API item confused

[mech212]

In API 650 according to item 5.1.5.9 e , the fixed roof tanks require top angle of minimum sizes and this angle is a curb angle that is attached to both shell and roof , now item 5.9.3.1 say that when the angle is located 0.6 m below the top of shell , so we must put angle at the top , so I am confused between 5.1.5.9 e that says we must put a top curb angle and between 5.9.3.1 that says that if the angle is below the top by 0.6 m , how can it be below the top when item 5.1.5.9 says that it must be at the top ?

 

[JStephen]

Fixed roof tanks normally require a top angle, although that has been relaxed in the latest revisions. This specifically refers to fixed roof tanks.

Open top tanks require a wind girder. Per 5.9.1, the wind girder is "at or near the top of the top course". The reference in 5.9.3.1 (which is 5.9.3.2 in the latest edition) is saying that when the wind girder is more than 2' below the top of the shell, an angle is also required at the top. This is unrelated to the fixed-roof requirements.

 

[mech212]

Thank you for your answer , another question in fixed roofs we use the details of appendix F and calculate its area that must be same or greater than area in item 5.1.5.9 e , does this mean that if we use any detail that have top angle of the minimum thickness so we don't need to calculate the effective area ?