Papers by Keyword: X70 Steel

Abstract: During the process of Carbon Capture and Storage, some impurity may be found in the supercritical CO₂ fluid. The changes in corrosion of X70 Steel in water-saturated supercritical CO₂ system caused by impurity has been studied by the simulation experiment. The average corrosion rate was got from weight loss measurement. The morphologies and compositions of corrosion products were analyzed by SEM, EDS and XRD. It was observed that the existence of separate impurity would aggravate the corrosion of X70 steel in the water-saturated supercritical CO₂ system. The average corrosion rate was the highest when NO₂ or SO₂ was included, followed by H₂S, and the average corrosion rate was the smallest when O₂ was contained. Among them, X70 steel suffered local corrosion when NO₂ was contained. The corrosion scale was monolayer structure of FeCO₃ under the supercritical CO₂-H₂O system. After the addition of O₂, Fe₂O₃ appeared in the corrosion scale, indicating that the oxygen corrosion process occurred. While with the addition of H₂S, corrosion scales were double layers. FeS was mainly present in the outer layer. The corrosion process was controlled by CO₂ and H₂S. The corrosion products were mostly FeSO₃·xH₂O and a spot of FeCO₃ when SO₂ was contained. SO₂ mainly governed the corrosion process. Besides, corrosion product was Fe₂O₃ without FeCO₃ in the supercritical CO₂-H₂O-NO₂ system, NO₂ completely controlled the corrosion process.

Abstract: When austenite is deformed within the austenite phase field, it partially transforms dynamically into ferrite. Here, plate rolling simulations were carried out on an X70 steel using rough rolling passes of 0.4 strain each. The influence of the number of roughing passes on the grain size and volume fraction of induced ferrite was determined. Up to three roughing passes applied at 1100 °C followed by 5 finishing passes at 900 °C were employed. The sample microstructures were analysed by means of metallographic techniques. Both the critical strain to the onset of dynamic transformation as well as the grain size decreased with pass number during the roughing simulations. For the finishing passes, the mean flow stresses (MFS`s) applicable to each schedule decreased when a higher number of roughing passes was applied. The volume fraction of dynamically formed ferrite retained after simulated rolling increased with the roughing pass number. This is ascribed to the increased amount of ferrite retransformed into austenite and the finer grain sizes produced during roughing. The forward transformation is considered to occur displacively while the retransformation into austenite during holding takes place by a diffusional mechanism. This indicates that both dynamic transformation (DT) and dynamic recrystallization were taking place during straining.

Abstract: The influences of testing specimen thickness (TST) on fracture toughness, including drop weight tear test shear area (DWTT) and crack tip opening distance (CTOD), are studied by experimental method for X70 steel. Results show that DWTT and CTOD reduce gradually with the specimen thickness increasing, showing an apparent TST effect. DWTT results also show that the TST effect is more significant at the middle transition temperature range. Parameters including J-integral, constraint parameters (T₃₃&T_z) and plastic volume ratio (V_r) of SENB specimens with different thickness are calculated by FEA method. Then the TST effect correlation of |T₃₃|, T_z and V_r are compared. All parameters show a strong thickness dependent. Crack tip constraint parameters, |T₃₃| and T_z, have a similar variation tendency, but different from that of J. Contrary, V_r has a more similar variation tendency with J. Therefore, plastic deformation behavior cannot be ignored during studying the TST effect of X70 steel. V_r can be treated as an alternate parameter to explain TST effect.

Abstract: Considering the mechanical properties of X70 pipeline steel after repeated welding heat cycles, preheating and interpass temperature controlling are often adopted in the welding technology, which widely increase the welding construction time and lower the construction efficiency, thus improve the construction cost of pipelines. According to the present welding process of X70 pipeline steel, non-preheating welding technology was proposed in this paper. The experiment results show that the properties of the weld joint of X70 pipeline steel with non-preheating achieves the requirement of specified standard. Furthermore, this method simplifies the welding construction processes and improves the construction efficiency. Key Words:X70 Steel; Non-Preheating; Welding Technology

Abstract: The paper presents results of the numerical modelling of the plates accelerated cooling process after the rolling process. Research were carried out for one of the plate rolling mill technological conditions. Presented in the paper research were done for a few variants for X70 steel grade. As a result of the carried out research temperature distribution on the cross section of the cooled plates for the analyzed variants of the accelerated cooling process were obtain.

Abstract: The effects of preparation conditions on the synthesis of polyaniline and its anticorrosion performance were investigated using single-factor method. The experimental results showed that the better conditions for electrochemical synthesis of polyaniline films are 0.5 M aniline, 0.8 M H2SO4, range of sweep voltage 1.6 V~-0.3V (Init =-0.3V), sensitivity 1.e-002, sweep segment 8, scan rate 0.1V/s. The anticorrosion performances of polyaniline films were investigated in 5% and 2.5% MgCl2 solutions respectively. Polarization and AC impedance technique tests proved that the polyaniline film owned a better anticorrosion performance to X70 in 2.5% MgCl2 solution than the denser one. And, it was found that polyaniline films adhered to X70 steel exhibited good barrier properties for a prolonged corrosion process. The above results provided some experimental data and theoretical guidance of polyaniline anticorrosion properties for some metals, especially for metals using in oil and natural gas industry.

Abstract: Metal magnetic memory technology is a passive magnetic method of non-destructive testing based on the residual magnetic field of a ferromagnetic component. The MMM measurements were performed on a series of X70 pipeline steel samples for various values of uniaxial elastic and plastic deformation from zero up to about 20% strain. The outcomes evidence that the metal magnetic memory gradient index m can be used to evaluate the stress-strain state of ferromagnetic materials under tensile stresses. The tensile stress effect on the gradient index m significantly in elastic stage, but the gradient index m remained unchanged in the plastic deformation stage.

Abstract: Electrochemical impedance spectrum (EIS) technology and microscope analysis were used to investigate the corrosion behaviors of X70 pipeline steel in 0.5 M NaHCO₃ + 0.5 M NaCl mix solution. The effects of applied stress on the open circuit potential (OCP), polarization resistance and surface microscope were summarized. The results show that OCP of X70 steel decreased linely with applied stress increasing. The polarization resistance also decreased with the increase of stress. The electrode reaction on X70 steel surface changed from activation control to diffusion control and mixed control and corrosion resistance of X70 pipeline steel declined. The number and the diameter size of pit on the sample surface increase with applied stress increasing.

Abstract: Fatigue crack growth (FCG) tests have been performed in an X70 steel with various microstructures (respectively in the as-received and the normalized condition). The effect of room temperature creep (RTC) on FCG behavior has been investigated by comparing with single wave overloads (SWOL). The as-received X70 pipeline steel has high FCG rate at the near-threshold region. While at the Paris region, FCG rate seems insensitive to the microstructure. In both conditions, time-dependent deformation is observed at crack tips (i.e., RTC), which increases with increasing stress-intensity-factor. And this deformation has a high value in the normalized state, under identical testing conditions. Both RTC and SWOL can bring subsequent fatigue crack growth a very short initial acceleration before deceleration, whereas the former induces more serious deceleration and retardation, which attributes to more significant crack closures.