I have to tell you that these tubes (316 stainless steel) were used and I bought them for a few money and cleaned with caustic soda.
Today I have asked again the seller which was the previous use of the tubes and he told me that they were parts of a big boiler, so there was hot water inside... in his opinion there is no safety issue because it was only water but now I have understood that the blue and black layers are probably oxides of the heating circuit... and I think that it is a very bad thing!

at the moment, my chiller is made with a new copper coil, i have only a meter of this bad tube that connect the end of the coil to the demijohn in which I collect the spirit. All the rest is made with new and safe materials.
What do you think about it?

I know that the most sure and easy reply you can give me is to throw away everything I distilled but, as homedistillers like you are, please consider that I made 10 stripping runs of Grappa and now I have about 100 liters of low wines... and also 2 spirit runs but for sure I don't want to drink that spirits, so the question is:
if I redistill EVERTHING, can I be safe? (I have already changed the bad tube with a new copper tube)
Thank you!!!