attachment of external structures 1

[precisionengineer]

I am working on a project where a significant amount of seperate structural steel (independantly supported) catwalks/beams and cantilevered - has been "hard" attached to several new tanks on this project( I have never seen this done). I cannot find reference to whether this is allowed or not per API 650. Thoughts?

 

[JStephen]

I was thinking API-650 had a requirement that this not be done- will have to check when I get to the office. Usually a bridge between tanks will be fixed on one end and slide on the other.

If the tanks settle at different speeds/ angles, it will load the steel (and the tanks) in unanticipated ways.

If one tank blows up or ruptures, it could damage the adjacent tank through the steel.

 

[precisionengineer]

Thank you for your response.... will be most interested in learning what you find with reference to code. I have never seen this done, but came into this project well into the building phase and came across this issue by total accident. I have raised a flag within this company...

To continue the thought further - if the tank bulges due to "pruduct fill", this puts additional stresses on the points of contact on the steel which I believe will/may cause tank shell failure at said point (1/4" wall thickness).

 

[JoeTank]

API-650 requires that the purchaser specify the magnitude of loads applied to the shell. It further states that the loads should be distributed into the shell by structural members... typically in a horizontal orientation, rolled to the tank radius. The method of aanalysis and design is not addressed, so it becomes a matter of agreement between the parties. This is an area for which there are few references in open literature. It's usually an experienced-based design method developed by the tank building firms. And, they don't share that stuff!

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[JStephen]

Paragraph 12 in Table 3-17 of API-650:
"A tank runway that extends from one part of a tank to any part of an adjacent tank, to the ground, or to another structure shall be supported so that free relative movement of the structures joined by the runway is permitted. This may be accomplished by firm attachment of the runway to one tank and the use of a slip joint at the point of contact between the runway and the other tank. (This method permits either tank to settle or be disrupted by an explosion without the other tank being endangered."