API-653 Appendix B has EVERYTHING you need to know about the flatness of a tank bottom. It has everything from edge settlement to localized bulges away from the shell. All acceptance criteria and calculations are given as well.
Thank you , I will ask for help from my NDT inspector because contractualy it only aplies API 650 for contruction, 653 is for repair, does it also aply for this case?
Does B.3.3 "Internal bottom settlements or bulges", is the one that aplies? in our case the bulge is manifested along the whole plate´s 20 feet, wich means the plates were not properly inspected before installing. Is B.3.3 the section that aplies? been B = 0.37R, again in our case the bulge has an R = 6/2 feet, so B=0.37*(6/2*12)= 13.32 inches, isn´t that too much!!!!!? maybe it will never happen... in our case the bulge is about 1 inch
Hi Bonswa
Well, our API inspector accepted my sugestion to use ASTM A 6/A 6M, and the constructor accepted it having to repair, this standard gives 29 mm for this 5/16"x 1800 mm sheet. The matter here was that the material was unaceptable, and ASTM was the spec for this
App. B of API-653 applies to localized settlement or bulges, not to general out-of-plane distortion as occurs in new tank bottoms.
ASTM A6 would apply to the plate before it is cut or welded. Additional distortion will be generated in processing the plate, and the A6 tolerances would not be applicable to a tank bottom after welding.
One of the tank standards includes a statement that out-of-plane weld distortion equal to 1% of the tank radius is not uncommon.
Usually tank bottoms will have some springy areas where they are not in uniform contact with the subgrade, and these are not objectionable.
