I have started reviewing a copy of the final draft of API-650 11th Edition Addendum 1. I have not seen a lot of major changes. I do see that they have corrected Appendix E and it appears that it is the same as Addendum 4 of the the 10th Edition including the errata. Other areas I will be reviewing as to the affect on designs are the definition of Pe, the definition of material thicknes in 5.3.5, changes to manholes and nozzles, changes in frangible roof designs, and a change in maximum rafter spacing. I will be reviewing these and will comment more after Addendum 1 is released by API.
I will also be attending the API committee meetings in New Orleans the middle of April. I will let you know if any important information comes out of that meeting.
We are continually updating, correcting, and adding to ITSdesign, our API-650 and AWWA D-100 design software. Changes to ITSdesign are automatically received by our users the next time they start ITSdesign on their computer. All updates are automatically downloaded from our internet site.
Wednesday, March 5, 2008
In API-650 11th Edition Appendix R, there is a factor of 0.40Pe (external pressure) or 0.40Pi (internal pressure) added to various loading conditions. This same factor is used when determining anchor bolt loads on anchored tanks due to wind or seismic. However, there is also a note that says that if the operating pressure divided by the design pressure is greater than 0.40, the purchaser should consider using a higher value than the 0.40. How many times do we see a operating pressure but no specified design pressure? Many times the purchaser only knows the pressure he wants for operating and specifies that as the design as well. If you just plug these values into the formulas given then you will be designing a tank for less than what the operating conditions will be. We probably do not want to increase the design pressure to 2 1/2 times the operating pressure if the purchaser has not specified this condition as this will greatly increase the thicknesses or cause a requirement for anchorage or stiffeners. However, care then needs to be taken to address these other conditions to make sure we are providing an adequate design. Towards this end, our ITSdesign software now incorporates a check for the ratio of the operating to the design pressure, flags this condition, and provides the option to increase the factor beyond the 0.40 value as needed.