446 stainless steel wire, serious corrosion

[fusitexa]

hi,

guys, i need your help.

i have a terminal, there is 3 pins in it and they are made of copper core wire with jacket 446 stainless steel.
the terminal was returned from one customer, and it was found that one of the pins was broken. on the broken pin's surface , i found serious corrosion as the attached photo shows.

BTW, the terminal was used in refrigeration compressor.

can anyone give me some suggestion why this could happen, and how? also, any good ways to prevent it to happen?

thanks in advance.

 

[mrfailure]

The surface has the appearance of intergranular attack in the photo. Is there an electrolyte present at the terminal? Did you do EDS analysis on the surface shown to determine if foreign contaminants were present? Also, did you prepare a mount to see what the attack looks like? These will help you understand what happened.

 

[EdStainless]

Yes, you need to look at the microstructure.
The condition of the 446 may have been wrong in the first place.
Or they may have exposed it to very aggressive chemicals and they don't want to mention it.

What refrigerant is in the compressor?


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Plymouth Tube

 

[fusitexa]

mrfailure, edstainless, thanks for your reply. it is very useful.
according what i know, the refrigerant is R22. and the compressors were used in train, which was located on the top of it.
eds test was done, and it is shown in the attached file. the photo is in BEC mode. and the pin was Electronless Nickel plated. you should know that there was discharge, may be continuous discharge in service, and the results was in some location of pin, the pin was melted, which also shown.
i will do micro-structure examination.

 

[fusitexa]

photo of melting pin

 

[mrfailure]

Melting is a good term - the globule and patterns indicate localized heat damage. I do not understand this system enough to be sure, but could there have been and electric arc?

 

[fusitexa]

mr,

yes, it could be. indeed, it is sure that there was electric arc during service.

 

[BOBGTM]

I guess this is a GTM part made by Fusite, right? Is this a 3:1 copper core or 2:1 corpper core pin? What is pin size?

 

[EdStainless]

So, you are down to either:
1. a poor fit to the female connector (either size or not fully engaged) (mechanical)
2. electrical overload (electrical)
3. surface corrosion that raised resistance and lead to arcing (corrosion)

Look at the other pins for signs of corrosion or arcing.

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Plymouth Tube

 

[BOBGTM]

One more question: is the contacts pre-Ni plated or post-Ni plated?