Roof Design - API-650 Tanks

[Tomtation]

In API-650 10th edition, article 3.10.2.3: "Roof plates of supported cone roofs shall not be attached to the supporting members". Question 1: Does anyone know the reason for this?
Question 2: Doesn't this exclude the use of external roof stiffeners?

 

[JStephen]

I think the general idea is to allow a roof failure without rupturing the shell or shell-to-bottom joint.

I believe this has been modified in the 11th edition, where such attachment can be made with customer's approval.

 

[vesselguy]

JStephen is correct on that.

API650 is a Standard, it is not a Code, therefore you don't follow it like the bible. Yes, you can have external stifferners on roof instead of a internal support structure. Do that a lot in copper mining projects where acid mists will corrode the internal roof rafters and hence we put the supports on the outside and welded them to the roof plates (obviously).

 

[JoeTank]

I disagree with vesselguy comment that API-650 does not have to be followed. When the state building code mandates use of NFPA-30 for flammable and combustible liquids, its a direct tie into API-650 and oither standards. These standards now take on weight of a Code. His cited example of use at non-petroleum site would be correct, but not so if it a petroleum product.

Joe Tank

 

[Tomtation]

I've been reading the interpretations on the API web site. From what I've read, I believe that a conical roof with stiffeners only (no girders and columns) is considered self-supported and therefore the stiffeners can be welded to the roof. Does anyone diagree with this?

To vesselguy, I'm aware that API-650 is a standard and not a code but contractual stipulations require me to follow API-650, and trying to get exceptions accepted is often a waste of time.

 

[JoeTank]

Tomtation... I concur with you about rafters welded to roof plate for a self-supported roof.

Joe Tank

 

[MJCronin]

Tomtom...

Consider posing on

http://www.ast-forum.com.

There are many interesting and active discussions on API-650 code interpretations.

-MJC