Tuesday, January 18, 2011
Frangible roof design of anchored tanks
At the API committee meeting in November I brought up the subject of the frangible roof design requirements. In particular I asked about the requirement if 220.127.116.11.d which says "For anchored tanks of any diameter, the tank shall meet the requirements of 18.104.22.168.a and the anchorage and counterweight shall be designed for 3 times the failure pressure calculated by F.6 as specified in 5.12." One of the requirements is in 22.214.171.124.a.5 which gives the maximum area of the compression ring that you can have and still be considered frangible. I asked if this requirement can be removed when the tank is anchored since we have to design the anchorage for 3 times the failure pressure which is based on the actual area of the compression area. After some discussion the committee as a group decided that you still must meet the area requirement of 126.96.36.199.a.5. What this means is that for smaller diameter tanks meeting the frangibility requirements is very difficult. For shop built tanks built to Appendix J meeting the frangibility requirements is next to impossible.