The wall thickness of a steel pipe can not be the same everywhere, and the wall thickness varies objectively in its cross section and longitudinal tube body, namely, the wall thickness is uneven. In order to control this nonuniformity, the allowable standard of wall thickness is specified in some steel pipe standards. The general requirement is not more than 80% of the wall thickness tolerance (after consultation by both sides of supply and demand).

Ellipticity

Cross section of the tube are outside the range phenomenon, namely the existence of the maximum outer diameter is not perpendicular to the minimum and maximum diameter, diameter and the minimum diameter difference is the ellipticity (or roundness). In order to control the ellipticity, the allowable specifications of ellipticity are specified in some steel tube standards, which are generally stipulated to be no more than 80% of the outer diameter tolerance (after consultation by both sides of supply and demand).

Curvature

The steel pipe is curved in the length direction, and the curve is expressed by numbers, that is called bending degree. The standard of bending is generally divided into the following two kinds:

A, local curvature: a meter long ruler in the amount of steel pipe on the maximum bending, measure the height (mm), which is a numerical local curvature, the unit is mm/m, said method such as 2.5mm/m. This method is also applicable to the end curvature of pipe.

B, the total length of bending: use a string from the ends of the pipe, bend pipe maximum height measurement (mm), and then converted into length (in meters) the percentage of full length is length of pipe bending.

For example: the length of pipe is 8m, the maximum height of 30mm, the length of pipe bending should be:

0.03 / 8m * 100%=0.375%