1 specification analysis, uneven wall thickness: wall thickness can not be the same purpose in the wall thickness of the phenomenon exists in the cross-sectional and longitudinal tubular body, that is uneven thickness. In order to control such unevenness, the allowable index of uneven wall thickness specified in some steel standards generally does not exceed 80% of the wall thickness tolerance (implemented after mutual negotiation).
2, ovality: the phenomenon of unequal diameter, that is, the tube cross-section circle, there is not necessarily perpendicular to each other the maximum outer diameter and minimum outer diameter, the maximum and minimum outer diameter of the difference between the oval (or circle). In order to control the specification of the ellipticity steel standard, the specification of the ellipticity is generally defined as not exceeding 80% of the diameter tolerance (implemented after mutual negotiation).
3, bending: steel pipe in the longitudinal direction of the curve, with its graph that curve curvature or curvature. Curvature specified in the standard is generally divided into the following two:
First, the local curvature: with a meter long ruler * maximum number of bends, measuring the chord height (mm), is the local curvature value in mm / m units, expressed as 2.5mm / m. This method is also suitable for tube end bending.
Total length of curvature Total length: Tighten the ends of the tube with a thin string to measure the maximum chord (mm) of the elbow and convert it to the length (in meters), which is the total length of curvature in the length of the pipe.
4, different sizes: size tolerance or standard size is more than allowable deviation. Here the "size" mainly refers to the outer diameter and wall thickness of steel. It is often said that excessive habits are "tolerant and overbearing", that the deviation is called the inaccuracy of the tolerance and should be called "deviation from the spectrum." Deviations here may be "positive" or "negative," with few "positive" and "negative" deviations occurring in the same lot.