Question: For DN700, with a pressure of 4.2 Mpa, what is the wall thickness?

The comparison table I saw online doesn’t have this level :(

You still lack the necessary conditions; use the operating temperature and material specifications. Refer to the national standards 50316 and GB20801 for calculations – it’s quite fast

There is no pressure rating for this; the nearest equivalent is PN40. For PN40-DN700 cast steel bodies, the wall thickness is 23.8 mm. For specific details, refer to GB26640

Yes, you must specify the temperature, the medium, as well as the medium to be used. Here is the basis for the calculation. Code for Design of Industrial Metal Piping (GB 50316——2000) 6.2 Straight Pipes 6.2.1 Calculation of the thickness of straight pipes subjected to internal pressure shall comply with the following provisions: 6.2.1.1 When the calculated thickness of a straight pipe is less than 1/6 of the outer diameter of the pipe, its calculated thickness shall not be less than the value calculated according to Equation (6.2.1-1). The design thickness shall be calculated according to Equation (6.2.1-2). (6.2.1-1) (6.2.1-2) (6.2.1-3) The determination of the Y coefficient shall comply with the following provisions: At that time, it shall be selected according to Table 6.2.1 ； At that time, in equation (6.2.1-4), —— represents the calculated thickness of the straight pipe (mm); —— is the design pressure (MPa); —— is the outer diameter of the pipe (mm); —— is the inner diameter of the pipe (mm); —— is the allowable stress of the material at the design temperature (MPa); —— is the weld joint coefficient ； ——Design thickness of straight pipe (mm); ——Sum of thickness additions (mm); ——Thickness reduction additions, including machining, grooving, and thread depth, as well as negative deviations in material thickness (mm); ——Corrosion or abrasion additions (mm); ——Coefficient. Coefficient Y values Table 6.2.1 Materials Temperature (°C) ≤482 510 538 566 593 ≥621 Ferritic steel 0.4 0.5 0.7 0.7 0.7 0.7 Austenitic steel 0.4 0.4 0.4 0.4 0.5 0.7 Other ductile metals 0.4 0.4 0.4 0.4 0.4 0.4 Note: (1) Y values for temperatures between those listed in the table can be calculated by interpolation. (2) For cast iron material, Y=0. 6.2.1.2. When the calculated thickness of the straight pipe is greater than or equal to 1/6 of the outer diameter of the pipe, or when the ratio of the design pressure to the product of the allowable stress of the material at the design temperature and the weld joint factor is greater than 0.385, special consideration must be given to factors such as fracture theory, fatigue, and thermal stress in calculating the thickness of the straight pipe. 6.2.2 The thickness and reinforcement requirements for straight pipes subjected to external pressure shall comply with the provisions of the current **standard ‘Steel Pressure Vessels’ GB150.

I’m sorry, the formula didn’t appear. It’s hard to be sure if you check on your own. For general cases, a rough calculation can be done using the formula: Thickness = PD/2