Monel K500 corroded seriously 3

[albtnt]

Dear guru:

There is a shaft of a cooling water pump(sea water) that corroded seriously. The shaft is made of Monel K500. Since K500 is famous for its resistence to corrosion and is usually used for marine service, I have no idea what happened to this shaft.

Can someone give me some suggestion on this issue? I do really appreciate any help from you.

PS: photo of the shaft is attached

 

[TVP]

The following is an excerpt from the Special Metals publication on MONEL® alloy K-500 (

http://www.specialmetals.com/documents/Monel alloy K-500.pdf):

The combination of very low corrosion rates in high velocity sea water and high strength make alloy K-500 particularly suitable for shafts of centrifugal pumps in marine service. In stagnant or slow-moving sea water, fouling may occur followed by pitting, but this pitting slows down after a fairly rapid initial attack.

Here is a link to another Special Metals publication specific to corrosion:

http://www.specialmetals.com/documents/SM Aqueous Corrosion Book.pdf

 

[EdStainless]

What are the other metals in the construction?
What do you know about S and ammonia compounds in the water?
Is this used continuously or were there periods when it was stagnant?

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Plymouth Tube

 

[albtnt]

1. The other metal in the construction is made of stainless steel. As you can see in the photo, the stainless steel is folded into a ring which hold K500 tightly.

2. Another photo in the attachment shows that K500 corroded differently from the two sides of stainless steel. The left side, K500 corroded much more seriously than the right side. Since the whole shaft is of the same material. I guess that the environmental difference might be the cause.

3.The left side is hold in the turbine. Is it possible that the left side is in a stagnant environment?(compare with the right side)

4.Since the left side is hold in the turbine, is it possible that the leakage current from the motor find it's way to ground on the left side?

 

[EdStainless]

So the SS bushing runs in the rubber bearing.

My hunch is with contaminants in the stagnant water.

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Plymouth Tube