Tolerances to ISO 18286 hot rolled stainless steel quarto plate

For continously hot rolled plate (CPP), ISO 9444 is applicable.  

ISO 18286 replaces EN 10029 which was not specifically for stainless steel. It removes some anomalies and ambiguities from that standard.

One interpretation of the standard is that no ground area of the plate may fall below the minimum thickness tolerance. This is in contrast to EN 10163 which was referred to in EN 10029 and allowed some areas to be below minimum thickness.

The 4 Classes of thickness tolerance (A-D) in EN 10029 have been replaced by one class which is similar to Class B - minimum tolerance of 0.3mm under nominal thickness.

There are no tolerances on the maximum difference allowed within a plate.

The flatness tolerance is dependent on grade.

Provision is made for different width and length tolerances depending on the method of cutting.

The tolerance under nominal thickness is 0.3mm.

1. It is not possible to make an exact comparison with EN 10029 as the thickness bands are different. However, the following comparison of some typical thicknesses gives an idea:
2. For plates with trimmed edges, the thickness shall be measured at any point > 10mm and < 75mm from a longitudinal edge.

In general, wider plate has more generous tolerances than in EN 10029.

There are 3 classes of tolerance for width and length for plates with trimmed edges A - C. This is dependent on the method of cutting the plates.

Class A - cutting method not specified. By implication includes shearing.

Class B - flame-cut plate. Probably intended to mean plasma.

Class C - abrasive cut plate. Probably intended to mean water-jet cutting.

There is no mention of other cutting methods such as laser.

Tolerances on mill edge plate shall be agreed at the time of enquiry and order.

Tolerances on plates with a nominal length of > 20000mm shall be agreed at the time of enquiry and order.

1. For plates of thickness > 100mm width and length tolerance for Class C must be agreed at the time of the enquiry and order.

For plate with trimmed edges, the edge camber shall not exceed 0.5% of the nominal length of the plate. Out of squareness shall not exceed 1% of the nominal width of the plate. For comparison, EN 10029 has an edge camber of 0.2% and out of squareness of 1%.

For plate with untrimmed edges in the enquiry and in the purchase order, the edge camber and out of squareness shall be limited so that it is possible to inscribe a rectangle of the nominal length and width of the ordered plate within the delivered size. In EN 10029, the inscribed rectangle definition was not restricted to plates with untrimmed edges.

There are two levels of tolerance normal (Class N) and special (Class S). The class shall be specified at the time of enquiry and order. If not specified, the manufacturer can supply to either class.

For both classes the tolerance is dependent on the steel type:

Type A - All grades not of type B

Type B - stainless steel grades with Ni > 20% OR Mo > 2% or N > 0.11%.

1. Unless otherwise specified, the measuring length is at the manufacturer's discretion.
2. If the distance between the points of contact of the straight edge and plate is < 1000mm, the deviation shall comply with the following:

   Steel Type A - Maximum of 1% of the distance between the points of contact between > 300mm and < 1000mm.

   Steel Type B - Maximum of 1.5% of the distance between the points of contact between > 300mm and < 1000mm.

   but not exceeding the values in the table for Class N.

1.  Unless otherwise specified, the measuring length is at the manufacturer's discretion.
2. If the distance between the points of contact of the straight edge and plate is < 1000mm, the deviation shall comply with the following: 
   Maximum of 0.5% of the distance between the points of contact but not exceeding the values in the table for Class S. (By implication, this note applies to steel type A since for steel type B, tolerances are agreed at the time of enquiry and order. However, the standard is somewhat unclear. It is also not clear why the 300mm minimum length does not apply for class S as compared with class N).

It is quite difficult to compare the flatness tolerances in EN 10029 and ISO 18286, as the definition of steel types is totally different. In EN 10029 which was for all steel, steel types were L and H split by yield strength above and below 460 N/mm2. This meant that most stainless steel fell into steel type L. Even the nitrogen strengthened steels were in this type. Therefore, 304 and 316 were given the same flatness tolerance. The effect of the new standard is to put Mo and N bearing steels into the steel type B and therefore giving  less stringent flatness tolerances than previously.

An approximate comparison is shown in the following table for a 10mm plate in various grades of steel using the 2000mm measuring length:

It can be argued that neither standard is completely consistent on this subject. For example, martensitic grades in the quench and tempered condition or high yield strength PH grades are expected to have a better flatness than 316. This may not be realistic.

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