X80 Pipe Steels Research Articles

A novel process involving multiple strengthening mechanisms for production of low-residual stress X80 pipe steel based on ultra-fast cooling

Abstract This work aims at developing low-residual stress heavy gauge X80 pipe steel. A novel processing route involving combined mechanisms of precipitation strengthening and refining grain was first proposed based on ultra-fast cooling. Compared with conventional laminar cooling process, the high cooling rate of ultra-fast cooling and the induced re-reddening could promote the acicular ferrite transformation and nano precipitations, which ensured the toughness and strength at the same time. With ultra-fast cooling, the X80 pipe steel could be prepared at high coiling temperature instead of low coiling temperature less than 400 °C and the X80 pipe steel exhibited low-residual stress. Besides, this work also indicated a wide processing widow under ultra-fast cooling.

The Structure and Mechanical Properties of Low Carbon Steel after Controlled Rolling and Low-Temperature Treatment

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Corrosion Behavior of X80 Pipe Steel under HVDC Interference in Sandy Soil

With the development of high voltage direct current (HVDC) systems, some pipelines have been badly interfered. The corrosion mechanism of pipelines has not been clearly clarified. In this work, laboratory experiments were designed to study the corrosion behavior of X80 steel under HVDC interference in sandy soil. The corrosion rates were related to the change in direct current (DC) density, which experienced three stages in the interference process. As soon as high DC interference voltage was applied to the working electrode, the current density increased sharply to a peak value in a few seconds. It then decreased rapidly to a steady value over dozens of seconds. Finally, it remained steady for the remaining time. With the measurement of local soil properties, the change in DC density was attributed to the local soil temperature increment, the water content decrement, and the substantial growth in the soil spread resistance. Moreover, the parameters contribute to the corrosion reaction during the interference process. The corrosion products were characterized at different times of interference via Raman spectroscopy. Lepidocrocite was produced under high DC density and then transformed to hematite under low DC density. Based on the above, the corrosion model during HVDC interference is proposed.

Fatigue Crack Growth Rate of High Strength Pipe Steels

Fatigue crack growth rate is a significant mechanical property of high strength pipe. Some properties of fatigue crack propagation can be obtained by evaluating the mechanical performance of the material. In this study experiment studies were conducted with the fatigue crack growth rate test for two commonly used high strength pipe steels, X70 and X80 pipe steels, and the relationships between the length of the crack (a) and the number of the loading cycles (N) were derived. In addition, the crack tip opening displacement Δδ was calculated. Based on the experimental results, a regression equation was fitted for da/dN and Δδ. Results showed that the regression equation is similar to the Paris Formula, and X80 pipe steel has lower crack growth rate than the X70 pipe steel.

Microstructure and disperse phases of X80 pipe steel for gas pipelines

Microstructure and disperse phases of X80 pipe steel for gas pipelines