Damage and Tarnish on Inco625 parts

[fpm]

Hi all,
My company uses Inconel 625 parts in a water spray nozzle. The nozzle sprays fresh water at around 80-90degC and 50-90psi. pH is pretty neutral. The suspended solids content of the water is less than 5mg/l and dissolved iron is less than 0.5mg/l.

Our problem is that we have had returned nozzle parts from customers with damage after less than 1 year. The part is a small disc, roughly 12mm diameter, with a 3.5mm diameter hole in the centre through which the water flows. There is evidence of corrosion/erosion on the inner hole edge, and a brown tarnish on the material. The tarnished area is still smooth and hard, no flaking or pitting.

I'm very surprised that we see tarnish and damage on Inco625 from spraying fresh water at pretty low temps and pressures. Anyone any ideas as to possible causes?

Thanks,
FP

 

[EdStainless]

Are these systems ever cleaned or sanitized?
Any chance that they were running these at a lot higher pressure/flow than normal?
You can get cavitation damage on 625 orifice plates.

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Plymouth Tube

 

[fpm]

No, they're not usually cleaned out, there are changeable filters in the upstream lines which would be swapped on a regular basis, but the system woudn't be flushed with any sort of cleaning chemicals.

There's always a chance of much higher pressure I guess, since the customer controls the water pressure. Generally they run at 50-60 psi, we state a permitted max of 90psi, but I would doubt if they ever even see 90 psi to be honest.

 

[metengr]

fpm;
Local erosion damage does not surprise me considering the size of the orifice you stated above. Have you calculated flow rates? You might be surprised at the velocity through the orifice at even 50-60 psi.

 

[TVP]

Have you examined the orifice using a magnifying lens or microscope? I agree with the other 2 gentlemen, cavitation/erosion is a definite possibility with such a small orifice size.

 

[EdStainless]

If it turns out that you have erosion or cavitation damage I would suggest that you look at using a Co based alloy such as Ultimet. These alloys are not hard, but they resist cavitation damage very well.

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Plymouth Tube

 

[SJones]

As to the tarnish, what is the piping material conveying the water to the nozzle?

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[fpm]

Thanks folks. I'll try to look into cavitation. We have an even smaller orifice later in the flow path in the same nozzle that is less than 1mm in diameter, which we have had no problems with. Mind you, the nozzle assembly is pretty complex, so the 2 parts are not necessarily seeing the same conditions.

We have seen this problem only on 2 customer units, and the major variable is the quality of the input water, so I had thought that it was likely to be a water-borne problem. Water samples we got back were within our recommended specs though, although there's no way to know if those samples were truly representative of normal running conditions.

The pipework feeding the unit is all 316SS.