The so-called package Singh effect refers to polycrystalline metal is pre-loaded to produce a small amount of plastic deformation (1% to 4%) after uninstalling, then if the same load, the elastic limit rises, the reverse of the elastic limit decline; but if the material pre-deformation is too large (> 4%), followed by reverse load, elastic limit there is no lift. This phenomenon is a German scientist bauschinger first discovered in 1886, it is named after its name. Cause Bauschinger effect produced is because polycrystalline metals due to different grain orientations, resulting in stress in the role of grain boundaries when deformation caused.

Deformation strengthening, also known as hardening or strain hardening, referring to the metal in the deformation process, when the stress exceeds the yield strength, plastic strain deformation resistance increases with the increase of the phenomenon, which is to increase the deformation resistance increases dislocations motion the result of.

Steel plate in coils or pipe, expanding (reducing), tensile test specimens subjected to flatten process complex tension and compression deformation and deformation effects package Singh strengthening effect throughout the metal deformation always, their mutual action determines the ultimate tensile properties of steel pipe.

Here compressive deformation refers only to the steel pipe wall thickness of the whole subject to the same degree of compression deformation, such as the O UOE molding, ERW in sizing will make the pipe-wall deformed by compression. If at this time to measure the tensile properties of the pipe, they should focus on considering bauschinger effect, it may reduce the yield strength of the pipe. If a large amount of compression (such as ERW), but also to give due consideration to the compression deformation hardening effect brought about its ultimate strength ERW pipe it has an important influence.

Expanding and compression and contrast, through-wall steel pipe to produce the same level of tensile deformation. Expanding the role of hardening caused by the tensile properties of steel pipe will have a more substantial increase.

Step UOE pipe produced in the process of metal deformation are: pre-bending and U shape, O shape, expanding and flattening the sample. Bending and flattening the sample, are pre-bending and U bending process molding produced little effect on the package Singh effect, affect the ultimate tensile properties of steel is O molding process and expanding. O molded steel pipe is compressed, so reducing the yield strength; expanding the steel pipe is stretched, so that increased yield strength. In addition to steel ultimate tensile properties depending on the degree of compression and expanding, but at the same time also depends on the material microstructure and strength level. In actual production, the plant is often based on the microstructure and properties of raw materials within the standard range, appropriate adjustments to the amount of compression and expanding capacity to meet the performance requirements of tensile steel required, thus demonstrating the flexibility UOE pipe(lsaw steel pipe).