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Zn25 vs ZnNi12 - Expected lifetime for marine indoors

Q. Hi,

I am currently deciding what coating to use for some steel parts (structural and free-cutting steel) and have narrowed it down to these:

Electroplated coating ISO 19598 -- Fe//Zn25//Cn//T0
Electroplated coating ISO 19598 -- Fe//ZnNi12//An//T0

The latter is about 40% more the more expensive based on our offers, but that's really the deciding factor here.

The lack of any top coat is due the the possible reduction in conductivity, and uncertainty related to whether this impacts touch safety (the components in question are used in switchboards, where earthing is critical).

Some context:
- Design life targeted for 30 years
- Other parts are hot-dip galvanized sheet metal with zinc-aluminium (Galfan), in which these parts may be in contact with
- Installation area is indoors onboard a ship (near generators and other equipment), so a marine climate, but heated and ventilated area (our best guess is something like C3 to C4)
- Some of the components make up a door locking systems, and may be subject to some abrasion

What do you consider to be the better option here?

M Eie
- Oslo Norway
November 27, 2023