Do Plated Parts Have a Shelf Life?
Q. I work at a plant that fabricates parts for airlines. We have a lot of our parts chromated, anodized and cadmium plated. My question is: Do these plating types have a shelf life of any kind. Sometimes we make an excess on parts and they have already been plated and we put them in a small stock room until we get another order for the same parts. I had been told in the past that these parts would eventually tarnish or discolor. Others who work here disagree with that, so it would be helpful to us to know the real answer so that we might can avoid ruining some good parts. Thanks for any assistance.Kelley Damron
manufacturing - Greenwood, South Carolina, USA
A. One important factor that would decide if you have a shelf life on your parts is if all surfaces of the parts have a coating or plating on them. We make tubular components which are plated on the outside, but not the inside. Often, we require a rust-inhibitor to keep our parts from rusting on the shelves before they are used.
If these parts don't have bare areas on them, then they ought to be fine. There really isn't much of a difference if the part is in service or sitting on a shelf. That is assuming that the environment where you are keeping these parts is not abnormally harsh. If you have air with excessive acid, moisture, or heat, then the air may be attacking your parts.
One other thing worth mentioning is white corrosion. Sacrificial platings are there to sacrifice themselves to rust instead of the metal of your part. In the auto industry, we often have around a 96 hour salt spray requirement to 5% white corrosion. This is so that a car will have a good showroom appearance before white corrosion sets in later after the purchase. You may want to investigate how your parts resist white corrosion and if there would be a problem. This is the one problem I would imagine with having a part sit on a shelf.
Rochester Hills, Michigan
December 18, 2013
Q. "There really isn't much of a difference if the part is in service or sitting on a shelf."
May I ask why so? Won't a plated part in service be subject to much harsher conditions (rain, etc.)?
- Chennai, Tamil Nadu, India
December 18, 2013
A. Hi Harish. Actually, that is not what Tim was trying to say. He was saying that once a part is built, it is probably slowly but continuously suffering corrosive attack.
Yes, "in service" in the rain is usually harsher than sitting on a shelf -- an exception might be if the storage shelf is in a plating shop with acid vapors in the air :-)
Ted Mooney, P.E. RET
Pine Beach, New Jersey
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