Basemetal with 'problem' properties like P22 or old, brittle oil tank material can be improved with "Buttering".
The P22 can be buttered with 625 or 309 and then PWHT'd. Then 300-series stainless can be welded to it without engendering more PWHT, that would damage the 300 s/s. You won't be welding to the P22, you will be welding to the butter.
To be able to add a large nozzle, or replace a door-sheet on a tank that was built with material that has known brittle-fracture properties, you "Butter" all the cut edges of tank with E7018 or some other very ductile weld material.