SECTION VIII DIVISION 2 2007 EDITION: COMPLETE REWRITE 5

[Steven444]

BACKGROUND

The 2007 Edition of ASME Section VIII, Division.2 of the ASME Boiler and Pressure Vessel Code is a complete rewrite of the 2004 edition that updates and modernizes the Code to provide for major technical advances in pressure vessel analysis, design, construction and related sciences such as materials, welding and nondestructive examination. In addition, the rewrite is structured in order to make it more user-friendly for both users and the committees that maintain it. New and updated technology includes:

• Toughness requirements

• Material procurement table

• Conical transition reinforcement requirements

• Opening reinforcement rules

• Local strain criteria for design by analysis using elastic-plastic analysis

• Plastic collapse from multiple loading conditions

• Fatigue design based on structural stress method



ORGANIZATION of NEW CODE

The organization of the new code is very different from the current code, utilizing a flat modular structure that facilitates future revisions and additions. The code consists of nine parts as follows:

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, normative and informative annexes are utilized within each Part, eliminating the use of mandatory and nonmandatory appendices that, traditionally, are placed in the back of the code. Details are as follows:

Part 1 - General Requirements

This Part addresses the scope of this code with respect to the types of pressure vessels covered, and the geometric boundary for the stamped item. In addition, this Part covers unit of measurement, reference standards, technical inquiries and global definitions. Either US customary, or SI, or local customary units may be used to demonstrate compliance with the code. Annex 1.C provides guidance for the use of US Customary and SI Units within this code.



Part 2 - Responsibilities and Duties

This Part consolidates responsibilities and duties of the User, Manufacturer, and Authorized Inspector. The most significant change concerns certification of the Manufacturers Design Report (MDR) by a Registered Professional Engineer (RPE) and the Users Design Specification (UDS). It provides an alternative to RPE certification that will facilitate the use of the new Section VIII, Division 2 outside of North America.



Part 3 – Material Requirements

This Part contains several significant enhancements to the 2004 edition of Section VIII, Division 2. The allowable stress basis is set to UTS/2.4 at room temperature and 2/3Sy at design temperature. This aligns the new code with current European pressure vessel standards. The toughness rules were updated, and the minimum Charpy V-Notch impact test requirement was set to 20 ft-lb (27 J). Impact test exemption curves for carbon and low alloy steel are now provided with and without the influence of postweld heat treatment (PWHT). The option to establish the design minimum design metal temperature (MDMT) using fracture mechanics methodology has been added. A master stress-strain curve which utilizes minimum specified yield strength, minimum specified ultimate tensile strength, and elastic modulus functions to introduce temperature dependence. Two sets of design fatigue curves are provided:

(1) Smooth bar design fatigue curves using the current design methodology as presented in Appendix 5 of the current VIII, Div.2; and

(2) Welded joint design fatigue curves utilizing the new Master S/N Curve and the Structural Stress Method for determining the equivalent structural stress.



Part 4 - Design by Rule Requirements

Numerous enhancements were introduced in the design by rule section, several of which are highlighted below:

• A new format that enhances readability and facilitates computer implementation.

• Weld joint efficiencies that permit less than 100% volumetric examination for main vessel welds.

• Explicit design rules for combined loadings (i.e. pressure, weight, wind and earthquake), as well as adoption of the ASCE 7-2002 Load Combination Methodology

• New design rules for ellipsoidal and torispherical heads.

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

• New opening reinforcement rules based on pressure-area stress calculation.

• New rules for conical transitions subject to internal and external pressure.

• Inclusion of bellows and tubesheet design rules based on Part UHX from Section VIII Division 1.

• Inclusion of design rules for jacketed vessels, noncircular vessels, and vessel supports.



Part 5 - Design by Analysis Requirements

The design by analysis section was reorganized based on the mode of failure as follows:

• Protection against plastic collapse

• Protection against local failure

• Protection against collapse from buckling

• Protection against failure due to cyclic loading

Another significant change is that the minimum wall thickness can be established using design by analysis (DBA) rules in lieu of design by rule (DBR) requirements. Some other enhancements to Part 5 are:

• Introduction of Structural Stress concepts that provide a new fundamental method to compute membrane and bending stresses using finite element analysis (FEA) that is mesh insensitive. This method is used when performing a fatigue analysis of welded joints.

• New requirements for design based on local failure strain, replacing the existing limits on triaxiality.

• A new procedure for elastic-plastic design using FEA and the Master Stress Strain curve.

• A new method for fatigue assessment based on Structural Stress concepts for assessment of welded joints.

• Explicit DBA rules for evaluating collapse from buckling

• Recommendations for linearization of stress results from FEA for stress classification



Part 6 Fabrication Requirements

Part 6 contains a consolidation of fabrication requirements from the 2004 edition of Section VIII, Div.2 Parts AM and AF, as well as some fabrication rules from Section VIII, Division 1.





Part 7 Examination Requirements

Requirements for examination of welded joints have been completely rewritten in Part 7. These utilize the concept of defining "examination groups" for pressure vessels, based on the practice used in several European standards. With the introduction of weld joint efficiencies, partial radiography is an option. Unlike the spot radiography (RT) rules of Section VIII, Division1, where 1% of a weld joint is examined, Part 7 partial radiography will require between 10 and 25% of the weld to be examined. Other significant features of Part 7 include:

• Provision for UT in lieu of RT.

• More extensive visual examination requirements, similar to PD 5500

• For vessels for which the fatigue analysis as mandatory, all surfaces of pressure boundary components (internal and external) shall be examined by MT or PT following a hydrostatic pressure test. This requirement is taken from Section VIII, Division 3, KE-400.

• A normative Annex outlining Inspector and Manufacturer duties for inspection and examination.



Part 8 Pressure Testing Requirements

The hydrostatic test pressure factors are now set to the greater of 1.43 x MAWP or 1.25 x MAWP(ST/S), bringing them in alignment with the PED. The pneumatic pressure test option is retained; however, when used, the vessel must be monitored by acoustic emission examination during the test. Finally the Manufacturer must maintain complete records of the final pressure test.



Part 9 Overpressure Protection

Basic rules for overpressure protection will be virtually identical to that currently published in Section VIII, Division 1. For that reason, most rules for overpressure protection will reference Section VIII, Division 1.



SUMMARY

A completely new and more user-friendly organizational structure, coupled with adoption of the latest technology available for construction of pressure vessels has resulted in a new Section VIII Division 2 that will serve industry for decades to come. Other activities related to the project included beta testing by current Section VIII, Division 2 U2 Certificate Holders, and preparation of a separate Examples Manual. The new Section VIII, Division 2 (2007 Edition) will be published on July 1, 2007, and will become mandatory January 1, 2008. A code case has been approved (Code Case 2575) that will allow for an 18-month transition period during which Section VIII, Division 2 Certificate Holders will be able to construct to either the old VIII-2 (2004 Edition through 2006 Addenda) or the new Section VIII, Division 2.

 

[hgamboa]

Dear Steven, would you please explain a little more the procedure about UDS. It is mandatory to fabricator of vessel under ASME section WIII, Div. 2 to obtain that certification. How much is the cost?

Regards,

Horacio
Mechanical Engineer

 

[eliebl]

For guidelines of application in Alberta please go to

http://www.absa.ca.

There is also a comittee report posted that may give some insight.

EJL

 

[davefitz]

from this summary, it appears that sect VIII div 2 is evolving toward the PED ; at some point they may become equivalent.

 

[hgamboa]

Thanks Steven. The link you recommended is very complete and useful to me.

HORACIO

 

[davefitz]

The links to the alberta press vessel code by eliebl and isthill are valuable- they include comments/reminders that caution the designer that the use of the lower safety factors, which compete with the EU codes, are not accompanied by any training or operating limitations imposed onthe PV operator/owner.

They indicate that , in alberta, and probably elsehwere , there is significant "mission creep" or continuous operations of the PV beyond the original desing limits assumed by the designer. This may have worked out OK with large safety factors, but the lower factors suggest that they should be accompanied by strict training of operators and defined operating limits, and the operating paramenters should be monitored and available to inspectors on demand- which I think is doen in the EU and which rationalises the lower safety factors.

 

[gr2vessels]

The Div 2 UDS, MDR certification in USA is still attributed to a Registered PE, but now any Registered and Chartered Engineer qualified by the local authority to review and certify the mentioned documents is accepted by the ASME Code, be that in India, Australia or South Africa...For the local authority, that also implies some sort of legal responsibility for the provider(s) of such certification. Also, I believe that first time in the Code, is now recognised that one only PE cannot be qualified to certify design, fabrication, material selection, etc, hence the "plural" certification is quite prominently worded in the Code.
Just a few quick words for you..
Cheers,
gr2vessels