GB/T 25198-2010 \"Pressure Vessel Heads\" – How should the thickness δs of the head material be selected?

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This post was last edited by 511948814 on 2022-9-2 at 14:05. In GB/T 25198-2010 \"Pressure Vessel Heads\", Page 56, under \"Appendix J (Informative Appendix) Reduction Rate of Head Forming Thickness\", the thickness used is the thickness of the steel material, δs. As indicated in the symbol explanations on Page 5 of this standard, δs represents the thickness of the head material – that is, the thickness of the material used in manufacturing the head, which is also the specified thickness stated in the material quality certificate, in mm. Question 1: If the thickness of the head cover material is determined based on the thickness of the material used in production, does this thickness refer to the nominal thickness of the steel plate used, or rather to the nominal thickness minus the actual negative deviation in thickness – that is, the actual thickness of the steel plate after cutting? Question 2: If the thickness of the head cover material is to be based on the specifications stated in the material quality certificate, GB/T 247-2008 \"General Provisions for Packaging, Marking, and Quality Certificates of Steel Plates and Steel Strips\" requires that only the specifications be indicated in the quality certificate. However, the thickness values provided by the manufacturers I have dealt with are nominal thicknesses, without any indication of the negative deviation from that thickness. May I ask, when calculating the thickness reduction rate of the head, should the negative deviation of the head thickness δs be taken into account for the material thickness of the head?