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Associate

Join Date: Jan 2009
Posts: 44

ASME CODE Section VIII Div 1 vs Div 2

11/16/2011 4:07 AM

What is the main difference between Div 1 and Div 2 of ASME CODE sec viii (boiler and pressure vessel code). I just want to clarify which of the two Div 1 or Div 2 based pressure vessel will cost more? ignore all benefits of the more costly Div... Thanks

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Guru

Join Date: Jul 2005
Location: Stoke-on-Trent, UK
Posts: 2347
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#1

Re: ASME CODE Section VIII Div 1 vs Div 2

11/16/2011 7:47 AM

From memory, Div 1 allows higher design stress, hence possibly thinner plate, but requires more stringent non-destructive testing. Which is more economical depends on the details. In general, I'd expect smaller, lower-pressure vessels to favour Div 2 (as there's less steel to minimise) but if there's no reason (eg client's spec) to go for one or the other, I would leave it up to the vessel builder, and let him choose the more economical Div.

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Join Date: Feb 2009
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#3
In reply to #1

Re: ASME CODE Section VIII Div 1 vs Div 2

11/17/2011 11:46 AM

Codemaster: Are you sure that allowable stress in Section VIII Div 1 higher than in Div 2? Please check again to ASME Section II Part D. As my experience, Div 2 has higher allowable stress, which means the nominal thickness will be thinner than if you use Div 1. Div 2 is an alternative rules for pressure vessel, its quality control and inspection will be more stringent. The thinner its thickness, the lower its weight, the cheaper its price. But i dont know for the detail prices of its quality control and inspection.

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Guru

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#5
In reply to #3

Re: ASME CODE Section VIII Div 1 vs Div 2

11/17/2011 1:38 PM

No, I'm not sure, that's why I said from memory. I was basing it on BS5500, which has construction categories 1, 2 and 3. Cat 1 has the highest allowable stress, and requires 100% NDT. If it's the other way round in ASME VIII I hope it didn't confuse the OP too much, but I'm sure he'd understand the point I was making. BTW, I can't work out from blackpanic73 in #4 which way round it is.

Nowadays there's a European standard, which I haven't got, but I've an old copy of BS5500, and in that allowable stress is derived from the ultimate tensile stress Rm and the yield stress Re. Cat 2 has spot NDT, and Cat 3 visual inspection only. Apart from restrictions on material and thickness, Cat 1 & 2 allowable stress = Rm/2.35 or Re/1.5, whichever is lower. Cat 3 allowable stress = Rm/5.

I still think if there are no constraints it's best to leave the vessel supplier with a free hand to get the cheapest price.

A comment from shanii to say whether we've been any help would be nice.

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Power-User

Join Date: Dec 2010
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#2

Re: ASME CODE Section VIII Div 1 vs Div 2

11/16/2011 11:42 AM

Codemaster has almost explained the difference. I want to add up as below:

Normally process licensor know the required criticality of the equipment and if any other process factor or standard comes in and decide the design critaria over and above the SME Sec VIII then Div 2 is specified and in case equipment is to be designed critically based on ASME sec VIII then div 1 is considered even for low pressure equipment.

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Commentator

Join Date: Sep 2011
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#4

Re: ASME CODE Section VIII Div 1 vs Div 2

11/17/2011 12:29 PM

the main difference between DIV I and DIV II as following:

- DIV II cover design pressure from 15 psi up to 3000 psi if design pressure increse over than 3000 psi use DIV II up to 10000 psi. but you can DIV II in the range of DIV I

- DIV I based on maximum stress theory but DIV II based on maximum shear stress throry.

please review scope for each code to know more.

the thickness calculated under DIV I is higher than thickness calculated under DIV II for the same design pressure in range of design pressure of DIV I

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#6

Re: ASME CODE Section VIII Div 1 vs Div 2

11/18/2011 1:40 AM

By chnace I happened to came across a very interesting and important document, which can clear some of the doughts between the two divisions of sec VIII. Please go through the attached discussion.

DISCUSSION ON ASME SECTION VIII DIVISIONS 1 AND 2 AND THE NEW DIVISION 3

3rd Annual Pressure Industry Conference, Banff, Alberta, Canada, February 1999.

Section VIII Division 1

Section VIII Division 2

Section VIII Division 3

"Unfired" Pressure Vessel Rules

Alternative Rules

Alternative Rules for High Pressure

Published

< 1940 1968 1997

Pressure Limits

Normally up to 3000 psig No limits either way, usually 600+ psig No limit; Normally from 10,000 psig

Organization

General, Construction Type & Material

U, UG, UW, UF, UB, UCS, UNF, UCI,

UCL, UCD, UHT, ULT

General, Material, Design, Fabrication

and others

AG, AM, AD, AF, AR, AI, AT, AS

Similar to Division 2

KG, KM, KD, KF, KR, KE, KT, KS

Design Factor

Design Factor 3.5 on tensile (4* used

previously) and other yield and

temperature considerations

Design Factor of 3 on tensile

(lower factor under reviewed) and other

yield and temperature considerations

Yield based with reduction factor for

yield to tensile ratio less than 0.7

Design Rules

Membrane - Maximum stress

Generally Elastic analysis

Very detailed design rules with Quality

(joint efficiency) Factors. Little stress

alaysis required; pure membrane

without consideration of discontinuities

controlling stress concentration to a

safety factor of 3.5 or higher

Shell of Revolution - Max. shear stress

Generally Elastic analysis

Membrane + Bending. Fairly detailed

design rules. In addition to the design

rules, discontinuities, fatigue and other

stress analysis considerations may be

required unless exempted and guidance

provided for in Appendix 4, 5 and 6

Maximum shear stress

Elastic/Plastic Analyses and more.

Some design rules provided; Fatigue

analysis required; Fracture mechanics

evaluation required unless proven leakbefore-

burst, Residual stresses become

significant and maybe positive factors

(e.g. autofrettage)

Experimental Stress

Analysis

Normally not required Introduced and may be required Experimental design verification but may

be exempted

Material and Impact

Testing

Few restrictions on materials; Impact

required unless exempted; extensive

exemptions under UG-20, UCS 66/67

More restrictions on materials; impact

required in general with similar rules as

Division 1

Even more restrictive than Division 2

with different requirements.Fracture

toughness testing requirement for

fracture mechanics evaluation

Crack tip opening displacement (CTOD)

testing and establishment of KIc and/or

JIc values

NDE Requirements

NDE requirements may be exempted

through increased design factor

More stringent NDE requirements;

extensive use of RT as well as UT, MT and PT.

Even more restrictive than Division 2;

UT used for all butt welds, RT otherwise,

extensive use of PT and MT

Welding and

fabrication

Different types with butt welds and

others

Extensive use/requirement of butt welds

and full penetration welds including nonpressure

attachment welds

Butt Welds and extensive use of other

construction methods such as threaded,

layered, wire-wound, interlocking stripwound and others

User

User or designated agent to provide

specifications (see U-2(a))

User's Design Specification with detailed

design requirements (see AG-301.1)

include AD 160 for fatigue evaluation

User's Design Specification with more

specific details (see KG-310) including

contained fluid data, etc with useful

operation life expected and others.

Designer defined

Manufacturer

Manufacturer to declare compliance in

data report

Manufacturer's Design Report certifying

design specification and code compliance in addition to data report

Same as Division 2

Professional

Engineer

Certification

Normally not required Professional Engineers' Certification of

User's Design Specification as well as

Manufacturer's Design Report

Professional Engineer shall be experienced in pressure vessel design

Same as Division 2 but the Professional

Engineer shall be experienced in high

pressure vessel design and shall not sign

for both User and Manufacturer

Safety Relief Valve

UV Stamp UV Stamp UV3 Stamp

Code Stamp and

Marking

U Stamp with Addition markings

including W, P, B, RES; L, UB, DF; RT, HT

U2 Stamp with Additional marking

including HT

U3 Stamp with additional marking

denoting construction type; HT, PS, WL,

M, F, W, UQT, WW, SW

Hydrostatic Test

1.3 (Was 1.5 before the use of the 3.5

Design Factor in the 1999 Addenda)

1.25 1.25 (may be exempted for

autofrettaged vessels)

* In 1998, Code Cases 2278 and 2290 for ASME Section VIII Division 1 allowed for alternative maximum allowable design stresses based on a factor of

3.5 under certain provisions instead of a factor of 4 used by the Code. These code cases were incorporated into the Code in 1999.

Common Features:

Jurisdiction may have requirements in addition to Code

Mandatory Manufacturer's Quality Control System Implementation and Audit Requirements

Code Stamp Authorization through ASME Accreditation and Authorization

Authorized Inspection Agency in accordance with QAI

Authorized Inspector with Jurisdictional approval and certification

Manufacturer being held accountable for Code Stamp Application and full Code Compliance

NDE Personnel to SNT-TC-1A

Note: This brief comparative table is presented for discussion and does not represent the opinion of the ABSA, the ASME or the ASME Boiler and Pressure Vessel Code Committees. Readers are advised to consult with the ASME Code Section VIII Divisions 1, 2 & 3 for details

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