API steel tank erection

There is no need to to pour a concrete slap under the whole bottom of storage tank, only it is necessary to make a ringwall slap under the tank shell in accordance with API 650. Therefore, you can use any compacted sand under the whole bottom without a precise flatness.

For welding of bottom plates, it is permitted per API to use a lap joints. If you use butt joints, I prefer you install all plates with tack welding first, followed by completing the whole welds.

Thanks for your comment. In my case the tank bottom will elevated 4 m above the ground, so the whole round concrete slab is nessesary. The tank is only designed as per API : its designation is a settler with slow rotating mixer blades close to the bottom. It is clear for me that all bottom plates will tack welded and more- weigth of tack welded rolled plates of tank shell have to put on perimeter of the bottom, and all bottom plates will welded with root welds and just upper runs have to be as far as possible one from another. I need the advise about proved method of the welding runs sequence and orientation in order minimise bottom plates deviation from horizontal. I can't many time to cool each weld and minimum 2 welders will engaged simultanesly for bottom welding.

Do you have any methods to improvise in putting the bottom plates in place apart from using an air winch to pull in the plates?