Hi John, Since Ariel Oil Tanks are probably all made the same way....I split my 1946 VB600 oil tank to cure some bad internal rust and dig out accumulated and hardened grud in the bottom that would not shift shaking with nuts and bolts and kero/diesel or with a sharpened rod down through the filler hole.
Carefully grinding with a disk grinder around the top of the welded seam allowed the tank to easily come apart and still leave plenty of lip metal for eventually re-welding. Once I had the internals sorted I took the tank to a specialist welding shop ( as I don't have any tig or mig welding gear ).
Using a skilled person resulted in a nice "puddled" seam just like when the tank was new.
Also after welding, bung up the bottom holes and fill with some Kero and leave it standing for a few days to make sure there are no pin hole leaks.
Mine had to have one re-welded.
1946 VB600 rigid Tele
1933 Austin 10
2008 Fraser Clubman (like lotus 7 only better )