Spiral Steel Pipe Residual Stress

Residual stress is the member which has not been exposed to the initial stress loads on the section member already exists many causes, wherein the welding residual stress is a very important one, in addition to the steel in the process will produce stresses involved during welding is a weldment local heating process and then gradually cooled, non-uniform temperature field will allow each part of the weldment uneven deformation, resulting in a variety of welding residual stresses. Internal stress of welded components generated by the welding called welding stresses the role of time can be divided by the instantaneous welding stress and welding residual stress. A welding process, welding stress is called instantaneous instantaneous welding stress, which change over time. After remaining in the weldment welding residual stress is called stress. For steel, the welding residual stress and deformation structure is an important factor affecting the fracture strength, fatigue strength and structural stability. Welding residual stress significantly reduces the effective proportional limit welded parts material, the structure is one of the important reasons brittle fracture. Tensile residual stress in welded structures will reduce the ability of structural fatigue and corrosion; residual compressive stress will reduce the stiffness of the compression members, so that the stability capacity. 


Spiral welded steel pipe in the petrochemical, heat and urban drainage pipe network engineering and other fields have a wide range of applications, especially in the long-distance transportation of oil and natural gas pipelines are more widely used. Oil, gas pipeline network, almost all spiral welded steel pipe, with high security, durability and economic rationality. Since the diameter of the spiral welded steel plates generally unrestricted width of the plate width coil manufactured by a variety of different specifications, there is no need of a wide steel plate width. This gives the plate manufacturing, transportation convenience, than the flat strip steel used in a much lower price, suitable for China's actual situation. A problem is present in spiral welded steel pipe after welding to produce elastic recovery, pre-exposed to the equivalent of a pipe circumferential tensile stress, the stress is reduced and the stress corrosion ability of the pressure pipe. 


Forming a continuous spiral welded steel pipe, the welding method of manufacturing is now widely used to hold the inner and outer-supporting two kinds of molding method can be obtained by adjusting the shape and size of the different pipe. In order to prevent excessive bending height, roll forming three points of contact with the steel plate is generally not much difference, manufacturers are using less than the amount of molding, pipe radius of curvature radius of curvature is relying on the order of the rollers (or outside hold rolls) are formed that in the order of the roll (or outside hold roll) in steel is actually elastic and plastic deformation mixed. After spiral welded steel pipe along the direction of the bus after the cut, there must be a certain amount of circumferential opening that steel complex there is a certain amount of bombs, pipe there is a residual internal stresses. Because of the internal stress, the outer pipe is a tensile stress, and therefore, this will reduce the bearing capacity of the steel pipe, increasing the external pipe corrosion, to adversely affect the use of steel.