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MINUTES

Meeting of the API SUBCOMMITTEE ON VALVES

AND WELLHEAD EQUIPMENT (API SC6)

at the

85th Exploration and Production Standards Conference on Oilfield Equipment and Materials

of the

AMERICAN PETROLEUM INSTITUTE

Hyatt Regency, Calgary, Alberta, Canada June 26, 2008

***

David Cole, Chairman Ed Baniak, API Staff Representative

Roy W. Benefield, Secretary

AMERICAN PETROLEUM INSITUTE Upstream Standards 1220 L Street, NW

Washington, DC 20005

Subcommittee 6 – Valves and Wellhead Equipment June 26, 2008

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85th Exploration and Production Standards Conference on Oilfield Equipment and Materials API Subcommittee 6 – Valves and Wellhead Equipment

Hyatt Regency, Calgary, Alberta, Canada Thursday, June 26, 2008

Chair: David Cole 1. Opening of the meeting (David Cole): - Meeting opened by chairman, David Cole.

a. Safety Issues - He started with safety information on how to evacuate the room b. Housekeeping Issues - keep the aisle way clear.

2. Roster Update (Ed Baniak) – Comments on interest and voting. 3. Roll call to establish quorum (Ed Baniak):

a. Establish quorum – Established. See sign-up sheet (Attachment 1). b. Update on voting categories - There are two voting categories: one for 6A and one for

6D types of documents. 4. Adoption of the proposed agenda (David Cole) – Motion made, seconded and passed to

adopt the agenda as published. 5. Adoption of the minutes from Houston, TX (winter meeting), March 4, 2008 (David Cole) –

Motion made, seconded and passed to adopt minutes of last meeting. 6. Ballots since last meeting (Ed Baniak): - Ballot comments should be made in the comment

page on the ballot wed-site, if possible. a. Ballot 1406 (Reaffirmation of API Spec 6AV1) – closed 4/29/08 – Ed Baniak reported

the ballot passed. b. Ballot 1420 (Repair/Remanufacture – Spec 6A) – closed 5/15/08 – Ballot passed with

one negative and comments to be resolved. Sterling Lewis will report on this. c. Ballot 1432 (ISO/DIS 10423 – USTAG) – open (closes 7/1/08) – Still open. d. Ballot 1442 (Addendum 2 – Spec 6A) – open (closes 7/2/08) – Still open.

7. Task Group Chair/Project Group Leader reports: a. API Spec 6A/ISO 10423

i. Castings/Forgings (Ed Baniak) – Question is what does API need to resolve this issue. Castings allowed in 6A but not ISO 10423 at PSL 3 and above. Attempts have been made over the past year to obtain work from ISO workgroup that meets the requirements of API. Motion was made, seconded and passed to form a task group to evaluate the use of castings for pressure containing 6A equipment including the review of the results of the poll of API Monogram licensees on this subject. Volunteers signed up. A task group chairman will be announced and volunteers are requested to contact him at that time.

ii. Current Status (Ries Langereis) –Ries Langereis reported on status of ISO 10423 issues. Ballot due to close in USA on July 1, 2008 (Attachment 2).

iii. Repair/Remanufacture (Sterling Lewis) –Sterling Lewis reported on the actions of R/R Task Group. Ballot has passed 15 to 1 with editorial comments. Recommendations were made from the task group for publication and future action (Attachment 3). Motion was made, seconded to accept the recommendations of this task group that is to publish the document for the 19th edition of 6A and to forward to the ISO 10423 WG 3 for inclusion/consideration in ISO 10423 and 6A 20th Edition. Motion passed.

b. API Spec 6D/ISO 14313 (Rick Faircloth) - Rick Faircloth reported on the actions of this subcommittee and the documents involved. ISO DIS 14723 – 2nd edition passed DIS with 100% affirmative voting. A new WG 18 has been approved to publish document by May 2011. Identical adoption into 6D with no regional annex (Attachment 4).


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c. API Spec 6DSS/ISO 14723 (Rick Faircloth) . Audit check list on 6DSS is in process. (Attachment 4) Motion made, seconded and passed to accept the 6D/6DSS report.

d. API Spec 6AV1 Workgroup (Eric Wehner) – Erick Wehner reported on the 6AV1 task. A meeting is planned for next quarter and at the API Winter Conference (Attachment 5).

e. API TR 6AF/6AF2 Revision (Shyam Patel) – Shyam Patel reported that he has submitted a report on this action. It is proposed that these documents be balloted as there are changes. A new revision number will be assigned. They will be balloted separately. Motion made, seconded and passed to ballot the changes of TR 6AF and TR 6AF2.

f. API 6HP (Earl Shanks) – Earl Shanks presented a report on this task group. It involves groups other than SC6. Work started in 2005 because of high performance requirements in the industry. Object is to develop the design verification and validation process for high pressure/temperature applications. ASME Section VIII procedures are being considered. ASME recommends fracture mechanics methods for the large forgings involved. Stress Engineering was contracted to do the writing. An example procedure was presented at the 2007 conference. Analysis has been performed and data is being formatted for the report. The technical document will proceed.

7. Summary/Update of Prior Meeting Discussions: a. 20K Flanges/High Strength Bolting Materials (Shyam Patel) - Shyam Patel reported.

The task group consists of 6 manufactures, 2 users and 1 consultant. See attachment for details of the report. Flange design and verification are in process (Attachment 6).

b. Transfer of Standards out of SC6 (14A/14B/14L) (Ed Baniak) – Ed Baniak reported that the standards assignments have been concluded. They are now assigned to SC19 and are no longer under SC6.

c. Transfer of Standards into SC6 (11IW) (Ed Baniak) – This document has been assigned to SC6. It may be necessary to contact licensees and users for input on this standard.

8. Status of Work Plan and Action Plan Update (David Cole): a. API Spec 6FD (Fire Test for Check Valves) 1995/Reaffirmed 2003 – The chairman

asked for a decision on need to reaffirm or withdraw. Motion made, seconded and passed to ballot Spec 6FD for reaffirmation.

b. API Spec 6A718 (Nickel Based Alloy 718) 2005 – The chairman reported that we need to be thinking about reaffirmation in the future. Tim Haeberle suggested that we reactivate the task group to evaluate the need for reaffirmation and possible changes. Motion made, seconded and passed to reinstate the 6A718 task group. Volunteers are requested to contact Tim Haeberle.

c. API Spec 11IW (Independent Wellhead Equipment) Reaffirmed 2008 – The chairman reported that this document is now under SC6. It has been reaffirmed twice with no changes. Interested parties are welcome. It was suggested that licensees and users of this equipment be contacted.

9. New Business – a. Audit Effectiveness (Bud Wrightman) - Bud Wrightman discussed audit effectiveness.

Questions are developed for audits of API Spec 6A. A request was made for volunteers from SC6 to rank the questions and develop new ones. An e-mail will be sent to SC6 chair requesting volunteers.

b. API Bull Plug Issue (David Zollo) - David Zollo presented this issue for AWHEM. It has been found that API bull plugs cannot be made up according to the requirements API specifications. David reported on testing results and recommendations. Coatings are recommended to prevent galling, but torque is still high. Dimensional changes are required to allow proper make-up. Dimensions were presented on the 2”


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size. New dimensions are recommended to reduce the torque required for make up. Also, bull plugs should not be rated above 10,000 psi working pressure. Other sizes need to be evaluated (Attachment 7). Motion made, seconded and passed to ballot the proposed changes as an Addendum to API Spec 6A to add coatings for all sizes of bull plugs and the dimensional changes presented for the 2” size. Each change (coating and dimensions) will be balloted separately. AWHEM is requested to provide recommendations and dimensions for the other sizes of API bull plugs.

c. Review of ASME Code Section VIII Division 2-2007 (John Fowler) - John presented a summary of the ASME Code changes and pointed out how API specs are affected. See attachment for details. Recommendations are included. The chairman supports the formation of a work group. It was recommended that SC6 identify people willing to work on this issue (Attachment 8). Motion made, seconded and passed to form a task group to evaluate changes needed to SC6 documents as a result of the new ASME Codes, dependant on outcome of the ECS. John Fowler was appointed chairman of the ASME Codes Task Group. Volunteers are requested to contact him. The ECS will be requested to consider standardizing the design stress analysis methods for all API committees/subcommittees.

d. Coordination between API committees and ISO groups (Chairman) – The chairman requested and received support from SC6 to work with Ries Langereis to investigate how other API subcommittees are working with their ISO counterparts and bring a report back to SC6 in the 2009 winter meeting.

10. Actions Item Summary – Five ballot items: a. Changes to TR 6AF b. Changes to TR 6AF2 c. Reaffirmation of API 6FD d. Change to API 6A – Add Coatings for all Sizes of Bullplugs e. Change to API 6A – Change dimensions with respect to Bullplugs

11. Upcoming Meetings: a. E&P 2009 API Winter Conference in San Antonio, TX (January 19-23, 2009) b. E&P 2009 API Summer Conference in Westminster, CO (June 22-26, 2009)

12. Adjourned - Motion made, seconded and passed to adjourn.

kurylac

Text Box

Attachment 1

Attachment 2

API SC6- ISO 10423 WG3one world standard

1. Current differences-Castings vs.Forgings-Repair and re-manufactureL t t NACE-Latest NACE

-General update/wishes

One world standardOne world standard

• Castings and forgings difference ISO APICastings and forgings,difference ISO API• Workgroup under Alfred Kruyer,concluded

forgings superior for PSL2+forgings superior for PSL2+• All major suppliers /users specify forgings• Has been kept as such in DIS march

2008• Leave this issue with API SC 6


• Repair and re-manufacture-ISO Annex JRepair and re manufacture ISO Annex J• No such requirement in API 6A,something

should be there • Meanwhile WG3 studied current version Ann.J

with other external requirementsq• Present overview, conclusion no changes kept in

current DIS• API has now come with acceptable re-phrasing

WG3 seriously considers change into FDIS

One world standardOne world standard• New NACE included in API 6A-19th• Project group within WG 3 • Initiated industry survey amongst users and y y g

suppliers re experience with new NACE• Main conclusion :new NACE can be

i l t d id d t i ki iimplemented provided extensive marking is introduced Cl,PH,H2S in ISO 10423

• ASTMA A 453 grade 660 use is limited• ASTMA A 453 grade 660 use is limited• Overall API NACE implementation has been

included in DIS


• General update needed from API errataGeneral update needed from API errata list

• Awhems has made list of updates which• Awhems has made list of updates which are needed,wished and proposedA ti F h d li ti d h• Austin Freeman has made listing and has provided overview

• Any proposed change must have general support


• Overall conclusion :we have never beenOverall conclusion :we have never been so close to the above

• With the available effort and will we can• With the available effort and will, we can make it! And shall.W h ll i b t ff t f FDIS d• We shall give our best effort for FDIS end year!!!

• Would like to thank all those that made present DIS possible

Attachment 3

American Petroleum Institute

API SC6 Task Group Update on Repair and Remanufacture of

Spec 6A Valves and Wellhead Equipment

Thursday, June 26, 2008 Calgary, Canada

• Summer Conference 2007, task group initiated work to create Annex for Repair and Remanufacture that contains language acceptable for API policies.

Primary Considerations Avoid a regional Annex O

Minimize changes to ISO 10423 Annex J

Users expressed a desire to recertify equipment

API will not license Repair and Remanufacture Winter Conference 2008, Draft document was presented and the Subcommittee passed a motion to Ballot it as API 6A Annex J.

Primary Differences Requirement to document equipments Original Product Definition (OPD).

Limits application of Annex to user owned equipment, repaired or remanufactured back to OPD requirements and returned to user's service.

Documentation provides for a Certificate of Conformance, enabling recertification of equipment back to the OPD.

May 2008, Ballot passed with 15 affirmative, 1 negative, 3 did not vote. Summer Conference 2008, Comment resolutions were presented to and accepted by Task Group with editorial changes. Chairman will send out the written notice of ballot resolutions with Meeting Minutes. Additionally, the Task Group received positive feed back from the ISO representatives present.

Recommendation Task Group recommends to SC6 that the balloted document, with proposed

editorial changes, be approved for publication in the 19th edition of API Spec 6A as Annex Q.

Task Group recommends that Annex Q be forwarded to the ISO 10423 WG 3 for inclusion/consideration in the next revision of ISO 10423.

It was recommended that a future change to the NDE requirements for PSL 3 be increased to evaluate high stress concentration areas for crack propagation and that the original surface NDE be repeated.

Attachment 4

Rick Faircloth 3250 Briarpark Drive

Sr. Principal Engineer Houston, Texas 77042 Engineered Valves Tel 1.28.-261.3672 Fax 1.281.261.3635

Date: June 25th, 2008 Attention: API 6D/6DSSTask Group Members

Subject: Minutes of meeting on 6D/6DSS Revisions and Corrections

Location: 85th Exploration & Production Standards Conference on Oilfield Equipment and Materials held at the Hyatt Regency Hotel Calgary, Albert Canada

Minutes

1. Status report on publication of API Spec 6DSS 1st Edition August 2007 Subsea pipeline valves include API Regional Annex G was given and advised the TG of its use and that API Quality programs has issued three Monogram 6D licenses.

2. Status report on ISO TC67 SC2 WG9 ISO DIS 14723 -2nd Edition was given to the TG on the recent DIS voting and the WG9 technical experts have meet to resolve the comments received during the voting. Out of (23) P-members countries there was 100% of the member countries in favor of the DIS and 0% percent negative.

3. Status report on ISO TC67 SC2 WG18 ISO 12490 (NWI/596) - Actuation Mechanical Integrity and Sizing Rules for Pipeline Valves. This is a new ISO standard which was recently approved during the 24th plenary meeting of TC67 SC2 in Copenhagen. The plan is the have a standard issue by May 2011. Bothe manufactures and operators have nominated technical experts to work on this ISO standard.

4. Status report on the ISO TC67 SC2 publication of ISO- 14313 Pipeline valves

December 15, 2007 and adopt back and publication of 23rd Edition of API spec 6D. Note that this edition of API 6D is an identical adoption of ISO with only a regional annex to address the API monogram program. Some minor editorial mistakes were found in the text and the Chairman 6DTG will contact the ISO CS for possible issuance of a corrigenda which will be then issued as a Errata to API 6D.

5. Status report on audit check list questions for new API Spec 6DSS and updated

check list questions on API6D 23rd Edition. API will be using a contractor to assist in developing the audit checklist questions to cover these two standards latest editions. 6DTG will assist in ranking the questions as well as providing additional question for the auditors.

Attachment 4

Rick Faircloth 3250 Briarpark Drive

Sr. Principal Engineer Houston, Texas 77042 Engineered Valves Tel 1.28.-261.3672 Fax 1.281.261.3635

New business -

Discussion and possible action to include a special annex to address API 6A PSL 1, 2, 3 requirements into API spec 6D. TG discuss this issue found there was no wide industry need, therefore no further action was taken.

Discussion was raised from the 6DTG members to review the upcoming API 6A annex on repair and remanufacturing to see if the wording of OPD might be used on the next revision of API RP 6DR.

Meeting was concluded at 11:00 am. Regards,

Rick Faircloth

Chairman- 6D/6DSS TG on Revisions and Corrections

Attachment 5

API SC6 Project Group Report: 26 June 2008

API Spec 6AV1 Workgroup

Eric Wehner, Chair

Objective: Harmonize and combine 6AV1 with Annex I of API 6A. Eliminate redundancy and propose single document to cover validation of SSV/USV valve designs.

Status:

Spec 6AV1 passed reaffirmation ballot with no changes.

Three WG members identified, including chair.

Will recruit member/input from Southwest Research Institute.

No meetings held yet.

Action Plan:

Schedule meeting for Q3 2008.

Cameron resource to complete comparison review of 6AV1 & Annex I prior to meeting.

Complete proposal for SC6 by winter meeting Q1 2009.

API 20K Flange Design Task Group

API SC6 Task Group

Date: June 26, 2008.

Attachment 6

2

Design Analysis Procedure

Yes

No

Design Verification

Design meets

Static Load

requirementsR

edesig

n

Design Validation

Testing

No

Fatigue Analysis

Design meets

Fatigue life

requirements

Yes

Redesig

nSealability Analysis

Design Flange

Functional Design Specification

Static Loads per Task Group Consensus

Dynamic Loads-TBD

3

Bolt Diameter Estimation

Bolt Diameter Based on Internal Pressure + Gasket Load and 20 No. bolts

(Estimate purposes only, Bolt Strength > 4” Dia & Temp Derating not included)

Bolt Grade B7 L7 B7M L7M

A453

Gr.660

120K

yield

135K

Yield

>2.5 Dia, Yield Strength, psi 95000 95000 80000 80000 95000

Test Pressure Condition, Bolt Dia

(Bolt Stress at 83% Sy) 4.75 4.75 5.25 5.25 4.75 4.25 4

Observation: Large Bolt Diameter.

Concerns/Design Considerations:

1. For High Strength Bolts-Tapped Hole depth need to be adjusted for material yield differences.

2. Availability of bolt material with uniform cross sectional properties.

3. Ability to achieve uniform make-up through applied torque.

4. Larger Flange OD. Increase in equipment weight. Increased cost.

5. Monolithic equipment design: Increased Handling weight & Machining Cost.

4

Alternate Bolt Materials

Higher Strength, >120 to 130 ksi yield may be needed

Higher than 120 Yield Strength Inconel 718 not included in API 6A718 --- 130 ksi/150 ksi may be included in next revision.

Inconel 925 is being considered by NACEOther candidate material under consideration

Alloy bolting, hardness 34 Rc/strength is limited due to Hydrogen Embrittlement when connected to C P protection

5

API 6A- Ring Gasket Material

6

BX-164 Seal Ring Gasket

At Make-up condition entire gasket(316 S.S,) cross section yields Gasket leakage concerns: (a) Cyclic loads, (b) At high temperature New Cross section to be designed. (Reference: R. Eichenberg’s method.) New Cross section is under development. Design guidelines & Test protocol for Gasket needs to be established.Concerns: Cost of testing . Material Selected will verify performance of that material.

7

BX-164 Seal Ring GasketDesign Parameters Check per Eichenberg Method

API 6A Dimensions

Ring No. Bore Dia Max Bore Pressure Rating Height Width

B B max P H A

BX164 18.75 18.78 10K-15k 1.185 0.968

Eichenberg Design parameters checked

10ksi WP 15ksi WP 20ksi WP

Ring No. Bore Dia Ht of Gskt Width of Gskt Width of Gskt Width of Gskt

B

BX164 18.75 1.170 0.968 1.185 1.368

8

Hydril 18-3/4” 20 ksi Flange Design (Preliminary)

Stress Calculations Method: ASME Section VIII, Division 2, Appendix 3

9

Summary

• Bolt Size affects flange OD.

− Need higher strength bolt material

− Deepwater application requires considerations for affects of CP protection and potential exposure to well bore fluid when insulated,

− Bolting Allowable being reviewed. Recommendation to follow.

• BX-164 Gasket is inadequate. New Gasket is needed.

− Material selection for subsea use may qualify only one gasket material

• Flange Design Method/Allowable being reviewed. Recommendation to follow.

− API 6A + ASME Sect VIII (Edition referenced in API 6A)

or

− ASME Sect VIII, 2007 Edition

1

API Bull Plug Issue

Attachment 7

2

Issues With Bull Plugs

• Not making up API recommended two turns past hand-tight

• Not being able to remove the bull plugs after being tightened

• If removed, bull plugs and companion flanges showing signs of galling

3

Test Summary

• 2” bull plugs from two vendors used

• Four separate bull plugs tested

– Standard bull plug with no changes

– Deeper bore: 2.5”

– Chamfer added: 30

– Xylan coating added to standard bull plugs

• Pipe dope added to each bull plug

• Each bull plug screwed in hand-tight to companion flange

• Distance from last thread to flange measured

• Torque wrench used to measure required torque to achieve two turns past hand-tight

• Distance from last thread to flange measured

• Removal of bull plug attempted

• Number of turns and removability were recorded

4

Bull Plugs From Vendor A

Part Thread Length Last Thread to Flange Distance

(Hand-tight)

Last Thread to Flange Distance

(Torque)

Torque Applied Turns Removability/

Condition

1 - Standard 1.187 0.375 0.225 1100 1 1/3 Yes - Galling

2 - Standard 1.187 0.331 0.174 850 2 No – 1/4 Turn

3 - Standard 1.189 0.376 0.201 650 2 Yes - Galling


5 - Standard 1.194 0.395 0.263 1200 1 1/2 No – 3/4 Turn

6 - Bore 1.187 0.381 0.209 800 2 Yes - Galling

7 - Bore 1.185 0.391 0.195 1250 1 7/8 No – 1/16 Turn

8 - Bore 1.191 0.396 0.25 1300 1 7/8 No – 1/8 Turn

9 - Bore 1.185 0.402 0.251 1000 2 Yes - Galling

10 - Bore 1.184 0.357 0.175 1050 2 Yes - Galling

11 - Chamfer 1.165 0.372 0.211 1300 1 7/8 Yes - Galling

12 - Chamfer 1.19 0.381 0.169 750 2 No – 1 1/4

13 - Chamfer 1.183 0.38 0.246 1300 1 3/4 No – 3/16

14 - Chamfer 1.182 0.38 0.22 1000 2 Yes - Galling

15 - Chamfer 1.19 0.366 0.181 1400 2 No – 1/2 Turn

16 - Coated 1.189 0.369 0.222 450 2 Yes – No Galling





5

Bull Plugs From Vendor B

Part Thread Length Last Thread to Flange Distance

(Hand-tight)


(Torque)

Torque Applied Turns Removability/

Condition


2 - Standard 1.072 0.342 0.162 1400 1 15/16 No – 1/16 Turn

3 - Standard 1.09 0.319 0.157 1400 2 No – 1/2 Turn

4 - Standard 1.08 0.305 0.142 1300 2 No – 1/4 Turn

5 - Standard 1.089 0.307 0.152 1250 1 3/4 No – 0 Turns

6 - Bore 1.1 0.317 0.17 1300 1 7/8 Yes - Galling

7 - Bore 1.076 0.336 0.134 1450 1 7/8 No – 0 Turns

8 - Bore 1.08 0.295 0.157 1300 1 2/3 No – 1/16 Turn

9 - Bore 1.079 0.289 0.134 1375 1 15/16 Yes - Galling

10 - Chamfer 1.079 0.285 0.104 700 2 Yes – No Galling




14 - Chamfer 1.068 0.31 0.17 900 2 Yes – No Galling

15 - Coated 1.068 0.369 0.208 700 2 Yes - Galling





20 - Coated/Bore 1.182 0.334 0.18 1100 2 Yes – No Galling

6

Coatings

• Xylan coated bull plugs met API make-up requirements

• An alternative to Xylan coating the bull plugs is to Phosphate coat them

• Phosphate coated met API make-up requirements as well

7

Phosphate Coated Bull Plugs

PartThread Length

Last Thread to Flange Distance (Hand-tight


(Torque Turns Removability/ Condition

1. Phosphate1.050 .286 .101 2 Yes – No Galling

2. Phosphate 1.050 .296 .133 2Yes – No Galling









8

Coatings – Recommended API 6A Changes

10.21.4 Coating

Bullplug threads shall be zinc or tin electroplated or phosphated, or processed by some other acceptable method

which will minimize galling and develop the maximum leak resistance characteristics of the connection. The

threads shall be gauged after coating.

10.21.5

10.21.6

10.21.7

9

Current API Design

4.00”

1.50”

1.06”

2” Plug Dimensions

10

Proposed Design for 2” Bull plug

11

Conclusion

• Besides Phosphate coating for all bull plugs the following changes are recommended for the 2” bull plug:

– Deeper bore

– 30 Chamfer

– Larger ID

12

Design Displacement Force Change % Change

inches lbs

Current API 0.1739 5730 0 0%

Add Chamfer 0.1739 5410 320 6%

Deeper Bore 0.1739 5580 150 3%

Deeper Bore + Chamfer 0.1739 5240 490 9%

Deeper Bore + Chamfer + Larger ID 0.1739 4135 1595 28%

13

ISO Change Conflict

14

ISO Change Conflict

1

Review of the ASME Code Section VIII Division 2 – 2007 as

it affects API specifications

Prepared for The American Petroleum

Institute, Washington, DC

By John H. Fowler, PE

On-line Resources, Houston, TX

Attachment 8

2

Summary

The ASME Code Section VIII Division 2 has been totally rewritten with the 2007 edition. Several API Specifications reference this Code for quality control and design methods.

Main areas of concern: those specifications that use ASME Section VIII Division 2

» Appendix 4 design methodology,

» Appendix 5 fatigue analysis methodology, and

» Appendix 6 experimental stress analysis.

Since Appendix 6 has been replaced by a substantially identical Annex 5.F in the new specification, this report focuses mainly on Appendices 4 and 5 in the old specification and the corresponding Parts 5.0 and 5.5 in the new Code, with additional consideration of rules in Part 4.0 of the new Code.

Changes to API Specifications 6A, 16A, 16C, and 17D are recommended.

3

Objectives

Provide a comparison of the rules of the

ASME Code Section VIII Division 2 before and

after the 2007 rewrite of the specification.

Clarify how the API Specs which reference the

ASME Code have changed the allowable

stresses of the code.

Recommend how the API Specifications

should address the new Code if at all.

4

API Spec references to Section VIII Div 2

API Specifications 6A cites the ASME Code Section VIII Division 2 for an alternative way to calculate the size of a Qualification Test Coupon used to determine material properties.

API Specifications 6A, 6H, 16A, 16C, and 17D all reference the design methods of Appendix 4 but permit higher allowable stresses.

API 17D references the fatigue analysis methods of Appendix 5.

5

API Spec references to Section VIII Div 2

Ref in Old Div 2 Location in New Where referenced Comments

AM201, 202 3.10.4 6A: 5.6.2 c, 5.7.2.3

16A: N/A

17D: Ref. 6A

Alternative sizing rules for QTCs:

New code virtually identical to

old.

Appendix 4 Part 5 6A: 4.3.3.2, 4.3.3.6; 6H:

5.1a.

16A: 5.4.2.2

16C: 3.1.1

17D: Appendix E

Strength analysis: methods changed.

Appendix 5 Part 5.5 17D: 303 Fatigue analysis: methods changed.

Appendix 6 Annex 5.F 6A: 4.3.3.4;

6H: 5.1c;

16A: 5.4.2.4

16C: 3.1.3

Experimental stress analysis: no

significant change.

6

New and Old Code Comparison

The new ASME Section VIII Division 2 has been reorganized but still has very similar methodology. The principal difference is that the new code uses von Mises equivalent stress, while the old code used stress intensity

Stress intensity is based on the Tresca, or maximum shear stress theory of failure. The stress intensity is defined as twice the maximum shear stress due to the combined stresses. When the stress intensity reaches the yield strength of the material, yielding is expected to occur.

Equivalent stress is based on the value of the distortion energy due to the combined stresses at a point. Distortion energy is the portion of the strain energy that results in a shape change of the material, not merely a volume change. Von Mises and others observed that failure in ductile materials can more accurately be predicted by comparing the distortion energy to a critical value where yielding will occur. The “equivalent stress” is a number that can be compared to the yield strength to predict yielding.

Equivalent stress is considered a more accurate predictor of failure than stress intensity for ductile materials. It is either equal or lower in value than the stress intensity, thus it is less conservative.

7

Design Stress (Sm or S) Comparison

Old Section VIII Division 2: New Section VIII Division 2: API 6A, 16A, 16C, 17D

Design stresses based on stress

intensity.

Design based on von Mises

equivalent stress

Design stresses based on

stress intensity.

Design stress or stress intensity = lower of:

1/3 ST ST /2.4 6A, 17D: 0.5 ST

(1.1* STRT)/3 6A, 17D: 0.5 STRT

2/3 SY SY /1.5 2/3 SY

2/3 SYRY SYRY /1.5 2/3 SYRY

RT = temperature derating factor for tensile strength

RY = temperature derating factor for yield strength

ST = minimum specified tensile strength

SY = minimum specified yield strength

8

Membrane stress limit at test pressure

Allowable general primary membrane equivalent stress or stress intensity

Old Div. 2 New Div. 2 6A, 17D 16A,

16C:

Reference AD-

151.1

Reference 4.1.6.2 4.3.3.2 5.4.2.2

Hydrostatic Test Pneumatic (gas)

Test

0.9 SY 0.95 SY 0.80 SY 0.83 SY 0.9 SY

Allowable primary membrane plus bending stress intensity = lower of:

1.35 SY 1.43 SY 1.20 SY NR NR

2.15 SY-1.2Pm 2.43 SY-1.5Pm 2.20 SY-1.5Pm NR NR

Pm = primary membrane stress

NR = no requirement

9

API Distortion Energy Theory method

API 6A, 16A, 16C and 17D allow design

based on the distortion energy theory, limiting

maximum von Mises equivalent stress to the

yield strength at test pressure.

This is the value at the highest-stress location

in the vessel wall.

Specs 6A and 17D exempt secondary and

peak stresses from this limit, however Specs

16A and 16C do not.

10

Wall thickness comparison

The following chart shows the ratio of required wall thickness to inside radius for several pressure ratings.

This comparison assumes that the new ASME Section VIII Division 2 is used with the same allowable equivalent stresses as the existing API rules specify for allowable stress intensities.

Test pressure is used as the controlling case with an 83% of yield strength as the limiting membrane stress intensity or equivalent stress.

As can be seen, the new Section VIII Division 2 Part 5 rules permit thinner walls than any of the other current methods for operating pressures of 10,000 psi and higher. The largest percentage difference is in the 20,000 psi rated equipment where a 7% reduction in wall thickness would be possible.

11

WP, psi Ptest, psi SY , ksi 6A, 17D

ASME

16A/C

ASME

API Dist.

energy

Old Div

2

New Div

2 Part 4

New Div

2 Part 5

Percent

thinner

2,000 4,000 60 0.084 0.077

0.063 0.084

0.084 0.073 -15.381

3,000 6,000 60 0.128 0.118

0.100 0.128

0.128 0.111 -11.262

5,000 7,500 60 0.163 0.1490.130 0.163

0.163 0.140 -7.904

10,000 15,000 60 0.355 0.3230.328 0.355

0.351 0.300 7.121

10,000 15,000 75 0.355 0.3230.237 0.274

0.272 0.233 1.657

15,000 22,500 75 0.441 0.4000.443 0.441

0.435 0.372 7.000

20,000 30,000 75 0.635 0.5710.804 0.635

0.6190.528

7.531

Wall thickness comparison

12

More about the previous table

The use of the von Mises equivalent stress instead of stress intensity is the reason for the difference between the “Old Div. 2” and “New Div. 2” columns.

The “API Distortion Energy” method is the alternative allowed by 6A, 16A and C, and 17D. This method permits the equivalent stress at the inside surface to reach the yield strength at test pressure. This method permits thinner walls at low pressures, even thinner than the new ASME rules.

The new ASME Code Section VIII Division 2 has two design sections. Part 4 is called “Design by Rules” and Part 5, “Design by Analysis.”

Part 4 of the new code contains rules for designing wall thickness for a variety of vessel shapes, reinforcement around outlets, flanges and clamps, and other common vessel configurations. The rules are relatively conservative compared to Part 5. The equation for minimum wall thickness is

where D is the inside diameter, P the pressure, S the allowable stress, and E the joint efficiency or casting quality factor.

Part 5 has rules for design by analysis, which can be by finite-element analysis or other means. Wall thickness in the above table is based on the general primary membrane equivalent stress in an infinitely long cylinder with full pressure end load. The data in the table above were calculated based on membrane equivalent stress in an infinite cylinder.

Specification 17D has special rules in Appendix E for the pressure design of mudline equipment. The method uses elastic analysis and equivalent stress, with higher allowable stresses than the methods shown above. All stresses are considered primary so no high secondary stresses are allowed. As an alternative, the ASME rules are also permitted.

13

Section VIII flange design by

rules (old & new)

Section VIII Division 2 design

by analysis (old & new)

API 6A, 16A, 16C, 17D

Lowest of:

ST / 5

STRT / 4

SY / 4

2 SYRY/3

SY / 3

SYRY/3

0.83 SY up to 250 ºF (121 ºC)

0.83 SYRY over 250 ºF

Example: ASTM A193 GR B7 @ room temperature

25,000 psi 35,000 psi 87,150 psi

Allowable Bolting Stress

14

More on bolting allowables

The API allowable stresses are much higher than allowed by any other comparable code.

API rules do require consideration of hydrostatic test loading, external loading, and thermal loads.

ASME does not require consideration of stresses at hydrostatic test conditions but does require consideration of external loading and thermal effects.

The API type 6BX flanges were originally designed using a maximum bolt stress of 0.5 SY at room temperature operating conditions, which is more conservative than the present API 6A rules.

15

Flange Design

An important consideration in acceptance of the new code is whether it would permit flanges to be weaker than the current rules.

The effect on Technical Reports 6AF, 6AF1, and 6AF2 which rate flanges with combinations of external load and temperature, should also be considered.

Traditionally the rules used for flange design are those of Appendix 2 of Section VIII Division 1. In addition, it was permitted by Section VIII Division 2 to design flanges using finite-element methods and the stress categories and limits imposed by Appendix 4. This latter methodology was used in the development of TRs 6AF, 6AF1, and 6AF2.

The new rules would permit higher external loading since the stresses are evaluated using the von Mises rather than the Tresca criterion. However, since the present ratings are more conservative than if they were revised, there is no compelling reason to update these publications.

16

Flange Design, cont.

Part 4.16 of the new code documents “Design by Rules” methodology for flanges.

These rules are updated from the old traditional flange design methods.

First, they consider external forces and moments using the “Equivalent Pressure” method of the M. W. Kellogg book, Design of Piping Systems.

Second, the equations for the various constants used in the calculations have been combined to eliminate calculating a number of C constants. The design curves of the old Appendix are not shown, forcing the analyst to work through all the algebra to come up with the constants.

Allowable stresses for the flange and hub are higher than before, but bolt stresses are limited to the same low values as Section VIII Division 1, i.e. 25,000 psi for B-7 studs.

17

Clamp Design

The new ASME Code has a section on clamp

design which is based on Appendix 24 of

Section VIII Division 1.

The author believes these rules are based on

the AWHEM method developed by Dr. Harry

Sweet, which was used to design the

Specification 16A clamp hubs.

18

Design by Analysis

The specific section of ASME Section VIII Division 2 referenced in Specs 6A, 6H, 16A, 16C, and 17D as a design method is Appendix 4 of the old edition. This is replaced by Section 5 in the new edition.

The new code, like the old, requires analysis to determine the amount of protection from four failure modes: plastic collapse, local failure, collapse from buckling, and failure from cyclic loading.

19

Plastic Collapse

For plastic collapse, analysis by linear elastic methods is not recommended for wall thicknesses thicker than R/4, where R is the inside radius.

Elastic analysis is not permitted when yielding occurs in 5% of the wall thickness or more.

For those cases elastic-plastic analysis is required.

This might rule out elastic analysis for most 10,000 psi and higher rated equipment, as well as many heavy-wall wellhead housings designed for lower pressures.

This is a much more stringent and costly requirement than the existing code.

20

Plastic collapse, cont.

When permitted, elastic analysis uses a “hopper diagram” similar to that of the old code. Only primary stresses are considered for the purpose of resisting plastic collapse.

When elastic analysis is not permitted, the next resort is limit analysis. This method involves finite-element analysis assuming an elastic – perfectly plastic material. Instead of the stress criteria for elastic analysis, the collapse load for the component is found, which must exceed the various loading combinations in Table 5.4.

The previous code also permitted limit load analysis, but simply required that the design load be no more than two-thirds of the collapse load.

If the component does not satisfy the limit load analysis criteria or shows weakening under load, then an elastic-plastic analysis is required.

21

Plastic collapse, cont.

The elastic-plastic analysis is used to find the collapse resistance of the component based on a representation of the material that includes work hardening after yield. This is the most accurate method of modeling. The component is analyzed with increased loading above the rating of the equipment, per Table 5.5, and if collapse does not occur the component is acceptable.

For elastic-plastic analysis, the previous code simply required that the rated load be no more than two-thirds of the collapse load. Again, a consideration of strain concentrations was also required for any fatigue analysis.

The new Code (Tables 5.3 – 5.5) specifies load combinations to be used for elastic, limit load, and elastic-plastic analysis. A difference is that in the consideration of earthquake, wind and other occasional loads, instead of multiplying the allowable stress by 1.10, the pressure used in the analysis is multiplied by 0.90 and the earthquake loads by 0.7. Thus, wind, snow and other occasional loads are considered at their full value.

22

Local failure

The concern related to local failure is the possibility of initiating a fracture. Two criteria are presented for this type of failure.

First, elastic analysis may be used as above, and in addition the stresses shall be checked to be sure that the sum of the principal stresses at any point is less than 4S, where S is the basic allowable membrane stress. This criterion is the same as the previous standard.

Alternatively, an elastic-plastic analysis may be run. In this case, the triaxial strain is compared to a limit which may be based on the material’s specified minimum elongation or reduction in area.

23

Buckling

For components loaded in compression,

buckling analysis is required.

This would apply to casing head housings and

subsea wellhead housings, where the tubular

loads put the housing wall in compression.

Requirements are given for elastic and

elastic-plastic analysis.

24

Cyclic Loading

The new code permits a design to be exempted from fatigue analysis based on successful experience with comparable equipment.

It also gives formal methods in part 5.5 for determining whether fatigue analysis is required.

Specifications 6A, 16A and 16C do not presently require fatigue analysis, although BOPs are routinely analyzed for fatigue by most major manufacturers due to the large number of full working pressure cycles they experience.

Since 6A equipment sees only mild cyclic service with declining pressure, fatigue is probably not an issue. An exception may be 6A valves that are used on BOP stacks.

Spec 17D mentions “fatigue consideration” for several components but does not specifically require fatigue analysis or provide cyclic service requirements. Spec 17D does reference ASME Section VIII Division 2 Appendix 5 as an acceptable method for fatigue analysis.

25

Comparison of fatigue analysis methods

For Appendix 5, the stress range for each type of cycle was calculated. For example, a connector might see make and break cycles, hydrostatic test cycles, operating pressure cycles, and wave action cycles. A limiting number of cycles is then found for each cycle type from the fatigue curves. The expected number of each type of cycle is divided by the limiting number to come up with a usage factor. The sum of the usage factors for all the cycle types then is limited to 1.0.

The new code has revised the methods of Appendix 5 to a more elaborate method of cycle counting which requires knowledge of the order of the various cycles. These methods are explained in Annex 5.B. Either elastic or elastic-plastic finite-element analysis can be used. In addition to fatigue failure, methods to assess stress ratcheting and progressive distortion are provided.

26

Section VIII Division 2 Part 4

The new Section VIII Division 2 has design methods divided into two major sections: Part 4 (Design by Rule) and Part 5 (Design by Analysis). The methods for flange design and clamp connection design mentioned above are in Part 4.

This revised Design by Rule section has many useful techniques that are applicable to valves and wellhead equipment, such as (besides flanges and clamps) cylindrical and spherical wall thicknesses, reinforcement of nozzle connections, design of flat covers and blind flanges, and many other features. The rules are generally conservative and simpler to use than the finite-element methods in Section 5. Previously API specifications referred only to Appendices 4 and 5 which correspond to Part 5 of the new Code.

However, in the author’s experience, the rules of Part 4 are equally important and the corresponding parts of the old code have been used extensively in design by manufacturers.

Consideration should be given to permitting the use of both Section 4 and 5, with appropriate adjustments to allowable stresses.

27

QC requirements in Section VIII Div 2

Charpy test requirements in the ASME code are more conservative than API. The required impact energy is determined by the type of alloy and wall thickness.

All materials are volumetrically inspected. Castings with thick walls are both radiographed and ultrasonically tested. Casting and forging surfaces are also MT or LP tested.

API, on the other hand, permits design calculations to be performed based on the assumption that all material is perfect, and then imposes various levels of NDE depending on the PSL, to identify and quantify defects.

The ASME QC requirements are similar to the API requirements for PSL 3 and 4 equipment.

28

Conclusions

The quality control requirements of PSL 3

approximate those of Section VIII Division 2

Current API rules permit a safety factor of

approximately 2, whereas the new Division 2

rules require a safety factor of 2.4 based on

tensile strength.

Use of the new methods would permit less

robust designs unless the allowable stress is

adjusted for the new methods.

29

Recommendations

Continue to permit the methods of the old ASME Code Section VII Division 2 (2004 and earlier).

Permit the new ASME Code Section VIII Division 2, Parts 4 and 5, with reduced allowable stresses compared to the current API allowable stresses for the ASME method, for all pressure containing equipment (bodies, bonnets, and OECs)

If one compares the wall thickness in the table on page 4 for Section VIII Division 2 Part 5 to the old Section VIII Division 2 wall thickness, you find about a 17% - 18% thicker wall in the old code. Therefore the use of the same allowable stress basis as is used by the new ASME Code, giving a safety factor of 2.4 vs. 2.0, is suggested for use of the new ASME Code, Parts 4 and 5.

The present limits in Specifications 16A and 16C for the maximum membrane equivalent

stress at test pressure (0.9 Sy) should be retained and adopted for 6A and 17D.

The present limits for bolt stress, 0.83 Sy at the highest load condition, should be retained in

lieu of the lower allowable values in the ASME Code.

The present limits for impact strength should be retained. The limits of Section VIII Division 2

2007 should be permitted by agreement. These limits are higher and vary according to wall

thickness.

ECS should form an ad hoc committee to coordinate the implementation of these new rules, and prevent unnecessary differences between specifications. In addition API should consider requiring consideration of actual in situ loading / life cycle analysis.

30

Spec 6A Recommendations

Combine subclauses 4.3.3.2 (ASME Method) and 4.3.3.6 (Non-standard materials design requirements) to be called the “Classical ASME Method”, and specifically reference Section VIII Division 2 – 2004. Keep the numbering of 4.3.3.2.

Subclause 4.3.3.4: (Experimental Stress Analysis) Change the reference from Appendix 6 to Annex 5.F.

Add a new subclause 4.3.3.6 “New ASME Method” as follows:

» The design methodology of the ASME Code, Section VIII Division 2 – 2007 may be employed as follows:

» The allowable stress S shall be determined using the rules of the 2007 ASME Code Section II Part D, Appendix 10.

» The methods of Part 4, Design by Rules, and Part 5, Design by Analysis, are permitted for all pressure containing equipment. For equipment rated 10,000 psi and higher it is strongly recommended that the user should consider specifying PSL 3 or higher.

» Maximum primary membrane equivalent stress is limited to 90% of the minimum specified yield strength of pressure containing equipment at hydrostatic test pressure.

31

Spec 16A Recommendations

Split subclause 5.4.2.2 into two subclauses:

5.4.2.2.1 – Classical ASME Method – include

the present subclause.

5.4.2.2.2 – New ASME Method – add the

material above for Spec 6A subclause 4.3.3.6.

Correct the reference in 5.4.2.4 (Experimental

Stress Analysis) as above.

32

Spec 16C Recommendations

As with Spec 16A, divide paragraph 3.1.1 into

two paragraphs:

3.1.1.1 – Classical ASME Method – include

the present material.

3.1.1.2 – New ASME Method – add the

material above for Spec 6A subclause 4.3.3.6.

Correct the reference in 3.1.3 (Experimental

Stress Analysis) as above.

33

Thank You

John H. Fowler, PE

On-Line Resources, P O Box 925393,

Houston TX 77292

Phone 713-688-0767

FAX 713-688-7610

E-mail – [email protected]

Web Page –

http://members.aol.com/OLREngineering

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