Bottom distortion 2

[ll23]

Hello Group is there any reject criteria for Bottom distortion in API 650 Storage Tank, we are working with 8 mm thick plate, using a SAW process, we are actually correcting the more visible buckle in bottom, but if there are is any measurement that i could apply for detecting these deformations

 

[chicopee]

Shine a flash light beam across the floor of the tank and you will see the undulations.

 

[LittleInch]

You can always try the famous "Fat Guy Test". See

http://www.eng-tips.com/viewthread.cfm?qid=352287

Some flexing is nearly inevitable due to only welding from one side and the size of plates used. Whether it's significant is the question.

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

 

[ll23]

First excuse me for not respond at time, second thanks a lot for the tips, I was talking with our construction department, because our client says that is zero tolerance for bumps in a API 650 storage tanks, I really don't know where is it says that, the only paragraph that comments something is "7.2.2.1 After the bottom plates are laid out and tacked, they shall be joined by welding the joints in a sequence that the Manufacturer has found to result in the least distortion from shrinkage and thus to provide as nearly as possible a plane surface." I think that can be some bumps in the bottom, but we are working to provide a flatter bottom, cutting the plates that are more affected.

 

[LittleInch]

Recently I saw a tank bottom being welded with several large concrete blocks in line either side of the floor weld to reduce plate lifting during welding. Rest of the floorlooked very flat, it was a cryogenic task so needed a flat floor to sit on the insulation.

Normally you don't really need a super flat floor.

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

 

[ll23]

Thank´s LitleInch

 

[IFRs]

API 650 is for fully supported flat or slightly coned bottoms. The plate is not normally stressed during operation and is not really part of the pressure boundary. When the tank is filled, the bottom plates take the shape of the foundation under them with no ill effect. Typical distortion is of zero consequence and cosmetic only, not worth trying to fix. Sometimes plate from coil has residual stresses that are not removed during the de-coiling process and manifest themselves as buckles after welding. A temper pass can eliminate much of this and is standard for most modern suppliers. Unless your distortion is in the critical zone near the tank shell, or is extreme, I'd leave it alone. My opinion only, and not having seen the actual steel could be inappropriate for your particular conditions.

 

[ll23]

IFRs thanks, that's exactly my point, the distortions were formed in welded sections that were flat, and now are bumped that is caused by the heat of day; we are working in without roof in a very hot enviroment; Actually we are closing the remaining sections of the bottom providing dead weights near the weld pad and we are obtaining good results.