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Ovality of steel tubes (out of roundness), is the difference between max. and min. diameters readings taken in the same given section. Ovality shall be within OD tolerance.
(absolute value in mm)
(in %)
Eccentricity of steel tubes (mean deviation), is a measure of the distance between centres of the outside and inside diameters. Eccentricity shall be within WT tolerances and is calculated from the WT in one cross section using formula:
(absolute value in mm)
(in %)
Tube straightness deviation (e) indicates the maximum deviation of the tube from a line joining its two ends, where L is the length of the tube. It is given in percentages per unit length. Usually required straightness is 3 mm for 1 meter.
(in %)
Eccentricity -
An eccentric tube is one which has the centre of the circle formed by the OD (outside diameter) which is at a different point from the centre of the circle formed by the ID (inside diameter), so the two circles are not concentric. Eccentricity can be checked by determining the wall thickness around the tube at any cross section to establish maximum and minimum.
The tube’s eccentricity (in mm) at that cross section would be one half the difference between the minimum wall thickness (t2) and the maximum wall thickness (t1).
Wall Run-Out -
This is derived from the tube’s eccentricity. It is the variation in wall thickness compared to the specified nominal wall (total Δ wall).
Wall run-out can be related to eccentricity:
SA 999
1. Permissible Variation in Outside Diameter
1.1 Variations in outside diameter, unless otherwise agreed upon, shall not exceed the limits given in Table 1. The tolerances for outside diameter include ovality, except as provided for in 12.2 and 12.2.1. (See Note 2.) 1.2 For thin-wall pipe, defined as pipe having a wall thickness of 3 % or less of the specified outside diameter, the diameter tolerance of Table 1 is applicable only to the mean of the extreme (maximum and minimum) outside diameter readings in any one cross-section. 1.2.1 For thin-wall pipe, the difference in extreme outside readings (ovality) in any one cross-section shall not exceed 1.5 % of the specified outside diameter. NOTE 2—Thin-wall pipe usually develops significant ovality (out-of- roundness) during final annealing, straightening, or both. The diameter tolerances given in Table 1 are usually not sufficient to provide for additional ovality expected in thin-wall pipe.
SA 1016
1. Permitted Variations in Wall Thickness 1.1 Variations from the specified minimum wall thickness shall not exceed the amounts prescribed in Table 2. 1.2 For tubes 2 in. [50 mm] and over in outside diameter and 0.220 in. [5.6 mm] and over in thickness, the variation in wall thickness in any one cross section of any one tube shall not exceed the following percentage of the actual mean wall at the section. The actual mean wall is defined as the average of the thickest and thinnest wall in that section. Seamless tubes ±10 % Welded tubes ±5 % 9.3 When cold-finished tubes as ordered require wall thick- nesses 3⁄ 4 in. [19.1 mm] or over, or an inside diameter 60 % or less of the outside diameter, the permitted variations in wall thickness for hot-finished tubes shall apply. 2. Permitted Variations in Outside Diameter 2.1 Except as provided in 10.2.1, 10.3, and 25.10.4, variations from the specified outside diameter shall not exceed the amounts prescribed in Table 3. 2.2 Thin-wall tubes usually develop significant ovality (out-of-roundness) during final annealing, or straightening, or both. Thin-wall tubes are defined as those with a specified wall 3 % or less than the specified OD, or with a wall specified as 0.020 in. [0.5 mm] or less. 2.2.1 1 The diameter tolerances of Table 3 are not suffi- cient to provide for additional ovality expected in thin-wall tubes, and, for such tubes, are applicable only to the mean of the extreme (maximum and minimum) outside diameter read- ings in any one cross section. However, for thin wall tubes the difference in extreme outside diameter readings (ovality) in any one cross section shall not exceed the following ovality allowances: Outside Diameter, in. [mm] Ovality Allowance 1 [25.4] and under 0.020 [0.5] Over 1 [25.4] 2.0 % of specified outside diameter For cold-finished seamless austenitic and ferritic/ austenitic tubes, an ovality allowance is necessary for all sizes less than 2 in. [50.8 mm] outside diameter, because they are likely to become out of round during their final heat treatment. For such tubes, the maximum and minimum outside diameter at any cross section shall not deviate from the nominal diameter by more than 60.010 in. [60.25 mm]. However, the mean diameter at that cross section must still be within the given permitted variation given in Table 3. In the event of conflict between the provisions of 10.2.1 and those of 10.3, the larger value of ovality tolerance shall apply.
