1 The thickness of the blank of the head should consider the amount of thinning during the process to ensure that the measured minimum thickness of the finished product after the head is formed meets the regulations.

　　2 In the preparation of blanks and subsequent manufacturing, mechanical damage to the material surface should be avoided. Sharp scratches, grooves and other defects on the anti-corrosion surface of the material should be repaired. The slope of the repair range is at least 1:30. The depth of the grinding requirements, according to the different design methods and materials, according to (1) ~ (4).

　　1)For nickel and nickel alloy heads, copper heads and steel heads designed according to GB150, the grinding depth should not be greater than 5% of the material thickness δs and not greater than 2mm, otherwise it should be welded. For composite boards, the grinding depth shall not be greater than 30% of the thickness of the cladding and not greater than 1 mm, otherwise it shall be repaired by welding.

　　2)For steel heads designed according to JB 4732, the thickness after grinding should not be less than the designed thickness, otherwise it should be welded. For composite boards, the grinding depth shall not be greater than 30% of the thickness of the cladding and not greater than 1 mm, otherwise it shall be repaired by welding.

　　3)For aluminum and iron heads, the grinding depth should not be greater than 5% of the thickness δs of the aluminum material (or iron material) at this part, and not more than 2 mm, otherwise it should be welded.

　　After welding, it is necessary to inspect the part repaired welding in accordance with the relevant standards.