API 650 Approved Agenda Items

We have just posted a new version of ITSdesign in which we did some minor corrections. One of those was to add the test pressure (1.25P) to the liquid height instead of just P for hydrotest when F.7 calculations are required. We also increased the allowable anchor bolt diameter for some grades of material and added A1554-105. We also did some other minor corrections.

The big change is that we have added several approved agenda items from the API committee meetings to our program. You must have client approval to be able to use agenda items that have been approved but not published in an addendum. These are items that will be published in the next addendum. Several of these affect shop built tanks as we have approval to use the materials at DMT listed in Appendix A without the impact testing. We also can build a shop built tank out of material thicker than 1/2". The other big change is changes in the wind calculations in 5.11 and changes in the formulas in Appendix F. These changes will have an affect on whether anchorage of tanks is required for wind and for wind/pressure combinations.

What Seismic Factor to use for Anchor Chairs?

One of our clients brought up a disturbing point in API 650 Appendix E for Seismic designs. I have queried several engineers and reviewed this matter and am still confused as to how to apply this. The problem is as follows. In E.6.2.1.2 the last paragraph says that when you have a mechanically anchored tank, the anchor embedment or attachment to the foundation, the anchor attachment assembly and the attachment to the shell shall be designed for PA. It then defines PA as the lesser of the minimum yield strength of the anchor bolt multiplied by the as-built cross-sectional area of the anchor or THREE times PAB. PAB is given in equation E.6.2.1.2-2 and is the load on the bolt due to seismic. Now the problem. E.7 is Detailing Requirements and the paragraphs in E.7 apply when SDS>0.05g which happens to be any time seismic design is required. E.7.4 says that connections and attachments for anchorage and other lateral force resisting components shall be designed to develop the strength of the anchor or FOUR times the calculated element design load. Based on E.7.4 the value in E.6.2.1.2 should then be 4 and not 3. Until we can get a definitive answer from API on this issue, we have modified our ITSdesign software for Addendum 2 designs to use 4 instead of 3. For many tanks this will have no affect. However, for some tanks it will place an increased design load on your shell and could cause you to need higher chairs or thicker bottom shell plate. All comments on this issue are appreciated.