You don't say how thick the shell is, what grade of material, where, how deep and widespread the corrosion is, if yo are near existing butt seams, corner welds, penetration welds or PWHT assemblies. These are important data for the decision process.
You may be better off removing the shell plate and butt welding in patch plates. You may be better of using lap patches. Weld buildup and grinding may be appropriate also.
You plan should include NDE, perhaps both before and after the repairs.
Possible NDE to consider, depending on shell information and repair method: UT prior to repair looking for internal laminations and other plate flaws and MT looking for surface cracks that may propagate during repairs. MT completed welds.
