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"Fish mouth" on top of oil storage?

"Fish mouth" on top of oil storage?

"Fish mouth" on top of oil storage?


Hi Eng-Tips!

I´m working with new design of a vertical oil storage steel tank (3000m3) roof. The roof of the tank is fixed to the shell on top. I´m looking for something called a “fish mouth” on the roof. It is the weakest point of the roof. If an explosion inside the tank occurs, the weakest point “fish mouth” will open the roof first, instead of the whole roof will blow away from the tank! Do you know where to find more information about a “fish mouth” design?

Kind regards

RE: "Fish mouth" on top of oil storage?

Is it similar to to the "emergency roof vent / manway cover"?

RE: "Fish mouth" on top of oil storage?

Never heard of such a thing.

3000m3 is a decent size and if you're worried about an explosion then use a frangible roof.

No pressure relief device is going to be fast enough to prevent damage if its just a small hole.

Why are you trying to design a tank and not just use an established code such as API 650?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: "Fish mouth" on top of oil storage?


You seem to be talking about something called a "frangible roof design" (FRD) which is mentioned in API-650 and several other references.

Yes, failure of the roof to shell joint becomes important under fire or emergency conditions. ...But there is a lot more to the story

There have been several threads on the Storage Tank forum and other places dealing with this type of design.

Some things you should know are:

- As per API-650, its not suitable for smaller diameter tanks (What is the diameter of your tank and what, specifically is being stored ?

- Robust tank anchorage design and bolt sizing is also very important

- FRD is an older method of shell protection; Insurance companies like to see properly sized emergency vents on the tank

- FRD is also discussed in Storage Tank Design Code EN 14015; Appendix K,

Research Article here: https://www.osti.gov/biblio/379775-evaluation-desi...

Also see this discussion: https://www.eng-tips.com/viewthread.cfm?qid=394841

Give us more details about your particular tank design ... Can you post a drawing or sketch ?

Are you a new hire and is this the first storage tank that you have been assigned ?

What is the Code of Record for this tank ?... Where will the tank be located ?

I have never heard of this design called a "fish mouth"

Sr. Process Engineer

RE: "Fish mouth" on top of oil storage?

Suggest that you repost in the "Storage Tank Engineering" forum ....

Sr. Process Engineer

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