Diagram showing the relationship between various thicknesses of pressure vessels

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(1) Calculate the thickness: Take the operating pressure into account, and use the calculation method specified in the standards to determine the thickness； It is the thickness that ensures the container’s strength, stiffness, or stability under design conditions. (2) Design thickness: the sum of the calculated thickness and the corrosion margin ； It is the thickness that ensures the container meets the requirements for strength, stiffness, or stability under design conditions, while also fulfilling the expected design life requirements of the container. (3) Nominal thickness: The design thickness plus the negative deviation of the steel thickness, rounded up to the thickness of the standard steel specification ； It is generally the thickness indicated on the design drawings. (4) Effective thickness refers to the nominal thickness minus the corrosion allowance and the negative deviation in steel thickness ； It is the thickness that determines the actual load-carrying capacity of the container, and is generally used to verify the strength and stability of the container ； It is also the main parameter for determining the maximum allowable operating pressure. (5) Minimum forming thickness: The minimum thickness required after forming the compressed component to meet the design specifications. The minimum forming thickness can be understood as the minimum thickness of a compression member required to ensure strength, stiffness, and service life. In the design documents, the minimum forming thickness can be: ① Design thickness: For shells, it refers to the sum of the calculated thickness of the shell and the corrosion allowance ； For the takeover area, in addition to the calculated thickness of the shell and the corrosion allowance, the reinforcement thickness required for opening reinforcement must also be taken into account. ②The maximum thickness that can be achieved after manufacturing and shaping, given the nominal thickness of the component. End cap marking: EHA 1200X12(10.4)-Q345R GB/T25198-2010; the value 10.4 within the parentheses represents the minimum forming thickness. ③Nominal thickness minus the negative deviation of the steel plate is equivalent to effective thickness plus corrosion allowance. The minimum forming thickness must be greater than or equal to the design thickness. (6) Steel thickness: The steel thickness of a pressure vessel shell refers to the thickness of the material actually used to manufacture that shell element, that is, the thickness specified in the steel quality certificate; it is the thickness that determines the technical requirements for vessel manufacturing.