Hello everyone, I have included some images of how fitup tabs can be used to help with the fabrication of a tank. This example is a "scaled down" version of larger types of this sort of design. The tabs that you see are sheared with a taper on one edge to help with line-up and rounding of the bottom rolled section.Typically the circle representing the inner diameter of the tank would be scribed or otherwise marked on the bottom plate and the lineup tabs would be located along this line on the inside of the circle. The tabs on the other rolled sections are used to help with the initial fitup of the section to section pieces and then the fabricator/fitter would likely have to utilize wedges/dogs, keyplates(this term and tool courtesy of other forum members), or similar types of hi-low adjustment fitting tools. This tab arrangement can be used on numerous other applications as well as the one that I have shown here.
     For example: if you were stacking plates vertically for a particular application and wanted to be able to fit them edge to edge, you could put tabs on both sides of the lower plate at various locations along the seam, thus allowing for an initial alignment and support of this seam while tacking it together. Hope this makes sense and also hope others might chime in here with further examples and pictures if possible. Best regards, Allan