Bend Tube Is Stronger Than Straight Tube
Bend Tube Is Stronger Than Straight Tube
Once the tube material has been bent beyond its elastic limit, the thickness of the tube wall on the inside of the bend will be compressed, while the tube wall on the outside of the bend will be stretched, or thinned. This results in work hardening of the bent material. Work hardening increases the strength of the material.
If a length of tube containing a bend is capped with a Swagelok tube fitting and then pressurized to the bursting point of the tube, the tube will visibly expand along the straight lengths much more than it will at a bend, and when it eventually bursts, it will burst in a straight length (typically along the longest straight length).
The work hardening that occurs during bending increases the strength of this stretched material more than enough to offset the loss of strength resulting from the thinning of the wall.
However, if a bend is made in the wrong location or in the wrong direction, it cannot be unbent. This makes it critical to learn how to correctly bend tube.
In this figure, tubing bursts on the straight portion showing an increased tensile strength of material at the bend.
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