Streaks on Machined SS304 after Electropolishing

What was the operation immediately prior to the electropolishing?

Was any surface grinding done?

There is a good possibility that the operation was done using a wheel that was previously used to machine/grind a CS or any other material with quite different Electropotential.

I have seen these in a lot of stainless steel components (of course not electropolished ones, rather components left for some times on LIFO system) where rust marks have formed due to imporper usage of grinding wheel. And these etch marks have surprisingly similarity with those.

Kind of looks like dish washer streaks, like the acid wasn't completely rinsed off before drying.

Chorium burn out.

Your SS is from rolled material (naturally, what else),

and you will see the internal structure after removing the deformed surface.

I experienced this very often on anodising.

I had examples where the grainy structure of either granular or lengthwise distorted crystallites of the metals was showing up as a beautiful black and white = shiny surface.

Try slight anodising with your material, may be you see something similar! (Submerged in your electropolishing liquid).

RHABE

I agree with Rhabe that the streaks are a result of the roller. It appears to me however that the electro-polishing (normalizing) process may not have been sufficient. I don't know a lot about it but it could have been a weak solution, improper current and or insufficient duration. I think that purchasing plate with a specified mill finish would help for the next run.

I got that once when I was using a brass wire brush in the pre-clean process. I switched to Stainless Steel wire brushes, and the problem went away.

Not saying this is your problem, but a check of the brushes and grinders for contamination might prove fruitful.