Welded pipes or highway bridges bear the impact load of vehicles, and bridge steel requires certain strength, toughness, and good fatigue resistance, with high requirements for the surface quality of the steel. Bridge steel is often made of alkaline open hearth killed steel, and ordinary low-alloy steels such as 16 manganese, 15 manganese vanadium nitrogen, etc. have been successfully used.

This type of welded pipe mainly ensures its mechanical properties, so its grade reflects its mechanical properties, represented by Q+numbers, where "Q" is the Chinese Pinyin prefix of the yield point "qu" character, and the number represents the yield point value. For example, Q275 represents a yield point of 275MPa. If the letters A, B, C, and D are marked after the grade, it indicates that the quality grade of the steel is different, and the amount of S and P decreases in order, while the quality of the steel increases in order. If the letter "F" is marked after the grade, it is boiling steel, if "b" is marked, it is semi killed steel, and if "F" or "b" is not marked, it is killed steel. For example, Q235-A · F represents A-grade boiling steel with a yield point of 235 MPa, and Q235-c represents C-grade killed steel with a yield point of 235 MPa.