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Frangible Joint

Thursday, December 07, 2017   By: Roberto [1892] 0 Stars
Dear Srs.,

Lets say I have a project with the following characteristics:

1 - 5 equal lined tanks with diameters of 16.3 meters and 26.4 meters in height.

2 - Type of roof = Dome Self-Supported Radius = 0,8 D

3 - Roof Thickness = 3/8 9,5 mm

4 - The tanks are connected at the top by a platform structure.

5 - All the tanks with internal floating roofs

6 - The tanks were designed with 0,8D dome roof with 3/8 thickness to adequately withstand the self-weigth and weights of the platform structure / internal floating roof.


a Is frangible joint roof mandatory?

b Is it possible to design a frangible roof considering the project above?

c One way to obtain a frangible joint is when the roof plates are welded to the compression ring with a 3mm seal weld only, and when the roof plates are not fixed to any roof supporting structure. Considering the project above, the roof thickness is 9,5 mm and AWS recommends a minimum weld size of 3/16 4,8mm and also there is the platform structure which stiffens the roof. Then we conclude that considering a 3mm weld wont be effective, right?

Thank you.


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Friday, December 08, 2017   By: DavidR@Fast.net [39] 5 Stars
As noted on the other online forum where you posed the same question, if they are API 650 Annex H internal floating roof tanks, unless you are inerting the space above the floating roof, the tanks will have circulation vents and therefore do not need fragible joints or emergency vents.

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Monday, December 11, 2017   By: Roberto [1892] 0 Stars
What about Ballooning effect due an internal explosion?

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Friday, December 08, 2017   By: ITS [1678] 4 Stars
Frangible joints were never intended for the application you mention.

I also do not see the how the AWS applies, maybe i am old school in design.

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Monday, December 11, 2017   By: Roberto [1892] 0 Stars
If they are API 650 Annex H tanks they have circulation vents and do not need fragible joints..

Is there any reference standard, guide, etc that corroborates the above statement?

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Monday, December 11, 2017   By: BABRTs 973 [53] 5 Stars
Due to the venting, there will not be a accumulation of vapors which could result in the need for a frangible joint.

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Monday, December 11, 2017   By: Roberto [1892] 0 Stars
What about Ballooning effect due to an internal explosion?

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Wednesday, December 13, 2017   By: DavidR@Fast.net [39] 5 Stars
The open area of the circulation vents is far greater than that needed for emergency venting - try running the calculations to see for yourself?

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Published on ast-forum.com


Atmospheric Design Pressure
By: Fathi [46]

The whole story is to avoid brittle fracture=

Test temperature shall be equal or warmer than Minimum Metal Design temperature at Test pressure.

I would limit my minimum testing temperature for a tank (or even for a vessel or a piping system) by the =

Temp = maximum of [ Min(lower shell) , Min(shell# 2) ....Min (Upper shell) ]

For a Shell# i the minimum is function ( of shell tickness , Material group ) and this can be found in API 650 , Fig 2-1

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