Hello Simone, I aplogise for using your last name. I couldn't figure out which was your first, and which was your last.

From -40C to 50C generally a non austenitic steel has the same design stress. After 50C the design stress is govenered by the formula: f = min(Rm/2,4; Rp0,2%t/1,5). The streses may begin to drop at different temperatures for different materials. Using your exmaple, we consider a P235GH material. If we take the value from EN 20216, Rp0,02t at 200C it is 170 MPa. Thus, the final stress value would be 170/1,5 = 113,333 MPa. If you take the 0,2% proof stress from EN10028, you will get a different value from if you take it from EN 20216, which is a piping material.

We used the piping material specification for the production of the Caesar material database.

In America we are not so familiar with the EN materials that are used in Europe. We are always open to correction if we err. Also, we do not have ready access to the European code committees. I have tried to raise a question with them but I never got a reply.