For the X80 pipeline steel, electrochemical impedance spectroscopy and potentiodynamic polarization curves were employed to examine the electrochemical corrosion behaviors of its base metal and weld joint under varying test in NS4 simulated soil solution. The Arrhenius equation was further applied to evaluate how temperature impacts their corrosion behaviors. It was found that the weld joint of X80 pipeline steel possesses a microstructure rich in low-potential bainite, with grain sizes coarser than those of the base metal. Both the base metal and weld joint exhibited typical anodic dissolution features without apparent passivation. As the temperature increases, the corrosion current density (Icorr) of the base metal increased from 13.73 to 24.76 & micro;A/cm2, while that of the weld joint rose from 14.42 to 29.52 & micro;A/cm2. In parallel, the activation enthalpy (Delta Ha0) of the base metal and weld joint decreased from 5.742 to 5.243 kJ/mol and 3.826-3.327 kJ/mol, respectively. Accompanied by a corresponding decrease in corrosion resistance. At the same test temperature, the weld joint of X80 pipeline steel demonstrated inferior corrosion resistance relative to its base metal, which was reflected by a higher corrosion current density and lower polarization resistance. Throughout the tested temperature range, the corrosion process of both the base metal and weld joint of X80 pipeline steel was dominated by cathodic diffusion control.

This study investigated the stress corrosion behavior of X80 pipeline steel in NS4 soil simulation solution through slow strain rate tensile tests (SSRT) and fracture morphology observation. The results indicated that with the negative shift of applied potential, the stress corrosion sensitivity of X80 parent metal and welded joints increased. The elongation loss after fracture for welded joints was 2% to 6% higher than parent metal, and the reduction in area was 10% to 14% higher than parent metal. The fracture morphology of X80 parent metal exhibited cleavage fracture at -1300 mV (vs. CSE), while the welded joints showed cleavage fracture at -1100 mV (vs. CSE). According to the interpolation method, the parent metal has a cracking risk between -970 mV and -1050 mV (vs. CSE), with a higher risk of hydrogen embrittlement below -1050 mV. The welded joints have a cracking risk between -890 mV and -960 mV (vs. CSE), with hydrogen embrittlement risk below -960 mV. The conclusion is that the maximum negative protection potential for X80 pipeline steel should not be lower than -960 mV (vs. CSE).

To enhance the surface protection of exposed moving parts made from magnesium alloys, this study focuses on developing high-performance micro-arc composite (MCC) coatings on AZ80 wrought magnesium alloy substrate. AZ80 alloys were fabricated through forging at different temperatures (250 °C, 350 °C, and 450 °C) to investigate the influence of thermal deformation on substrate properties. Subsequently, micro-arc oxidation (MAO) coatings and MCC coatings were applied to the forged alloys. Comprehensive analyses—including microstructural characterization, salt spray corrosion tests, and stress corrosion cracking (SCC) evaluations—were conducted under both static and stress conditions. Among the forging temperatures, 250 °C produced substrates with refined grains and a favorable distribution of β-Mg17Al12 precipitates, resulting in improved baseline corrosion resistance. MAO coatings offered moderate protection, primarily delaying corrosion initiation and crack propagation under stress environments. Building upon this foundation, MCC coatings—fabricated by electrostatic spraying to form an inner-embedded and outer-wrapped structure over the MAO layer—demonstrated significantly superior protective performance. Under both static and stress corrosion scenarios, the MCC coatings effectively suppressed SCC initiation and progression, highlighting their potential for robust surface protection in demanding service environments.

The effects of different Cl- concentrations on the corrosion behavior of pure zirconium and its welded joint were studied by electrochemical test and numerical fitting, and the mechanism was discussed. The results showed that：In the solution containing Cl-, the potentiodynamic polarization curves of industrial pure zirconium base metal and its welded joint show certain passivation behavior, and with the increase of Cl- concentration, the corrosion tendency of the base metal and welded joint increases, the potentiodynamic polarization curves move to the lower right, the polarization resistance of the material decreases, the corrosion current density increases, and the corrosion resistance deteriorates. Compared with the base metal, the corrosion current of the welded joint is larger and the pitting potential is lower under the same Cl- concentration, and the difference in microstructure is the main reason for the poor corrosion resistance.

The oxidation behavior, oxidation morphology, and oxidation products of pure Ti joint welded by tungsten inert gas welding technique at 550 degrees C for different durations (2, 4, 6, and 8 h) and those at different temperatures (650, 750, 850, and 950 degrees C) for 4 h were investigated. Results show that at 550 degrees C, the oxidation time has a slight influence on the oxidation behavior of welded joint. The oxidation temperature has a significant impact on the oxidation behavior, and the higher the temperature, the more severe the oxidation of welded joints. The oxidation kinetics is very close to the quasi-linear law at low temperatures. With increasing the temperature, the oxidation rate is increased exponentially. Additionally, the oxidation products generated on the surface of welded joint are TiO 2 with anatase and rutile structures, and the temperature barely has effect on the TiO 2 type. The oxidation process of pure Ti welded joint can be described as follows: oxygen atoms are absorbed on the surface; oxides preferentially nucleate in the defective zone; oxides grow laterally and the oxidation film becomes thicker. At relatively higher temperatures, the cracks or voids appear in the oxidation film, which become the transmission channels of O atoms, leading to the high diffusion rate of O and Ti atoms and high oxidation rate.

针对苏77、召51区块N80油套管钢出现的腐蚀穿孔问题,利用高温高压模拟实验和电化学极化曲线法研究了 RX-204B和IMC-80BH等两种常用缓蚀剂的作用机理及防腐效果.通过扫描电镜对去除腐蚀产物前后的试样表面形貌进行观察;采用能谱分析仪对腐蚀产物进行成分分析.结果表明:两种缓蚀剂均为吸附膜阳极控制型缓蚀剂,由于成分不同,官能团的作用机理不同,不同浓度下两种缓蚀剂的极化曲线变化规律存在一定差异.明确了两种缓蚀剂的腐蚀机理及最佳加注浓度,形成了适用于苏77、召51区块气井井筒工况的最优防腐工艺.

A novel Mg–Zn–Zr–Y–Cu alloy was fabricated, and its corrosion behaviour was investigated in the present work. The results showed that, compared with Mg–6Zn–0.5Zr (ZK60) alloy, Mg–6Zn–1Y–0.5Cu–0.5Zr (ZWCK6100) alloy exhibited finer recrystallised (DRXed) and unDRXed grains, more homogeneous microstructure, and contained CuMgZn and I phase (Mg3Zn6Y) in addition to α-Mg, Zn2Zr, MgZn2 precipitates. As a result, ZWCK6100 alloy had a lower corrosion rate and higher corrosion resistance, underwent slightly localised corrosion in 3.5 wt-% NaCl solution, implying that the combined addition of Y and Cu was conducive to improving the corrosion resistance of Mg alloys.

In this paper, the corrosion behavior of 2205 duplex stainless steel coiled tubing in acidizing and production environments was studied by high-temperature and high-pressure corrosion weight loss tests, stress corrosion cracking test, electrochemical tests, microscopic morphological analysis and corrosion product analysis. The results show that in the acidizing environment, the duplex stainless steel has high corrosion rates especially in the acidizing solution with high HCl concentration, with the selective dissolution of ferrite phase. In the production environment containing CO2 and H2S, the duplex stainless steel has excellent resistances to corrosion and stress corrosion cracking. With the increase of pH value, the pitting potential and polarization resistance exhibit the increasing trend, indicating the better passivation performance. Therefore, 2205 duplex stainless steel coiled tubing can be recommended to be mainly used for the operations in production environment rather than acidizing operations.

X52 pipeline steel has been widely used for long-distance transmission for oil and gas, there is a lack of evaluation of such pipelines steel in service. Thus, the present work mainly focuses on the effect of cathodic protection potential on stress corrosion cracking (SCC) behavior of a in service for 20 years X52 pipeline steel. The SCC behavior was systematically studied by electrochemical method, slow strain rate tension (SSRT), and surface analysis techniques in near-neutral NS4 solution. The results show that the SCC mechanism of base metal (weld joint) belongs to the anodic dissolution, anodic dissolution + hydrogen embrittlement, and hydrogen embrittlement when the E app is − 664 mV (− 738 mV), − 664-− 872 mV (− 738-− 980 mV), and < − 872 mV (− 980 mV), respectively. The SCC susceptibility of base metal and weld joint gradually increases with the negative potential application and then increases sharply when the potential is negative than − 1100 mV. The fracture morphology also changes with the E app and gradually becomes cleavage fracture with the negative shift of potential.

The strengthening mechanism and stress corrosion cracking (SCC) behavior of a new Mg-6Zn-1Y-0.5Cu0.5Zr alloy (given the name "ZWCK6100 '') were investigated in this work. The results showed that the microstructure, mechanical properties and stress corrosion resistance were significantly affected by the combined addition of Cu and Y. The alloy consisted of alpha-Mg, Zn2Zr, CuMgZn, rod-shaped MgZn2 precipitates and I phase (Mg3Zn6Y), and displayed a balance between strength and ductility, with the yield strength, ultimate tensile strength and elongation being 320.3 MPa, 351.5 MPa and 19.8%, respectively. The main strengthening mechanisms were found to be grain refinement, second phases and texture. In addition, the stress corrosion resistance was assessed by slow strain rate testing and fractography. These tests showed that ZWCK6100 alloy exhibited improved SCC resistance and low SCC sensitivity in 3.5 wt% NaCl solution. The novel ZWCK6100 alloy may serve as a promising magnesium alloy for industrial applications. (c) 2022 Elsevier B.V. All rights reserved.

某西部油田高温高压气井连续油管在下井过程中发生断裂,采用宏观观察、无损探伤、化学成分分析、力学性能试验、金相检验、扫描电镜及能谱分析等方法,分析了连续油管断裂的原因.结果表明:该连续油管在下井过程中,管壁发生结腊,连续油管受到压缩载荷,导致下井受阻,当压缩载荷超过材料屈服强度后,连续油管发生压缩变形,随后发生断裂.

This paper investigates the fatigue behavior of S135 high-strength drill pipe steel under tension–torsion multiaxial loading. Based on the concept of critical plane during fatigue, the fatigue model under the combined loading of tension–torsion is established. The proposed model is validated, and the predicted results are in good agreement with the experimental testing results. The maximum relative errors between the estimation and the experiment are mostly within the range of factor two to three for proportional, and 90° non-proportional tension–torsion loading. Meanwhile, the failure mechanism is also discussed through fracture analysis.

The influences of the forging process and micro-arc oxidation (MAO) coating on the corrosion behavior of ZK60 wrought magnesium alloys exposed to salt spray and constant stress corrosion conditions were investigated. The microstructure of the ZK60 Mg alloy specimens forged under different temperatures (i.e., 250, 300, and 450 °C) was characterized using metallography, EBSD, and SEM. It was demonstrated that the ZK60 alloy forged at 300 °C (i.e., ZK60EF-300) had finer grain and uniformly distributed β-phase and, thus, better corrosion resistance than the ZK60 forged at 450 °C. At the lower forging temperature (250 °C) twins formed in the ZK60 alloy, which accelerated the corrosion of the ZK60E-250 specimen. The MAO coating provided robust corrosion protection for all the ZK60 wrought Mg alloy substrates. The salt spray corrosion test results showed that when the MAO coating broke down at certain weak sites, the corrosion performance of the coated Mg alloy was predominantly determined by the alloy substrate. The stress corrosion behaviors of the uncoated and MAO-coated ZK60 alloy specimens were also investigated under a constant load of 80 MPa in 3.5 wt.% NaCl solution. The MAO coating was found to improve the stress-corrosion resistance of the ZK60 alloy pronouncedly.

为充分了解HFW焊管焊缝沟槽腐蚀机理,及其对高频电阻焊管力学性能的影响,从而探索出有效降低HFW焊管沟槽腐蚀敏感性的方法,从沟槽腐蚀影响规律、测试方法等方面对国内外现阶段沟槽腐蚀研究成果进行分析汇总,着重分析了几种主要的沟槽腐蚀敏感性测试方法,对其优劣性进行了对比.同时,根据沟槽腐蚀研究现状以及相关知识产权的情况,发现目前国内外尚无统一标准的焊缝沟槽腐蚀深度的测量设备或装置,对沟槽腐蚀敏感系数临界值也缺乏工程依据,其失效判定的有效性有待进一步探讨.

The relative content of strengthening element tantalum (Ta) and oxidation-resistant element chromium (Cr) is an essential value for superalloys to obtain an excellent combination of oxidation resistance and mechanical properties. In the present paper, the isothermal oxidation behavior of several single crystal Ni-base superalloys with different Ta/Cr (wt. %, similarly hereinafter) ratios at 1000 °C in static air has been systematically investigated to explore the optimal Ta/Cr for excellent oxidation resistance. A detailed microstructure study using X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and an electro-probe microanalyzer (EPMA) was performed to reveal the oxidation products and mechanisms. For all alloys, a three-layer structured scale consisting of an outer (Cr, Al, Ti, Ni, Ta)-O layer, an inner Al2O3 layer and an inner nitride layer was formed. As Ta/Cr increased, the amounts of Ta-containing products, cracks, holes and inner nitride increased. Meanwhile, the completeness of the Al2O3 layer got worse. It was shown that if Ta/Cr ≤ 0.5, Ta increased the growth rate of Cr2O3 via the doping effect induced by Ta cations. If Ta/Cr > 0.5, Ta reduced the completeness of Cr2O3 through competitive growth of Ta2O5 and Cr2O3. A good oxidation performance can be expected with the value Ta/Cr ≤ 0.5.

Station and valve chamber design often encounter the situation of drilling hole at the main pipeline and welding boss-backing to connect the branch pipe. Boss hole location should generally be at least 100 mm away from the longitudinal weld or spiral weld. However, because the electric resistance weld (ERW) is difficult to distinguish in practice, some bosses mounting position coincide with ERW or close to. In this paper, the influence of boss-backing welding directly on the longitudinal weld to the original residual stresses of ERW pipe was studied. The microstructure of pipe body and longitudinal weld after welding was also analysis. The testing results showed that the overall residual stresses of ERW pipe were relatively small. Residual stress at the longitudinal weld region were smaller than those at the pipe body region. After the boss-backing welding, the axial residual stress at the longitudinal weld and the circumferential residual stress at the pipe body region near the intersection increased sharply to 2.5 (444 MPa) and 3.8 (433 MPa) times, respectively. The invaded width and depth to the ERW pipe after welding were about 15.167 mm and 3.376 mm. Granular bainite with necklace type M-A constituents could be observed at the invaded zone. It is suggested that small welding heat input should be adopted for boss-backing welding.

在对钛及钛合金的热氧化行为国内外研究现状调研的基础上,分析了钛与钛合金在多种环境中的热氧化进程,以及相应的氧化产物,深入分析此类氧化现象的具体影响要素,并且对实际的热氧化行为研究前景进行了展望.

The electrochemical corrosion behavior of TA2 base metal and welded joint in Cl- containing (3.5%NaCl, 5.0%NaCl, 7.5%NaCl) solutions was studied by electrochemical test method. The results show that with the increase of Cl- concentration, the open circuit potential (OCP) of TA2 base metal and welded joint shifts negatively, the polarization resistance decreases gradually, and the corrosion current density increases. Compared with the base metal, the microstructure of the welded joint is different, which changes their corrosion resistance. It shows that the OCP of the welded joint shifts negatively, the polarization resistance is larger, and the corrosion current density is smaller, which indicates that the corrosion resistance of the welded joint is better.

Wrought Mg alloys have attracted increasing attention for automotive applications due to their homogeneous microstructure and enhanced mechanical properties compared to as-cast alloys. However, in real service conditions, Mg structural components are susceptible to early failures due to the synergistic effects of corrosion and mechanical loading, which severely hinder their high penetration in the automotive industry. Therefore, the corrosion protection of Mg structural components is of crucial importance. In this work, AZ80 and ZK60 Mg alloys were forged under different temperatures, and then treated with micro-arc oxidation (MAO) and micro-arc composite coating (MCC) which is the MAO plus E-powder coating. The effects of forging processing parameters on the microstructure and corrosion properties of the alloys were analyzed, and the corrosion performances of the MAO-, MCC-coated Mg alloys were characterized through salt spray corrosion test. Experimental results demonstrated that the MCC coating provided robust corrosion protection for the wrought Mg alloys.

The welded joint of industrial pure zirconium (R60702) was treated by surface high energy shot peening (HESP). The microstructure, surface grain size, micro distortion, gradient structure and crystal orientation were characterized by optical microscope (OM), X-ray diffraction (XRD) and electron back scattered diffraction (EBSD). A surface roughness measuring instrument was used to measure and evaluate the surface roughness, and an electrochemical workstation was used to study the corrosion resistance of R60702 welded joints. The results show that after HESP treatment, a gradient structure is formed on the surface layer of the industrial pure zirconium welded joints with a thickness of about 110 mu m, and the grains of top layer reach the nanometer level. In the process of surface nanocrystallization, twins and dislocation slip are the main deforming mechanism. After HESP treatment, the self-corrosion potential of R60702 welded joints is positively shifted, and the corrosion current density is reduced. HESP treatment makes the surface structure of the three areas of the welded joints uniform, and the self-corrosion potential tends to be uniform, which effectively inhibits galvanic corrosion.