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Overview of Pressure Vessel Design
Instructors Guide
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CONTACT INFORMATION
ASME Headquarters1-800-THE-ASME
ASME Professional Development1-800-THE-ASME
Eastern Regional Office Southern Regional Office8996 Burke Lake Road Suite L102 1950 Stemmons Freeway Suite 5068Burke, VA 22015-1607 Dallas, TX 75207-3109
703-978-5000 214-800-4900800-221-5536 800-445-2388
703-978-1157 (FAX) 214-746-4902 (FAX)
Midwest Regional Office Western Regional Office1117 S. Milwaukee Avenue 119-C Paul DriveBuilding B, Suite 13 San Rafael, CA 94903-2022Libertyville, IL 60048-5258 415-499-1148
847-680-5493 800-624-9002800-628-6437 415-499-1338 (FAX)847-680-6412 (FAX)
Northeast Regional Office International Regional Office326 Clock Tower Commons 1-800-THE-ASME
Route 22Brewster, NY 10509-9241845-279-6200800-628-5981845-279-7765 (FAX)
You can also find information on these
courses and all of ASME, including ASME
Professional Development, the Vice
President of Professional Development,
and other contacts at the ASME Web
site......
http://www.asme.org
You can also find information on these
courses and all of ASME, including ASME
Professional Development, the Vice
President of Professional Development,
and other contacts at the ASME Web
site......
http://www.asme.org
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Overview of Pressure Vessel Design
By:
Vincent A. Carucci
Carmagen Engineering, Inc.
Copyright 1999 by
All Rights Reserved
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TABLE OF CONTENTS
Abstract 5
Introduction..6
Organizing Unit Responsibilities..7
Instructor Guidelines and Responsibilities.9
Overview of Pressure Vessel Design Outline/
Teaching Plan11
Instructor Notes.13
Appendix A: Reproducible Overheads
Appendix B: Course and Instructor Evaluation Form
Appendix C: Continuing Education Unit (CEU) Submittal Form
Course Improvement Form
Instructors Biography Form
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ABSTRACT
Pressure vessels are typically designed, fabricated, installed, inspected, and testedin accordance with the ASME Code Section VIII. Section VIII is divided into threeseparate divisions. This course outlines the main differences among the divisions.
It then concentrates on and presents an overview of Division I. This course alsodiscusses several relevant items that are not included in Division I.
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INTRODUCTION
This Overview of Pressure Vessel Design course is part of the ASME InternationalCareer Development Series an educational tool to help engineers and managerssucceed in todays business/engineering world. Each course in this series is a 4-
hour (or half-day) self-contained professional development seminar. The coursematerial consists of a participant manual and an instructors guide. The participantmanual is a self-contained text for students/participants, while the guide (thisbooklet) provides the instructional material designed to be presented by a localknowledgeable instructor with a minimum of preparation time.
The balance of this instructors guide focuses on:
1. Organizing Unit Responsibilities
2. Instructor Guidelines and Responsibilities
3. Comprehensive teaching materials which may be used as is or adaptedto incorporate experiences and perspective of the instructor.
Welcome to the ASME International Career Development Series! We wish you allthe best in your presentation, operation and delivery of this course.
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Suggested Outline/Teaching Plan
Time,
min.
Major
Interval
Class Segment Sub-Segment
Interval
Sub-SegmentOverheads/Participant
Pages5 Introduction/Logistics
Outline ModuleOV 1Part. 65
10 Introduction
5 Module based primarily on theASME Code Section VIII, Division
1. Divisions 2 and 3 will be brieflydescribed
OV 2Part. 65
10 Main Pressure Vessel Components OV 3-9Part. 67
10 Scope of ASME Code Section VIII
Division 1
Division 2
Division 3
OV 10-13Part. 75
25 General
5 Structure of Section VIII, Division 1 OV 14Part. 78
15 Material Selection Factors
Strength
Corrosion Resistance
Resistance to Hydrogen Attack
Fracture Toughness
Fabricability
OV 15-31Part. 79
20 Materials of Construction
5 Maximum Allowable Stress OV 32-34
Part. 87
10 Exercise 10 Material Selection Based On FractureToughness
OV 35-38Part. 91
10 Break 10
10 Design Conditions and Loadings
Pressure
Temperature
Other Loadings
OV 39-43Part. 92
25 Design for Internal Pressure
Weld Joints
Cylindrical Shells
Heads
Conical SectionsSample Problem
OV 44-55Part. - 98
55 Design
20 Design for External Pressure andCompressive Stresses
Cylindrical Shells Other Components
Sample Problem
OV 56-65Part. 109
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Suggested Outline/Teaching Plan, continued
Time,
min.
Major
Interval
Class Segment Sub-Segment
Interval
Sub-SegmentOverheads/
ParticipantPages
10 - 50 Major Break Lunch or Major Break
15 Exercise 15 Required Thickness for Internal
Pressure
OV 66-68
Part. - 118
20 Reinforcement of Openings (IncludeSample Problem)
OV 69-84Part. 119
10 Flange Rating (Including Sample
Problem)
OV 85-90
Part. 127
15 Flange Design OV 91-97Part. 131
50 Design(Contd.)
5 Maximum Allowable WorkingPressure (MAWP)
OV 98Part. 138
10 Break
10 Local Loads OV 99
Part. 139
20 Other Design
Considerations
10 Vessel Internals OV 100-102Part. 141
10 Acceptable Welding Details OV 103-106Part. 143
20 Fabrication
10 Postweld Heat Treatment
(PWHT)Requirements
OV 107
Part. 146
10 Inspection OV 108-113Part. 148
15 Inspection andTesting
5 Pressure Testing OV 114-115
Part. 152
10 Closure 10 SummaryQuestionnaire (fill in and collect)CEU Form (hand out individual
responsibility to return)
OV 116Part. - 155
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Course discusses pressure vesseldesign and is introductory in nature.
2. Based on ASME Code Section VIII.
3. Preliminary emphasis is on Division1 but Divisions 2 and 3 arehighlighted.
4. Introduces several items that are notcovered in the ASME Code.
Major Learning Points
Course Introduction
1
OVERVIEW OF
PRESSURE VESSEL DESIGN
By: Vincent A. Carucci
Carmagen Engineering, Inc .
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. The objective: Provide a generalknowledge of design requirementsfor pressure vessels.
2. This is not a comprehensive course.It provides sufficient information for
management personnel to have anoverall understanding of this
subject. Individuals having moredetailed responsibility will receive asolid starting point to proceedfurther.
3. Review outline.
4. Establish schedule.
5. Participation is key:
Questions
Discussion/interaction
Major Learning Points
Establish course objectives.
Outline course content, a road map.
2
Course Overview
General
Materials of Construction
Design
Other Design Considerations
Fabrication
Inspection and Testing
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Describe what a pressure vessel is.
2. Note that pressure vessels are usedin a wide variety of industries. Theycan be designed for a wide variety ofconditions and in a broad range of
sizes.
Major Learning Points
Define pressure vessels.
Identify wide variety of industrialapplications.
3
Pressure Vessels
Containers for fluids under pressure
Used in variety of industries
Petroleum refining
Chemical
Power
Pulp and paper
Food
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Use this and following overheads todescribe main pressure vesselcomponents and shapes.
2. Shell is primary component thatcontains pressure. Curved shape.
3. Vessel always closed by heads.
4. Components typically weldedtogether.
5. Vessel shell may be cylindrical,spherical, or conical.
6. Multiple diameters, thicknesses ormaterials are possible.
7. Saddle supports used for horizontaldrums.
Spreads load over shell.
One support fixed, other slides.
Major Learning Points
Main pressure vessel components andconfigurations.
4
Horizontal Drum on
Saddle Supports
Figure 2.1
Nozzle
ShellA
A
Head
SaddleSupport
(Fixed)
Saddle Support
(Sliding)
Head
SectionA-A
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Most heads are curved shape forstrength, thinness, economy.
2. Semi-elliptical shape is mostcommon head shape.
3. Small vertical drums typicallysupported by legs.
Typically maximum 2:1 ratio ofleg length to diameter.
Number, size, and attachmentdetails depend on loads.
Major Learning Points
Main pressure vessel components andshapes.
5
Vertical Drum
on Leg Supports
Figure 2.2
Head
Shell Nozzle
Head
SupportLeg
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Nozzles used for:
Piping systems
Instrument connections
Manways
Attaching other equipment
2. Ends typically flanged, may bewelded.
3. Sometimes extend into vessel.
Major Learning Points
Main pressure vessel components andshapes.
6
Tall Vertical Tower
Figure 2.3
Trays
Nozzle
Head
Shell
Nozzle
Cone
Shell
Nozzle
NozzleSkirtSupport
Head
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Skirt supports typically used for tallvertical vessels:
Cylindrical shell
Typically supported from grade
2. General support design (not just forskirts)
Design for weight, wind,earthquake.
Pressure not a factor.
Temperature also aconsideration for materialselection and thermalexpansion.
Major Learning Points
Main pressure vessel components andshapes.
7
Vertical Reactor
Figure 2.4
Inlet
Nozzle
Head
Shell
UpperCatalyst
Bed
Catalyst Bed
Support Grid
Lower
Catalyst
Bed
Outlet
Collector
Head
Support
Skirt
Outlet
Nozzle
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Spherical storage vessels typicallysupported on legs.
2. Cross-bracing typically used toabsorb wind and earthquake loads.
Major Learning Points
Main pressure vessel components andshapes.
8
Spherical Pressurized
Storage Vessel
Figure 2.5
CrossBracing
Support
Leg
Shell
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Vessel size limits for lug supports:
1 10 ft diameter
2:1 to 5:1 height/diameter ratio
2. Vessel located above grade.
3. Lugs bolted to horizontal structure.
Major Learning Points
Main pressure vessel components andconfigurations.
9
Vertical Vessel on
Lug Supports
Figure 2.6
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Section VIII is most widely usedCode.
2. Assures safe design.
3. Three divisions have differentemphasis.
Major Learning Points
Define scope of ASME Code SectionVIII.
10
Scope of ASME Code
Section VIII
Section VIII used worldwide
Objective: Minimum requirements for safe
construction and operation
Division 1, 2, and 3
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Review scope of Division 1.
2. Division 1 not applicable below 15psig.
3. Additional rules required above 3000psig.
4. Items that are connected to pressure
vessels not covered by Division 1,except for:
Their effect on pressure part.
Welded attachment to pressurepart.
Major Learning Points
Scope of Division 1
Exclusions from scope
11
Section VIII Division 1
15 psig < P 3000 psig Applies through first connection to pipe
Other exclusions
Internals (except for attachment weld to vessel)
Fired process heaters
Pressure containers integral with machinery
Piping systems
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Review differences betweenDivisions 1 and 2.
2. Division 2 allowable membranestress is higher.
3. Division 2 requires more complexcalculations.
4. Division 2 does not permit somedesign details that are permitted inDivision 1.
5. Division 2 requires more stringentmaterial quality control, fabrication,
and testing requirements.
Major Learning Points
Differences between Division 1 and 2.
12
Section VIII, Division 2,
Alternative Rules Scope identical to Division 1 but
requirements differ
Allowable stress
Stress calculations
Design
Quality control
Fabrication and inspection
Choice between Divisions 1 and 2 based oneconomics
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Review application of Division 3.
2. Newest Division of Section VIII andhas least applicability.
3. After this point, this course onlyaddresses Division 1 requirementswhen code-specific items arediscussed.
Major Learning Points
Scope of Division 3
13
Applications over 10,000 psi
Pressure from external source, processreaction, application of heat, combination
of these
Does not establish maximum pressurelimits of Division 1 or 2 or minimum limits
for Division 3.
Division 3, Alternative Rules
High Pressure Vessels
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Review Division 1 organization
2. Fabrication methods:
Welded
Forged
Brazed
3. Material classes Carbon and low-alloy steel
Non-ferrous metals
High alloy steel
Cast iron
Clad and lined material
Ductile iron
Heat treated steels Layered construction
Low-temperature material
4. Highlight several mandatory andnonmandatory appendices.
Major Learning Points
Basic organizational structure ofDivision 1.
14
Structure of Section VIII,
Division 1 Subsection A
Part UG applies to all vessels
Subsection B
Requirements based on fabrication method
Parts UW, UF, UB
Subsection C
Requirements based on material class
Parts UCS, UNF, UHA, UCI, UCL, UCD, UHT,ULW, ULT
Mandatory and Nonmandatory Appendices
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. ASME Code does not specifyparticular materials to use in eachapplication. Owner must do this.
2. ASME Code specifies permittedmaterials and the requirements that
these must meet.
Major Learning Points
Primary factors that influence pressurevessel material selection.
15
Material Selection Factors
Strength
Corrosion Resistance
Resistance to Hydrogen Attack
Fracture Toughness
Fabricability
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Strength: Materials ability towithstand imposed loading.
2. Higher strength material thinnercomponent.
3. Describe properties that are used todefine strength.
Major Learning Points
Material strength and pressure vesseldesign.
16
Strength
Determines required component thickness
Overall strength determined by:
Yield Strength
Ultimate Tensile Strength
Creep Strength
Rupture Strength
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Corrosion is thinning of metal.
2. Adding extra component thickness(i.e., corrosion allowance) is mostcommon method to addresscorrosion.
3. Alloy materials are used in serviceswhere corrosion allowance would be
unreasonably high if carbon steelwere used.
Major Learning Points
Importance of corrosion resistance inmaterials selection.
17
Corrosion Resistance
Deterioration of metal by chemical action
Most important factor to consider
Corrosion allowance supplies additionalthickness
Alloying elements provide additional
resistance to corrosion
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Low-temperature H2 attack cancause cracking.
2. Higher temperature H2 attack causesthrough-thickness strength loss andis irreversible.
3. H2 attack is a function of H2 partialpressure and design temperature.
Increased alloy content (i.e., Cr)increases H2 attack resistance.
Reference API-941 for NelsonCurves.
Major Learning Points
Hydrogen attack can damage carbonand low-alloy steel.
18
Resistance to
Hydrogen Attack
At 300 - 400F, monatomic hydrogenforms molecular hydrogen in voids
Pressure buildup can cause steel to crack
Above 600F, hydrogen attack causes
irreparable damage through component
thickness
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Describe brittle fracture asequivalent to dropping a piece ofglass.
2. Material selection must ensure thatbrittle fracture will not occur.
Major Learning Points
Brittle fracture and its consequences.
19
Brittle Fracture
and Fracture Toughness Fracture toughness: Ability of material to
withstand conditions that could cause
brittle fracture
Brittle fracture
Typically at low temperature
Can occur below design pressure
No yielding before complete failure
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. A brittle fracture will occur the firsttime the appropriate conditionsoccur.
2. Brittle fracture occurs withoutwarning and is catastrophic.
Major Learning Points
Three conditions that are required for abrittle fracture to occur.
20
Brittle Fracture and
Fracture Toughness, contd
Conditions required for brittle fracture
High enough stress for crack initiation and
growth
Low enough material fracture toughness attemperature
Critical size defect to act as stress
concentration
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Describe influence of material andtemperature factors on fracturetoughness.
2. Other factors increase brittle fracturerisk.
Major Learning Points
Primary factors that influence materialfracture toughness.
21
Factors That Influence
Fracture Toughness Fracture toughness varies with:- Temperature
- Type and chemistry of steel
- Manufacturing and fabrication processes
Other factors that influence fracture
toughness:
- Arc strikes, especially if over repaired area
- Stress raisers or scratches in cold formed thickplate
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Charpy V-Notch test is most widelyused measure of material fracturetoughness.
2. Describe test set-up.
Major Learning Points
Charpy V-Notch testing.
22
Charpy V-Notch Test Setup
Starting Position
Hammer
Scale
Pointer
End of swing
Anvil
Specimen
h'
h'
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. ASME Code contains brittle fractureevaluation procedure.
2. Review components to be included -only items that relate to structuralintegrity of pressure-containing
shell.
Major Learning Points
Components to consider is ASME Codebrittle fracture evaluation.
23
ASME Code and
Brittle Fracture Evaluation
Shells
Manways
Heads
Reinforcing pads
Backing stripsthat remain inplace
Nozzles
Tubesheets
Flanges
Flat cover plates
Attachments essentialto structural integritythat are welded topressure parts
Components to consider
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Describe the distinction betweenMDMT and CET.
MDMT is a materialproperty.
CET is an environmental factor.
2. Important to understand thisdistinction.
Major Learning Points
Two temperatures to be considered inbrittle fracture evaluation.
24
Temperatures to Consider
Minimum Design Metal Temperature
(MDMT)
Lowest temperature at which component has
adequate fracture toughness
Critical Exposure Temperature (CET)
Minimum temperature at which significant
membrane stress will occur
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Outline ASME procedure.
2. Details described in followingoverheads.
Major Learning Points
Simplified ASME brittle fractureevaluation procedure.
25
Simplified ASME
Evaluation Approach Material specifications classified into
Material Groups A through D
Impact test exemption curves
For each Material Group
Acceptable MDMT vs. thickness where impact
testing not required
If combination of Material Group andthickness not exempt, then must impact test
at CET
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Materials are grouped based oncommon fracture toughnessproperties.
2. Groups A through D move fromworst to best fracture toughness.
3. Point out several common materials.
SA-516 Gr. 65 and 70 are CurveB if not normalized.
Most pipe, fittings and forgingsare Curve B.
Major Learning Points
Material group classifications for brittlefracture evaluations.
26
Material Groups
Table 3.1 (Excerpt)
MATERIAL
GROUP APPLICABLE MATERIALSCurve A A l l c a r b o n a n d l o w a l lo y s t e e l p l a t es , s t r u c t u ra l s h a p e s , a n d b a r s n o t
l i s t ed i n Curves B , C & D
S A - 2 1 6 G r . W C B & W C C , SA - 2 1 7 G r . W C 6 , i f n o r ma l i z e d a n d t e m p er e do r w a t e r - q u e n c h e d a n d t e m p e r e d
Curve B S A - 2 16 G r . W C A , i f n o r m al i z ed a n d t e m p e r ed o r w a t e r - q u e n c h e d a n dt e m p e r e d
S A - 2 1 6 G r . W C B & W C C f o r m a x im u m t h i c k ne s s o f 2 i n . , if p r o d u c e d
t o f i n e g r a i n p r a c t i c e a n d w a t e r - q u e n c h e d a n d t e m p e r e d
S A - 28 5 Gr . A & B
S A- 41 4 Gr . A
S A- 5 15 G r. 6 0
S A - 5 16 G r . 6 5 & 7 0 , i f n o t n o rm a l iz e d
E x c e p t f o r c a s t s t e e l s , a l l m a t e r i a l s o f C u r v e A i f p r o d u c e d t o f i n e
g r a i n p r a c t i c e a n d n o r m a l i z e d w h i c h a r e n o t i n c l u d e d i n C u r v e s C & D
A l l p i p e , f i tt i n g s , f o r g i n g , a n d t u b in g w h i c h a r e n o t i n c lu d e d i n C u r v e sC & D
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Identify other common materials.
SA-516 Gr. 55 and 60 are CurveC if not normalized.
SA-516 (all grades) is Curve D ifnormalized.
2. Highlight points.
Lower strength grades of samespecification have betterfracture toughness.
Normalization improves fracturetoughness.
Major Learning Points
Material group classifications for brittlefracture evaluations.
27
Material Groups, contd
Table 3.1 (Excerpt)
MATERIAL
GROUP APPLICABLE MATERIALS
Curve C S A - 1 8 2 G r . 2 1 & 22 , i f n o r m a l i ze d a n d t e m pe r e d S A -3 02 G r. C & D
S A - 3 3 6 G r. F 2 1 & F 2 2 , i f n or m a l i z ed a n d t e m pe r e d
S A - 3 8 7 G r . 2 1 & 22 , i f n o r m a l i ze d a n d t e m pe r e d
S A - 5 1 6 G r . 5 5 & 6 0 , i f n ot n o r m al i z e d
S A -5 33 G r. B & C
S A -6 62 Gr . A
A l l m a t e r i a l o f C u r ve B i f p r o d u c e d t o f i n e g r ai n p r a c t i c e a n d
n o r m a l i z e d w h i c h a r e n o t i n c l u d e d i n C u r v e D
Curve D S A- 20 3 S A-537 C l. 1 , 2 & 3
SA-508 Cl . 1 S A - 6 1 2 , i f n o rm a l i z e d
S A -5 16 , i f n o rm al iz e d S A - 6 6 2 , i f n o rm a l i z e d
SA-524 Cl . 1 & 2 S A-7 3 8 G r . A
Bolting Se e F ig u re U CS-6 6 o f th e A SME Cod e Se c t io n V I I I , D iv . 1 , fo r im p ac t
and Nuts t e s t e x e m p t i o n t e m p e r a t u r e s f o r s p e c i f i e d m a t e r i a l s p e c i f i c a t i o n s
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Describe relationship betweenMaterial Group, componentthickness, and MDMT.
2. Impact testing not required if point is
at or below curve (i.e., OK if MDMT CET).
3. Example: 1.5 in. thick Group B
material does not require impact
testing if CET 50F.
4. If not exempt, must impact testmaterial at CET.
5. Exemption means there is enoughexperience that material hasadequate fracture toughness withoutneed for further testing.
Major Learning Points
Impact test exemption curves.
28
Impact Test Exemption Curves
for Carbon and Low-Alloy Steel
Figure 3.1
Nominal Thickness, in.
(Limited to 4 in. for Welded Construction)
0.394 1 2 3 4 5
140
120
100
80
60
40
20
0
-20
-40
-55-60
-80
MinimumD
esignMetalTemperature,
F
Impact testing required
D
C
BA
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Review additional requirements.
2. Note that most flanges will notrequire impact testing.
Major Learning Points
Additional impact test requirements.
29
Additional ASME Code ImpactTest Requirements
Required for welded construction over 4 in.thick, or nonwelded construction over 6 in.
thick, if MDMT < 120F Not required for flanges if temperature
-20F Required if SMYS > 65 ksi unless
specifically exempt
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Overview of Pressure Vessel Design
Instructors Personal Notes
Instructors Outline
1. Review additional requirements.
2. PWHT reduces MDMT by 30Fprovided PWHT not required by
Code and resulting MDMT -55F.
3. Can take MDMT credit if componentthickness greater than needed (i.e.,calculated stress < allowable stress).
Major Learning Points
Additional impact test requirements.
30
Additional ASME Code
Impact Test
Requirements, contd Not required for impact tested low
temperature steel specifications
May use at impact test temperature
30F MDMT reduction if PWHT P-1 steel
and not required by code
MDMT reduction if calculated stress
Recommended