A dent, a cut or a patch of corrosion found at a visual inspection doesn’t retire a cylinder by itself, but every kind of defect has a limit. Most limits depend on the outside diameter or the minimum design wall thickness, so the same 0.5 mm pit can pass on one cylinder and fail on another.
Pick the standard (ISO-18119, or CGA C-6 and C-6.1 for US steel and aluminium cylinders), pick the defect and enter what you measured. The calculator shows pass or fail for each rule, the limit, and how much margin is left or by how much the defect is over.