Features in drawn SS tube
Features in drawn SS tube
(OP)
My company is investigating a new source for stainless steel tubing and have obtained a sample for examination. Inspection of polished sections under an optical microscope source revealed particular features all around the internal surface (see attached image). From looking at the image can anyone suggest what they are and how they are caused?
The material is 316 and the cert states the material is to ASTM A269 and ASTM A213.
Thank you in advance.
The material is 316 and the cert states the material is to ASTM A269 and ASTM A213.
Thank you in advance.





RE: Features in drawn SS tube
This appears to be corrosion attack of the ID tube surface. The surface is highly irregular and looks like there must have been a contaminant present if this is the only surface that was affected. I have seen both stress corrosion cracking and intergranular oxidation appear like this without further investigation.
What was the appearance of the OD surface?
Can you come back information as to how were the tubes manufactured?
RE: Features in drawn SS tube
RE: Features in drawn SS tube
Apologies I meant to have included that the tube was cold drawn and then bright annealed!
RE: Features in drawn SS tube
I've seen something like this to a far less degree, only 2 or 3 indications. This was attributed to problems in the mill that made strip for the tubes.
Can you comeback with the size of tube?
Seamless or Welded?
Was any testing like eddy current preformed?
RE: Features in drawn SS tube
Per ASTM A269 specification was there a hydrotest performed or nondestructive electric test? This is important because if water quality was not controlled during hydrotest this could be all corrosion attack.
RE: Features in drawn SS tube
RE: Features in drawn SS tube
RE: Features in drawn SS tube
Learn the rules,so you know how to break them properly.
Dalai Lama
_____________________________________
RE: Features in drawn SS tube
Out of curiosity, how precisely does one make 1/8" OD x 0.049" wall tubing anyway? OK, how do they make 1/16" x 0.004" ID capillary tubing? It amazes me that it's even possible.
RE: Features in drawn SS tube
Thin wall tubing is made by welding a sheet into a tube or piercing a rod. Then, the tube diameter and wall thickness are reduced by drawing them through a die with our without a plug or mandrel put inside the tube.
RE: Features in drawn SS tube
Learn the rules,so you know how to break them properly.
Dalai Lama
_____________________________________
RE: Features in drawn SS tube
RE: Features in drawn SS tube
RE: Features in drawn SS tube
RE: Features in drawn SS tube
Learn the rules,so you know how to break them properly.
Dalai Lama
_____________________________________
RE: Features in drawn SS tube
I appreciate your help.
RE: Features in drawn SS tube
The tube itself should have been bright annealed after all mechanical forming operations are completed. If the post by metengr is correct as it pertains to this tube there should be not weld.
It is also hard to comprehend that the amount of O2 available in the tube of this size could caused this anomaly.
RE: Features in drawn SS tube
That is a good point. It is possible that the tube had intermediate anneal(s) to get it to final size, so there could have been exposure to oxygen at multiple times. I think you may be surprised at how little oxygen is required to produce this defect - it is < 100 µm, so it isn't horrible. It isn't good, either.
RE: Features in drawn SS tube
Another thing that would nice is look at the inside surface to see if the indications are truly just radial or say helical surface breaking form tearing while drawing.
I been trying to recall a visit I made many years ago to a manufacturer of small diameter tubes as to the exact process. I hope I have a trip report.
RE: Features in drawn SS tube
We make a lot of tubing down to 1/8", as hard as it is to purge it is much harder to clean.
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Plymouth Tube