Thank you for your reply.
Indeed, the diameter will be quite easier to determine than the length of these pipes. Moreover, they all have constant diameter (3, 4, 5, 6, 8, 10, 12, 14, 16 or 20 mm). By extracting caps of the pipe I should be able to find the diameter with an acceptable accuracy.
Unfortunately, this has not been created in Rhino, so I cannot consider the geometry as a perfect pipe-shaped. I noticed that some of them are open and few little parts of surfaces may be missing depending on the object. But I don’t need the exact length (ceiling to centimeter should be enough), so I guess I could maybe start with rebuilding an approaching pipe. Which is kind of difficult without having the initial curve …
Anyway, I will investigate your idea of evaluating opposite points on the pipe and analyse their intermediate curve.