OK then, gussets are a poor solution for higher pressure tanks with external nozzles proturding from the tank - even those with modest external load on the nozzle.
Flip the problem around: I have a (30 plus year old) horizontal lube oil reservoir at essentially atmospheric pressure. 10 ft diameter, 30 feet long with F&D ends. Plain steel - 7/16 wall thickness.
Client has a main AC lube oil inside (suction is 3 ft above the bottom) and a backup DC lube oil pump with its suction about 16 inches above the bottom.
His shutdown AC pump is outside the tank on the pit floor, with its suction directly into the bottom of the tank. If there is a pipe break outside the tank, obviously all of the tank oil could leak out and he loses all LO pressure, because even the DC pump can't take a suction if the tank is dry.
So - can he extend the outside shutdown pump suction up into the tank by 42 inches, using gussets to reinforce the 42" stub inside the tank to prevent vibration and fatigue cracking? I would use a pad at the tank inlet itself. (There are welding, safety, access and cleanliness issues of welding inside an empty lube oil tnk, but they are straightforward relatively easily solved.)
A 42" inch stub into the tank would life his shutdown AC pump suction high above the "reserve pool" of oil inside the tank, so the DC pump could keep oil to his bearing as the plant shuts and cools down as the hypothectical original oil leak is fixed leak.
