatigue curves.

A loading is for a relatively short duration would describe the type of loading. Whether. A loading is steady, continuous, nonsteady, variable or temporary will have an effect on what level of stress will be acceptable.

The major loadings acting on a pressure vessel are caused by:

•Internal pressure

•External pressure

•Weight of the vessel and contents, including internal components that transmit loads to the pressure vessel

•Wind and seismic forces

•Connecting piping and the weight of external appurtenances, that is, platforms, etc.

•Differential thermal expansion or temperature gradients

•Cyclic forces

The above loadings should be considered during the design in order to prevent failure from any of the failure categories mentioned earlier. The loadings are usually static, or the amplitude and frequency of their fluctuations are such that they can be considered to be so. However, cyclic loads of sufficient magnitude can result in a fatigue failure and it may be necessary to consider them in the design of a pressure vessel. For example, pressure fluctuations that exceed 20% of the design pressure and cyclic temperature gradients greater than 50°F (10°C) between adjacent locations can cause fatigue.

1.3.4: Maximum stress analysis

Pressure vessels normally are designed in the form of cylinders, spheres, ellipsoids, etc. When the wall thickness is small when compared with other dimensions (Rm/t > 10), where Rm is radius and t is thickness, pressure vessels are referred to as membranes and the associated stresses resulting from the contained pressure are called membrane stresses. These membrane stresses are average tension or compression stresses. They are assumed to be uniform across the vessel wall and act tangentially to its surface. The membrane or wall is assumed to offer no resistance to bending. When the wall offers resistance to bending, bending stresses occur in addition to membrane stresses.

In pressure vessels subjected to internal or external pressure, stresses are set up in the shell wall. The stress is triaxial with three principle stresses defined as:

σx = longitudinal/meridional stress

σϕ = circumferential/latitudinal stress

σr = radial stress

In addition to the three principle stresses, there may be bending and shear stresses. The radial stress is a result of the pressure acting directly on the vessel wall and causes a compressive stress equal to the pressure. In thin-walled vessels this stress is very small when compared to the other principle stresses and is generally ignored. Thus, for purposes of analysis it is assumed the stresses are biaxial. This assumption greatly simplifies the method of combining stresses in comparison to triaxial stress analysis. For thick-walled vessels (Rm/t < 10), the radial stress cannot be ignored, and formulas are quite different from those used in thin-walled shells.

ASME Code, Section VIII, Division 1, is based on design-by-rules and thus uses a higher safety factor to allow for unknown stresses in the vessel. The higher safety factor will impose a penalty on design but requires significantly less analysis. Membrane stress analysis makes the following simplifying assumptions:

•Stress is biaxial

•Stresses are uniform across the shell wall

For thin-walled vessels these assumptions have proven to be reliable. No vessel meets the criteria of being a true membrane, but we can use this tool with a reasonable degree of accuracy. In summary, membrane stress analysis is not completely accurate but allows certain simplifying assumptions to be made while maintaining a fair degree of accuracy.

1.3.5: Maximum stress theory

Maximum stress theory is the oldest, most widely used and simplest to apply. ASME Code, Section VIII, Division 1 use the maximum stress theory as the basis for design. This theory simply states that the breakdown of material depends on the numerical magnitude of the maximum principle stress. Stresses in the other directions are disregarded. Thus, only the maximum principle stress, used for biaxial stress assumed in thin-walled pressure vessels, must be determined. While the maximum stress theory accurately predicts failure in brittle materials, it is not always accurate for ductile materials. The reason for this is that ductile materials often fail along 45o to the applied force by shearing long before the tensile or compressive stresses are maximum.

Fig. 1.1 illustrates the maximum stress theory for the four states of biaxial stress. As shown in Fig. 1.1, the uniaxial tension or compression lies on the two axes. Inside the box, outer boundaries, is the elastic range of the material. Yielding is predicted for stress combinations by the outer line.

Fig. 1.1

Fig. 1.1 Graph of maximum stress theory. Quadrant I, biaxial tension; Quadrant II, tension; Quadrant III, biaxial compression; Quadrant IV, compression.

1.3.6: Maximum shear stress theory

The maximum shear stress theory states that the breakdown of material depends only on the maximum shear stress attained in an element. It assumes that yielding starts in planes of maximum shear stress. According to this theory, yielding will start at a point when the maximum shear stress at that point reaches one-half of the uniaxial yield strength, Fy. Thus, for a biaxial state of stress where σ1 > σ2, the maximum shear stress will be (σ1 > σ2)/2. Yielding will occur when

si5_e

ASME Code, Section VIII, Division 2 utilize the maximum shear stress theory. This theory closely approximates experimental results and is easy to use. This theory also applies to triaxial states of stress which predicts that yielding will occur whenever one-half the algebraic difference between the maximum and minimum stress is equal to one-half the yield stress. Thus, for a triaxial state of stress where.

σ1 > σ2 > σ3, the maximum shear stress is (σ1 > σ3)/2.

Yielding will begin when

si6_e

where:

Fy = minimum specified yield strength at design temperature

Fig. 1.2 illustrates the maximum stress theory for the four states of biaxial stress. Comparing Fig. 1.1 and Fig. 1.2 will illustrate the major differences between the two theories. Fig. 1.2 predicts yielding at earlier points in Quadrants II and IV. For example, consider point B of Fig. 1.2. It shows

Fig. 1.2

Fig. 1.2 Graph of maximum shear stress theory.

(σ2 = (−) σ1; therefore, the shear stress is equal to σ2 – (− σ1)/2, which equals

σ2 + σ1/2 or one-half the stress which would cause yielding as predicted by the maximum stress theory.

1.3.7: Comparison of the two theories

Both theories are in agreement for uniaxial stress or when one of the principle stresses is large in comparison to the others. The difference between the two theories will be the greatest when both of the principle stresses are equal.

When using ASME Code, Section VIII, Division 1 Design-By-Rules simple analysis, it makes little difference whether the maximum stress theory or the maximum shear stress theory is used. According to the maximum stress theory, the controlling stress governing the thickness of a cylinder is σϕ,circumferential stress, since it is the largest of the three principle stresses. According to the maximum shear stress theory, the controlling stress would be one-half the algebraic. Difference between the maximum and minimum stress:

•The maximum stress is the circumferential stress, σϕ

si7_e

•The minimum stress is the radial stress, σr

si8_e

•Therefore, the maximum shear stress is:

si9_e

ASME Code, Section VIII, Division 2 uses the term stress intensity, which is defined as twice the maximum shear stress. Since the shear stress is compared to one-half the yield stress only, stress intensity is used for comparison to allowable stresses or ultimate stresses. In other words, yielding begins when the stress intensity exceeds the yield strength of the material.

In the preceding example, the stress intensity would be equal to σϕ − σr, and

si10_e

where:

P = internal pressure

R = radius

t = thickness

Assume a cylinder with the following:

P = 400 psi

R = 24 in

t = 0.5 in

Using the above, compare the maximum stress theory and the maximum shear stress theory.

•Maximum stress theory

si11_e

•Maximum shear stress theory

si12_e

For thick-walled vessels (Rm/t), the radial stress becomes significant when defining the ultimate failure of the pressure vessel. The maximum stress theory is unconservative for designing these vessels. Because of this, this text has limited its coverage to thin-walled pressure vessels where a biaxial state of stress is assumed to exist.

1.3.8: Classes of stresses

ASME Code, Section VIII, Division 1 categorizes the various loads which develop stresses in pressure vessels. Classes of stress are defined by the type of loading which produces them and the hazard they represent to the vessel. Three classes of stress are summarized as follows:

•Primary stress

•General

▪Primary general membrane stress, Pm

▪Primary general bending stress, Pb

•Primary local stress, PL

•Secondary stress

•Secondary membrane stress, Qm

•Secondary bending stress, Qb

•Peak stress, F

1.3.8.1: Primary stresses

Primary stresses are those developed in each component of a vessel due to sustained internal and external loads. Thermal stresses are never classified as primary stresses. The fundamental characteristic of primary stress is that they are not self-limiting, that is, there is no redistribution of load or reduction of stress will occur despite yielding within the component; primary stresses are not reduced by the deformations they produce. Therefore, primary stresses that exceed the yield strength of the material will cause failure either by gross plastic deformation or by bursting.

Primary stresses are the most significant stresses that occur in pressure vessels and their limits for design are set both to prevent plastic deformation and to provide a factor of safety against bursting.

Primary general stresses are further divided into primary membrane stresses and primary bending stresses because different stress limits are applied for design, depending on the type of primary stress.

1.3.8.1.1: Primary membrane stress

Primary membrane (Pm) stresses are tensile or compressive stresses that are uniform through the entire cross-section of a pressure vessel. Gross plastic deformation will occur when the stresses exceed these the yield strength of the material. These stresses are remote from discontinuities such as head-shell intersections, cone-cylinder intersections, nozzles, supports, and other attachments. Examples of primary membrane stresses are:

•Circumferential and Longitudinal stress due to internal pressure.

•Axial tensile and compressive stresses due to wind and earthquake loads.

•Axial compression due to the weight of a vertical vessel.

•Longitudinal stress in horizontal vessels due to bending between saddle supports.

•Membrane stress in the nozzle wall within the area of reinforcement due to pressure or external loads due to piping connections.

•Membrane stress in the center of the flat head.

The design limit for primary membrane stresses is the maximum allowable design stress for the material at the design temperature. Primary membrane stresses cannot exceed two-thirds of the yield strength. Stresses that act intermittently and for short durations, for example, wind and earthquake loads, can be increased to 1.2 times the maximum allowable design stress.

1.3.8.1.2: Primary bending stress

Primary bending (Pb) stresses are due to sustained loads and are capable of causing collapse of the vessel. Primary bending stresses are different from tension to compression. Through the cross-section of a vessel shell component. Higher stresses are required to produce failure by plastic deformation in bending than for tensile or compressive loads. There are relatively few areas where primary bending occurs. Bending stresses are more likely to be the predominant stress in the following:

•Bending stress in the center of a flat head or crown of a dished head.

•Bending stress between the ligaments of closely spaced openings.

•Bending stress in a shallow conical head.

Higher stress limits are usually incorporated into the design rules and equations for components that conform to the acceptable design details depicted in the ASME Code.

1.3.8.1.3: Local primary membrane stress

Local primary membrane (PL) stress is not a classification of stress but a sub-category of primary membrane stress. Local primary membrane stress is a combination of the primary membrane stress, (Pm), plus the secondary membrane stress, (Qm), produced from sustained internal, and external loads. The stresses have been combined so as to limit the allowable stress for a particular combination to a level lower than that allowed for other primary and secondary stresses. A local primary membrane stress may exceed the stress limit for a primary membrane stress. If the higher stress is localized it can be redistributed to the stiffer portions of the pressure vessel if yielding occurs. Even though the redistribution upon localized yielding usually prevents failure of the pressure vessel, any deformation associated with yielding would be unacceptable. Therefore, an allowable stress lower than secondary stresses is assigned for the material of construction at the design temperature, which could be as high as the minimum yield strength.

Local primary membrane stresses are a combination of membrane stresses only. Thus, only membrane stresses from a local load are combined with primary membrane stresses and not bending stresses. The bending stresses associated with local loading would be secondary stresses.

The local primary membrane stress from a sustained load is

si13_e

where:

PL = local primary membrane stress

Pm = primary membrane stress

Qm = secondary membrane stress

Examples of local primary membrane (PL) stresses in pressure vessels are:

•Head-to-shell junctions

•Cone-to-cylinder junction

•Shell-to-nozzle junction

•Head-to-skirt junction

•Shell stiffening ring junction

•Vessel support lugs

•External attachments

1.3.8.2: Secondary stresses

Secondary stresses differ from primary stresses because they are self-limiting. Self-limiting means that local yielding and minor distortions can satisfy the conditions which caused the stress to occur. Secondary means stresses are developed at the junctions of major components of a pressure vessel. Secondary stresses develop at structural discontinuities. Radial loads on nozzles produce secondary mean stresses in the shell at the junction of the nozzle. Secondary stresses are strain-induced stresses.

Secondary stresses are divided into two additional groups, membrane and bending. Examples of each follows:

•Secondary membrane stress, (Qm)

•Axial stress at the junction of a flange and the hub of the flange.

•Membrane stress in the knuckle area of the head.

•Membrane stress due to local relenting loads.

•Thermal stresses produced by temperature gradients in the shell, or by differences in temperature between the nozzle and shell.

•Secondary bending stress, (Ql)

•Bending stresses at head-to-shell junctions.

•Bending stresses at cone-to cylinder junction.

•Bending stress in the shell at nozzles.

•Bending stress at vessel stiffening or support rings and external attachments.

Unlike primary stresses, secondary stresses are reduced in magnitude by the local yielding, before gross plastic deformation or bursting can occur.

The stress limit for secondary stresses is three times the maximum allowable design stress for the material of construction at the design temperature. Therefore, the secondary stress is permitted to be as high as twice the yield strength, but it is reduced in magnitude by local yielding. Structural discontinuities that develop secondary stresses should be separated by a distance of at least 2.5mt to avoid additive effects that could. Increase the total secondary stress above three times the maximum allowable design stress.

1.3.8.3: Peak stress

Peak (F) stresses in pressure vessels are generally the highest stresses that exist in various components of the vessel. They apply to both sustained loads and self-limiting loads. They are distinguished from primary and secondary stresses in that they do not produce a significant peak distortion, but they need not be localized nor necessarily self-limiting. Peak stresses are additive to primary and secondary stresses present at the point of the stress concentration. Peak stresses are only significant in fatigue conditions or brittle materials. Peak stress limit for peak stresses is three times the allowable design stress for the material of construction.

Examples of peak stresses in pressure vessels are:

•Stresses at the corners of a discontinuity and fillets of nozzles.

•Thermal stresses in a wall related to cladding or weld overlay.

•Thermal stresses caused by a sudden change in the surface temperature.

•Stress due to a notch (stress concentration) effect.

1.3.9: Stress categories

Once the stresses of a component are calculated, they must be combined, and this final result compared to an allowable stress. Refer to Table 1.1. The combined classes of stress due to a combination of loads acting at the same time are stress categories. Each category has assigned limits of stress based on the hazard it represents to the vessel. Table 1.1 is based on ASME Code, Section VIII, Division 2 but simplified for application to Division 1 vessels and allowable stresses. Table 1.1 should be used as a guide as Division 1 recognizes only two categories of stress—primary membrane stress and primary bending stress.

Table 1.1

Notes: Qm, membrane stresses from sustained loads; Q⁎m, membrane stresses from relenting, self-limiting loads; S, allowable stress as per ASME Code, Section VIII, Division 1, at design temperature; Fy, minimum specified yield strength at design temperature; UTS, minimum specified tensile strength; Sa, allowable stress for any given number of cycles from design fatigue curves.

1.4: Discontinuity stresses

Pressure vessels are constructed of components of different thickness, material, and diameter. If components were allowed to expand freely, they would have different displacements. Since all components form a continuous structure they must deflect and rotate together. The differences in movement at junctions result in local deformations and generate local discontinuity stresses. Other items, such as stiffening rings and internal bulkheads (weirs), also effect the cylinder deformation and introduce local stresses.

Stresses created by the joining of two shell components will cause discontinuity stresses. Under constant static pressure and with ductile materials, discontinuity stresses can be kept low by proper design. However, the discontinuity stresses become important under cyclic loads or at low temperatures where the ductility of the material is reduced. Discontinuity stresses must be added to the membrane stresses developed by other loads as discussed in Section 1.3.8.

Structural discontinuities are normally broken into two categories:

•Gross structural discontinuities—affect a large portion of a structure and have significant effect on the overall stress pattern. All of the junctions between shell components fall in this category.

•Local structural discontinuities—are sources of stress that affect only a small volume of material and do not have a significant effect upon the overall stress pattern. They usually produce peak stresses. Refer to Section 1.3.8.3.

Discontinuity stresses are secondary stresses and are self-limiting. Once the vessel has yielded, the stresses are reduced and will not lead to failure. Design on the junction of the two components is a major consideration when trying to reduce the discontinuity stresses. Since discontinuity stresses are self-limiting the allowable stress can be very high.

ASME Code, Section VIII, Division 1, specifically addresses the discontinuity stresses at cone-cylinder junctions where the included angle is greater than 60o. Code Paragraph 1–5(e) recommends limiting combined stresses (membrane plus discontinuity) in the longitudinal direction to 4SE and in the circumferential direction to 1.5SE.

ASME Code, Section VIII, Division 2, limits the combined stress, primary membrane, and discontinuity stresses to 3Sm, where Sm is the lesser of 2/3Fy or 1/3(UTS), whichever is lower. Refer to the following references for detailed information regarding the calculation of discontinuity stresses, specifically;

•American Society of Mechanical Engineers Boiler and Pressure Vessel Code, Section VIII, Division 2, Article 4–7.

•Hicks, E.J., Pressure Vessels-A workbook for Engineers, Pressure Vessel Workshop, Chapter 8, Energy-Sources Technology Conference and Exhibition, Houston, American Society of Petroleum Engineers, January 19–21, 1981.

•Pressure Vessel and Piping Design, Collected Papers. 1927–1959, ASME, 1960.

1.5: Fatigue analysis

Fatigue analysis is beyond the scope of this text but the designer should be aware of conditions that would require a fatigue analysis to be made. ASME Code, Section VIII, Division 1, does not specifically provide specific criteria for vessels in cyclic service. On the other hand, ASME Code, Section VIII, Division 2 has established specific criteria for determining when a pressure vessel must be designed for fatigue.

Code formulas for design of vessel heads, for example, can result in yielding in localized zones. Localized stresses exceeding the yield point may be encountered even though low allowable stresses have been used in design. Thus, while safe for static conditions of loading, would develop a progressive fracture after a large number of repeated loadings due to these high localized and secondary bending stresses. Vessels in cyclic service require special considerations in both design and fabrication.

Thermal variations and other loadings can also result in fatigue failure. Heat exchanger equipment subjected to temperature variations could experience fatigue failure. Thus, in these cases design details are very important.

The need for a fatigue evaluation is a very complex and should be left to those experienced in this type of analysis. ASME Code, Section VIII, Division 2, Paragraph AD-160 provides specific requirements for determining if a fatigue analysis is required. For additional information regarding fatigue analysis refer to Pressure Vessel and Piping Design, Collected Papers. 1927–1959, ASME, 1960.

1.6: Thermal stresses

Thermal expansion issues can occur whenever there is a:

•Considerable difference between the vessel operating temperature and the temperature of the environment surrounding the vessel.

•Restricted expansion or contraction.

•Temperature gradient within a vessel component that creates a differential expansion.

Thermal stresses are considered secondary stresses and will not cause failure in ductile materials when temperature difference first occurs, but they can cause failure after repeated cycling due to thermal fatigue.

The difference in temperature between the inside and outside of a vessel depends on the thickness of the shell and the degree of insulation. Uninsulated thick-walled vessels are more susceptible to failure by thermal stresses than insulated thin-walled vessels. Stresses are compressive at the inner surface, where the temperature is the highest, and tensile at the outside. Failure from fatigue will originate at the outer surface, where thermal stresses add to the tensile stresses from internal pressure.

Another location for hot vertical vessels to experience thermal stresses is the support skirt. At the shell-to-skirt junction the temperature of the shell and the skirt will nearly be the same. However, the temperature will decrease from the joint down. The temperature difference causes a rotation of the skirt end which is restrained by the welded joint. In addition to the thermal stresses, radial deformation of the shell under internal pressure will cause discontinuity stresses. The shell insulation is normally extended below the skirt-to-shell weld so as to minimize thermal stresses at this location. The skirt should be long enough to minimize the temperature difference between the bolted-down base of the skirt and the concrete foundation, thus preventing any distortion and local thermal stress at this location.

Normally thermal stresses are minimized by

•Reducing external constraints

•Providing local flexibility capable of absorbing the expansion

•Selecting proper materials or combination of materials

•Selective use of thermal insulation.

References

[1] Moss D. Pressure Vessel Design Manual. third ed. Elsevier Science and Technology; 2004.

[2] ASME Boiler and Pressure Vessel Code, Section VIII, Division 2. 2019 ed. American Society of Mechanical Engineers; 2019.

[3] Popov E.P. Mechanics of Materials. Prentice Hall, Inc.; 1952.

[4] Bednar H.H. Pressure Vessel Design Handbook. Van Nostrand Reinhold Co.; 1981.

[5] Harvey J.F. Theory and Design of Modern Pressure Vessels. Van Nostrand Reinhold Co.; 1974.

[6] Hicks, E. J. (Ed.), Pressure Vessels—A Workbook for Engineers, Pressure Vessel Workshop, Energy-Sources Technology Conference and Exhibition, Houston, American Society of Petroleum Engineers, January 19–21, 1981.

[7] Pressure Vessel and Piping Design, Collected Papers. 1927-1959. American Society of Mechanical Engineers; 1960.

[8] Brownell L.E., Young E.H. Process Equipment Design. John Wiley and Sons; 1959.

[9] Roark R.J., Young W.C. Formulas for Stress and Strain. fifth ed. McGraw Hill Book Co.; 1975.

[10] Burgreen D. Design Methods for Power Plant Structures. C.P. Press; 1975.

[11] American Society of Mechanical Engineers. Criteria of the ASME Boiler and Pressure Vessel Code for Design by Analysis in Sections III and VIII, Division 2. American Society of Mechanical Engineers; 2017.

[12] ASME Boiler and Pressure Vessel Code, Section VIII, Division 1. 2019 ed. American Society of Mechanical Engineers; 2019.

[13] Pressure Vessel Manual. San Francisco, CA: Chevron Corp.; 1990.

2: History and organization of codes

Abstract

This chapter discusses common uses of pressure vessels, history of pressure vessel codes; ASME Code, Section VIII, Division 1; ASME, Section VIII, Division 2; organization of the ASME Boiler and Pressure Vessel Codes; worldwide pressure vessel codes and differences between piping and pressure vessels. This chapter concentrates on Section VIII as it covers the mandatory requirements, specific prohibitions and nonmandatory guidance for materials, design, fabrication, inspection, testing, markings and reports, overpressure protection and certification of pressure vessels operating at either internal or external pressures exceeding 15 psi (103.3 kPa). In addition, the piping code requirements of ASME B31.1, B31.3, B31.4, B31.5, and B31.8 are also discussed.

Keywords

ASME Code; Section VIII; Division 1 and 2; ASME B31.1; ASME B31.3; ASME B31.4; ASME B31.8; ASME Section I Power boilers; ASME Section II Materials; ASME Section IV Heating boilers; Section V Nondestructive examination; ASME Section IX Welding and brazing

2.1: Overview and objectives

This chapter discusses the following topics:

•Use of pressure vessels and equipment

•History of pressure vessel codes in the United States

•Organization of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code

•Updating and interpreting the code

•ASME Code stamps

•Organization of the American National Standards Association ASME B31 Code for Pressure Piping

•Some other pressure vessel codes and standards in the United States

•Worldwide pressure vessel codes

•ASME Code, Section VIII, Division 1 versus Division 2 and Division 3

•Design criteria, ASME Code, Section VIII, Division 1

•Design criteria, ASME Code, Section VIII, Division 2

•Welding criteria, ASME Code, Section IX

•ASME Code, Section I, Power boilers

•Additional requirements employed by users in critical services

Objectives

•Understand the Administration of Pressure Vessels and their Basic Mechanical Elements and Design

•Be familiar with

○What constitutes a Pressure Vessel

○Codes and Standards

○Differences between Pipe and Pressure Vessel

○Pressure Vessel Basic Mechanical Design

2.2: Pressure vessels and equipment

Process vessels are used at all stages of processing oil and gas from initial separation; processing, conditioning, and treating; and storage. Pressure vessels are made in all sizes and shapes from less than an inch and greater than 150 ft (50 m) in diameter (refer to Fig. 2.1). They can be buried in the ground or deep in the ocean. Most are positioned on the ground or supported on platforms.

Fig. 2.1Fig. 2.1

Fig. 2.1 (A) Typical vertical pressure vessel. (B) Typical horizontal pressure vessel.

Internal pressures range from less than 1-in. (2.54 cm H2O) water gauge pressure to greater than 300,000 psi (2,068,427 kPa). The normal range for mono-block construction is between 15 and 5000 psi (103.4 to 34,474 kPa).

The ASME Boiler and Pressure Vessel Code, Section VIII covers all pressure vessels other than those covered by boiler or nuclear component Codes. The Code specifies a minimum internal pressure from 15 psi (103.4 kPa). The Code excludes vessels where:

•Internal design pressure does not exceed 15 psi (103.4 kPa) with no limits on size

•Inside diameters do not exceed 6-in. (15 cm), with no limitation on pressure

The ASME Code jurisdiction terminates at one of the following:

•First circumferential welded joint in welded-end connections

•Face of the first flange in bolted piping connections

•First threaded joint for piping and instrument connections

•Attachments to the pressure vessel boundary

The Code may require special design requirements at internal pressures above 3000 psi (20,684 kPa). Any pressure vessel that meets all the requirements of the ASME Code, regardless of the internal or external design pressure, may still be accepted by the authorized inspector and stamped by the manufacturer with the ASME Code symbol.

For design purposes, a pressure vessel is defined as a component which satisfies the following:

•Accumulates or contains a fluid (gas or liquid)

•Pressure of fluid > 15 psi (103.4 kPa)

•Inside diameter > 6 in. (15 cm)

•Exceptions to these basic criteria exist

Fig. 2.2 is a pressure vessel flowchart which can aid in determining if a process component is a pressure vessel.

Fig. 2.2

Fig. 2.2 Pressure vessel flowchart.

2.2.1: Differences between a pipe and a pressure vessel

Confusion frequently arises when classifying piping system components. Differentiating between pressure vessel components and piping components can sometimes be difficult. Components should be considered pressure vessels if

•Primary function is not to transport fluid, but to process fluid by distillation, heat exchange, separation of a fluid or removal of solids, catalytic reaction.

•Primary function is to contain fluid under pressure.

Pressure vessels fabricated from off-the-shelf pipe components and fittings are still considered pressure vessels. American Petroleum Institute (API) storage tanks may be designed for and contain no more internal pressure than that generated by the static head of fluid contained in the tank.

Components should be considered piping if

•Its primary function is to transport fluid from one location to another. This can include manifolds and enlargements used for pulsating dampening.

•It is available off-the-shelf from piping equipment suppliers. This can include filters, strainers, steam traps, expansion joints, and metering devices.

2.2.2: Why codes?

Codes provide a safe and acceptable set of rules for the design, fabrication, and testing of boilers and pressure vessels.

2.3: History of pressure vessel codes in the United States

In the late 1800s and early 1900s, explosions in boilers and pressure vessels were frequent. A firetube boiler explosion on the Mississippi River steamboat Sultana on April 27, 1865, resulted in the boat sinking within 20 min and killing 1500 people.

One of the greatest disasters occurred at the R.B. Grover & Company shoe factory in Brockton, Massachusetts on the morning of March 20, 1905. At around 8:00 AM there were around 400 employees working when a boiler exploded, shot through the roof and caused the building to collapse. The boiler traveled several hundred feet, damaging a number of buildings and coming to rest on the wall of a house. Escaping gas fueled an intense fire that engulfed the shattered building. Fifty-eight people were killed, 150 were injured and $400,000 in property damage (refer to Fig. 2.3). Thirty-six of the victims were never identified and were buried in a common grave in Melrose Cemetery, where a monument to the victims was later erected by the city. A fund started for the widows and orphans of the disaster raised over $100,000. Families of many of the victims placed small memorial stones in rings around Melrose Cemetery monument, which still holds a place of honor in that cemetery (refer to Fig. 2.4).

Fig. 2.3

Fig. 2.3 Before and after photos of Grover Shoe Company disaster on March 20, 1905.

Fig. 2.4

Fig. 2.4 Melrose cemetery monument.

Another explosion in a shoe factory in Lynn, Massachusetts, in 1906 which resulted in death, injury, and extensive property damage. These tragedies were the primary reasons why the Massachusetts governor directed the formation of a Board of Boiler Rules. The first set of rules was approved in 1907. The code was three pages long! The State of Ohio followed with their own Code in 1908. These regulations differed from state to state and often contradicted one another.

In 1911, the ASME Boiler and Pressure Vessel Code Committee was established to perform the following functions:

•Formulate minimum rules for the construction of boilers

•Interpret the rules when requested

•Develop revisions and additional rules as needed

Following appeals from both manufacturers and users, the ASME issued ASME Rules for Construction of Stationary Boilers and for Allowable Working Pressures in 1915. This ultimately became Section I, Power Boilers of the ASME Code. This was the beginning of the various sections of the code, which ultimately became Section I, Power Boilers.

In 1925, the first ASME Code of Pressure Vessels was issued. It was titled Rules for the Construction of Unfired Pressure Vessels, Section VIII. It applied to vessels over 6 in. (15 cm) in diameter, volume over 1.5 ft³ (0.139 m³), and pressure over 30 psi (206.8 kPa).

In 1931, a joint API-ASME committee was formed to develop an unfired pressure vessel code for the petroleum industry. In 1934, the first pressure vessel code for the petroleum industry was issued, and for the next 17 years, two separate unfired pressure vessel codes existed. In 1952, the two codes were consolidated into one, titled ASME Unfired Pressure Vessel Code, Section VIII.

In 1968, the original code became Section VIII, Division 1, Pressure Vessels, and another part was issued, which was Section VIII, Division 2, Alternate Rules for Pressure Vessels. The ASME Boiler and Pressure Vessel Code is issued by the ASME. The ASME Boiler and Pressure Vessel Code has been established as the set of legal requirements in many countries of the world.

Most piping systems are built to the ASME Code for Pressure Piping B31; there are a number of different piping code sections for different types of systems, specifically, Section I uses B31.1 and Section VIII uses B31.3.

2.4: Organization of the ASME Boiler and Pressure Vessel Code

The ASME Boiler and Pressure Vessel Code is divided into the following:

•Sections

•Divisions

•Parts

•Subparts

Some of these sections relate to a specific kind of equipment and application; specific materials and methods for application and control of equipment; and care and inspection of installed equipment. At the present time, the code includes the following sections.

2.4.1: Section I Power boilers

This section provides requirements for all methods of construction of power, electric, and miniature boilers; high-temperature water boilers used in stationary service; and power boilers used in locomotive, portable, and traction service.

Rules pertaining to the use of the V, A, M, PP, S, and E Code symbol stamps are also included. The rules of this section apply to the boiler and to external piping, valves and fittings in which steam or other vapor is generated at a pressure exceeding 15 psi (103.4 kPa) and high-temperature water boilers intended for operation at pressures exceeding 160 psi (1103 kPa) or temperatures exceeding 250°F (121°C).

Superheaters, economizers, and other pressure parts connected directly to the boiler without intervening valves are considered as part of the scope of Section I. This section is briefly reviewed in this text.

2.4.2: Section II Materials

This section of the ASME BPVC consists of four parts.

2.4.2.1: Part A Ferrous materials specifications

This part is a supplementary book referenced by other sections of the Code. It provides material specifications for ferrous materials which are suitable for use in the construction of pressure vessels. These specifications specify the mechanical properties, heat treatment, heat and product chemical composition and analysis, test specimens, and methods of testing. They are designated by SA numbers and are derived from American Society of Testing Materials (ASTM) A specifications.

2.4.2.2: Part B Nonferrous material specifications

This part is a supplementary book referenced by other sections of the Code. It provides material specifications for nonferrous materials which are suitable for use in the construction of pressure vessels. These specifications specify the mechanical properties, heat treatment, heat and product chemical composition and analysis, test specimens and methodologies of testing. They are designated by SB numbers and are derived from ASTM B specifications.

2.4.2.3: Part C Specifications for welding rods, electrodes, and filler metals

This is a supplementary book referenced by other sections of the Code. It provides mechanical properties, heat treatment, heat and product chemical composition and analysis, test specimens and methodologies of testing for welding rods, filler metals, and electrodes used in the construction of pressure vessels. These specifications are designed by SFA numbers and are derived from American Welding Society (AWS) specifications.

2.4.2.4: Part D Properties (customary/metric)

This part is a supplementary book referenced by other sections of the Code. It provides tables for the design stress values, tensile and yield stress values as well as tables for material properties (Modulus of Elasticity, Coefficient of Heat Transfer, etc.).

2.4.3: Section III Rules for construction of nuclear power plant components

Section III addresses the rules