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Carbon steel heads are widely used in petroleum, chemical equipment, machinery manufacturing, transportation, electric power, nuclear industry, etcThe inner diameter of the vessel Di=4000mm, the calculated pressure Pc=0.4MPa, the design temperature t=50 ℃, the head is a standard elliptical head, the material is 16MnR (the allowable stress of the material is 170MPa only at the design temperature), the negative deviation of the steel is not more than 0.25mm and not more than 6% of the nominal thickness, the corrosion allowance C2=1mm, and the welded joint coefficient of the head butt welding= 1。 Calculate the calculated thickness, design thickness and nominal thickness of the elliptical head.
KpDi
Calculated thickness δ=----------------= 4.73mm
2[ σ] t Φ- 0.5pc
Calculated thickness δ d= δ + C2=4.73+1=5.73mm
Considering the effective thickness of standard elliptical head δ E shall not be less than 0.15% of the head inner diameter Di, effective thickness δ e=0.15%Di=6mm
δ e> δ D, C1=0, C2=1, nominal thickness δ n= δ e+C1+C2=6+0+1=7mm
Considering that the thickness of the standard specification of steel has been increased by 1mm, the first design round value △ 1=1, so δ n=8mm。
According to the technical data of professional head manufacturer Di=4000 δ The thinning amount of head processing of n=8 is C3=1.5mm, and the second round value of thickness is △ 2=0.5.
If the forming thickness of the head is required to be no less than the nominal thickness δ N minus the negative deviation of steel plate C1, then the feeding thickness:
δ s= δ N+C1+C3+△ 2=8+0+1.5+0.5=10mm, while the minimum thickness after forming is 8.5mm. If the head forming thickness is adopted, it shall not be less than the design thickness δ D (should be taken δ E value), then the feeding thickness: δ s= δ d（ δ e) +C3+△ 2=8mm, and the minimum thickness after forming is 6.5mm, which is greater than the effective thickness δ E. More than the design thickness δ D and calculated thickness δ。
It can be seen from the above that the difference between the feeding thickness of the head and the weight is as much as 300 kg due to the two different requirements.
