Concentricity refers to the quality or characteristic of different circles having a common center.

“In the figure above, the tubing cross section on the left shows concentric inner and outer tubing walls with consistent wall thickness. The tubing on the right shows non-concentric inner and outer tubing walls, and the tubing wall thickness varies.”

In the case of tubing, concentricity is another means to describe the variation in wall thickness. Slight variations in wall thickness mean that certain points along the inner or outer wall of the tubing are at a slightly different distance – or radius – from the average center of the tube. Put another way, if the radius was held constant while the actual tubing wall distance from center varied, the result would be a circle with a fluctuating center and a tubing with less than ideal concentricity. Note also that tubing concentricity is measured along the central axis of the length of the tubing and not just in a single cross section. Thus, in reality almost all types of tubing have some variation in concentricity over the length of the tubing, even if only very small.

The following formula is used to determine a tube’s concentricity:


C = concentricity of the tube

W min = the minimum wall thickness

W max = the maximum wall thickness

The result of this calculation is a percentage. A tubing with perfect concentricity has the same thickness for W min and W max and thus has a concentricity of 100, or 100%.

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