stainless steel hydraulic tubing discoloration

[ottlaw2]

Does anyone using seamless stainless steel hydraulic tubing in .50" with .035 wall see any residue-roughness-discoloration on the inside of the tubing. We usually buy in 1000' qtys and have been seeing discoloration on the inside of the tubing. Sometimes it appears to be mill scale, black in color. We've just recieved a batch that has green on the inside.
We have seen the same problem in .750 x .049 wall but rarely.
I have been told it depends on the mandrel they run it on when they form the tube.
Anyone know if this is true?
Thanks

 

[TomZhang08]

Hi,

My friend told me that your tubing was not picked completely.

Hope help of you.

 

[metalonis]

It is most likely residue from impurities present at the final amnnealing step.