Uneven wall thickness of steel pipe

Steel tube wall thickness is not same, may on the cross section and longitudinal tube body wall thickness range phenomenon exists objectively, which is called the uneven wall thickness. To control this heterogeneity, in some steel standard provides a uniform wall thickness to allow indicators, the general requirement does not exceed 80% of the wall thickness tolerances.

Ovality of the circular cross section of the pipe there is a diameter ranging phenomenon, that there is not necessarily perpendicular to the maximum diameter and the minimum diameter, the maximum diameter and the minimum diameter is the difference between the ellipticity (or roundness). In order to control ovality, and some steel standard provides the allowable ovality index, generally defined as no more than 80% of diameter tolerance.
Characterized uneven wall thickness in the same cross-section thickness of the thickest point A, a thinnest point in the steel spiral longitudinal distribution, large or small pitch. Steel head, tail extent than the middle of uneven thickness serious, if pipe in the middle of the unevenness in thickness with a nominal wall thickness tolerance within 80%, then the removal of the head, tail portion of uneven thickness remains qualified products; such as pipe middle unevenness in thickness beyond the nominal wall thickness tolerance zone 80%, then the whole pipe as substandard goods, reducing the finished product rate.
Such as uneven wall thickness of the pipe longitudinal pitch larger part is due to the heating, resulting in a long pass cross-section billet temperature unevenness actions, such as ring bottom uneven pits formed at the material level, the tube and increase the contact surface of the hearth, the heating time is too long, the heating temperature is too high, the tube and the bottom exists between a large number of iron skin, resulting in a cross-section through a long tube temperature uneven perforation capillary to form a larger longitudinal thickness unevenness pitch. If the wall thickness uneven pitch is small, it is piercing units improperly adjusted due to its characteristic spiral motion, pitch size and perforation pitch equal to the capillary outlet.