API 650 Frangible Roof Hydro Test

[mattjl1980]

We're building a 95' ID fixed frangible roof MDI tank with a nitrogen blanket. The shell is 32' high and the design liquid level is 31'. When reading 7.3.7.1 it gives you the option of either vacuum testing the roof plates and the remaining 1' of vert or filling the tank with air and snooping unless you are building a frangible roof.

My question is when using the Decision Tree in annex F if I fall in the basic design does this exempt me from having to fill the void with air and snooping? I would rather vacuum box the roof and shell.

Thanks in advance!


7.3.7.1 Upon completion, the roof of a tank designed to be gas-tight (except for roofs designed under 7.3.7.2, F.4.4, and F.7.6) shall be tested by one of the following methods.
a) Applying internal air pressure not exceeding the weight of the roof plates and applying to the weld joints a bubble
solution or other material suitable for the detection of leaks.
b) Vacuum testing the weld joints in accordance with 8.6 to detect any leaks.

 

[JStephen]

I'm not sure where the issue is. The wording in 7.3.7.1 doesn't mention frangibility or lack thereof that I see, nor does the decision tree in Appendix F. "Unless you are building a frangible roof" isn't in there.