A Prognostics Method Based on Back Propagation Neural Network for Corroded Pipelines

A method that employs the back propagation (BP) neural network is used to predict the growth of corrosion defect in pipelines. This method considers more diversified parameters that affect the pipeline’s corrosion rate, including pipe parameters, service life, corrosion type, corrosion location, corrosion direction, and corrosion amount in a three-dimensional direction. The initial corrosion time is also considered, and, on this basis, the uncertainties of the initial corrosion time and the corrosion size are added to the BP neural network model. In this paper, three kinds of pipeline corrosion growth models are constructed: the traditional corrosion model, the corrosion model considering the uncertainties of initial corrosion time and corrosion depth, and corrosion model also considering the uncertainties of corrosion size (length, width, depth). The rationality and effectiveness of the proposed prediction models are verified by three case studies: the uniform model, the exponential model, and the gamma process model. The proposed models can be widely used in the prediction and management of pipeline corrosion.

The effect of time variation on the steels corrosion rate in 0.5 M H2SO4 solution

Previous researches have carried out studying the corrosion behavior of steels, the most frequently used steels are medium carbon steel, alloy steel, and stainless steel. This is due to their wide range of applications. So, corrosion behavior is necessary to be analyzed for every steel type because of its wide function. This study was aimed to analyze the corrosion rate, macrostructure, and the XRD results of the AISI 1045, AISI 4140, and SS 304 which represent every steel type. Then, the steels were exposed to the 0.5M H2SO4 solution with various corrosion times. The variation of the corrosion time was 48, 96, and 144 hours. The results of this study revealed that AISI 1045 showed the highest corrosion rate with the value of 183.7 mpy at 144 hours of the time variation. All specimens obtained an increase in the corrosion rate with the increase in the corrosion time. Furthermore, for the macrostructure results, AISI 1045 and AISI 4140 gave obvious rust on the surface of the specimens for all time variation. The corrosion spots appear in the time variation of 96 and 144 hours for SS 304 specimens. XRD analysis confirmed the presence of metal oxides as corrosion products.

Effect of Alkali Seepage Erosion on Physical and Mechanical Properties of Laterite

Using a modified permeameter, laterite samples that were corroded and permeated by alkaline solutions at different concentrations for varying amounts of time were subjected to triaxial compression tests, chemical composition analysis, particle composition tests, and microstructure analysis. The results showed that the strength parameters c, φ, and K of the laterite samples that were corroded by alkaline-solution permeation were reduced with increasing corrosion time and alkaline-solution concentration. The alkaline-solution corrosion had a minor effect on the strength parameters n and Rf. The contents of Al2O3 and Fe2O3 in the laterite fluctuated and decreased with increasing alkaline-solution concentration and corrosion time. There were no distinct patterns in the relationships between the SiO2 content and the increases in the alkaline-solution concentration and corrosion time. Due to the corrosion during the alkaline-solution permeation, the content of clay particles increased with increasing time and concentration of the alkaline solution. After the permeation with the alkaline solution, the soil particles became smaller and were arranged in an ordered state. The analysis suggested that the permeation effect of the alkaline solution changed the chemical composition of the laterite and the connecting strength of the soil particles, resulting in changes in its physical and mechanical properties.

Damage Evolution of Concrete Piles Mixed with Admixtures in Marine Corrosion and Freeze-Thaw Environment

Marine corrosion and freeze-thaw environment will bring serious damage to marine concrete structures, leading to affect the safety and service life of structures. With the help of artificial climate and environment simulation laboratory, the variation of the compression strength and elastic modulus of concrete with the number of freeze-thaw cycles and corrosion time under the corrosion and freeze-thaw environment is studied. The results show that both of them firstly increase and then decrease with corrosion time. When the corrosion time is 270 d and the freeze-thaw time is 90 times, the strength of concrete decreases by 13% and the elastic modulus decreases by 5%. Then, based on the theory of damage mechanics, the damage evolution and constitutive model of concrete under the marine corrosion and freeze-thaw environment are established. Compared with the experimental results, it is found that the model can well describe the damage evolution characteristics of concrete under marine corrosion and freeze-thaw environment. Finally, a numerical model is established on the basis of elastic modulus and strength degradation model of concrete under marine corrosion and freeze-thaw environment. Elevated pile caps of concrete pile component are taken as an example to analyze the process of damage, and the change rules of displacement, deformation, and damage of concrete pile are obtained.

The Effect of Immersion Corrosion Time on Electrochemical Corrosion Behavior and the Corrosion Mechanism of EH47 Ship Steel in Seawater

In this paper, electrochemical corrosion tests and full immersion corrosion experiments were conducted in seawater at room temperature to investigate the electrochemical corrosion behavior and the corrosion mechanism of high-strength EH47. The polarization curve, EIS (electrochemical impedance spectroscopy), SEM (scanning electron microscope), and EDS analyses were employed to analyze the results of the electrochemical corrosion process. The electrochemical corrosion experiments showed that the open circuit potential of EH47 decreases and then increases with an increase in total immersion time, with the minimum value obtained at 28 days. With an increase in immersion time, the corrosion current density (Icorr) of EH47 steel first decreases and then increases, with the minimum at about 28 days. This 28-day sample also showed the maximum capacitance arc radius, the maximum impedance and the minimum corrosion rate. In the seawater immersion test in the laboratory, the corrosion mechanism of EH47 steel in the initial stage of corrosion is mainly pitting corrosion, accompanied by a small amount of crevice corrosion with increased corrosion time. The corrosion products of EH47 steel after immersion in seawater for 30 days are mainly composed of FeOOH, Fe3O4 and Fe2O3.

On Novel Aspects of Hydrogen Effects on Applied Stress - Coupled Micromagnetic Activity in a Mild Steel After Exposure to NaCl – Water Solution: A Combined Approach

Hydrogen produced after exposure of a low – carbon steel to corrosive NaCl – Water solution may affect various its tensile mechanical and magnetic microstructural behaviour in a complex manner. This was investigated by introducing a relevant micromagnetic specific emission (ME) - response of this ferromagnetic material, where related processes and parameters of micromagnetic activity and mechanical response were implemented. In this manner, it was demonstrated that an increase in the hydrogen accumulation with corrosion time leads to an associated increase in the embrittling effect expressed by a substantial loss in the ductility of material. The competive and opposing effects of cumulative hydrogen, applied stress and plastic strain – induced microstructural damage were related to the specific ME- response parameter by which an increased magnetic hardening tendency of material with corrosion time was possible to establish. In this fashion and by using a stress as well as strain mode of presentation- aided combined approach, the complex interplay between micromagnetic activity, hydrogen accumulation and applied stress-strain was better revieled and analysed. It was also shown that the embrittlement is a product of hydrogen accumulation introduced by two highly localized processes. As such, accumulation occurs in two characteristic parallel ways: one of a common lattice diffusion and one of hydrogen transport and redistribution by moving dislocation towards the affected sites. Concerning the highly localized effects the dominating role of hydrogen – induced damage in form void initiation and growth over the hydrogen – assisted stress relief was reasonably demonstrated by using a simple modelling approach. Based on a mechanism of moving dislocation – assisted interaction between commulative hydrogen and magnetic domain walls, a Portervin – Le Chatelier – type micromagnetic process of a cooperative-corelated domain wall transport was proposed to explain certain subtle, quasiperiodic behaviour of ME- response. In the frame of the above findings the superior sensivity of ME – response compared to the mechanical one in early detecting cumulative hydrogen – assisted microstructural damage changes can be d educed.

Experimental Study on the Relationship between the Natural Frequency and the Corrosion in Reinforced Concrete Beams

Due to many nondamage factors such as temperature, humidity, carbonation, and corrosion effects on natural frequency, the key problem of the application frequency-based method to detect damage is to reveal the rules of these factors affect natural frequency and further to eliminate their effects. The long-term characteristics of reinforced concrete structures require a lot of attention, especially in corrosive environment. In this paper, an experimental investigation was conducted to study the deflection and natural frequency of reinforced concrete beam in a marine environmental chamber for six corrosion stages (accelerated corrosion for 0, 20, 40, 70, 100, and 140 days). The experimental results demonstrated that deflection increases with corrosion time, while natural frequency decreases with corrosion time. Based on the accelerate corrosion test data of reinforced concrete beams, the general expression of the relationship between corrosion depth and natural frequency has been established through the fitting curve method. The polynomial model has been selected for establishing the relationship between steel corrosion depth (including the main reinforcement and stirrup) and natural frequency. The reason for selecting the polynomial model is that the sum of squares due to error (SSE) is closer to 0 and the coefficient of multiple determination (R-square) is closer to 1. This investigations help to discriminate the cause of reinforced concrete beams natural frequency change, to eliminate nondamage factors affects, and to apply many structural damage identification methods effectively.

Effect of Corrosion Time on the Synergistic Corrosion of Q235 Steel in Sodium Aluminate Solutions

During Bayer alumina production with high-sulfur bauxite, the sulfide ions in the sodium aluminate solution caused serious corrosion to Q235 steel, which is the material of the tank equipment. This study investigates the effect of corrosion time on Q235 steel synergistic corrosion in sodium aluminate solution using the weight-loss method and electrochemical measurements. The results indicate that the corrosion rate decreases sharply, the rate equation satisfies the mathematical model of power function at the initial stage of corrosion, and the transformation of unstable iron sulfide to stable iron oxide at the later stage results in the decrease in sulfur content in the corrosion products and surface pseudo-passivation. There are two main types of corrosion products, as follows: one is the octahedral crystal particle, which is composed of Fe2O3, Fe3O4, Al2O3 and NaFeO2, and the other is the interlayer corrosion between the surface layer and the matrix, which is composed of FeS, FeS2 and MnS2. At day 3, the dynamics of the Q235 steel electrode is controlled by charge transfer and ion diffusion. However, at other times the dynamics are mainly controlled by charge transfer.

Mechanical properties and damage mode of cemented tailings backfill in an acidic environment

SYNOPSIS The properties and deterioration in strength of cemented tailings backfill (CTB )in the underground acidic environment under oxidizing conditions were studied. X-ray diffraction analysis and scanning electron microscopy of the surface of the CTB was carried out, and the sulphuric acid corrosion mechanism elucidated. The properties tested included compressive strength, elastic modulus, cohesion, internal friction angle, variation in the hydrogen ion concentration, and stress-strain relationship in different corrosion periods. The damage model of the CTB was established considering the effects of parameters such as corrosion time and strain on the damage evolution. It was found that the compressive strength, elastic modulus, cohesion (binder effect), and internal friction angle increased at first and then decreased with exposure time. In the long term, the peak stress decreased with corrosion time while the peak strain increased; elastic modulus, and deformation modulus also decreased. The damage caused by corrosion and by load were related by means of a mathematical model, which revealed the relationships between sulphuric attack, load, and damage to backfill in complex underground environments. During corrosion, the expansion of gypsum and ettringite caused microfractures in the CTB. With increasing corrosion time, micro-cracks developed and proliferated. The mechanism of corrosion damage was found to be the dissolution of hydrogen ions and a sulphate ion reaction that produces an expansive substance, resulting in deterioration of the strength of CTB. Keywords: underground environment, sulphuric acid corrosion, porosity, cemented tailings backfill, damage evolution model.