Features in drawn SS tube 1

[will123123]

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.

 

[EdStainless]

A light Oxalic etch would be good, if these features do not run deeper than one grain they might be IGA from carbon contamination. Again, this may have happened at an intermediate anneal.
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