Tolerances for bright drawn, ground, turned and polished stainless steel bars are included with the general standard for otherbright stainless steel bars in EN 10278.
The standard mentions the shapes round, hexagon, square and flat, but not all of these cross sections have specific tolerance tables. This article will only show the tolerances for stainless steel bars for the sections specifically covered. All dimensions are in millimetres (mm).
These tolerances can be used in conjunction with bars specified to EN 10088-3
Finish condition and tolerance classes
EN 10278 has the symbols for finishes, as shown below.
Tolerances on dimensions (diameter, thickness, width) are those established by ISO 286-2. The tolerance classes that are applicable to various finish conditions and sections are shown in the table below.
|Finish condition||Tolerance class to ISO 286-2|
R = round; S = square; H = hexagon
The tolerances (or limit deviations) for the whole range tolerance “ISO” classes covering round and hexagon bars is shown in table below. The ranges are all +0, all minus ie for a 20mm bar to tolerance class h9 with a tolerance range of 0.052, the tolerance is -0.052/+0, giving an acceptable product size range of 19.948 to 20.000mm.
Tolerances on cross sections
Drawn round bars, hexagon and square bars
Drawn round bars are covered by class h10, except for any supplied in the quenched and tempered condition (ie martensitic stainless grades), which are covered by class h11
Hexagon and square bars are covered by class h11 in sections sizes up to 80mm and class h12 in section sizes over 80mm. Ground finished products are covered by class h9.
Out of round (ovality)
The standard states that the maximum deviation from “out of round” shall not be more than half the specified tolerance but never above the upper limit of the tolerance.
Tolerances on straightness
The standard covers covers both stainless and non-stainless steel families. Only the tolerances relating to stainless steels are shown in the following table.
|Product form||Nominal dimension||Deviation|
|Squares and hexagons||up to 75||1.0|
|Flats||width below 120||1.5 on width / 2.0 on thickness|
|width at or over 120 and w/t below 10:1||2.0 on width / 2.5 on thickness|
|width at and over 120 and w/t at or over 10:1||2.5 on width / 3.0 on thickness|
Methods of measurement
Except for straightness, EN 10278 does not provide guidance on the measurement of the specified dimensions and how to verify whether or not the tolerance limits have been met.
The standard outlines two methods for measuring straightness.
The preferred method involves supporting the bars on a suitable surface to eliminate or minimise sagging. If a 1 metre long straight edge is placed on the bar at any position, then the maximum gap between the bar and straight edge is measured by a suitable means such as inserting feeler gauge. The bar is deemed straight if the gap is less than that shown in the table in the ‘Tolerances on straightness’ section, above.
The standard also describes a dial gauge method as an alternative to the gap measurement method.
Source: Zhejiang Yaang Pipe Industry Co., Limited (www.yaang.com)