Taking the elliptical head  as an example, the appendix of GB/T 25198- -2010 "Pressure Vessel Head", the thickness reduction rate of the head may be greater than that shown in Figure 1, but the law reflected in Figure 1 has been produced in practice The proof is correct, based on this analysis.

Take an elliptical head as an example, the drawing specification is: DN2000 mmx25 mm, and the feeding thickness is 28 mm. The elliptical head is roughly divided into three areas: the small thinning area at the top of the head, the small thinning area in the transition area, the large opening in the transition area and the straight side section area. The actual wall thickness of the small and thinned area on the top of the head is ≥26.9 mm, the actual wall thickness of the large and thinned area in the transition zone of the head is ≥25.2 mm, and the wall thickness of the large mouth and straight edge section of the head transition zone is ≥27.4 mm. The allowable deviation of thickness specified in GB/T 713-2014 "Steel Plates for Boilers and Pressure Vessels" is Grade B in GB/T 709- -2006 Dimensions, Shape, Weight and Allowable Deviations of Hot-rolled Steel Plates and Steel Strips" 5. .

For a head with a feeding thickness of 28mm and a thickness of 24.7mm after forming, if the nominal width ≤1500mm steel plate is used, the actual thickness of the head in most ranges has exceeded the upper limit thickness of the 25mm steel plate (26.1 mm); if the nominal width is> For 1500~2500mm steel plate, the actual thickness of the head in most ranges also exceeds 25 mm, and the upper limit thickness of the steel plate (26.3 mm). Therefore, for the head, the actual thickness of the head in most ranges should be considered to belong to the >25 mm column.