Mechanical strength refers to the function of a metal material under static load of moderate plasticity or fracture. Tension, compression, meandering and shearing are all forms of load. The mechanical properties of a square tube refer to the power of a metal to resist destruction under the action of a charge load. It can be called charge trap toughness, strength, plasticity, angle. Degree under static load, many machine parts are working in a cyclic state, so it will make the square tube fatigue; Brinell hardness, Rockwell hardness and dimensional hardness are commonly used methods of fatigue. Because the angle is the criterion for measuring the hardness and softness of a metal material, the most commonly used method is the indentation angle method, which uses the pressure of a given load shape to press into the surface of the metal material under a given load and then according to the degree of indentation.

　　Mechanical strength refers to the function of a metal material under static load of moderate plasticity or fracture. Tension, compression, meandering and shearing are all forms of load. The mechanical properties of a square tube refer to the power of a metal to resist destruction under the action of a charge load. It can be called charge trap toughness, strength, plasticity, angle. Degree under static load, many machine parts are working in a cyclic state, so it will make the square tube fatigue; Brinell hardness, Rockwell hardness and dimensional hardness are commonly used methods of fatigue. Because the angle is the standard to measure the soft and hard of metal materials, the most commonly used method is the indentation angle method, this method is to determine the number of load shape of the pressure into the surface of the metal material under a certain load, and then according to the degree of indentation, to determine the angle of plasticity is said to be metal materials; Under normal load, even if surface deformation occurs, there will be no complete damage.

　　The longitudinal welded pipe has the advantages of simple production process, high production efficiency, low cost and rapid development. The strength of spiral welded pipe is generally higher than that of straight seam welded pipe. It can be produced with narrow blank with larger pipe diameter. It can also be produced with the same width of blank with different pipe diameter. However, compared with the straight seam pipe of the same length, the weld length is increased by 30~100% and the production speed is low.

　　Therefore, small diameter welded pipes are mostly welded longitudinally, while large diameter welded pipes are mostly spiral welded.