The paper describes the present methodology for assessment of safety of bridges and the remaining life of steel railway bridges. The majority of railway existing bridges are riveted, and this field has been researched in former studies, but there are also many welded bridges. Many bridges are still in operation after damages, several phases of repair and strengthening. The replacement of old bridges raises some technical and financial problems. This is the main reason why new method for assessment, based on fracture mechanics principles is researched.