How many armor soldiers did the Roman soldier bring to the battlefield

[Leoshenlong]

Why would he do that? And when would he change armours? Where woul;d he keep that 'second armour' in the meantime?

Because I know many soldiers still keep their old armor, if they are stationed for a long time then when they change positions they have to bring them when going to the battlefield.  I think it could happen.  A typical example is the Battle of Teutoburg, which is being ambushed on the march, most likely the soldiers are carrying both Segmentata and Hamata.

It may be the case that officers would have more then one armour but I doubt the rank and file would under normal circumstances, the easiest way to carry armour on the march is to wear it, most armour can weigh quite a bit and you'd have to allow for this extra armour in the baggage since the men are unlikely to want to carry an additional armour themselves...
So say a typical armour weighs 12kg, that means approx an extra metric ton per century of 80 men, I'm sure they have more important items to transport then this additional massive load which would be surplus to requirements...
However I would expect that extra sets of armour would be carried in the baggage in case of need, a few per unit would suffice... the recent find in germany may be such an item.

I am thinking about 1 case.  I have read somewhere an opinion that the soldiers after having segmentata, they still retain the hamata.  With the characteristics of long-term stay, they cannot take them home for storage.  as far as I know the 3 Roman legions on their journey from summer camp to the winter fortress, had abruptly changed direction through the teutoburg forest according to the report of an Arminius rebellion.  which means at that time they are most likely wearing more old armor