Discussion:

Theoretically, the flattened length is half the circumference,14 mm× 3.14 ÷ 2 = 21.98 mm.

But a circular tube always has a thickness,

If the inner diameter is 4mm, then only the diameter of 4mm is squashed, and the rest is not squashed, then the length should be:

(14mm-4mm)+4mm× 3.14 ÷ 2 =10mm+6.28mm =16.28mm.

If the inner diameter is 10mm, then the one with the diameter of 10mm is squashed, and the length after squashing is:

( 14mm- 10mm)+ 10mm×3. 14÷2 = 4mm+ 15.7mm = 19.7mm

Of course, it depends on the physical properties of the pipeline, such as hardness and ductility. Some pipes are hard to crush.

This is just my personal opinion, right? Good luck, goodbye.