Sacrificial anode body to preserve tiny spring 2

[magusinp]

I have designed a device which has an Inconel X750 spring within a large 316 SS body. The Inconel is passivated so its corrosion potential is -0.3, the 316 SS (active) has a potential of -0.79. The spring material is only 0.025" thick. The SS body is a piece of 1 1/2" thick bar stock with a hole drilled in it for the passage of various chemicals through the ball check spring mechanism. The idea is that the stainless body would become the sacrificial anode to preserve the spring. We also are planning on making the body out of HC-276 (potential -0.71)

Is this a good idea?

 

[mcguire]

The spring will be fine. As long as the corrosion the 316 experiences is tolerable, the system will be okay. But, if that is the case the spring would have been okay without cathosic protection.

 

[magusinp]

It sounds like you are saying that the corrosion due to chemical attack cannot be mitigated by directing it toward the anodic material. The two types of corrosion are not interrelated. That is, corrosion due to chemical attack is not related to galvanic corrosion.

 

[Metalguy]

magusinp,

McGuire is correct. The active 316 can offer protection to the Inconel X. For example, it is possible to prevent carbon steel corrosion by hot sulfuric acid using impressed current, but it takes a lot of amps.

However, your spring may be subject to SCC, depending on how much stress its under. There have been SCC failures in high temp. water where oxygen is the only corrodent present. If you get SCC, consider using Inconel 718 springs.

 

[unclesyd]

I think magusinp is correct in his statement in that being cathodic will not help in a direct chemical attack. It can mediate SCC but doesn't do as good on SC and has very little affect on chemical dissolution.

We saw this in several expensive lessons involving Hastalloy C. These were inservice failures verified by laboratory tests.

 

[Metalguy]

It all depends on what the corrodent is. It's well known that zinc is anodic to alum. at amb. temps., and will prevent seawater attack of alum.

The behavior of a bimetallic couple wrt corrosion can be complicated, but most of the factors are well known.