Q345 seamless pipe belongs to low alloy series – low alloy high strength structural steel (GB / t1591-1994). Q345A, B, C, D and E are the representative grades of this kind of steel. Compared with carbon structural steel, Q345A has the advantages of high strength, good comprehensive performance, long service life, wide application range and relatively economic. It is widely used in bridges, ships, boilers, vehicles and important building structures.