Modernization of Pressure Vessel Design Codes ASME Section VIII, Division 2, 2007 Edition

7/26/2019 Modernization of Pressure Vessel Design Codes ASME Section VIII, Division 2, 2007 Edition

1/5

Journal ofPressure Vessel

Technology Technical Briefs

Modernization of Pressure Vessel

Design Codes ASME Section

VIII, Division 2, 2007 Edition

T. P. PastorP.E.

HSB Global Standards,

Hartford, CT

D. A. OsageP.E.The Equity Engineering Group, Inc.,

Shaker Heights, OH 44122

The technology for pressure equipment design continues to ad-vance each and every day. The ASME Boiler and Pressure VesselCode has been keeping pace with these advances over the last 92

years. As far back as the 1960s, it was recognized that the specialrequirements for design of pressure vessels operating at pressuresover 2000 psi (13.7 MPa) called for special rules, and ASMEissued Sec. VIII, Division 2 of Alternative Rules for Pressure Ves-sels. Since that time, the understanding of failure mechanisms andadvances in material science, nondestructive testing, andcomputer-aided design has progressed to the stage where a newapproach was needed not only in the content of design codes butin the way they are presented and organized. This paper intro-duces the newly issued ASME Sec. VIII, Division 2 of 2007 editionand explores the technical concepts included and the new formatdesigned for ease of use. Included are results of test exercisessponsored by ASME giving actual applications of the new Code

for design of vessels. This paper demonstrates ASMEs commit-ment to provide manufacturers and users of pressure equipmentwith the most up-to-date technology in easy to use standards thatservice the international market. DOI: 10.1115/1.2794737

Introduction

In 1998, the ASME Boiler and Pressure Vessel Committee au-thorized a project to rewrite Sec. VIII, Division 2 of PressureVessel Code. This decision was made shortly after the design mar-gin on ultimate tensile strength was lowered from 4.0 to 3.5 inSecs. I and VIII, Division 1 VIII-1. ASME saw the need toupdate Sec. VIII, Division 2VIII-2 to be more competitive withother international standards, and in lieu of revising the existing

standard, the decision was made to perform a clean sheet rewrite.By doing so, it was felt that not only could the standard be mod-ernized with regard to the latest technical advances in pressurevessel construction but it could be structured in a way to make itmore user friendly for both users and the committees that maintainit.

Development Process

Traditionally, the development of new standards by ASME iscarried out by volunteers who populate the different committeesresponsible for any given standard. The last major standard devel-

oped in this way was Sec. VIII, Division 3, which took nearly15 years to complete. Recognizing that the user community maynot have the patience to wait 15 or more years for this neededupdate to Sec. VIII, Division 2, ASME decided to use an outsideorganization to develop the first draft of the new standard. Theproject was awarded to the Pressure Vessel Research CouncilPVRC, who in turn formed the Task Group on Continued Mod-ernization of Codes to oversee the development of the new ASMESec. VIII, Division 2 code. PVRC has utilized professionals withboth engineering and technical writing expertise to develop newtechnology and the initial drafts of the new VIII-2.

A Steering Committee made up of ASME Sec. VIII memberswas formed to provide technical oversight and direction to thedevelopment team with the goal of facilitating the eventual bal-loting and approval process. ASME also hired a Project Manager

PM to manage all of the activities required to bring this newstandard to publication. Some of the PMs responsibilities in-cluded the following:

coordinating balloting process to Subcommittees and Boilerand Pressure Vessel BPV Standards Committee

addressing accreditation issues relative to a possible overlapof the old and new VIII-2

managing validation of all equations, and overseeing devel-opment of an example manual

coordinating beta testing of the standard arranging presentation forums during the ballot process, and working with ASME publication to prepare the first edition

of the new standard

The project began with the development of a detailed table of

contents containing every paragraph heading that would appear inthe new standard, and identifying the source for the content thatwould be placed in this paragraph. In preparing such a detailedtable of contents, the lead authors were able to quickly identifyareas where major development effort was required to produceupdated rules. A list of some of the new technology produced forthe VIII-2 rewrite includes the following:

toughness requirements material procurement table design by rule for the creep range conical transition reinforcement requirements opening reinforcement rules

Contributed by the Pressure Vessel and Piping Division of ASME for publication

in the JOURNAL OFPRESSUREVESSELTECHNOLOGY. Manuscript received July 26, 2007;final manuscript received September 14, 2007. Review conducted by G. E. Otto

Widera.

754 / Vol. 129, NOVEMBER 2007 Copyright 2007 by ASME Transactions of the ASME

Downloaded 12 Nov 2007 to 130.64.2.235. Redistribution subject to ASME license or copyright, see http://www.asme.org/terms/Terms_Use.cfm


2/5

local strain criteria for design by analysis using elastic-plastic analysis

limit load and plastic collapse analysis for multiple loadingconditions

fatigue design for welded joints based on structural stressmethod, and

UT in lieu of RT for examination

Organization of New Code

Overview.The organization of the new VIII-2 is very different

from the current standard, utilizing a flat modular structure tofacilitate future revisions and additions. The standard is made upof nine parts.

Part 1: General Requirements Part 2: Responsibilities and Duties Part 3: Material Requirements Part 4: Design-by-Rule Requirements Part 5: Design-by-Analysis Requirements Part 6: Fabrication Requirements Part 7: Inspection and Examination Requirements Part 8: Pressure Testing Requirements Part 9: Pressure Vessel Overpressure Protection

In addition to these nine parts, normative and informative an-nexes are utilized within each part, eliminating the use of manda-

tory and nonmandatory appendixes that are traditionally placed inthe back of the standard.

Part 1: General Requirements. Part 1 addresses the scope ofthe standard with respect to the types of pressure vessels covered,as well as the definition of the geometric boundary for thestamped item. In addition, this part covers units of measurement,reference standards, technical inquiries, and global definitions.Similar to other ASME BPV standards, US Customary, SystmeInternationale SI, or local customary units may be used to dem-onstrate compliance with the standard. Guidance for the use of USCustomary and SI units is also provided.

Part 2: Responsibilities and Duties. Part 2 consolidates re-sponsibilities and duties of the user, Manufacturer, and Authorizedinspector. The most significant change in this area has to do with

Registered Professional EngineerRPEcertification of the Manu-facturers Design Report MDR and the Users Design Specifica-tionUDS. An alternative to RPE certification is provided, whichwill facilitate the use of the new VIII-2 outside of North America.This alternative will require that the engineer certifying either theUDS or MDR has the requisite technical and legal stature, andjurisdictional authority to certify such a document.

One other significant change concerns maintenance of records.The Manufacturer needs to supply to the user the complete tech-nical file containing all pertinent documentation related to theconstruction of the vessel, as well as retain these records for aminimum period of 3 years after the vessel is stamped. Some ofthe records that must be retained by the Manufacturer are thefollowing:

users design specification manufacturers design report manufacturers data report, and manufacturers construction records, including welding pro-

cedure specifications, procedure qualification records,records of all heat treatments, results of all production testplates, NDE procedures, results of all NDE examinations,etc.

Part 3: Material Requirements. Part 3 contains several sig-nificant enhancements relative to the existing VIII-2.

The allowable stress basis is set to the minimum of UTS/2.4at room temperature, and YS/1.5 at both the room tempera-

ture and design temperature, for design temperatures belowthe creep range. This aligns the new VIII-2 with currentEuropean pressure vessel standards.

Allowable stresses are provided for design in the creeprange using the allowable stress criteria of Sec. VIII, Divi-sion 1.

The toughness rules were updated and the minimum Charpy

V-Notch impact test requirement was set to 27 J 20 ft lb.In addition, impact test exemption curves for carbon andlow alloy steel are now provided with and without the in-fluence of PWHT. Finally, the option to establish the design

MDMT using fracture mechanics methodology has beenadded.

A master stress-strain curve has been developed, which uti-lizes MSYS, MSUTS, and elastic modulus functions to in-troduce temperature dependence. This stress-strain curve isused when applying the design-by-analysis rules of Part 5,as well as when performing buckling calculations when it isnecessary to determine the tangent modulus.

Two sets of design fatigue curves are provided:

1. smooth bar design fatigue curves using the same designmethodology as presented in Appendix 5 of the currentVIII-2, and

2. welded joint design fatigue curves utilizing the new mas-ter S/N curve and the structural stress method for deter-mining the equivalent structural stress.

Part 4: Design-By-Rule Requirements. The VIII-2 rewritewill contain both design-by-rule and design-by-analysis options.Numerous enhancements were made to the design-by-rule proce-dures in Part 4, several of which are highlighted below.

A new format was introduced to present the design rules ina manner to enhance readability and facilitate computerimplementation of the required calculations.

Weld joint efficiencies are introduced in the VIII-2 rewritepermitting for the first time less than 100% volumetric ex-amination for main vessel welds.

Design by rule for the creep range is provided. Introduction of explicit design rules for combined loadings

i.e., pressure, weight, wind, and earthquake, as well asadoption of the ASCE 7-2002 Load Combination Method-ology.

New design rules for cylindrical shells, spherical shells andheads, ellipsoidal heads, and torispherical heads.

External pressure rules based on Code Case 2286 and uti-lizing the tangent modulus derived from the master stress-strain curve given in Part 3.

New opening reinforcement rules based on pressure-areastress calculation.

New rules for conical transition subject to internal/externalpressure.

Inclusion of design rules for layered vessels. Inclusion of design rules for stayed construction, jacketed

vessels, noncircular vessels, and vessel supports. Inclusion of bellows and tube sheet design rules based on

Part UHX from VIII-1.

Part 5: Design-By-Analysis Requirements. Part 5, the design-by-analysis section, was reorganized based on the mode of failureas follows:

protection against plastic collapse protection against local failure protection against collapse from buckling, and protection against failure due to cyclic loading

Another significant change is that the minimum wall thickness canbe established using design-by-analysis rules in lieu of the design-by-rule requirements in Part 4. This is a significant departure from

Journal of Pressure Vessel Technology NOVEMBER 2007, Vol. 129 / 755



3/5

the philosophy that exists in the current VIII-2.Some other enhancements to Part 5 are shown below.

Continued use of stress classification and the Hopper dia-gram.

Introduction of structural stress concepts that provide a newfundamental method to compute membrane and bendingstresses using finite element analysis FEA that is meshinsensitive. This structural stress method is also used whenperforming a fatigue analysis of welded joints.

New procedure for elastic-plastic design using FEA and themaster stress-strain curve.

New requirements for design based on local failure strainusing the master stress-strain curve, replacing the existinglimits on triaxiality.

Explicit design-by-analysis procedures for evaluating col-lapse from buckling including knock-down factor for shellimperfections.

New method for fatigue assessment based on structuralstress concepts for assessment of welded joints.

Normative annexes covering recommendations for lineariza-tion of stress results from FEA used in stress classification,design of perforated plates based on elastic stress analysis,and rules for experimental stress analysis are provided.

Part 6: Fabrication Requirements. Part 6 contains a consoli-dation of fabrication requirements from the original VIII-2 Part

AM and Part AF, as well as some fabrication rules from VIII-1.Similar PWHT requirements are planned for the initial release;however, new time-temperature-thickness criterion for PWHT isunder development.

Part 7: Examination Requirements. Rules for examination ofwelded joints have been completely rewritten in Part 7. The con-cept of defining examination groups for pressure vessels, basedon the practice used in several European standards, has been uti-lized. Also with the introduction of weld joint efficiencies in thenew VIII-2, the option for partial radiography is now available.However, unlike the spot RT rules of VIII-1 where 1% of a weldjoint is examined, when permitted in Part 7, the partial radiogra-phy rules will require between 10% and 25% of the weld to beexamined.

Other significant features of Part 7 include the following:

Provision for UT in lieu of RT; requirements are given re-garding when manual versus automated UT shall be per-formed.

More extensive visual examination requirements. For vessels for which the fatigue analysis is mandatory, all

surfaces of pressure boundary components internal and ex-ternal shall be examined by MT or PT following a hydro-static pressure test; this requirement is taken from Sec. VIII,Division 3, KE-400.

Part 7 also contains a normative annex outlining Inspectorand Manufacturer duties for inspection and examination.

Part 8: Pressure Testing Requirements. The hydrostatic testpressure in Part 8 is now set in accordance with Eq. 1; this isnow in alignment with the PED.

PT= max1.43 MAWP,1.25 MAWP STS 1

The ratio ST/S in Eq. 1 is the lowest ratio for the pressure-boundary materials, excluding bolting materials, of which the ves-sel is constructed.

The pneumatic pressure test option is retained. However, whenused, the vessel must be monitored by acoustic emission exami-nation during the test. Finally, the Manufacturer must maintaincomplete records of the final pressure test.

Part 9: Overpressure Protection.Basic rules for overpressure

protection in Part 9 are virtually identical to that currently pub-lished in VIII-1. For this reason, most rules for overpressure pro-tection in the new VIII-2 will reference VIII-1. Rules not coveredin VIII-1, such as Overpressure Protection by Design Code Case2211, will be presented in Part 9. An annex covering best prac-tices for the installation and operation of pressure relief devices,which is based on the latest revision to Appendix M of VIII-1, isalso provided.

Additional Development Steps

Overview.As stated earlier, in many respects, the developmentof this new Sec. VIII, Division 2 broke new ground for ASME,from subcontracting the writing of the first draft to an outsideorganization, to publishing the document in single column andformatting it to satisfy ISO guidelines. But, there were two otheractivities undertaken during this project to assure the highest qual-ity for the first edition: These were validation of all design rulesand beta testing of the document.

Design Validation.The new VIII-2 contains hundreds of equa-tions and polynomial expressions for curve fits used in the designrules. Even where rules were taken from Sec. VIII, Division 1, inmost cases, they were rewritten to facilitate computerization of therules. The net result was that to quality check each equation, fig-ure, and polynomial factor was a major undertaking such that if

committee volunteers were asked to perform this work, it wouldhave delayed publication of the document. Instead, an indepen-dent organization experienced in writing pressure vessel designsoftware was contracted to quality assurance QA check all de-sign rules in the new VIII-2. They performed this work by pro-graming all of the design rules in MATHCAD, and running numer-ous examples. Wherever possible, existing examples from the oldVIII-2 and VIII-1 were used for the validation work. In all, over athousand pages of calculations were performed, and the processdid identify some errors, mostly in the equations used to modeldesign curves. This validation work will also serve as the startingpoint for an examples manual to be developed for a future publi-cation.

Beta Testing.The Division 2 project team set forth a number ofgoals with the undertaking of this project, and everyone involved

was interested in receiving feedback from users of Sec. VIII, Di-vision 2. Normally, this feedback would be received once thestandard is published and used for production vessels; however, atest run prior to publication was required. To accomplish this,ASME authorized a project to beta test the standard during the laststages of approval. Invitations to participate in a beta test of thenew standard were sent to several existing Division 2 CertificateHolders. These Manufacturers were asked to select a recentlycompleted Division 2 vessel, and re-execute the project on paperusing the new standard. A large number of companies respondedto the invitation with a description of a vessel to be used in theevaluation.

The Subcommittee VIII Technical Steering Committee re-viewed the different proposals and made their selections to assurethat a diverse group of vessels were represented. The beta testers

were asked to provide feedback in the following areas:

overall ease of use of the standard change in wall thickness for main vessel components change in vessel weight reported as a percentage change change in welding, PWHT, and NDE costs change in production schedule reported as a percentage change in overall vessel cost reported as a percentage perform a fatigue analysis utilizing new structural stress

method general observations, including reporting any problems with

understanding the requirements of the code, missing or in-correct references, etc.

756 / Vol. 129, NOVEMBER 2007 Transactions of the ASME



4/5

Beta Test Results. Overall, the beta test of this new standardwas a resounding success and provided validation of many of thegoals set forth when this project was initiated. In general, theresults are as follows.

All of the beta testers reported the standard was easy to use,and that the design rules were clear and concise.

Several beta testers reported that they prefer the new formatof the document whereby the nomenclature, figures, andtables are all placed at the end of each part and that all of theweld joint figures are assembled in one place.

The beta test generated numerous questions on the standard,but no significant errors in the standard were identified dur-ing the test.

As expected, significant cost savings were reported due tothe increase in allowable stress for many carbon and lowalloy steels. Of equal importance, most of the testers also

reported a reduced amount of reinforcement required foropenings, resulting in a reduction in forged nozzle thickness. A summary of the beta test results is provided in Tables 15.

Summary

The majority of the goals outlined in 1999 for the rewrite ofSec. VIII, Division 2 have been satisfied in the draft approved bythe ASME BPV Standards Committee in February 2007. A com-pletely new and more user-friendly organizational structure to thebook coupled with adoption of the latest technology available for

construction of pressure vessels will hopefully result in a standardthat will serve the refining and petrochemical for decades to come.Ongoing activities related to the project include beta testing byexisting VIII-2 Certificate Holders, addressing accreditation is-sues, and preparation of a separate Examples Manual.

Table 1 Summary of beta test results: steam superheater.Comments:1 The new code provides a systematic approachto design with easy access to information.2The use of tablesand figures instead of graphs leads to better and precise re-sults. 3 The new format adopted is user friendly as it takesless time to find reference pages. 4 The design method foropenings and reinforcement provides a substantial decrease inhub thickness. 5 New code includes and accepts techniquessuch as TOFD, phased array, which is a welcome change andwill lead to definite improvements in quality and testing.

Item Shell Heads

Material SA-387 Gr11 Cl 2 SA-387 Gr11 Cl 2Design temperature C 410 410Allowable stress-old MPa 151.38 151.38Allowable stress-new MPa 151.38 151.38Required thickness-old mm 34.38 38.43Required thickness-newmm 34.59 33Change in vessel weight as a % 2Reduction in production timeas a %

N/A

Reduction in overall vessel costas a %

2.5

Table 2 Summary of beta test results: 53 ft diameter sphere.Comments:1Overall, the new Sec. VIII, Div. 2 code was foundto be well organized and logical in its layout. The equations arelocated near the text where they are referenced and this re-duces the time spent looking for the applicable equation. 2Having the NDE requirements summarized in a table is veryhelpful as are the diagrams and sketches of the welds. 3 Theopening reinforcement design method is logical and intuitive.

Item Shell Forging

Material SA-738 Gr B SA-387 Gr11 Cl 2Design temperature C 120 120Allowable stress-old MPa 195 148.9Allowable stress-new MPa 244 148.9Required thickness-old mm 42.74 N/ARequired thickness-newmm 33 N/AChange in vessel weight kg 51,000Reduction in production timeas a %

8


12.2

Table 3 Summary of beta test results: hydroprocessing reac-tor. Comments: 1 The beta test has confirmed the quality ofthe new code. 2 The revised design margins and related in-creased allowable stresses for some materials will result in sig-nificant savings in both time and cost.

Item Shell Heads

Material SA-336 F22V SA-542 Tp D Cl 4aDesign temperature C 454 454Allowable stress-old MPa 169 169Allowable stress-new MPa 199 199Required thickness-old mm 290 145

Required thickness-newmm 244 125Change in vessel weight as a % 13.8Reduction in production time 2 weeksReduction in overall vessel costas a %

12

Table 4 Summary of beta test results: hydrotreating reactor.Comments:1 New VIII-2 Code shows the requirements in de-tail for each item; therefore, confusion with Code interpreta-tions will be reduced. 2Examination requirements for the ma-terial are more severe. The cost and delivery impact for thematerial will be increased when purchasing the materials.

Item Shell Heads

Material SA-542 Type D Cl4a

SA-542 Type D Cl4a

Design temperature C 454 454Allowable stress-old MPa 168 168Allowable stress-new MPa 199.8 199.8Required thickness-old mm 167 95Required thickness-newmm 141 81Change in vessel weight as a % 14Reduction in production timeas a %

4


8

Table 5 Summary of beta test results: hydroprocessingreactor

Item Shell Heads

Material SA-336M F22V SA-542M Gr D Cl4a

Design temperature C 454 454Allowable stress-old MPa 168 168Allowable stress-new MPa 199.8 199.8Required thickness-old mm 304 152Required thickness-newmm 254 128Change in vessel weight as a % 17Reduction in production timeas a %

1


N/A

Journal of Pressure Vessel Technology NOVEMBER 2007, Vol. 129 / 757



5/5

The new Sec. VIII, Division 2 2007 edition will be publishedon July 1, 2007, and will become mandatory January 1, 2008. Acode case has been approvedCode Case 2575that will allow foran 18 month transition period during which VIII-2 CertificateHolders will be able to construct to either the old VIII-2 2004edition through 2006 addenda or the new VIII-2.

NomenclatureMAWP the maximum allowable working pressure

P the required hydrotest pressure

S the allowable stress at the design temperatureST the allowable stress at the hydrotest

temperatureUTS the ultimate tensile strength

YS is the yield strength

758 / Vol. 129, NOVEMBER 2007 Transactions of the ASME

Downloaded 12 Nov 2007 to 130 64 2 235 Redistribution subject to ASME license or copyright see http://www asme org/terms/Terms Use cfm

Documents

Modernization of Pressure Vessel Design Codes ASME Section VIII, Division 2, 2007 Edition