Papers by Keyword: X70 Pipeline Steel

Abstract: With the development of the natural gas industry, high flux natural gas pipelines will cause local deformation because of pressurization, which has an important effect in the service safety of pipeline materials. In this paper, the X70 pipeline steel with weld zone was studied, and the tensile test was used to simulate the uniaxial tensile stress. The results showed that the strain was mainly concentrated in the weld zone, which can imply that the weld zone has high strain hardening ability. The heat-affected zone with poor internal structure was prone to breakage. The research results can provide theoretical basis and experimental basis for pipeline steel welding process design and safety evaluation under high flux conditions.

Abstract: In this paper, the macroscopic mechanical behavior of tensile fracture of X70 pipeline steel is combined with the evolution of mesoscopic pores. The ABAQUS finite element software was used to analyze the variation of pore volume fraction in the tensile failure process of unilateral notched specimens with Gurson-Tvergaard-Needleman (GTN) mesoscopic damage model. Combined with the unilateral notched tensile test and the numerical simulation results, the damage mechanics model of pipeline steel based on void volume fraction is established. The results show that the volume fraction of pores is a mesomechanical parameter based on the damage of the micro-holes in the metallic plastic material, which is a bridge between the mesoscopic damage characteristics and the macro-mechanical parameters. Establishing the damage mechanics model of high strength pipeline steel with hole volume fraction as damage variable can truly reflect the macro-meso-mechanics behavior of X70 pipeline steel during unilateral notching.

Abstract: Anti-H₂S X70 pipeline steel was developed. The microstructure of X70 pipeline steel was studied by the analysis of OM, SEM and TEM. The precipitation behavior was discussed. The comprehensive mechanical properties, HIC and SCC performance were systematically studied. The results indicated that the microstructure of the experimental steel was mainly acicular ferrite and granular bainite. The second phase precipitates dispersedly distributed in the matrix. The experimental steel possessed excellent strength, plasticity, low temperature toughness and low yield ratio. And therefore, the X70 pipeline steel in the study is suitable for sour service with the high strength, excellent toughness and low HIC&SSC susceptibility.

Abstract: The oleophobic surface has extremely broad application prospects in industrial production and daily life. It can prevent the adhesion of materials and fouling, and prolong the service life. In this investition, an oleophobic surface on X70 pipeline steel specimen was prepared successfully by the combination of sandblasting, chemical etching, and low energy modification. The microstructure and oleophobicity of the surface were studied by scanning electron microscope (SEM), contact angle tester, and confocal microscope. The results showed that micro-nanocomposite structure on the specimen was formed after sandblasting and chemical etching of concentrated hydrochloric acid aqueous solution. The low-energy modification of perfluorooctanoic acid anhydrous ethanol solution just covered the surface, but had no obvious influence on the surface morphology. After chemical etching and low-energy modification, the specimen processed by sandblasting for 30s obtained the better oleophobicity, and the maximum contact angle between the surface and engine oil was 130°.

Abstract: The continuous cooling transformation behaviors were researched on X70 pipeline steel through two pass deformation and non-deformed austenite using Gleeble-3500 thermal mechanical simulator, and static continuous cooling transformation curve and dynamic continuous cooling transformation curve were measured through thermal dilation method and metallographic method. The influence of cooling rate and deformation parameters on microstructure was analyzed. The results show that the hot deformation accelerates the acicular ferrite and polygonal ferrite phase transformation, increases the starting transformation temperature and the finishing transformation temperature significantly, and shifts the CCT curve moving upward to the left side corner. Acicular ferrite is obtained in practice using accelerated cooling rate after deformation Acicular ferrite can be obtained in wider range of cooling rates, and microstructure and island structure is finer through hot deformation.

Abstract: The main purpose of this study is to develop a numerical model to describe the static recrystallization kinetics in X70 pipeline steel. In order to investigate the static softening behavior, double-hit compression tests were performed on a Gleeble-3500 thermomechanical simulator over a temperature range of 950-1150°C. The interpass time varies from 1-500s. Different values were applied to estimate effects of strain rate and deformation on static recrystallization. The results show that factors such as high temperature, long holding time and lower strain rate will lead to the inclination of softening behavior. The static softening activation energy was obtained. The good agreement between the predicted values and experimental results indicated the validation of the developed model of this study.

Abstract: The DWTT fracture toughness of X70 pipeline steel with different content and grain size of polygonal ferrite was investigated. The results show that when the content of polygon ferrite is above 28%, the shear-area percentage of DWTT fracture begins to decrease instead of increase, while polygonal ferrite toughening effect weakens. It is the difference of the polygonal ferrite content that results in the difference of shear-area percentage of DWTT fracture.

Abstract: Microstructure and mechanical properties of X70 pipeline steel with polygonal ferrite plus granular bainite were characterized using tensile tests, Charpy V-notch impact tests, drop weight tear tests, hardness tests and scanning electron microscopy. The results of experiment indicated that X70 pipeline steel with polygonal ferrite plus granular bainite showed an excellent combination of high strength and toughness. The base metal with polygonal ferrite plus granular bainite microstructure exhibited perfect mechanical properties in terms of the transverse yield ratio of 0.81, elongation of 46%, an impact energy of 335 J at -10 °C and a shear area of 90% at 0 °C in the drop weight tear test. The heat affected zone contained coarse grain zone and fine grain zone, which exhibited good low temperature toughness of 216 J at -10 °C. The weld metal primarily consisted of intragranularly nucleated acicular ferrites which led to the high strength and toughness.

Abstract: Based on the actual production data of ASP (Angang Strip Production) hot strip rolling line, mechanical properties of thin gauge X70 pipeline steel were simulated by BP neural network method. Recursive functions were used to verify the mechanical properties which calculated by BP neural network. Based on predicted mechanical properties with high precision, BP neural network and Genetic Algorithm (GA) were combined to establish the temperature schedule of X70 pipeline steel during ASP hot strip rolling. It is shown that there are four important temperatures during ASP hot strip rolling, such as rough rolling temperature, refine start rolling temperature, refine finish rolling temperature and coiling temperature. Temperature difference of adjacent stages and temperature of former stage is a linear function relationship. For a given mechanical properties, deviations between simulated temperature and actual temperature are within ±10°C. This method can be used to produce different strips with the same compositions but different strengths by regulating suitable temperature schedule, so it is effective to resolve conflicts during hot strip rolling.

Abstract: A successful ultra fast cooling (UFC) technology has been applied to the plate rolling production line in Shouqin Metal Materials Co.Ltd.. Industrial trials are reported for the production of X70 pipeline steels (about 70000 t) under UFC conditions. Pipeline steels with reasonably good properties have been produced on an industrial scale. UFC improves the temperature uniformity, the mechanical properties and the plate profile of X70 pipeline steel. The impact values of X70 pipeline steel at UFC mode exceed the standard requirements of X80 pipeline steel. The productivity is enhanced because cutting quantity of head and tail of the plate is reduced. The enhancement of control accuracy of the red back temperatures is favorable for industrial production of X70 pipeline steel. The reduced production of the steel-making has been industrialized achieved, since a new composition was designed by reducing the vanadium content to less than 0.045wt.%.