Mn Pipeline Steel Research Articles

Mechanical properties and microstructure of longitudinal submerged arc welded joint of a new C–Mn steel sheet cladding fine grained ferrite in surface layer for a long distance transport pipeline

A new type of C–Mn pipeline steel plates with the ult5ra-fine grained ferrite in surface layer and the fine-grained ferrite in the central layer has been developed successfully. In order to manufacture the long distance oil pipelines using this new ultra-fine grain pipeline steel sheet, the microstructure and mechanical properties of the welded joints by the Longitudinal Submerged Arc Welding (LSAW), especially the impact toughness, need to be evaluated. Tensile tests, impact tests, are used to study the mechanical properties in this paper according the Chinese National standards. The metallographic technique and SEM are adapted to analyze the microstructure and impact fracture morphology of the LSAW joint. The research results show that the HAZ near the fusion line is a weak part of impact toughness of LSAW joint. However, the base metal is of the fine-grained and ultra-fine grained microstructure itself, and the heat treatment effects between the post-process welding seam and pre-process welding seam on the multi-layer and multi-pass submerged arc welding process, the impact toughness of the HAZ is greatly improved. The whole welded joint is better than the performance of ordinary pipeline steel, which is satisfied with the welding performance requirements of steel sheet engineering application, and can be used in long distance pipeline manufacturing projects.

Effect of Different Rolling Schedules on the Mechanical Properties and Microstructure of C Mn (V-Nb-Ti) Pipeline Steel

High strength low-alloy (HSLA) steels have been used for the production of welded pipes for more than 30 years. However, the alloy design of pipeline grades is being continuously modified and the process technology optimized because of increasing demand of high strength toughness combination requirement of pipeline steels. The HSLA steels have demonstrated superior mechanical properties through controlled rolling. In the present investigation, the effects of processing parameters, such as finish rolling temperature, rolling reduction and cooling rate, on the final microstructure and mechanical properties of a grade X70 type HSLA steel has been studied by tensile and charpy impact tests and optical microscopy. To yield better mechanical properties of X70 microalloyed steel grade, the optimization of the rolling process in the laboratory experiment and rolling mill has been carried out.

Effect of heat treatment on H 2S corrosion of a micro-alloyed C–Mn steel

The H 2S corrosion resistance of a C–Mn pipeline steel with three different microstructures has been evaluated using electrochemical techniques with a 3% wt. NaCl solution at 50 °C. Microstructures included martensite, ferrite, and ferrite + bainite. Electrochemical techniques included potenthiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), and electrochemical noise (EN) measurements. Most of the tests lasted 24 h. All techniques showed that the highest corrosion rate corresponded to the steel with a martensitic microstructure; up to one order of magnitude higher than the corrosion rate for steels with a ferritic + bainitiic microstructure, whereas the steel with the ferritic microstructure showed the lowest corrosion rate. EIS tests showed that the corrosion process was under charge transfer control, whereas EN results indicated that the three steels exhibited a clear tendency towards a localized type of corrosion. However, for longer immersion times, the steel with a martensitic microstructure tended to exhibit a mixture of uniform and localized attack. Results were discussed in terms of grain size, grain boundary energy, amount and distribution of particles found in each steel.

Effect of crack depth on fatigue crack growth rates for a C–Mn pipeline steel in a sour environment

Setting conditions for the avoidance of in-service crack growth in aggressive corroding environments has long been a major challenge owing to the number of variables that have a significant effect on material behaviour. The fatigue behaviour of API 5L X65 pipeline steel parent material tested in a sour environment has been investigated. Fatigue crack growth rate (FCGR) tests have been performed to evaluate the influence of crack depth on crack growth rate (d a/d N), over the range 2–10 mm. The results obtained showed crack growth rates for deep flaws to be a factor of 5–30 higher in the sour environment than in air, dependent on the applied stress intensity factor range (Δ K). Shallow flaws have been shown to grow up to an order of magnitude faster than deep flaws in a sour environment at the same value of Δ K. The results highlight a potential non-conservatism associated with using deep-crack data to predict the behaviour of shallow flaws. The observed behaviour is attributed to the uptake of hydrogen at specimen surfaces exposed to the sour environment.

Effects of isofield uniaxial cyclic stress on the magnetization of 2% Mn pipeline steel - behavior on minor hysteresis loops and small major hysteresis loops

The present results show that the sense of the stress-induced irreversible changes in the unstressed magnetization is not always towards the anhysteretic. Examples where the change is away from the anhysteretic are shown, as well as cases where the cyclic uniaxial stress does not cause an irreversible change in the sample's unstressed magnetization when that magnetization does not coincide with a point along the anhysteretic curve. Examination of the magnetization changes with cyclic stress along the upper or lower branches of a minor hysteresis loop suggests that the distance along that branch from the previous turning point is the most important factor in determining the sense of the stress-induced changes in magnetization. Initially the stress-induced changes in the unstressed magnetization occur in the same sense as they would have before the turning point, but the interaction between the domain walls and the pinning sites in the sample as the applied magnetic field changes after the turning point causes this stress-induced change to decrease in value and then reverse in sign. This suggests that the isofield cyclic stress-induced changes in the magnetization should be considered to be towards a local equilibrium condition rather than a global equilibrium condition (the anhysteretic curve).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effects of isofield uniaxial cyclic stress on the magnetization of 2% Mn pipeline steel-behavior on near saturation major hysteresis loop

Measurements of the effects of cyclic stress on the magnetization of a sample of 0.08%-C 2%-Mn pipeline steel are presented. The sample was magnetized to a position on the upper branch of the near saturation major hysteresis loop. Cyclic uniaxial tension or compression was then applied to the sample under isofield conditions. Two types of stress cycle were tested, one where the maximum stress applied to the sample increased after every cycle, and one where the maximum stress was held at a constant value for each cycle. Plots of the resulting changes in the magnetization indicated the presence of two types of irreversible behavior produced by the stress cycles-irreversible changes in the unstressed magnetization and stress-magnetization hysteresis. The former behavior was found to fall into three different categories that depended on the magnetization of the sample and the type of applied stress. These categories were analyzed in terms of the expected effects of the different stresses on the different magnetization mechanisms, namely, 180/spl deg/ domain wall motions, 90/spl deg/ domain wall motions, and domain magnetization vector rotations. >

Magnetization changes in 2% Mn pipeline steel induced by uniaxial tensile stress cycles of increasing amplitude

The application of cyclic stress to a ferromagnet normally gives irreversible magnetization shifts towards the anhysteretic magnetization. Here experimental measurements are presented that show the irreversible magnetization changes induced by cyclic uniaxial isofield stress applied after magnetization at particular points on minor hysteresis loops. Selecting the (M,H) point and magnetization history, then applying stress cycles of increasing amplitude enables irreversible changes, initially away from and later toward the anhysteretic curve, to be obtained. Examples of a second inversion (i.e., irreversible shifts initially toward, then away and subsequently toward the anhysteretic magnetization) with increasing amplitude cyclic uniaxial stress are also given. Preisach diagrams are used to interpret these results qualitatively in terms of local, more extensive and global anhysteretic states.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Investigation of the magnetic field and stress dependence of 180° domain wall motion in pipeline steel using magnetic Barkhausen noise

Magnetic Barkhausen noise (MBN) measurements were performed on 2% Mn pipeline steel samples as a function of magnetic field ( H) and as a function of orientation of an applied sweep field for various tensile and compressive stress values. For the magnetic field dependent measurements, the H field and stress were applied along the same axis, which was aligned within 10° of the sample's magnetic easy axis. Tensile stresses between 210 MPa and 0 and compressive stresses between 0 and -200 MPa were applied. The MBN signal was observed to initially increase with H followed by a decrease and eventual suppression of the MBN signal at higher H values. The application of tensile stress increased the total MBN signal and increased the field at which suppression occurred, while the application of compressive stress decreased the total signal with a corresponding decrease in the suppression field value. The stress and low-field behaviour of the MBN signal was correlated with the irreversible differential permeability ( μ IDP ) measured in a similar 2% Mn pipeline steel sample. The behaviour of the MBN signal as a function of H and stress was attributed to the effect of these parameters on the relative population and/or size of 180° domain walls, that is, the total 180° domain wall area, within the sample.

The effect of stress on the derivatives of magnetostriction in 2% Mn pipeline steel with respect to H and M

The results of a study of the changes in dλ/d H and dλ/d M with stress in a sample of 2% Mn pipeline steel are presented. After comparing the effectiveness of plotting data versus the magnetic field, H, and magnetization, M, plots of the total, reversible and irreversible components of both derivatives are shown. Both dλ/d H and dλ/d M show clear evidence for the existence of different forms of irreversible and reversible magnetic processes in the low and high magnetization regions. These mechanisms are identified with irreversible and reversible domain magnetization vector rotation in the high field region, and the creation and elimination of 90° domain walls in the low field region.

Effects of stress on the magnetostriction of 2% Mn pipeline steel

The effects of varying the order of the application of stress and a demagnetization procedure on the magnetostrictive behavior of a 2% Mn pipeline steel sample are studied and compared to the predictions of recent theory. Plots of magnetostriction versus both magnetic field and magnetization are given. Significant differences were found in the behavior of the magnetostrictive initial curve when the sample was both demagnetized and the measurements made under a constant stress as compared to the results when the sample was demagnetized and then stressed. Tension was also found to decrease the range and the hysteresis of the sample's saturation major magnetostrictive loops, while compression had the opposite effect. This behavior appeared to be independent of whether the stress was applied before or after the demagnetization process, and was found to be due to changes in magnetostriction at low magnetization values. Comparison of the sample's magnetostrictive behavior to theory showed that only some of the features seen experimentally were correctly predicted by theory. >

Effect of uniaxial stress on the reversible and irreversible permeabilities of 2% Mn pipeline steel

The results of a study of the effects of constant uniaxial stress on the irreversible and reversible differential permeabilities of minor and saturation major hystersis loops are presented, extending an earlier study which studied those permeability components on the initial magnetization curve. Tension was found to increase both the reversible and irreversible components of the saturation major loop differential permeability in the low magnetization region, and to decrease them in the high magnetization region. The opposite effect was found for compression. This effect was explained as the result of changes in the domain structure of the sample when stressed and a resulting change in the ratio of 90/spl deg/ of 180/spl deg/ domain walls. The differences between the upper and lower branches of the saturation major hysteresis loop reversible relative differential permeability were found to increase in tension and decrease in compression, with more complicated behavior occurring in the irreversible component. Minor loop behavior was also found to vary depending on the magnetization of the sample. In the low magnetization region tension was found to produce higher values and larger variations in both components of the relative differential permeability than the unstressed case, while compression produced lower values and smaller variations. The opposite behavior was found to be true in the high magnetization region, while an intermediate behavior with little or no change in both the relative differential permeability components was found to exist between the two extreme cases. The minor loops were measured from set values of the applied field, and tension was found to increase the corresponding values of magnetization, with compression causing a decrease in the magnetization values. The behavior of the minor loops was found to be related to the major loop behavior in the same region. >

The effect of stress and magnetic field orientation on surface Barkhausen noise in pipeline steel

Surface Barkhausen noise (SBN) measurements were made on a 2% Mn pipeline steel sample subjected to different levels of applied tensile and compressive isostress. The magnetic field direction was varied through a full 360 degrees . SBN voltage was found to depend on both stress level and magnetic field direction. The results were analyzed in terms of reorientation of magnetic moments from axial to circumferential directions with increasing tension. Compression was found to realign the magnetic moments in the axial direction.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of applied stress on the reversible and irreversible differential permeabilities in 2% Mn pipeline steel

The contributions of reversible differential permeability (RDP) and irreversible differential permeability (IDP) to the total measured permeability have been derived from initial magnetization curves for a 2% Mn pipeline steel. In general, the effects of uniaxial stress on the IDP were significantly greater than on the RDP, and all the observed changes tended to be smaller at high magnetizations. At lower magnetization RDP tended to increase initially with tensile stress, while IDP was almost unaffected. On the other hand, compressive stress gave generally larger decreases both in RDP and IDP. The observed variations of RDP and IDP were, however, found to be complex functions of the magnetization. >

Magnetization changes induced by stress under constant applied field in 2% Mn pipeline steel

Reversible and irreversible magnetization components have been derived from cyclic stress applied to initial magnetization curves at different magnetization levels and for different stress cycle amplitudes. The irreversible and reversible magnetization components derived were found to vary symmetrically and antisymmetrically with the applied stress, respectively. The variation of the irreversible magnetization component with applied compressive and tensile stresses was found to be in qualitative agreement with the extended Brown's theory of L. Brugel and A. Rimet (1965, 1966).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Pneumatic stressing mechanism for magnetomechanical studies

A low-pressure pneumatically controlled stressing mechanism for investigating the effects of uniaxial stress on the magnetostrictive and magnetomechanical behavior of 2% Mn pipeline steel is described. The apparatus uses microcomputer control and data logging. It has been developed to allow convenient stress cycling so that reversible and irreversible changes can be separated. Irreversible stress-induced changes in magnetization are toward the anhysteretic, in accordance with Jiles–Atherton theory. Reversible magnetomechanical effects may be correlated with reversible magnetostrictive effects.

Thermodynamic correlation tests between magnetostrictive and magnetomechanical effects in 2% Mn pipeline steel

The thermodynamic correlation between magnetostrictive and magnetomechanical effects is tested using reversible measurements of the uniaxial isostress magnetostrictive and isofield magnetomechanical coefficients. All measurements are on samples of the same 2% Mn pipeline steel, using both tensile and compressive stresses. The agreement is claimed to be satisfactory considering the high sensitivity required for the measurements.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Measurements of reversible magnetization component

Measurements of the reversible component of magnetization or reversible (backward) differential permeability made on 1% Mn pipeline steel at numerous points around major and minor hysteresis loops and on initial and anhysteretic curves are described. It is found that the reversible component of magnetization is a single-valued, even function of magnetization under all these conditions. It is independent of the field or the magnetic history. >

Effect of order of stress and field application on the measured flux density in 1% Mn pipeline steel

Experiments involving different orders of field and stress application on the measured flux density in 1% Mn pipeline steel samples were performed in order to examine the validity of LeChatelier’s principle. In the low-field regions the flux density in the sample was found to be strongly dependent on the order of applied stress and field, as stated by Bozorth. The results obtained for stress-induced magnetization changes were in accordance with the Jiles–Atherton theory.

Effect of stress on magnetization and magnetostriction in pipeline steel

Measurements of the effects of stress on the initial magnetization curve of a sample of 1 % Mn pipe line steel and on its reversible component are presented. Stress-induced changes in the reversible and irreversible magnetization components are shown. Examples of magnetization changes induced by tensile and compressive stress cycles of various amplitudes and at different fields are given. Magnetostriction measurements made on the same sample under various tensile and compressive stresses measured along anhysteretic and initial magnetization curves are included. A simple interpretation is suggested based on the assumption that stress changes the alignments of magnetic domain easy axes with respect to the strain.