Search

Tribomagnetization, a natural phenomenon known for decades, has many engineering applications today. However, its intrinsic origin remains controversial and the mechanistic-based model has not yet been developed to predict the tribomagnetization behavior. In this work, the origin of tribomagnetization is investigated via both the experimental and modeling approaches. For the first time, the expansion of surface plastic deformation to the subsurface layer (i.e., dislocation strain gradient) is characterized in conjunction with the tribological behavior of the interface. By performing the reciprocating sliding experiment in a pin-on-block contact configuration, the tribomagnetization evolution in different wear regimes is followed, the geometrically necessary dislocations (GNDs) developed in the subsurface are measured, and the formation of characteristic magnetic domains is revealed. A tribomagnetization model is proposed on the basis of the sliding-induced plastic deformation mechanism with GNDs, bringing the missing link with classical tribology and ferromagnetism. The model reveals that the surface plastic strain and width of a wear scar are two crucial factors in determining the surface magnetic field changes. We believe that the tribomagnetization originates from the magnetic distortion accompanied by the progression of GNDs in the subsurface. Our hypothesis is supported by the good agreement between the model prediction and experimental observation.

Pipelines are widely used in the oil & gas industry but defects seriously affect their safe operation. Therefore, it is necessary to perform non-destructive testing (NDT) to quantify the defects. In this study, a magnetic dipole model was established to characterise the defects and magnetic flux leakage (MFL) of defects was simulated using the finite element method (FEM) to reveal the spatial distribution of the magnetic vector. Magnetic signals were measured using a tunnel magnetoresistance (TMR) sensor array and the results showed that defects with different sizes could be quantified using the metal magnetic memory (MMM) method. Three-dimensional distribution of the magnetic signal and its gradient reflected the defect profile well and the gradient of the magnetic signal was found to reduce the effect of non-uniform magnetisation. Furthermore, experimental results were verified by comparison with the simulation results and the comparison results showed a consistent variation trend. Quantitative analysis was conducted and the characteristic parameters of the gradients could be used to quantify the defects.

Bolted structures are widely utilized in flange sealing of the petrochemical high-pressure facilities, measurement of axial force of bolted structures can contribute to monitor flange sealing status. In this paper, static tensile tests are conducted in laboratory. The stress distribution of bolt with different axial tensile load is analyzed by using finite element (FE) method. Two non-destructive testing (NDT) methods including ultrasonic testing and metal magnetic memory testing are used to measure axial force of two bolt materials (low-carbon steel 4.8 and medium-carbon steel 8.8 bolts) during the whole tensile process. For the ultrasonic testing, the test results show that there is a stable linear correlation between the axial force of the bolt and the ultrasonic time of flight (TOF), and the TOF measurement is upgraded by using cross-correlation analysis technique. For the metal magnetic memory testing, magnetic signals increase with the increase of axial force because of the effect of stress-magnetization. Furthermore, magnetic memory characteristic parameters have a good linear relationship with axial force within the scope of a certain stress. Therefore, metal magnetic memory testing can be used as a novel method to measure axial force of bolted structures. Finally, the advantages and drawbacks of these two NDT methods are analyzed, which can provide a reference for the engineering application of effective NDT methods and technologies in bolt axial force measurement.

In order to investigate the relationship between tribo-magnetization and wear phenomena, a series of sliding-friction tests were carried out using a pin-on-block reciprocator type device, which was specially designed to generate sliding friction and to detect magnetic fields. The tribological behavior was observed by a charge-coupled device (CCD) camera in real time, and the magnetic signal was detected by using a two-axis magnetic sensor. It was found that as the friction continues, both the tangential and the normal components of magnetic field on the material surface increase gradually, and that both the average value of the tangential magnetic field ΔH(x)mean and the peak-to-peak value of the normal magnetic field Vpp at the wear scar clearly reflect changes of the wear state. Furthermore, in order to better understand the tribo-magnetization phenomenon, the changes of surface morphology and wear debris in different wear stages were analyzed. Moreover, an improved magnetic dipole model that considered the distribution of magnetic charges on the worn surface was established. This model can successfully describe the tribo-magnetization phenomenon during the stable wear stage, and should be useful for characterizing frictional wear phenomena in the future.

In order to research the effect of magnetic field including in remanence and the earth's magnetic field on tribo-magnetization phenomenon, a new apparatus, which could shield the earth's magnetic field, was built to perform reciprocating friction test. Based on changes of surface magnetic field and SEM analyses, the whole friction process of different ferromagnetic materials was characterized. And the effects of wear degree, normal loads, materials and different remanence of blocks on changes in the surface magnetic field were examined. Experimental results show degree of wear, normal load and ambient magnetic field have a positive effect on tribo-magnetization. The increment of surface magnetic field in normal direction, which resulted from the constant earth's magnetic field, was about 0.05GS for pure iron.

To study the friction behavior of ferroalloy and wet granulation sulfur under low normal load conditions, a series of experiments were performed using a homemade rotating test apparatus. Scanning electron microscopy with an energy dispersive spectrometer (SEM-EDS) and X-ray diffraction (XRD) were utilized to examine the friction products. The experimentally monitored friction coefficient data were used to develop a finite element model to simulate the temperature field and a theoretical model to calculate the flash temperature of the contact area of the friction surface. The experimental, simulation, and theoretical results showed that the flash temperature of the friction surface is much higher than the average temperature of the friction surface and allows the reaction of iron and sulfur to form iron&ndash, sulfide compounds.

To monitor fatigue crack initiation and propagation, and to judge the fatigue damage status of ferromagnetic material, fatigue bending tests of four-point single edge notch bend (SENB4) specimens were carried out. Metal magnetic memory signals were measured during the whole fatigue process. The results showed that the fatigue process could be divided into four stages by observing the morphology of the fracture surface. With the increase of fatigue loading cycles, the tangential component of the magnetic field (Hx) and the normal component of the magnetic field (Hy) increased. At the notch Hx presented a &ldquo, trough&rdquo, shape and had a maximum value at the midpoint, while Hy at the notch rotated clockwise around the midpoint. Compared with the tangential characteristic parameters, the variation of normal characteristic parameters (i.e., maximum gradient value of Hy (Ky-max) and the variation range of Hy at the notch (∆Hyn), with the fatigue loading cycles are more similar to the variation of fatigue crack length with loading cycles), both Ky-max and ∆Hyn had a good linear relationship with fatigue crack length. Plastic deformation accumulated on both sides of the fatigue crack, and metal magnetic memory (MMM) signals measured from the specimens were able to indicate the location of the fatigue crack and the variation of the fatigue crack length. Furthermore, the distribution of magnetic signals was analyzed according to the theories of stress magnetization and magnetic flux leakage.

In this paper, a friction apparatus was developed to explore the magnetization phenomenon of pure iron during the friction process. A series of sliding-friction tests were carried out to study the tribo-magnetization effect under lubrication and non-lubrication condition. Furthermore, the correlation between the distribution and variation of magnetic domains and the metallographic structure of the materials were analyzed. And a model of tribo-magnetization was built. The results showed that the tribo-magnetization phenomenon under non-lubricated conditions was more significant than that under lubricated conditions because of the interaction between two interfaces which affected the range and deformation degree of the area of influence beneath the sliding surface. It was found that the generation of plastic deformation beneath a sliding surface is the principal source of magnetization.

The fatigue fracture of a drillstring could cause drilling disturbances and some negative impacts (e.g., economic loss) will be brought when restoring the drillstring to functionality. In order to evaluate the effects of the fatigue damage of the drillstring during drilling, a new apparatus, which could monitor the load level in real-time, was built to perform the four-point bending fatigue test on 35CrMo steel, a typical material of drillstrings. Such an apparatus is based on metal magnetic memory (MMM) technology and can acquire the tangential and normal components of MMM signals. Based on the analysis of the change of surface morphology and MMM signals, it was concluded that the variation of MMM signals could be divided into four stages, which are used to accurately describe the fatigue damage process of the drillstring. Additionally, the MMM signal characteristics are introduced to especially evaluate the fatigue damage of the drillstring, including crack initiation. Furthermore, the scanning electron microscopy (SEM) results demonstrated that morphologies of fatigue fracture were related to the variation of MMM signals. Linear fitting results indicated that fatigue crack length had a good linear relationship with the characteristics, so it is feasible to monitor fatigue damage and predict the residual life of a drillstring by using MMM technology.

In order to reveal tribo-magnetization phenomenon of ferromagnetic materials, a new apparatus which involved reciprocating friction tests of pin-on-block type under the geomagnetic field has been built to perform the tests. Based on the changes of the surface magnetic field of wear scar and the macroscopic and SEM analyses, it is concluded that tribo-magnetization of ferromagnetic materials is a two-stage process and the demarcation point of these two stages is the transition point of the friction forms. Furthermore, the shape and the position of wear scar can be estimated through measuring the surface magnetic field of wear scar.

During fracturing, high pressure pipe manifold can be easily damaged under the coupling effect of the internal high pressure and erosion. In order to reveal the damage mechanism, a new apparatus which can provide an axis tensile force for specimen has been developed and built to perform the tests. Based on the macroscopic and SEM analyses, it is demonstrated that the erosion at any orientation angle increases with the tensile stress and the maximum value occurs at 30°. Furthermore, the width and depth of scratches will also increase with the tensile stress at any impact angle.

It is common to see fire accidents caused by friction during the storage and transportation of wet granulation sulfur. To study the sulfur ignition mechanism under friction conditions, a new rotating test apparatus is developed to reproduce friction scenes at lab scale. A series of experiments are performed under different normal loads. The SEM-EDS and the XRD were utilized to examine the morphologies and compositions of the tested specimens and the friction products. Experimental results show that these two methods are mostly in agreement with each other. The iron-sulfide compounds are produced and the proportion of iron-sulfide compounds is reduced with normal loads increasing, compared to the total number of the friction products. The facts implied by the integration analysis of friction products with the temperature changes of the near friction surface unveil an underlying mechanism that may explain sulfur ignition by friction in real scenarios. The sulfur ignition may be mainly caused by the spontaneous combustion of iron sulfide compounds produced by friction under low normal load with 200 N. With the increase of normal loads, the resulting iron-sulfide compounds are decreasing and the high temperature from friction heat begins to play a major role in causing fire.

Theoretical analysis and field monitoring show that lateral vibration has very important effect on casing wear in deep & ultra-deep well drilling. The wear mechanism of casing under impact-sliding work conditions has been investigated and many experiments have been completed with a newly developed full-scale casing wear test machine. Test results present that adhesion wear, contact fatigue, and grinding abrasion are the main wear mechanisms under impact-sliding test conditions. The friction coefficient and linear wear rate of the casing rise obviously with an increase in impact load. And the larger the impact load, the rougher the worn surface of the casing. The linear wear rate decreased slightly but the average friction coefficient increased slightly with an increase in impact frequency under an impact load of 2,500 N. Both the linear wear rate of the casing and the average friction coefficient increased substantially with an increase in impact frequency under an impact load of 4,000 N. Under lower impact load conditions, grinding abrasion and contact fatigue are the main mechanisms of casing wear; under higher impact load conditions, adhesion wear and contact fatigue are the main mechanisms of casing wear.

Corrosion and sustained casing pressure have serious threats to the integrity of tubing of gas well. Researching the residual strength of corroded tubing has great significance to ensure the safety of gas well. The finite element method was used to study the relationships between residual strength and corrosion defects size, internal pressure, external pressure, axial load. The results show that, for tubing with uniform corrosion, the defect depth, internal pressure and external pressure have greater impacts on the von Mises equivalent stress of tubing, and the defect width and defect length have little effects on it. For tubing with pitting corrosion, the defect depth, internal pressure and external pressure have greater impacts on the von Mises equivalent stress of tubing, while the defect radius has little effect on it. These simulation data were fitted into the functions of residual strength of corroded tubing according to different corrosion morphology types. Both of the verifications of the fitting results show that most of the error between the original calculation data and the fitting calculation data is less than 4%. The fitting formulas can be used conveniently to evaluate the safety of the tubing of gas well with sustained casing pressure.Copyright © 2015 by ASME

Erosion-corrosion is a complex phenomenon in high-pressure pipe manifolds which may be caused by working ages, fracturing fluid and sand. It results in some amount of equipment failure and material loss. Consequently, it is necessary to improve erosion wear resistance of high pressure pipe manifolds in engineering. The aim of this work is to investigate the role of different parameters influencing erosion-corrosion. A new type of erosion tester was used as the test apparatus and test parameters such as impact time, sand size, flow velocity, impact angles and test solutions were varied to study their effect on erosion wear of 40CrNi2Mo alloy steel. The results indicate that the mass loss increases with time, sand size, and flow velocity. The most mass loss occurs at 30°. The erosion wear characteristic feature is micro-cutting action and the distortion wear, which is the same to the erosion wear rules of the typical plastic material.

Corrosion-induced pits will disturb the original stress distribution of casing and appear local high stress area. Through 3-D finite element analysis on casing with spherical and cylindrical corrosion cavity, the stress concentration degree and the influences of cavity shape, size and orifice diameter on stress concentration factor are determined and analyzed. The results show that the depth and shape of corrosion cavities are major factors impacting the stress concentration factor. For the casing with corrosion pits, the smaller orifice diameter, the more obvious influence of hemisphere effect on stress concentration factor. With the transition from shallow-spherical cavity to exact hemispherical cavity or from exact hemispherical cavity to deep-spherical cavity or from exact hemispherical cavity to cylindrical cavity, the changes of stress concentration factor show different characteristics.Copyright © 2010 by ASME

The weighting material in drilling fluid has very important effect on casing wear. By using the DCWT-1000 tester, a new impact-sliding tester for casing wear, a series of tests in impact-sliding work condition have been performed to investigate the effects of different weighting material doped in drilling fluid. The OE and SEM analysis presents that the iron ore powder doped in the drilling fluid led to the change in the wear mechanism from abrasive wear and adhesion wear to severe plastic flow and fatigue wear. The adhesion wear increasingly become severe with increasing iron ore powder content. While the barite doped in the drilling mud was beneficial to decreasing the adhesion wear and plastic deformation of the casing. Moreover, it is found that mixed weighting material with iron ore powder and barite in certain ratio has better effect on decreasing casing wear.Copyright © 2008 by ASME