Stainless steel identification

I have two 20' stainless steel tubes I'm trying to identify and find the value of. They've been sitting outside exposed for over 15 years and there's not even a single mark on them, so they're definitely stainless, I'm just not sure if it's 304 or 316. I tried an acid test but I'm not sure what the results mean, I took some shavings from it and mixed it with sulfuric acid and it was a very slow reaction (Overnight) but it turned dark green and crystalized, does that mean it's 304? Or 316?

Theres some markings on them: Id238294, m63wo, vallourec. clee 86455

Ultimately I'm trying to figure how much they're worth, they're both 20' long with 3" O/D, I/D is about 0.25 (I'll get an accurate measurement when I get a minute)