420, 303, and 304 SS and stray current failures 2

[TMcRally]

I have experienced circlip failures where the circlip fractures/separates in what appears to be similar to crevice corrosion.

The 420SS circlip is fitted on a shaft of 303SS which passes through a rose of 303SS, over the shaft and between the rose and the circlip is a 304SS washer.

The circlips fail to the point they can not withstand their own seated tension and separate. Some have a second (crack?) that has not broken. It appears to be an eroded shallow groove across the wide surface of the circlip, possibly an arc?

I have the same batch of circlips in stock and I have tested these to failure and they all have tested as you would expect a fit for purpose circlip to.

These have been installed for approximately 12months and are under cover but still exposed to the atmosphere and could get wet in a storm. The circlips are made in Italy.

I have jumped to the conclusion of stray current as they have been welding in the vicinity and it seems the only explanation that fits, I'm very happy to hear any other possibilities.

What do you think may have caused this and do I have a option to minimise the potential for future problems.

Thanks
Dave

https://files.engineering.com/getfi...4c3&file=Circlip_-_12_-_crack_or_arc_line.jpg

https://files.engineering.com/getfi...7a77b902a&file=Circlip_-_13_-_Failed_edge.jpg

https://files.engineering.com/getfi...11-4ec1af275ea6&file=Circlip_-_14_-_Whole.jpg

 

[BEMPE16524]

having said all the possibilities that you have mentioned, have you tried change to SS316 circlip?

R.Efendy

 

[TMcRally]

I was hoping to identify the problem first to be sure that is the correct option. I can't get 316 but I can get 304.

 

[BEMPE16524]

304 is not advisable as per what you have experience.
it will fail.

R.Efendy

 

[TMcRally]

Thanks for the feedback.

Would you say this has been caused by an arc from welding or a smaller stray current over a longer timeframe ?

Or something else ?

 

[TugboatEng]

I have experienced this as well. I attributed it to stress corrosion cracking. The snap ring would break without additional load applied. There would be multiple cracks in the broken pieces.

 

[Tmoose]

Is a potential parallel welding current path really thru the rose/washer/clip/shaft?

 

[TMcRally]

The external end of the shaft is a large T Handle, it is the only protrusion available nearby. While I don't know for sure, it seems logical that someone might attach the earth lead to the handle while welding the frame around it. I can't see any arcing on the external side of the 303SS T Handle, but it does appear to be arcing (looks like spark erosion) between the T and the rose.

Just guessing at possibilities.

 

[TMcRally]

TugboatEng

Thanks for your comments.

Do you know the material ?

Did it have the mark in my image 12 above ? Strange that the groove is not propagated like a stress fracture.

 

[TugboatEng]

How far from the nearest ocean are you?

 

[TMcRally]

Approximately 45klm or 28miles

 

[TugboatEng]

Not that close but not that far. Swimming pools, agriculture, sewage treatment, etc all put a lot of chlorides into the air. You said your comment gets wet sometimes from weather. As it drys out, even trivial amounts of chlorides on the surface eventually end up so concentrated they become nearly pure. This is a challenging condition for stainless steel alloys. You can consider regular rinsing of the part. Or. you may search for a less susceptible alloy. I tried using beryllium copper only because it was commercially available from my usual supplier. They broke while I was installing them. I ended up swapping everything out for plastic and never looked back.

 

[EdStainless]

I have seen people ground things to the wrong piping.
And then a poor power supply (or a failure) allows full mains voltage through the system.

The 420 should resist CSCC.
You could try clips made of 17-4PH, those should be common.

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P.E. Metallurgy, consulting work welcomed