P265GH is a carbon steel material in accordance with EN 10028-2 (equivalent to A515 Gr.60)
Properties shown in this standard vary on plate thickness.
Which code are you going to use in the equipment design?
For plate thickness up to 16 mm and at room temp.
yield stress is 265 MPa and ultimate stress is between 410 and 530 MPa per En 10028-2.
Re allowable stress see previous answer