Name that corrosion
Name that corrosion
(OP)
Application: Raw Water Pump Shaft
Material: A276 XM19 (Nitronic 50)
Fluid: Pond water. Slightly brackish (170 ppm Cl- or 1300 um/cm2).
We do inject biocide (i think NaOCl).
I can't recall ever seeing this corrosion in this application with the same material. We may have a material issue?
Thanks in advance.
Material: A276 XM19 (Nitronic 50)
Fluid: Pond water. Slightly brackish (170 ppm Cl- or 1300 um/cm2).
We do inject biocide (i think NaOCl).
I can't recall ever seeing this corrosion in this application with the same material. We may have a material issue?
Thanks in advance.





RE: Name that corrosion
RE: Name that corrosion
What was used as an assembly aid (oil or grease)?
What alloy was the mating material?
Have you checked chemistry? Just a Mo spot test would work for me.
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Plymouth Tube
RE: Name that corrosion
RE: Name that corrosion
1. Operated about 3/4 of the time. May sit idle for 1 week at a time.
2. Assembly aid, if any, would be graphite.
3. Mating materials: Impeller is NiAlBr (slide 2 top photos). Shaft sleeves are XM19 (slide 2 bottom left). Some corrosion where there is no mating matl (slide 2 bottom right)
Note that the upper shaft (can be partially seen on slide 2 top right photo) is the same material spec and does not show this corrosion.
RE: Name that corrosion
RE: Name that corrosion
Since graphite is the most noble in the series, you might want to rethink its use.
RE: Name that corrosion
RE: Name that corrosion
I sort of doubt MIC. Pictures of the surface fouling could change my mind though.
Either Cu and/ or graphite and a galvanic mechanism sounds more realistic.
Differences in surface condition between the two shafts can go a long way as the source of different corrosion results.
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Plymouth Tube
RE: Name that corrosion
I wouldn't expect that a tiny amount of graphite would lead to galvanic problems on such large/heavy parts, but I guess anything is possible...
RE: Name that corrosion
RE: Name that corrosion
Burnishing is a common process for pump components, there may be a 0.001-0.002" clearance between shaft and impeller by design, for larger components this makes assembly difficult. Flapper wheel inside the impeller bore, burnish the shaft with a strip of emery cloth. Dust from either or both shaft/impeller could have found it's way into the final assembly, trapped between mating components.
RE: Name that corrosion
RE: Name that corrosion
The shaft/impeller may have seen emory cloth for cleaning/smoothing (not necessarily for 'burnishing' but for cleaning/smoothing) so this may be a possibility.
I'll try to get a sample of the stuff and update this thread. Thanks.