By monitoring the alternating interference voltage at the intersections and parallels of gas pipelines with high-speed railways, the alternating voltage between the high-speed railway track supports and the ground, the alternating ground voltage gradient along parallel and perpendicular high-speed railway tracks, and the timing of train passages, the interference patterns caused by high-speed railways on pipelines are analyzed. A numerical model was developed to elucidate interference mechanisms. The conclusions indicate that the interference caused by the parallel and intersecting presence of high-speed railways and pipelines is far greater than that caused solely by the intersection of railways and pipelines. The peak alternating voltage interference on pipelines occurs at the insulation joints of the pipelines, the positions of the pipelines corresponding to the high-speed railway track circuits (AT), and the positions of the pipelines corresponding to the passage of trains. The alternating interference caused by high-speed railway lines on pipelines involves both resistive coupling interference and electromagnetic induction coupling interference, with the latter dominating.

In this study, the corrosion behaviour and corrosion mechanisms of X65 pipeline steel was examined in different production processes by using high-temperature and high-pressure autoclaves, conducting electrochemical testing, and employing multiphase flow loops. In addition, the protective effect of a corrosion inhibitor was examined. The results indicated that at a CO2 partial pressure of 0.04 MPa, the corrosion rate of X65 pipeline steel increased from 0.023 to 0.183 mm/a as the flow rate was increased from 0 to 4 m/s. This increase in the corrosion rate was attributable to an increase in wall shear stress caused by fluid flow, highlighting the effect of flow-accelerated corrosion. Under a CO2 content of 0.39 %-10 % (with a partial pressure of 0.04-1 MPa), the corrosion rate of X65 pipeline steel increased from 0.085 to 0.293 mm/a with increasing CO2 content. The addition of an LS-A-type imidazoline-based corrosion inhibitor concentration of 200 ppm, the corrosion inhibition efficiency reached 86.69 %.Study indicating high corrosion inhibition performance under field production conditions with temperatures not exceeding 40 degrees C and flow rates not exceeding 4 m/s.

This study, by using flow loop tests, investigated the erosion–corrosion behavior of carbon steel under conditions of extremely high flow velocity and elevated wall shear stress. The study demonstrated that wall shear stress and water content are the key parameters affecting the erosion–corrosion behavior of carbon steel. The corrosion rate of carbon steel increased with wall shear stress and water content. High wall shear stress disrupted the protective FeCO3 scales. When the wall shear stress reaches 212 Pa, the corrosion rate of carbon steel can reach 10.65 mm/y. In high-velocity CO2 wet gas pipelines, salt deposition (NaCl and CaCO3) occurs even under conditions of low water content and minimal medium salinity. This deposition significantly lowers the erosion–corrosion rate. Furthermore, high wall shear stress can degrade corrosion inhibitor films, but continuous injection maintains their protective effect because of the higher mass transfer rate of inhibitors under high flow velocities, emphasizing the necessity of continuous injection. Even at a wall shear stress of 106 Pa. the corrosion inhibition efficiency can approach 90

When a high-speed train is parallel with a pipeline, its power supply system provokes alternating current (AC) interference that results in the corrosion of the pipeline and a risk of electric shock to pipeline workers. Because trains are continuously moving, the AC interference on the pipeline changes, making mitigation design difficult. In this study, we used numerical simulation to study how the location of a high-speed train influences a pipeline. The results revealed the following: (1) AC interference on a pipeline mainly depends on the current in the rail, because a large amount of current leaks from the rail to the earth, generating a current imbalance. (2) While a train is running from TPSS to AT2, AC voltage peaks appear at the beginning, the ending of the parallel segment, and the middle of each AT section; therefore, the mitigating measurement, if needed, should be the priority at these positions. (3) Compared to the interference caused by a single train, the interference on pipeline is not doubled, but only increases slightly. Moreover, interference reaches its maximum not when two trains are at 5 and 15 km, but when they are at AT1 and 15 km. (4) Field testing was conducted on an actual gas pipeline in the Beijing area. The results showed that the field-tested AC voltage of the pipeline was generally consistent with the calculations.

With the large-scale construction of high-speed railways in China, pipelines are subject to increasingly severe alternating current (AC) interference. It's been found through detection that the AC interference parameters of pipelines near high-speed railways fluctuate greatly. Based on the field test data, this paper statistically analyses the fluctuation law of parameters on the pipeline. On this basis, an indoor simulation experiment was configured to explore the effect of AC current density and cathodic protection potential on dynamic AC corrosion. The results showed that for the same level of cathodic protection, a higher AC current density indicates a higher dynamic AC corrosion rate. When the AC current density increases to 100 A/m2 or higher, the corrosion rate tends to decrease first and then increase with the negative shift of cathodic protection potential. The corrosion risk assessment diagram under dynamic AC interference was drawn through the experiment of field buried coupon experiment and the laboratory simulation experiment. In addition, the mechanism of AC corrosion is discussed to provide a reference for assessing the corrosion risk under dynamic AC interference.

阐述了高压直流输电系统对埋地金属管道的干扰机理及造成的危害，总结了国内外评估此干扰问题的 现场测试方法，介绍了数值模拟计算方法在干扰研究中的应用以及影响因素与干扰规律，讨论了不同缓解方 法的可行性，最后指出了当前研究存在的问题，并展望了该领域的发展趋势。

The corrosion behavior of P110S steel in CO 2 -H 2 S-saturated completion fluid with pH buffer was studied using immersion tests and electrochemical tests. SEM, EDS, XRD, and potential-pH diagrams were used to analyze the corrosion scale characteristics. P110S steel experienced severe localized corrosion in CO 2 -H 2 S-saturated completion fluid despite the addition of pH buffer. The main component of the corrosion scale was mackinawite and FeCO 3 . The corrosion scale with mackinawite as the main component had an excellent protective effect on the matrix when the scale was intact. However, the corrosion scale was poorly bonded to the matrix and was prone to partial cracking and peeling, which was the cause of severe localized corrosion of P110S steel.

The failure mechanism and ultimate internal pressure of X52 grade steel pipe having gouged dent defects are studied using a full-scale burst experiment and finite element analysis. The accumulation and distribution of the equivalent plastic strain during denting, springback and pressurization process are analyzed. According to the test results and the morphology of the pipeline after burst, a failure criterion is proposed and verified using full-scale tests for two steels with different grades. The influence of defect sizes as well as the interaction of dent and gouge on the failure internal pressure is fully analyzed. Compound defects reduce the pipe strength more than the single defect and the influence degree varies with defect sizes. The findings of this paper are helpful to accurately predict failure internal pressure of pipelines having gouged dent, which is often required for pipeline evaluation and repair work.

The effect of H2S on the corrosion products for the corrosion of high strength sulfur-resistant steel was investigated in oilfield produced water under supercritical CO2 conditions by SEM-EDS, LSCM, FIB-SEM, XRD, XPS and theoretical simulation calculations. The results show that with the increase of PH2S, the corrosion degree changes from mild corrosion to moderate corrosion in SC-CO2 phase, while the corrosion rate decreases in aqueous phase. And also the localized corrosion was more severe in SC-CO2 phase. The structure of the corrosion product on high strength sulfur-resistant steel surface evolved from monolayer to bilayer with the increase of PH2S in the SC-CO2 phase. The bilayer corrosion product structure is composed of the inner layer of iron sulfide, FeCO3 and a small amount of Cr(OH)3, and outer layer of FeCO3. However, the corrosion products are bilayered structure in the aqueous phase, and the density of the scales increases with the increase of H2S partial pressure, which reduces the corrosion of high strength sulfur-resistant steel. The results provide guidance for the material selection of oil and gas fields.

In this study, the effects of hydrogen on the fracture toughness and crack propagation of X80 steel base metal and girth weld were assessed. The crack tip opening displacement (CTOD) tests were conducted under in-situ strong cathodic current hydrogen charging in simulated soil solutions and compared to the ones in air. Fracture surfaces and cracks were observed using scanning electron microscopy (SEM) and electron back-scattering diffraction (EBSD). Under in-situ cathodic hydrogen charging conditions, pre-hydrogen charging did not substantially affect the test results of fracture toughness, and hydrogen could quickly achieve the crack tips and exert its effect on crack propagation. In hydrogen-containing environments, X80 steel base metal and girth welds both experienced a decline in fracture toughness. The reduction of the fracture toughness in the base metal increased with increasing current density, reaching 33.2% at a current density of 50 mA/cm2. In turn, that of the girth welds remained almost unchanged, exceeding 45% at the current densities of 10 and 50 mA/cm2, indicating that the girth weld was more susceptible to hydrogen. The difference in the effects of hydrogen on the fracture toughness of the base metal and the weld was attributed to specific microstructural features of both materials. Compared with the weld, the base metal exhibited more refined microstructure, the higher HAGB fraction and the larger grain boundary density, which was conducive to crack arrest performance in hydrogencontaining environments.

Purpose - The purpose of this study is to elucidate the effects of electric-arc-induced ablation on the corrosion behavior of pipeline steel in neutral and high pH environments. Design/methodology/approach - Electrochemical testing, an atmospheric-pressure immersion experiment and various techniques (e.g. scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy) were used to examine the effects of electric-arc-induced ablation on the corrosion behavior of pipeline steel in neutral and high pH environment. Findings - Electric-arc-induced ablation occurred preferentially in areas of inclusion. The corrosion resistance of an ablation pit was lower than that of non-ablation areas. In the neutral soil solution, general corrosion was the dominant corrosion that affected pipeline steel; the effect of ablation was small but pitting corrosion could still be induced. In a high pH environment, the samples without ablation were passivated, whereas the samples with ablation pits could not be passivated; the ablation pits were likely to develop pitting corrosion. Originality/value - Electric-arc-induced ablation can reduce the corrosion resistance of pipeline steel under high-voltage direct current interference.

Dents are one of the most common defects in oil and gas pipelines that can reduce the load-bearing capacity of pipelines. Compound dents have an even greater impact on the load-bearing capacity. This paper summarizes the latest evaluation methods at home and abroad for dented pipelines. The research status of dented pipeline bearing capacity under typical loads such as internal pressure, bending moment, and axial force is presented in terms of experimental data and finite element analysis. The research suggests that the evaluation of residual strength of dented pipeline needs to be combined with finite element simulation. Full-scale tests on dented high-grade steel pipelines with large diameters under complex loads are needed. Parametric analysis should be carried out to comprehensively analyze the influencing factors and laws of pipeline residual strength. A fitting formula for limit load under different working conditions needs to be determined, to lay a foundation for dented pipeline engineering evaluation and residual strength prediction.

The corrosion behavior of super 13Cr SS under the effect of flow velocity in the ultra-HTHP supercritical CO2–H2S–Cl- environment was investigated. The results show the morphology and composition of the corrosion products of super 13Cr SS samples change with varying flow state. In the static condition, the layer consists of an inner layer of Cr(OH)3, a middle layer of Fe1−xS, and an outer crystalline FeCO3 layer. However, in the dynamic supercritical CO2 phase, a galvanic couple effect exists between the pyrrhotite and uncovered steel. Meanwhile, the velocity delays the deposition of FeCO3 and promotes the development of pitting.

A novel and effective water-soluble aldehydes (beta-HA) as corrosion inhibitor was synthesized for N80 steel corrosion in 15% HCl solution, and the corrosion inhibition performance was evaluated by using weight loss, electrochemical measurements, scanning electron microscope (SEM), quantum chemical calculation and molecular dynamics simulation (MDS). The results show that synthesized beta-HA showed excellent corrosion performance compared with MHB and PE for carbon steel in 15% HCl solution compared with MHB and PE, and the inhibition efficiency increased with increasing concentration of the inhibitor. The inhibition efficiency of beta-HA at 8 mmol/L reached the maximum value 94.08%. The inhibitor acted as mixed-type inhibitor via blocking both the anodic and cathodic reaction. The adsorption of inhibitors on N80 steel surface obeyed Langmuir adsorption isotherm, and the process contained chemisorption and physisorption. The Delta G(ads) of beta-HA was -28.81 kJ.mol(-1) under the standard atmospheric pressure. Moreover, the theoretical calculation parameters revealed stronger combination and higher interaction energy for inhibitor beta-HA comparing with MHB and PE, further demonstrating the correlation between the theoretical and experimental results.

The coupling of scratch with cathodic protection or dynamic DC stray current interference can threaten the pipeline safety. Slow strain rate tensile testing combined with scanning electron microscopy and finite element analysis is conducted to explore the effect of the scratch of X60 carbon steel in the soil environment, on hydrogen embrittlement sensitivity under cathodic protection and dynamic DC stray current interference. The results reveal that in air, when the scratch depth of X60 steel exceeds the critical value, its mechanical performance will be markedly affected. In cathodic protection or dynamic DC stray current interference environment, scratches cause stress concentration, and under the combined effect of stress-induced hydrogen diffusion and dislocation multiplication caused by the strain of the scratched area, the hydrogen content near the scratched area is higher than that in unscratched areas; thus, greater scratch depths increase the sensitivity of X60 carbon steel to hydrogen embrittlement.

The cracking susceptibility of two commercial API 5 L X80 steels was compared under acidic environment and electrochemical hydrogen charging. The microstructure and internal cracks of both steels were characterized by optical microscope (OM), scanning electron microscope (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) to elucidate the main factors affecting crack resistance. In comparison, the steel with slightly higher strength and hardness showed much higher hydrogen induced cracking susceptibility. Moreover, cracks in the steel with low hydrogen susceptibility exhibited a predominantly transgranular propagation mode, while a mixed intergranular and transgranular mode in the steel with high hydrogen susceptibility. Long grain boundaries connected along the rolling direction and irregular M/A constituents distributed along the grain boundaries was the main factor causing the reduction of hydrogen-induced crack propagation resistance.

The macromorphology, material properties and corrosion products composition of the corrosive perforated P110 tubing in a water injection well were characterized. Combined with the investigation of service conditions and tubing neutral point calculation, the reason of external corrosion perforation in the water injection well was analyzed. Results showed that the obvious localized corrosion morphology only appeared on the corrosion perforation P110 tubing among the whole well depth tubing, more specifically, the failed tubing’s corrosion morphology was ulcerative. Meanwhile the failed tubing was under the tubing’s neutral point and in sinusoidal buckling. The material properties of the perforated tubing met the requirements of P110 steel in API SPEC 5CT-2011. The tubing external corrosion products were mainly FeOOH and CaCO3. It was indicated that in the buckling state, P110 tubing and casing contacted to form a gap, and then crevice corrosion failure occurred. The corrosion type was oxygen absorption corrosion, and the main factors of corrosion were gap effect and dissolved oxygen content. The corrosion mechanism was the acidification autocatalytic effect of occluded corrosion cell.

The effect of turbulent flow on the corrosion behavior of 6.5Cr steel in CO2-saturated oil field formation water was examined using a rotating cylinder electrode. Electrochemical measurements demonstrated that increasing the flow rate could decrease the corrosion rate of 6.5Cr steel. When the rotation rate of the rotating cylinder electrode reached 2000 rpm, 6.5Cr steel could be passivated. Surface characterization and ion analysis results showed that increasing flow rate reduced Fe2+ concentration in the solution near the steel surface, inhibited FeCO3 deposition, and then increased Cr(OH)(3) concentration in a corrosion film.

The characteristics of calcareous deposits under strong cathodic current and their effect on hydrogen uptake of X80 steel in simulated soil environments were studied by scanning electron microscopy (SEM), hydrogen permeation technique, and hydrogen content tests. When the impressed cathodic current density was in the range of 10-75 mA/cm(2), granular or squamous CaCO3 deposits were generated on the surface, forming discontinuous surface layer with pores and gaps of various sizes. When the current density was increased to 100 mA/cm(2) and 125 mA/cm(2), a dense Mg (OH)(2) film was formed on the surface. With the increase of current density, the sub-surface hydrogen concentration and average hydrogen content first increased and then decreased, reaching the turning point at 75 mA/cm(2). Combined with the structure and component characteristics of calcareous deposits, the mechanism of their effect on hydrogen uptake was analyzed. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

目的 明确超级13Cr在超高温超临界CO2环境下的适用性、耐蚀性及腐蚀产物膜特征.方法 采用高温高压反应釜模拟气井井底超高温超临界CO2腐蚀工况,采用腐蚀失重法获取腐蚀速率,结合扫描电子显微镜(SEM)、能谱(EDS)及X射线衍射仪(XRD)对腐蚀产物特性进行分析研究.结果 在215℃、31.2 MPa CO2分压、7.24 kPa H2S分压下,超级13Cr在含饱和水的超临界相中及含饱和CO2的模拟凝析水相中均呈现均匀腐蚀特征,腐蚀速率分别为0.009 mm/a及0.126 mm/a.腐蚀受CO2-H2S共同控制.腐蚀产物呈双层结构,内层腐蚀产物以碳酸亚铁为主,外层以磁黄铁矿为主,且内外两层腐蚀产物膜结合较弱,易剥离.超临界相中,内外层腐蚀产物膜均较为稀疏,水相区内外层腐蚀产物膜更为致密,但外层腐蚀产物膜容易发生破裂剥落.结论 以0.125 mm/a作为油套管选材标准,对于仅含凝析水、无积水问题的气井,可选用超级13Cr作为油套管材质(温度≤215℃,CO2分压≤31.2 MPa,H2S分压≤7.24 kPa,Cl?质量浓度≤4646 mg/L),但对于井底有比较严重积水问题的气井,或者含水率较高的油井,超级13Cr并不适合.