wromero,

In case you are using the design conditions to evaluate the connection and the design condition is close to the temperature-pressure coverage limit for the material, the flange connection will always fail due to the butterfly effect.

I would use the maximum operating condition for the evaluation for the flange. If it still fails you are correct in increasing the class of the flange.

Additionally, equivalent pressure method mostly used for screening the flanges in the analysis for the conditions that thay are in. So you can select the same type (class and size) flange connection with the highest ratio of Pequivalent/Pallowable to reduce the number of calculation for the same range of the flanges. And then use the force and moment of this connection in the "Flange Analysis" option of Caesar II to check for strength and leak. If this calculation passes, the flange connection is adequate although the equivalent method gives more than 100% for the ratio.

Hope this helps.

Ibrahim Demir