tank bottom repair

[bhart192]

API 653 fig 9.6 note 3 , limits lap floor patch plates to a maximum of 24" in length measured along the shell in the critical zone, we have a small 26 dia. * 24 ft high AST with shell corrosion at the shell to floor joint along the entire perimeter , if the interior of the floor is ok can we install lap plates along the entire perimeter or does Note 3 prevent that . we will be replacing up to 12" of the 1st ring shell .

 

[IFRs]

I think you are looking at figure 9.13 which shows "Typical Welded-on Patch Plates on Tank Bottom Plates", not figure 9.6. This limits the size of a patch plate that is butted to the shell and does not extend through the shell. Your repair will include plates that extend through the shell and therefore are not limited in size. It is not that uncommon to replace the entire outer portion of a bottom, using lap- or butt- welded annular or sketch plates.

 

[bimr]

Yes, that is a common repair.