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This paper shows evidence of the capability of electron backscatter diffraction (EBSD) to accurately estimate the magnetocrystalline anisotropy energy (MAE) of API 5L steels. The crystallographic texture of five circular steel samples was characterized by X-ray global texture and EBSD microtexture measurements. The average MAE of each one of these samples was estimated from the set of individual grain orientations obtained from orientation maps measured by EBSD. The angular dependence of EBSD-derived MAE was compared with predictions made from X-ray texture and Barkhausen noise (BHN) measurements. The average MAE determined from the EBSD data is in good agreement with the predictions made from X-ray and BHN measurements for all the studied samples. This agreement can be explained by the fact that the number of grains used to predict the average MAE from the EBSD results was statistically sufficient to reproduce the MAE predicted by the other two methods. The EBSD measurement strategy for the accurate MAE estimation was established in terms of parameters such as the number of individual grain orientations to be measured, the sample's texture acuity and grain size, the use of equivalent orientations given by the statistical orthorhombic symmetry of the studied samples, and different measurement planes. [ABSTRACT FROM AUTHOR]

Abstract: This work presents the results of multiple weld repairs in the same area in seamless API X-52 microalloyed steel pipe. Four conditions of shielded metal arc welding repairs and one as-welded specimen of the girth weld were characterized to determine changes in the microstructure, grain size in the heat affected zone, and to evaluate their effect on the mechanical properties of the weld joints. The mechanical properties by means of tension tests, Charpy-V impact resistance and Vickers hardness of the welds were analyzed. The results indicate that significant changes are not generated in the microstructural constituents of the heat affected zone. Grain growth in the heat affected zone at the specimen mid-thickness with the number of repairs was observed. Tensile strength of the weld joints meets the requirement of the API 1104 standard even after the fourth weld repair. Significant reduction in Charpy-V impact resistance with the number of weld repairs was found when the notch location was in the intersection of the fusion line with the specimen mid-thickness. A significant increase in the Vickers hardness of the heat affected zone occurred after the first repair and a gradual decrease in the Vickers hardness occurred as the number of repairs increases. [Copyright &y& Elsevier]

Abstract: The effects of artificial aging on the microstructure in the weldment of an API 5L X-52 steel pipe were studied. Aging was performed at 250 °C over a period of 1000 h and values were recorded at every 100 h intervals. Transmission electron microscopy observations showed precipitation strengthening from nearly circular Nb–C containing nanoparticles for the base metal and heat affected zone, and cementite for the weld metal. The largest amount of precipitation in the weldment zone was obtained at 500 h, due to peak-aging, which showed the highest particle density. The weld metal was more susceptible to aging, exhibiting the highest increase in precipitation at 500 h, followed by the heat affected zone. After 500 h, the deterioration in the microstructure was caused by the coarsening of particles due to over-aging. The base metal showed the larger increment in particle size after 900 h of aging accompanied by a bigger decrease in fine particles than in the weld metal. [Copyright &y& Elsevier]

• New experimental evidence of crack initiation by SCC mechanism in pipeline steel. • Initiation and propagation of near-neutral pH SCC mechanisms were studied using EBSD. • New experimental evidence explaining the influence of crystallographic texture in SCC. • The strong {0 0 1}//ND texture fiber shows a higher susceptibility to develop SCC. This work studies the relationship between the early stage of stress corrosion cracking (SCC) mechanism and the crystallographic texture of API 5L X52 steel for sour service in a near-neutral pH solution. Experimental evidence of the SCC initiation of X52 steel for sour service was obtained using SEM and EBSD techniques. The results show that the crack initiation mechanism behaves like a synergistic combination of chemical attack and stress concentration at pits, being the last one the driving force to crack transition. In addition, it was found from both X-ray macrotexture and EBSD microtexture measurements that the cracks initiation process depends strongly on the material's texture characteristics and the presence of the texture fiber {0 0 1}//ND in X52 steel for sour service can increase its susceptibility to SCC. In a quantitative manner, the influence of the crystallographic texture in the SCC mechanism was explained through the relationship between the initiation of SCC cracks and the predictions of the anisotropy of Young's modulus using EBSD measurements. [ABSTRACT FROM AUTHOR]

A study on the probabilistic methodology for the estimation of the remaining life of pressurized pipelines containing active corrosion defects is presented. This reliability assessment is carried out using several already published failure pressure models. A steady state corrosion rate is assumed to estimate the growth in the dimensions of corrosion defects. The first-order second-moment iterative reliability method, the Monte Carlo integration technique and the first order Taylor series expansion of the limit state function (LSF) are used in order to estimate the probability of failure associated with each corrosion defect over time. The uncertainty of the statistical variables on which the LSF depends are modeled using normal and lognormal distributions and the sensitivity of pipeline reliability to these variables is evaluated. This extended probabilistic analysis framework is applied to a sample operating pipeline which was inspected using a high resolution magnetic flux leakage inspection tool. [Copyright &y& Elsevier]

• Presents a new system for the estimation of the stress in pipelines using MBN. • Proposes the parameters of MBN to estimate the stress amplitude and direction. • Proposes a model for the dependence of MBN on the applied stress. In the present work a new system for nondestructive evaluation of applied stress on the pipeline steels surface is proposed. This system is based on applying a magnetic field on the pipe surface, whose direction changes due to rotatory permanent magnets. The variation of magnetic field direction produces the Barkhausen signal, which is measured by a pick-up coil. The angular dependence of the magnetic Barkhausen noise signal energy is influenced by the pipe surface curvature due to the changing head-probe liftoff. Also, the said angular dependence changes with the applied tensile stress due to the magneto-elastic effect. The result of Barkhausen noise measurements in the pipeline surface submitted to applied tensile stress reveals that, since the effect of curvature on the angular dependence remains constant, the effect of applied stress could be determined by analyzing the angular dependence variation of the Barkhausen signal with the applied stress. [ABSTRACT FROM AUTHOR]

A model for the estimation of the time evolution of maximum depth of localized corrosion defects caused under oilfield produced water environments has been developed. It takes into consideration the chemical composition of the produced water and other physical parameters. Immersion tests were conducted using coupons of an API 5L X60 pipeline steel under different experimental conditions and periods. The time dependence of the maximum pit depth was modeled as a power function of time, which was successfully fitted to the obtained experimental data using regression analysis. The main result of this analysis was represented by a holistic model which includes the most important variables involved in the pipeline internal corrosion process in produced waters. [ABSTRACT FROM AUTHOR]

In this paper, a new portable magnetic perturbation probe using a Giant Magneto-Resistance (GMR) sensor to detect and characterize surface cracks in ferromagnetic steels is presented. Measurements from one tangential component of the magnetic flux density are obtained during a single scan over a crack, and two parameters are defined from the output voltage of the GMR sensor: the distance between the peaks, DX, and their voltage difference, DV. The correlations between DX and DV and crack features such as depth, width, and orientation angle are determined. Sensitivity analyses are performed based on the studied features. The probe permits the user to obtain the crack׳s orientation angle using only one measured tangential component of the magnetic flux density. A simple procedure to estimate the crack׳s features is proposed based on the presented analysis. [ABSTRACT FROM AUTHOR]

The present work analyzes the influence of electric conductivity on the Magnetic Barkhausen Noise (MBN) signal using a microscopic model which includes the influence of eddy currents. This model is also implemented to explain the dependence of MBN on the frequency of the applied magnetic field. The results presented in this work allow analyzing the influence of eddy currents on MBN signals for different values of the material's electric conductivity and for different frequencies of applied magnetic field. Additionally, the outcomes of this research can be used as a reference to differentiate the influence of eddy currents from that of second phase particles in the MBN signal, which has been reported in previous works. [ABSTRACT FROM AUTHOR]

This work studies the influence of the maximum applied magnetic field on the angular dependence of the energy of the Magnetic Barkhausen Noise signal in three different API5L pipeline steels. The results show that the shape of the angular dependence of the Magnetic Barkhausen Noise energy changes with the increase of the amplitude of the applied magnetic field. This phenomenon is a consequence of the presence of unlike magnetization processes at different magnitudes of the applied magnetic field. The outcomes reveal the importance of controlling the value of the maximum applied field as parameter for the improvement of the MBN angular dependence measurements. [ABSTRACT FROM AUTHOR]

A new Bayesian methodology for the analysis of external corrosion data of non-piggable underground pipelines has been developed. It allows for the estimation of the statistical distributions of the density and size of external corrosion defects from corrosion data samples taken at excavation sites along the inspected pipeline and can incorporate the detection and measurement errors associated with field inspections. Corrosion data obtained from field inspections of an upstream pipeline and from an in-line inspection of a transportation pipeline are used to illustrate and validate the proposed methodology. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a method for rapid quantification of long artificial cracks using a GMR-based eddy current sensor. The quantification is achieved simultaneously through a proposed phenomenological relationship between the crack''s dimension and two parameters extracted from the GMR output signal. The results show that the proposed method is valid and advantageous when a quick and reliable estimation of the crack''s dimension is necessary. A criterion taking into consideration the filling factor of the excitation coil is proposed in order to improve the system''s sensitivity. [Copyright &y& Elsevier]

Abstract: Cathodic hydrogen charging was applied to low-carbon pipeline-steel samples produced using different thermomechanical paths. The samples developed similar microstructures but different crystallographic textures and grain–boundary distributions. This made it possible to investigate the resistance to hydrogen-induced cracking (HIC) of steels with strong {111}ND and {112}ND texture fibres, steels with a dominating {001}ND texture fibre, and steels with close-to-random textures; {h k l}ND representing grain orientations with {h k l} planes parallel to the steel rolling plane. The results show that strong {111}ND fibre textures produced by warm-rolling schedules significantly increase HIC-resistance of pipeline steels, whereas {001}ND and close-to-random textures make steels HIC-prone. [Copyright &y& Elsevier]

Abstract: A new type of experiment is performed using a closed magnetic circuit configuration in order to study the influence of the magnetic field on pitting corrosion in low carbon pipeline steel. The statistical assessment of the pitting corrosion data shows that the magnetic field in the material under test reduces the extreme pit depths and also the average depth of the pit population. It is proposed that reduction in pit depth under the influence of remanent magnetization can be explained based on the behavior of the paramagnetic corrosion products under the influence of the magnetic field gradient produced inside pits. [Copyright &y& Elsevier]

Abstract: Electrochemical impedance spectroscopy (EIS) analyses are carried out to evaluate the passive features of tantalum oxide films (Ta2O5) formed at different potentiostatic conditions (0.5, 1.0, 1.5 and 2.0V vs SSE). A supporting electrolyte of 0.1M H2SO4 (pH 1) has been used to emulate acidic corrosive conditions for the growth of films with an n-type electronic character. A modification of the point defect model (PDM) accounting for the formation of molecular hydrogen (blistering damage) is used to fit the experimental EIS diagrams, and obtain the kinetic parameters that best describe the semiconductive behavior of the passive films. After this analysis, diffusivities in the order of 5.37±1.6×10−17 and 1.98±1.4×10−20 cm2 s−1 were obtained for the oxygen and hydroxyl vacancies , respectively. These findings show the capabilities of the EIS and the physicochemical modeling to account for the formation of valve-metal oxide films on a different range of conditions. [Copyright &y& Elsevier]

Abstract: A stochastic model previously developed by the authors using Markov chains has been improved in the light of new experimental evidence. The new model has been successfully applied to reproduce the time evolution of extreme pitting corrosion depths in low-carbon steel. The model is shown to provide a better physical understanding of the pitting process. [Copyright &y& Elsevier]

Abstract: The effects of aging in the tensile fracture behavior of welded joints of API5L-X52 pipe steel were studied by accelerating aging at 250°C for different periods of time. The weld metal, heat affected zone and base metal, showed an increase in yield strength while the strain-hardening exponent decreased at early stages of aging. A maximum strength and minimum hardening exponent was found at 500h due to peak-aging. Subsequently, both properties exhibited an opposite behavior due to over-aging. Tensile fractured specimens for the three different zones exhibited ductile failure, presenting microvoid morphology associated with the coalescence of microcavities. An increase in void density and a reduction in diameter during short periods in the fractured specimens were observed. The maximum density and minimum diameter of voids were obtained at 500h and were linked to the improvement of strength and precipitation of nanoparticles. Afterward, the fractured surfaces exhibited a reduction in density and the diameters of voids were larger, having been induced by the deterioration of strength and coarsening of particles. [Copyright &y& Elsevier]

Abstract: A continuous-time, non-homogenous linear growth (pure birth) Markov process has been used to model external pitting corrosion in underground pipelines. The closed form solution of Kolmogorov’s forward equations for this type of Markov process is used to describe the transition probability function in a discrete pit depth space. The identification of the transition probability function can be achieved by correlating the stochastic pit depth mean with the deterministic mean obtained experimentally. Monte-Carlo simulations previously reported have been used to predict the time evolution of the mean value of the pit depth distribution for different soil textural classes. The simulated distributions have been used to create an empirical Markov chain-based stochastic model for predicting the evolution of pitting corrosion depth and rate distributions from the observed properties of the soil. The proposed model has also been applied to pitting corrosion data from pipeline repeated in-line inspections and laboratory immersion experiments. [Copyright &y& Elsevier]

Abstract: The probability distributions of external-corrosion pit depth and pit growth rate were investigated in underground pipelines using Monte Carlo simulations. The study combines a predictive pit growth model developed by the authors with the observed distributions of the model variables in a range of soils. Depending on the pipeline age, any of the three maximal extreme value distributions, i.e. Weibull, Fréchet or Gumbel, can arise as the best fit to the pitting depth and rate data. The Fréchet distribution best fits the corrosion data for long exposure periods. This can be explained by considering the long-term stabilization of the diffusion-controlled pit growth. The findings of the study provide reliability analysts with accurate information regarding the stochastic characteristics of the pitting damage in underground pipelines. [Copyright &y& Elsevier]

Abstract: The role of microtexture in hydrogen-induced crack interaction and coalescence is investigated in line pipe steels using electron backscatter diffraction. Experimental evidence shows that, depending on the local grain orientation, crack interaction and coalescence can depart from the conditions predicted by the mixed-mode fracture mechanics of isotropic linear elastic materials. Stress simulation and microtexture analysis are used to explain the experimental observations. [Copyright &y& Elsevier]

Abstract: The block maxima and peak over threshold approaches to extremes have been applied to pitting corrosion data from laboratory-simulated buried line pipe steel. Both approaches have been useful for gaining a better understanding of pitting in low carbon steel. We show that the parent distribution of the extreme depths is the right tail of the observed pit depth distribution. The threshold approach proved more robust to maximum depth reduction, which results from the dependency between pit depths. A simplified sampling method is proposed for applying the threshold approach without the need for measuring the entire pit depth distribution. [Copyright &y& Elsevier]

Abstract: In this work, a new stochastic model capable of simulating pitting corrosion is developed and validated. Pitting corrosion is modeled as the combination of two stochastic processes: pit initiation and pit growth. Pit generation is modeled as a nonhomogeneous Poisson process, in which induction time for pit initiation is simulated as the realization of a Weibull process. In this way, the exponential and Weibull distributions can be considered as the possible distributions for pit initiation time. Pit growth is simulated using a nonhomogeneous Markov process. Extreme value statistics is used to find the distribution of maximum pit depths resulting from the combination of the initiation and growth processes for multiple pits. The proposed model is validated using several published experiments on pitting corrosion. It is capable of reproducing the experimental observations with higher quality than the stochastic models available in the literature for pitting corrosion. [Copyright &y& Elsevier]

The spatial distribution of plastic deformation and grain orientation surrounding hydrogen-induced cracks (HIC) is investigated in samples of API-5L-X46 pipeline steel using scanning electron microscopy and electron backscattering diffraction (EBSD). This work shows direct experimental evidence of the influence of microstructure, microtexture and mesotexture on HIC crack path. [Copyright &y& Elsevier]