The issue of negative deviation in steel plates
Thread Content
According to GB709-2006, hot-rolled steel plates are classified into three categories—N, A, and B—based on thickness deviation. When designing, for steel plates other than those specified in GB713-2008 (such as Q235-B), it is necessary to determine which category is appropriate; moreover, it is important to indicate on the drawings the category used in the calculations so that the manufacturing unit can make the appropriate purchases.
Q235-B should be classified as Class N.
I really want to know this too; could some expert please specify what the thickness deviations are for each of the N, A, B, and C categories?
It shall be in accordance with the standards applicable to the material.
After accounting for the negative deviation of the steel plate, as long as the thickness meets your requirements, it will be fine
Agree with what was said above. The choice of negative deviation should depend on rounding the calculated thickness from your drawing, plus the selected negative deviation, to the optimal nominal thickness.
It is clearly specified in GB709; you can check it yourself
I disagree with this view. If compliance is calculated using a Class B deviation design and it is not specified in the drawings, and the manufacturer uses steel plates according to Class N standards, there is a possibility of excessive deviations leading to insufficient strength. Of course, if the design is based on Class N deviations, no specification is necessary. If that is the case, then the design must be carried out based on Class N deviation calculations, which may also lead manufacturing units to use steel plates with a higher deviation level, resulting in unnecessary cost increases. I believe the deviation grade of the steel plate for the designed pattern should be indicated on the pattern. To discuss this with you all.
For steel plate grades marked with an R, the negative deviation is always zero; for other negative deviations, refer to HG20581
It is not zero; merely, the negative deviation for container plates per GB6654 is 0.25, and this can be omitted in design according to GB150. However, under the new standard GB713, the negative deviation for plates is 0.3. If following GB150-98, it cannot be omitted.