It's not going to trigger Art. 5. The West has no interest in a direct confrontation. Actually, the West would prefer if Russia didn't force their hand, because it would look like a typical discussion on here, where you start out with "Russia vs. US, who would win?" and inevitably, on page one, some guy goes "Yeah, but nukes!" and the discussion is over, because all that's left to do is see who is left after the fallout.
Some dumb pipeline that doesn't even belong to Europe? Yeah, not going to make anyone overly uncomfortable, although of course the horse will be beaten to a pulp diplomatically before all of this is over.