Fracture characteristics of ssaw steel pipe

A broken section along strict crystals - product surface separating the planes called cleavage plane. Along the fracture plane, the theoretical has with minimum breaking strength. Decision cleavage plane of factors specific surface energy y, the surface of the crystal plane spacing mountains and modulus of elasticity along the normal direction. Cleavage fracture with almost no plastic deformation, is a brittle fracture occurs in the body-centered cubic, hexagonal close-packed gold center. Fcc metals is generally not cleavage fracture occurs. The nature of the genus L ductile material gold sessions, shear fracture is the main fracture mechanism. Such as anti-corrosion steel alloy second phase particles to impede slippage, increasing the resistance to plastic deformation; when the plastic deformation increases, the second phase particles and the matrix interfacial peeling occurs Aung, produce tiny hole; hole formed, grew up with the merger will form a shear section. For high-purity metals, for there is no second phase particles, double metal wear-resistant composite pipe and will not yield: Health and tiny holes, the results of the battle was only shifted along the surface area is increasing, and finally the formation of slip planes separate section. Anti-corrosion steel composite spinning technology under special equipment for precise control, re-pressed wheel rotation and liner friction generates heat quickly reach the softening point of stainless steel, roller squeeze out of the outer tube is elastically deformed, the two create an interference together to achieve closely. From gold session histological point of view, it is divided into the fracture and transgranular fracture along the fracture goods.

In different directions along the spiral of the sample taken tensile and impact tests, found that test different directions of yield strength and ultimate strength difference is small, generally only in the 5-10% range, while the direction of the sample values of different cvn difference large, cvn value entirely with the angle changes. Spiral although yield strength and ultimate strength in different directions difference is small, showing a very slight strength anisotropy, however cvn value in different directions is a big difference, that exhibit very serious impact toughness anisotropy the consequences of this serious cvn anisotropy values generated by the fracture resistance is different in different directions: straight along the rolling direction, that is the same as the spiral weld direction, the fracture of least resistance, that is easy along cracking in this direction; perpendicular to the rolling direction of the fracture resistance of the maximum; in the axial direction, the fracture resistance in between.

For pipelines, the maximum principal stress is the hoop stress, that is the biggest driver of cracking along the axial direction. In other words, just from the stress situation, genetic defects most likely to crack the axial direction. For straight seam pipe, the direction of maximum and minimum driving directions crack fracture resistance is the same, and therefore the fracture must be carried out in the axial direction. However, for the ssaw steel pipe, the two are not the same.

Pipe defects are rarely found in the base material, generally in the weld or heat affected zone, and defects in the weld or heat affected zone is most consistent with the trend of the weld, ie straight seam pipe defects axial direction, the spiral ramp of the defects.