Strengths: It can destroy the forged structure of steel ingots, refine the grain of seamless steel pipe, eliminate the defects of microstructure, and then make the steel structure compact and improve the mechanical function. This improvement is mainly in the direction of rolling, then The seamless steel pipe is no longer an isotropic body at the inevitable level. The bubbles formed during the pouring, cracks and looseness can also be welded under the high level and pressure effect.
Defects: 1. After hot rolling, the non-metallic inclusions inside the seamless steel pipe (primarily sulfides and oxides, as well as silicates) are pressed into thin sheets, presenting a layered (sandwich) landscape. The function of the seam steel pipe to the tension is greatly deteriorated, and the layer can be broken when the weld seam is shortened. The partial strain induced by the weld seam shortening often reaches several times the strain of the yield point, which is much larger than the strain caused by the load.
2. Residual stress formed by uneven cooling. Residual stress is the internal self-phase equilibrium stress without external force effect. Hot-rolled steel of various cross-sections has such residual stress. The larger the cross-section size of ordinary steel, the more residual stress. Large. Residual stress is self-phase equilibrium, but it has an inevitable effect on the function of steel members under external force effects. For example, deformation, invariance, anti-euphemism and other aspects can produce helium.
3. Hot-rolled seamless steel pipe products, about the thickness and width of the side is not good control. We are familiar with thermal expansion and contraction, because the beginning of the hot rolling out even if the length, the thickness is up to standard, the final cooling will still be inevitable The negative difference, the wider the width of the negative difference, the thicker the thickness, the more distinct the display.
The flexible seamless steel tube has a four-layer structure, the innermost layer is an extruded thermoplastic tube that seals in the transport liquid; the central two-layer lining is filled with a carbon-filled polyethylene tube, which has a long-term exposure to ultraviolet light. The ability to radiate and remove external static electricity. The outermost layer is an extruded, thick outer shroud that is used to maintain the bottom layer of the tube from external influences.
The additional pressure for the specification of flexible seamless steel tubes meets the ANSI classification, such as grade 300 is equivalent to 5.15 MPa; grade 400 is equivalent to 6.89 MPa; grade 600 is equivalent to 10.3 MPa. The design of offshore flexible seamless steel pipes is based on API17J, 17K and RP17B. The design specifications for flexible steel pipes for land slightly deviate from the requirements of the API specification. The API17J classification method and data are used, and the pressure, tensile force and damage limit are within the limits of the rules. The experiment was carried out in accordance with the requirements of APIRP17B.
