Steel Tank Floor Repairs & Annular Ring 2

[jgorrz]

I inspected a 48-foot diameter steel tank and found severe pitting in the critical zone along approximately one-quarter of the tank. The addition of welded plate repairs is in progress. My question concerns what follow-up inspection procedures are required and whether or not a 24-hour hydrostatic test is needed. Original design plans for this tank are not available. The floor consists of overlapped welded steel plates. I could not detect the presence of an annular ring during the internal inspection, but there may be one beneath the floor. Is it likely that an annular ring exists below the floor or are all annular rings installed above the floor.

 

[IFRs]

Annular plates are typically part of the floor. They are neither above nor below. They replace the outer floor plates that have a radiused edge. The interior floor plates may lap on top of or underneath the annular plates, usually by 2" or so.

 

[JStephen]

Annular rings are primarily required for larger tanks, tanks with higher stressed shell (usually larger) or tanks in high seismic zones. If one of these does not apply, a tank of this size would not be built with an annular ring.