And here you go from skunkpharm.....
They list copper as fair, not because the butane attacks it, but because of sulfur compounds and water that may be present in the butane, which form sulfuric acid and attacks the copper. Dry low sulfur butane doesn’t present the same issues, but copper columns have to be kept meticulously clean of oxides, as for instance, welding copper without adequate respiratory protection, produces a medical condition known as fume fever. If you do not have the time or inclination to keep the extraction column pristine, glass or stainless is a better choice.
I'm pretty sure you won't clean that copper tubing to pristine state. I'm sure no one that uses copper does.