When HG/T20592 flanges are used as equipment flanges, is it necessary to conduct checks?

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A small device made of 304 material, with an outer diameter of 159, a wall thickness of 6, and an inner diameter of 147; its cylinder body is made from a steel tube with dimensions φ159×6. Operating pressure: 3.2 MPa; design pressure: 4.0 MPa. The SW6 software for hydrostatic testing calculates the value at 6.4 MPa. Operating temperature: 320°C, design temperature: 400°C. The upper head and the cylinder are connected using HG/T20592 flanges WN150-63RF. Question 1: This device has an inner diameter of 147 and a total volume of over 30L; is inspection required? Question 2: Referring to the pressure and temperature rating table in standard HG/T20592, for PN63, 2C1, with an operating temperature of 350°C, the maximum allowable operating pressure (gauge pressure) is 34.5 bar, which is equivalent to 3.45 MPa. However, the operating temperature of my device is only 320°C, and the operating pressure is 3.2 MPa, which is lower than the 3.45 MPa specified in the table. Can the WN150-63RF be used directly as the equipment flange? (I used SW6 software for the calculations, and found that the WN150-63RF case could not be processed successfully; the calculations could be completed only after increasing the effective thickness of the flange by 5 mm.) But many people on the Internet say that the SW6 software is too conservative in its calculations, and many standard flanges fail to pass the checks). Since the customer does not need to provide a calculation sheet, should the WN150-63RF standard flange be chosen directly? Is it still necessary to thicken it?