Hi Henrique,
I suggest you model the window and a shoulder as an Axisymmetric model. In the XY plane, the Y axis is the axis of revolution. Draw a rectangular surface from the origin 2.5 mm along the X axis and 1 mm along the Y axis. This defines your circular 5 mm diameter window in an axisymmetric model. Then draw a rectangular surface starting at X = 1.5, on the Y axis and go out to X = 3.5 and down to Y = -2.0 to make the blue part with a 2x2 mm cross section of an annular ring for the window to sit on. If you add a small radius on the corner, you can avoid high stress due to that sharp corner.
What version of ANSYS do you use? I can make that model very quickly for you to try out.
After you know the window can take the pressure, you will want to consider how to seal the window against the metal vessel.
What are the properties you have for diamond?
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