Thursday, December 13, 2012

API 650 12th Edition

The proof pages have been issued for review to the committee members for API 650 12th Edition.  This edition will be released later this spring and covers items approved by the committee.  There are some 27 agenda items that are being included in this edition.  It does not include items that were approved in the last couple of committee meetings.  We will be working on the changes to our ITSdesign software to include the changes that are coming.

Monday, December 10, 2012

Annular Ring Thickness Calculations

The following questions was posed to us:

1 - Current edition of section 5.5.3 of API-650 requires us to select the larger of
a) product design thickness plus corrosion allowance or
b) hydrotest thickness

2 - Note b to Table 5.1a requires us to use the larger of

a) product design stress or

b) hydrotest stress

in selecting the column to look at.

For a tank with
corrosion allowance = 1 mm  

bottom shell course thickness = 45 mm,
product design stress for bottom shell course = 220 MPa

hydrotest stress for bottom shell course = 240 MPa  :

item 2 above requires us to use the column for 240 MPa

bottom shell course thickness of 45 mm requires us to use the fifth line of Table 5.1a.

We end up with the 19 mm from among the tabulated values.

item 1 above requires us to use the larger of
a) 19 + 1 = 20 mm

b) 19 mm

If we could use the column for 220 MPa for the design conditions, then we would be comparing the value for design thickness as  a) 16 + 1 with the same b) 19 mm for the hydrotest condition.

With the way it currently reads we always end up having to add the corrosion allowance to the hydrotest thickness calculated.

Our response:

In reviewing the way 5.5.3 reads you are correct.  Since it specifies that you use the higher of the two stresses in determining which column you use and then must use the thickness shown plus corrosion allowance for the design condition, you will always be using the higher required thickness and then adding the corrosion allowance to that.  It would seem that we should be using the column that corresponds to the stress in the shell for whichever condition we are evaluating and use the whichever thickness is greater.  Since this is not how the standard currently reads, I have submitted an inquiry to the API committee for review.  It will take time to get a response and even longer if they decide to address the issue and make a change in the standard.

Monday, November 12, 2012

What questions do you have?

I have decided to do a question/answer for my blog. I would like you to email me a question you have about the API-650 standard that you would like answered on this blog.  Please ask one question per email.  Send your question directly to me at

In addition I will try to keep you up to date as to what is happening with the standard.  I am currently getting ready for the next API standards meeting and will post a brief update as I get information.