Can someone give more detail about denickelification?

[msilvame]

I've seem to have found a denickelification on a Monel alloy (63% Ni - 31% Cu) which was in contact with HF (40% and 70% concentration). I haven't find anything about this, denickelification seems to happen in cupronickels (30% Ni and 30% Cu) but not in base Ni alloys!
Can anyone give more detail about this?

 

[fitz]

I've seen what seems to be denickelification of Monel alloy tubes in high pressure feedwater heaters in an electricity generating station. I can't tell you much more except that it is a known phenomenon even in this high-purity steam/water environment.