An interesting thing has occurred with the design in API-650 11th Edition Addendum 1 with regard to Appendix F. With the changes, the design is now based on the yield strength of the material. When you look at the formula for P, the internal pressure, you will see that you have AFy which is the area times the yield strength. At first glance you would think that this will help you when you high strength materials. And in reality it does IF the shell, roof, and compression ring are all high strength material. However, if the shell and roof are high strength material and the compression ring is A36 material, then you have the same pressure as before. The yield strength, Fy, in the formula is based on the lowest yield strength of the compression area. Therefore, if the compression ring is the lowest yield strength, then that is the value you use.
An interesting thing occurs when you start looking at the area, A. The amount of area available in the shell and the roof have not changed. Those formulas are not based on the yield strength of the material. What did change is that the amount of area in the horizontal projection of the compression ring is based on the yield strength of the compression ring when the horizontal leg is not stiffened. In the previous editions this value was 16t. Now (in US units) it is the thickness of the material times 3000/(Fy)^0.5. Here is a list of what happens to the horizontal projection allowed (Le) for a thickness of 1/4".
16t = 4"
A36 material (Fy = 36000 psi) = 3.95"
A678A material (Fy = 50000 psi) = 3.35"
A240-304L SS (Fy = 25000 psi) = 4.74"
As you can see, the higher the yield strength of the compression ring, the smaller Le can be which reduces the area, A. Thus, if you used a high strength steel for the compression ring and the shell but used a low strength steel for the roof you will end up with a lower allowed internal pressure because the compression ring will not contribute as much area and the yield strength of the roof will be the governing value for Fy in the pressure formula.
If you really want to scratch your head about something, think about this. I could build a tank using a material with a yield strength of 50000 psi for the shell, roof, and compression ring and have it meet the frangibility requirements of 5.10.2.6. However, that same tank with the same thicknesses using a material with a yield strength of 36000 psi for the shell, roof, and compression ring would not necessarily meet the frangibility requirements of 5.10.2.6 (area of the compression area could be greater for the lower strength material).
Friday, June 12, 2009
Thursday, May 28, 2009
API Committee Meeting
There was a lot of discussion going on at the API Committee Meetings held the end of April. Some of it had to do with floating roofs and some with the wind loadings especially on uplift on the roof. Neither has been resolved and both are on going discussions. They are working on doing some testing for the wind uplift situation to try to resolve the conflicts.
With regard to API-650, the following agenda items were approved for publication.
1) Added shell nozzles in pipe sizes 50", 52", 54", and 60".
2) Added long welding neck flanges and lap joint flanges as acceptable flanges.
3) Revised some dimensions of flush cleanouts.
4) Revised the anchored and unanchored tank calculations in 5.11.2 and 5.11.3 to include a pressure combination factor applied to the internal pressure portion. Also added this factor and revised appropriate equations in Appendix R.
5) Deleted the joint efficiency requirements in the equations in Appendix V.
6) Changed the required dome roof depth in Appendix J to be a "Minimum" depth instead of a "Maximum" depth.
7) Revised Appendix J material reference to read that the material requirements of Appendix A apply as long as the material is 1/2" or less in thickness instead of requiring the material to meet Section 4 requirements.
8) Revised Appendix J to allow thicknesses greater than 1/2" as long as the material requirements of Section 4 are met.
It was also brought up that in some cases the formulas in Appendix P.3 for the curves did not calculate out to the same as values plotted on the curves. After a lot of discussion it was decided to temporarily remove P.3 from the standard until the discrepency can be corrected either in modification of the curves or modification of the formulas.
With regard to upcoming addendums, we were informed that the next addendum for API-650 will be issued sometime this fall and will include all items approved for publication prior to the April meeting. The items approved at the April meeting as well as the next two meetings will be published in the addendum that will be issued in the fall of 2010.
We still have many items being worked on for the next meeting. If you have some items you feel need to be addressed by the committee you can address them to API or let me know and I will see if I can get them addressed at the next meeting.
With regard to API-650, the following agenda items were approved for publication.
1) Added shell nozzles in pipe sizes 50", 52", 54", and 60".
2) Added long welding neck flanges and lap joint flanges as acceptable flanges.
3) Revised some dimensions of flush cleanouts.
4) Revised the anchored and unanchored tank calculations in 5.11.2 and 5.11.3 to include a pressure combination factor applied to the internal pressure portion. Also added this factor and revised appropriate equations in Appendix R.
5) Deleted the joint efficiency requirements in the equations in Appendix V.
6) Changed the required dome roof depth in Appendix J to be a "Minimum" depth instead of a "Maximum" depth.
7) Revised Appendix J material reference to read that the material requirements of Appendix A apply as long as the material is 1/2" or less in thickness instead of requiring the material to meet Section 4 requirements.
8) Revised Appendix J to allow thicknesses greater than 1/2" as long as the material requirements of Section 4 are met.
It was also brought up that in some cases the formulas in Appendix P.3 for the curves did not calculate out to the same as values plotted on the curves. After a lot of discussion it was decided to temporarily remove P.3 from the standard until the discrepency can be corrected either in modification of the curves or modification of the formulas.
With regard to upcoming addendums, we were informed that the next addendum for API-650 will be issued sometime this fall and will include all items approved for publication prior to the April meeting. The items approved at the April meeting as well as the next two meetings will be published in the addendum that will be issued in the fall of 2010.
We still have many items being worked on for the next meeting. If you have some items you feel need to be addressed by the committee you can address them to API or let me know and I will see if I can get them addressed at the next meeting.
Wednesday, May 20, 2009
API-650 11th Edition Addendum 1
It is now released! We have just released the revisions to ITSdesign to bring it into conformance with API-650 11th Edition Addendum 1. We have added a button so you can select whether you wish to use the 11th Edition or whether you wish to include Addendum 1. For Addendum 1 we have made changes to the Appendix F calculations as it now requires the use of yield strength of the material in the calculations. There are also changes to Appendix E to take care of adding a internal pressure factor in the calculation of J and changes in the calculation of annular rings. From the base code we have revised the check for maximum spacing of both inner and outer rafters, revised the check for minimum thicknesses in many places, and revised wind calculations. We have also added the requirements for duplex stainless per Appendix X. We will continue to add functions the ITSdesign program and will keep in conformance with the latest addendums.
Wednesday, April 8, 2009
Table 5-21a
It has been pointed out to me that I have an error in my previous blog concerning this subject. In it I stated that the multiplying factor 0.785 was left out. However, this factor should be 785. I double checked our ITSdesign software to confirm that we are using 785 and not 0.785. We are using the 785 factor. I will bring this up at the next API meeting to make sure this is corrected in the code.
Tuesday, April 7, 2009
ITSdesign Webinars Coming to Your Computer
Have you wanted to see how our ITSdesign software program before you downloaded your trial version? Have you wanted to have someone walk you through the ITSdesign program to show you how the various screens work? Would you like a live demonstration of the ITSdesign program? We will be starting to do live webinar demonstrations of our ITSdesign software. Right now we are setting up dates and times for these demonstrations. Within the next couple of weeks you will be seeing postings here on our blog giving dates and times we will be doing these webinars. The number of participants for each webinar will be limited and will be given out on a first come first serve basis. Check back to see when they will be held and how to sign up for one.
Thursday, April 2, 2009
Question on Table 5-21a
A question was asked concerning the formulas in Table 5-21a which is the Uplift Loads for SI units. The pressure formulas even in Addendum 1 to the 11th Edition have left out the multiplying factor 0.785 which is pi/4. Agenda item 650-646 revises the formula to include this multiplier. It also is revising the formulas in many other ways. ITSdesign uses the formulas approved in Agenda item 650-646. This was not approved soon enough to be part of Addendum 1 but should be part of the Addendum 2. I am not sure why this was not caught before Addendum 1 was published.
ITSdesign for 64 Bit Operating Systems
The PC computer industry is changing from 32 bit operating systems to 64 bit operating sytems. When the industry went from Windows98 to Windows XP operting systems we found that we had to modify our software to work on either operating system. The 64 bit operating system has been around for a while. However, it is just now that this operating system is becoming the standard rather than the exception. In looking at the computers available in retail stores, there are some 32 bit systems. However, there are an increasing number of 64 bit systems. In keeping with this trend, we have modified our ITSdesign software to work on not only Windows98 and Windows XP (32 bit) systems but also with the 64 bit systems. We have verified that ITSdesign will now operating on both the Windows XP 64 and the Windows Vista 64 operating systems. You can be confident that if you upgrade your computer to the 64 bit systems you will still be able to run our ITSdesign software. If you have not tried ITSdesign, go to our website at www.innovativetanksolution.com and download a trial copy.
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