CL300 in the design manual corresponds to 5.0MPa, which refers to the reference value of English pressure grade and nominal pressure PN, and is not a standard provision. The standards of early China were formulated with reference to the model of the former Soviet Union, which is still in use today, and is different from the standards of western countries. For example, the Class300 steel valve in American Standard must meet the working pressure of 300lb(2 1 bar) at 425.5℃, so its working pressure can be greater than 300 lb or even as high as 600 lb； below 425.5℃. However, China standard stipulates that the working pressure of PN25 steel valve is 25bar at 200℃, 23bar at 20 1~250℃, 20 bar at 25 1~300℃ ... at 201~ 425℃, Compared with China standard PN40, the working pressure should not be lower than American standard, and' PN50' is adopted to distinguish European and American series. Similarly, CL 150 corresponds to PN20, and CL600 corresponds to PN 1 10. .......
As for the flange thickness of CL600 and PN 1 10, I don't think the two standards can be completely consistent. Since the characteristics of CL600 flange in American standard have met the working conditions, it is not necessary to change it in national standard PN 1 10. If it is changed, it will be bad, and the dimensions of the two flanges will not be uniform.
Don't think that the standards in our country are perfect. Look carefully, our country's standards are full of loopholes. You don't know how the standards of our country are brewed, do you?