Disintegrate Armor

You target one creature within range and unleash a torrent of caustic spray that coats the target's armor and body. The target must succeed on a dexterity saving throw or be covered in the corrosive fluid, taking 6d6 acid damage. Additionally, nonmagical armor worn by the target, or a shield it is wielding (your choice), is partly dissolved and takes a permanent and cumulative -1 penalty to the AC it offers. Armor is destroyed if the penalty reduces its AC to 10, and a shield is destroyed if the penalty reduces its AC to 0. 

At Higher Levels: When you cast this spell at 5th level, the damage increases by 1d6 for each level above 4th. Additionally, when you cast this spell at 6th level, the penalty to the armor's AC increases by 1 to a total of 2, and the penalty increases by 1 again (total of 3) when cast at 8th level.