The part was coated by manufacturer itself and supplied to us.
I assume the part involved was original to the unit and not a refurbishment.
Unfortunately it's not my area of expertise but you may need to study the chemical aspects of nickel coating a little..
Regarding the corrosion, I suggest you directly query to the manufacturer as to whether (a) the "Ni" coating methodology is appropriate to yr usage as earlier described and (b) If the answer to (a) is Yes, was the coating perhaps imperfectly carried out or of sub-standard quality.
This document discusses some of the possibilities/criteria -
Nickel coatings.pdf 526.62KB