Effect of deteriorated microstructures on stress corrosion cracking of X70 pipeline steel in acidic soil environment

In order to investigate stress corrosion cracking (SCC) of X70 pipeline steel and its weld joint area in acidic soil environ-ment in China, two simulating methods were used: one was to obtain bad microstructures in heat affected zone by annealing at 1300°C for 10 min and then, quenching in water; the other was to get different simulating solutions of acidic soil in Yingtan in south-east China. The SCC susceptibilities of X70 pipeline steel before and after quenching in the simulating solutions were analyzed...     

Low-valence ion addition induced more compact passive films on nickel-copper nano-coatings

Ni-Cu nano-coatings were prepared by pulsed electroplating technique in the baths containing various amount of boric acid. Their microstructure, morphologies and corrosion resistance were characterized in detail. The addition of boric acid strongly influences on the microstructure of the Ni-Cu coatings. The coating with a grain size of 130 nm, obtained from the bath containing 35 g L⁻¹ boric acid, shows the highest corrosion resistance. This is attributed to the low-valence Cu ion (Cu⁺) additions in nickel oxide, which could significantly decrease the oxygen ion vacancy density in the passive film to form a more compact passive film. The higher Cu⁺ additions and the lower diffusivity of point defects (D₀) are responsible for the formation of more compact passive film on the coating obtained from the bath with 35 g L⁻¹ boric acid.     

Enhanced resistance of 2205 Cu-bearing duplex stainless steel towards microbiologically influenced corrosion by marine aerobic Pseudomonas aeruginosa biofilms

An antibacterial 2205-Cu duplex stainless steel(DSS)was shown to inhibit the formation and growth of corrosive marine biofilms by direct contact with copper-rich phases and the release of Cu~(2+)ions from the2205-Cu DSS surface.In this work,the microbiologically influenced corrosion(MIC)resistance of 2205-Cu DSS in the presence of the corrosive marine bacterium Pseudomonas aeruginosa was investigated.The addition of copper improved the mechanical properties such as the yield strength,the tensile strength and the hardness of 2205 DSS.Electrochemical test results from linear polarization resistance(LPR),electrochemical impedance spectroscopy(EIS)and critical pitting temperature(CPT)measurements showed that 2205-Cu DSS possessed a larger polarization resistance(R_p),charge transfer resistance(R_(ct))and CPT values,indicating the excellent MIC resistance of 2205-Cu DSS against the corrosive P.aeruginosa biofilm.The live/dead staining results and the SEM images of biofilm confirmed the strong antibacterial ability of 2205-Cu DSS.The largest pit depth of 2205-Cu DSS was considerably smaller than that of 2205 DSS after 14 d in the presence of P.aeruginosa(2.2μm vs 12.5μm).2205-Cu DSS possessed a superior MIC resistance to regular 2205 DSS in the presence of aerobic P.aeruginosa.     

The effect of temperature on hydrogen induced fracture in UNI 40NiCrM07 steel

The influence of the temperature on hydrogen embrittlement in UNI 40NiCrMo7 steel was evaluated by means of delayed failure tests. The tests were carried out in the temperature interval 2°–60°C using samples which had undergone two different heat treatments. Hydrogen was introduced into the samples in intensiostatic conditions (d.d.c. 10mA/cm²) by means of cathodic charge in a 0.1N sulphuric acid solution thermostatically maintained at the test temperatures. The results obtained showed a noticeable influence of the temperature on threshold load values and crack incubation times in the tests carried out on quenched material, whereas this influence was found to be negligible in the tests performed on tempered material. This different behaviour was attributed to the effect of the temperature on movement kinetics in the dislocations, responsible for the accumulation and transport of hydrogen into the zones of maximum stress, and on hydrogen diffusion in the metallic lattice.     

Electrochemical corrosion behavior of 300M ultra high strength steel in chloride containing environment

The electrochemical corrosion behavior of 300M ultra high strength steel in chloride containing environment was investigated by potentiodynamic polarization technique, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The results show that uniform corrosion occurs on 300M steel during the electrochemical measurements because no anodic passivation phenomenon is observed on polarization curves within the measurement range. The tests also show that 300M steel is highly susceptible to chloride containing solution, which is characterized by corrosion current density increasing with the addition of chlorides, and corrosion potential shifting towards positive direction and corrosion resistance decreasing, positively suggesting that chloride ions speed up the corrosion rate of 300M steel. Meanwhile corrosion products on the 300M steel surface formed during the salt spray test are too loose and porous to effectively slow down the corrosion rate. Additionally, a schematic structure of uniform corrosion mechanism can explain that 300M steel has better property of stress corrosion cracking (SCC) resistance than stainless steels.     

The influence of copper upon the atmospheric corrosion of iron

The atmospheric corrosion of pure iron and the binary alloy Fe-0.5Cu has been analyzed by a simultaneous measurement of the anodic current density of the metal dissolution and the cathodic current density of the O₂ reduction reaction during several wet/dry cycles using a magnetic and a gas volumetric technique, respectively. The results show three typical stages of the atmospheric corrosion: stage 1 (wetting of a dry surface): rapid corrosion with rust reduction as cathodic process; stage 2 (wet surface): slow corrosion with O₂ reduction as cathodic process; and stage 3 (drying out of the surface): very rapid corrosion with O₂ reduction as the cathodic process during critical wetting of the surface. The effect of copper is restricted to stage 3, where the corrosion rate is much smaller for the Fe-0.5Cu alloy than for pure iron. Two models are discussed to explain these results.     

库尔勒土壤环境中X70管线钢剥离涂层下的腐蚀特征

利用矩形剥离缝隙模型研究了库尔勒土壤模拟溶液中X70管线钢剥离涂层下的滞留液化学特征以及X70钢腐蚀特征.随着浸泡时间的延长,缝内滞留液的p H值逐渐下降直至稳定.Cl^-在缝内滞留液中有不同程度的聚集,其中在缝隙底部的质量浓度最高.SO₄^2-的质量浓度在腐蚀初期表现为随距离增加而降低,到腐蚀后期表现为随距离增加而升高.HCO₃^-和NO₃^-的质量浓度从漏点至缝底有小幅降低.阳离子的质量浓度变化不明显.缝内X70钢的腐蚀形貌表现为明显的点蚀,且随距漏点距离的增加,点蚀越严重.     

Molybdenum based amorphous and nanocrystalline coatings prepared by high velocity oxy-fuel spraying

The high velocity oxy-fuel(HVOF) based thermal spray process has developed as a potential advantageous approach for fabricating various kinds of functional coatings.In this article,the coatings of Mo-based alloy were synthesized using the HVOF process.The microstructure and the mechanical properties of the HVOF-processed coatings were investigated using SEM,TEM,XRD,and hardness and wear tests.Annealing treatment was applied to the as-sprayed coatings to develop the microstructure and its effect on the microstructure and mechanical properties of the coatings was examined.It is found that the HVOF-processed Mo-based alloy coatings are comprised of an amorphous splat matrix embedded with nano-sized crystalline particles.Annealing at temperatures over 950 ℃ results into crystallization of the amorphous matrix.The mechanical properties of the as-sprayed coatings are enhanced with annealing temperature up to 750 ℃ and from 950 to 1050 ℃,keeps constant between 750 and 950 ℃,and reduce over 1050 ℃.The change of the mechanical property with the microstructure was illustrated in the study.     

高分子涂料在烟囱腐蚀防护中的应用

燃煤电厂烟气经过湿法脱硫后,烟气的腐蚀性超过了原烟气的腐蚀性,湿烟气对烟囱内壁造成了严重的腐蚀。高分子涂料具有施工简单,工程造价低,适用烟囱范围广等特点,同时随着高分子性能的不断改进,防腐蚀效果突出,因而在烟囱防腐蚀中具有广泛的应用前景。本文综述了应用于湿烟囱防腐蚀领域的高分子涂料种类、主要性能及应用业绩情况,旨在为新旧湿烟囱保护措施的选择提供有益参考,还对高分子涂料在这一领域的发展前景做出了展望。