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Doorsheet Reinforcement

Tuesday, January 17, 2017   By: JES [1841] 0 Stars
Is there a rule of thumb re: width of doorsheet opening in a tank vs. tank diameter. I would expect that first shell course thickness will increase with tank diameter and, subsequently, the width of a doorsheet not requiring reinforcement.

Can anyone comment on this?
What analysis procedure would one use to evaluate likelihood of shell buckling?

Thanks.

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Tuesday, January 17, 2017   By: ITS [1678] 2 Stars
Well, there is no escaping the reinforcement of an opening 2 inches or greater. A door sheet is of course much larger. Regardless of the shell course, a large opening will weaken the area around the opening and would be evident in a 45 degree ripple, so it needs to be stiffened.

On the buckling issue of the shell I would refer to API Bulletin 2U, which I think was last updated in 2004. The root or basis of this rule of thumb on buckling stress is based on one-third or 1/3 of yield stress which means anything over that is fair game to a wrinkle or buckle in the shell.

Hope other have more insight...

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Wednesday, January 18, 2017   By: DavidR@fast.net [39] 5 Stars
It may be worth noting that during construction, it is fairly common to leave out a two-ring doorsheet for crane access especially or larger tanks or where site access around the tank is limited. The crane is used from the inside to pick and place upper ring steel and stays there for most of the cone roof structure. At or near the end of the job the crane moves out and those two shell plates are installed. These openings are often not braced and do not hinder the erector from maintaining API tolerances on the tank construction.

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Thursday, January 19, 2017   By: Tankee [235] 4 Stars
I have done it, and seen it performed with or without stiffening. I prefer stiffening, but the end result is the weld sequencing and keyplate usage and knowing how to use them during welding the doorsheet back in. As usual, knowledge and experience is key when welding doorsheets into place.

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