Yes it is mandatory to resist these we have to restist % of oxygen during welding .
Reason is this there is a chances of formation of oxide on weld and adjascent area heat sinks marks found with defferent colour which highlights a depletion of corrosive property.
By pickling passivation its help to reform that llayer and safe material and weld.
Its shouod be general practise no need to mention it as a stage in itp.
As per our manufacturing practise we did it regular basis and got good results.
It will help after installation during service also.
Go for it frelly it helps.
I m sharing my experience not bookish lines