MAWP is limited by ANSI flange in PV Elite

Basically, you are getting a "watch out" because the flange rating being used is below "normal" operating pressure of the device.

Valves have different ratings based on the temperature of the material being transferred- a 150 PSIG SWP valve is based on the temperature of saturated steam at 150 PSIG (Steam Working Pressure). The same valve may also have a 300 PSIG WOG rating that is based on "Water, Oil, or Gas" at essentially ambient conditions.

Flanges only know the pressure they are being exposed to and their ability to maintain facial contact sufficient to prevent leakage at that pressure (the fluid in the pipe is exerting pressure in all directions- radially and longitudinally. The longitudinal pressure, acting on the area of the pipe's diameter, creates pressure that is trying to separate the two pipes connected by the flange. The bolts (and the resistance to the bending torque of the flange faces) are resisting that pressure- regardless of the temperature of the fluid.

SO- if you have high pressure of a cool fluid, your flanges need to be rated to match the actual pressure to avoid leakage or rupture at the flange.