1. API Standard 6X: Design Calculations for Pressure-Containing Equipment
New Draft Standard under Subcommittee 6

2. Task Group Membership John Fowler – On-Line Resources - Chairman
Jim Britton – Cameron – 17D and 16C
Paul Bunch – Cameron – 16A and 17D
Jean Brunjes – GE – 6A
Bill Carbaugh – GE – 16A
Maynard Chance – West Engineering – All specs
Chris Johnson - NOV – 16A
Jim Kaculi – DrilQuip – 17D
Chris Kocurek – Cameron – 17D
John McCaskill - Expro – 16C
Nigel McKie – FMC – 17D
Mark Miser – DNV – All specs
Ramon San Pedro – Stress Engineering – all specs
Alireza Shirani – Cameron – All specs

3. History and Objective
API 6A, 16A, and 16C referenced the ASME Code Section VIII Division 2, 2004 Edition, Appendix 4.
Since referencing an obsolete spec is awkward, an Annex (Annex I) was prepared for 16A capturing the method from that ASME Appendix.
Subcommittee 6 proposed that the method be put in a separate document to assure uniformity.

4. Task Group Charge
Create a new API standard documenting the rules of the ASME Code, based on Annex I.
Problem: 16A and 6A used different allowable stresses.
Stress value
Spec 6A requirement
Spec 16A requirement
Max SI at test pressure
5/6 of Sy
90% of Sy
Sm for standard materials
2/3 of Sy
Sm for non-standard materials
Lower of 2/3 Sy or ½ Su
2/3 of Sy

5. Resolution
The task group consensus was to use the rules of 16A, since going to the slightly more conservative 6A rules would penalize 16A/16C users who had designed to higher allowable stresses.
The 90% of Sy used in 16A and 16C is the same as the limit in the 2004 ASME Code Section VIII Division 2
Using only the yield strength as a basis follows Section VIII Division 3 practice.

6. Changes to Annex I
Several revisions were made to the Annex I document to clarify the requirements, including several changes to the wording..
The uses of limit analysis and elastic/plastic analysis were clarified.
The requirement on the sum of the three principal stresses was clarified as to the calculation basis.

7. Status of the draft Standard
The TG finalized the draft and agreed it was ready for ballot.
API edited the document into standard API format and returned it to the TG for review.
After review the draft standard was be sent out for ballot by SC6, with an April 30 deadline.
SC 16 and SC 17 solicited comments from their member companies, which will be considered along with those from SC6 members.

8. Status of the ballot The ballot passed, with four negative votes.
Over 150 comments were made, which the TG has resolved.
A TG meeting was held May 14 and the negative voters were invited to attend.
Three of the negative voters agreed to withdraw their negatives, and the fourth was unable to attend.
Another TG meeting was held June 13, and all negative ballots have been resolved.

9. Revisions resulting from resolution of the ballot comments
Numerous editorial changes have been made, including moving material around to clarify requirements and follow the API Style Guide more closely.
An introduction was added to give background of the standard.
Definitions, abbreviations, and symbols were added, as well as equations showing requirements.
Stress components may be combined using vonMises equivalent stress (vs. stress intensity) if permitted by the product specification.

10. Revisions, cont.
Removed the note that if the material has a high yield/tensile ratio a lower Sm value may be used. This makes the Sm determination exactly like in 16A and 16C.
“Shall” substituted for more vague language several places to clarify that requirements are required.
Title changed to “Design Calculations for Pressure-containing Equipment.”
An “Extreme Conditions” paragraph will be added providing the “k” factor from ASME code.

11. Next Steps
After agreeing on disposition of all comments, the edited document and comment matrix are being returned to API. API can then, depending on the extent of the changes:
Accept the changes and publish the document
Recirculate the document for further comment
Re-ballot the document
Hopefully a new standard will be ready to be referenced by the new editions of 6A, 16A, and 16C.

12. Follow-on actions after publication of the new Standard
Specifications 6A, 16A and 16C should revise their design section to direct the designer to this new standard instead of the 2004 Code.
This may require several changes in the body of the specifications.
Since 17D refers to 6A for design requirements, no change is needed.
The 2004 ASME Code Section VIII Division 2 can be removed as a referenced standard, and Standard 6X added.