frangible area has to be more than F.5.1 area

[inammanj123]

hi

I am working on an API 650 tank with following parameters:

dia: 15.5 m, height: 11 m, Internal pressure: 5.6 kPa

The client is asking for frangible roof, but this is not possible because

i) minimum area required as per F.5.1 is coming out to be greater than frangible area as per 5.10.2.6.a.5

As per my understanding for roof to be frangible roof-shell compression area has to be less than frangible area of section 5 but at the same time area has to be more than area of F.5.1. So for frangible roof Internal pressure has to be less enough so that F.5.1 area is less than frangible area of section 5.

Secondly this is what exactly my client data sheet says along with roof to be frangible: "shell to bottom seam to 2-3 times greater than shell to roof joint e.g EN 14015"

Please can any one tell who can i calculate shell-bottom. Can i use arrendix v method.In apeendix v it calculates Xshell and Xbottom. But this area comes out to be very small.
In my opinon this is not possible in case of non frangible roof.


Thanks and Regards,
Inam

 

[fegenbush]

In your case, a frangible joint is not possible.

For small diameter tanks (15.5m diameter is small), it is often not possible to have a frangible roof joint for exactly the reasons you specify. A similar problem occurs for tanks designed for internal pressure.

The solution is to provide emergency venting in accordance with API 2000. Frequently, these are purchased products from vendors with known venting curves.

 

[Duwe6]

[what fegenbush said] Not possible to make a welded, frangible roof on small tanks. Period. I have thought about leaving 1-1½m unwelded on roof-to-compression ring seam, and just close it with caulk. But at the end of the day, Emergency Venting is just too easy and cheap. You install it in the roof manway, which API recommends to be 20" or larger. It gives lots of venting area for not a lot of money, and keeps the tank sealed tight at normal [low, breathing] pressures.