•The fatigue lives of 316LN stainless steel decrease with decreasing strain rate.•Fatigue cracks mainly initiated at pits and persistent slip bands.•Dynamic strain aging promoted fatigue cracks initiation in high-temperature water.Low cycle fatigue behavior of forged 316LN stainless steel was investigated in high-temperature water. It was found that the fatigue life of 316LN stainless steel decreased with decreasing strain rate from 0.4 to 0.004 %s−1 in 300 °C water. The stress amplitude increased with decreasing strain rate during fatigue tests, which was a typical characteristic of dynamic strain aging. The fatigue cracks mainly initiated at pits and slip bands. The interactive effect between dynamic strain aging and electrochemical factors on fatigue crack initiation is discussed.

•Boat-shaped sample was used to study fatigue behavior of Alloy 690 tubes.•Fatigue life of Alloy 690 tubes was longer at 5500 ppb dissolved oxygen than at <5 ppb dissolved oxygen.•Persistent slip bands facilitated rupture of oxide film on Alloy 690 tubes.•High oxide film growth rate at 5500 ppb dissolved oxygen prevents fatigue crack initiation.Corrosion fatigue behavior of Alloy 690 tubes used for actual steam generator (SG) was investigated in borated and lithiated high temperature water containing <5 ppb (by weight) and 5500 ppb dissolved oxygen (DO) using boat-shaped specimens. It was found that the fatigue life at 5500 ppb DO was longer than at <5 ppb DO. The surface cracks and fracture characteristics of the specimens after fatigue tests were carefully examined. The effects of DO concentration on fatigue crack initiation and propagation of Alloy 690 tubes in high temperature water are discussed.

•Heat-treatment is the best way to prepare long-term monitoring tungsten electrode.•Tungsten electrode made by immersion in HNO3 is unsuitable in B/Li environment.•Target factor analysis is used to investigate tungsten electrode.•Response mechanism of tungsten electrodes made by three ways are different.Tungsten/tungsten oxide electrodes were prepared by four kinds of methods and their pH response behaviors in lithium borate buffer solutions at 25 °C have been investigated by electrochemical measurements. It was found that tungsten/tungsten oxide electrode made by immersion in HNO3 solution was unsuited to the testing environment because it tended to exfoliate or dissolve during tests. All the other tungsten/tungsten oxide electrodes showed linear response to pH values and good stability during the long-term potential monitoring. The lower dissolution rate of tungsten/tungsten oxide electrode made by heat-treatment made it the best candidate for the long-term monitoring due to its compact oxide film formed on the surface. X-ray photoelectron spectroscopy and thermodynamic analysis have been done to evaluate pH response mechanisms of the corresponding electrodes.

The corrosion behavior of a thermal-sprayed stainless steel (SS)-coated Q235 steel has been investigated in simulated soil solutions using electrochemical measurements, x-ray photoelectron spectroscopy analysis, and scanning electron microscope. The as-received Q235 steel and galvanized steel for grounding grids were also examined for the purpose of comparison. The effects of pH value of testing solutions have been examined. The thermal-sprayed SS-coated steel showed the best corrosion resistance among the three kinds of materials. With increasing pH value, the corrosion resistance of SS-coated Q235 steel increased. In weak alkaline solutions, the SS-coated Q235 steel showed the largest polarization resistance (3.2 × 105 Ω cm2), the lowest anodic current density (1.4 × 10−2 μA/cm2), and the largest film resistance (4.5 × 106 Ω cm2), suggesting that the coated steel has the best corrosion resistance in weak alkaline environment. Related corrosion mechanisms are also discussed.

•Boat-shaped sample was designed to study fatigue behavior of Alloy 690 tube.•Alloy 690 tube had longer fatigue life than round-bar sample published in literature.•Persistent slip bands and electrochemical factors promoted fatigue crack initiation.•Hydrogen induced cracking assisted crack growth in high temperature water.Corrosion fatigue behavior of Alloy 690 tube used for actual steam generator (SG) was investigated in <5 ppb (by weight) dissolved oxygen borated and lithiated high temperature water by low cycle fatigue tests with boat-shaped specimens. It was found that the present tube materials had longer fatigue life than round-bar materials in open literature. The surface cracks were tortuous, typical crack branching and linkage were observed. The fracture surfaces were rough with well-defined fatigue striations. Related mechanisms of fatigue crack initiation and propagation of Alloy 690 SG tube in high temperature water are discussed.

•Boat-shaped sample was used to study LCF behavior of Alloy 690 SG tubes.•TiN and Al2O3/MgO inclusions were found in Alloy 690 SG tubes.•Broken TiN and TiN clusters facilitated CF crack initiation and propagation.•Inclusion-involved fatigue cracking mechanisms for Alloy 690 SG tubes were proposed.Influence of TiN inclusion on corrosion fatigue behavior of three types of as-received Alloy 690 steam generator tubes (J, C1 and C2) in borated and lithiated high temperature water was investigated. The volume fraction of inclusions in tube J, C1 and C2 were about 0.0894%, 0.0384% and 0.1843%. The fatigue life of tube C2 was slightly shorter than that of tube J and C1. Large broken TiN inclusions and TiN-inclusion clusters played a significant role on fatigue crack initiation and propagation for tube C2 in high temperature water. The inclusion-involved fatigue cracking mechanisms are discussed.

•Zn injection changed composition and structure of oxide films on 304 SS.•A few ppb Zn altered electrochemical behaviour, more Zn injection had little effect.•≤50 ppb Zn injection could significantly affect formation of Zn-bearing oxides.•A modified PDM is proposed to explain inhibition mechanism of Zn injection.The characteristics of oxide films formed on 304 stainless steel (SS) in borated and lithiated high temperature water with Zn injection of 0 ppb to100 ppb were investigated using in-situ potentiodynamic polarization curves, electrochemical impedance spectra at 573.15 K and ex-situ X-ray photoelectron spectroscopy (XPS). There was a high inhibition effect of Zn injection on the growth of oxide films in the testing solution. The lowest growth rate was corresponding to the highest Zn-injected level. The ≤50 ppb Zn injection based on plant experience could significantly affect the formation of Zn-bearing oxides on the surfaces, while >50 ppb Zn injection showed no obvious influence on the oxide films. A modified point defect model was proposed to discuss the effects of injected Zn concentrations on the oxide films on 304 SS in high temperature water.

The effects of pH and dissolved oxygen (DO) on electrochemical behavior and oxide films of 304SS in borated and lithiated high temperature water were investigated by electrochemical measurements, XPS analysis and SEM technique. An experimental potential–pH diagram for 304SS at 300 °C was constructed. The safe potential–pH zone for minimizing corrosion degradation enlarged in high-pH deaerated solution. As pH increased, the protective property of the oxide films increased, and the concentration of Ni and Fe on film surface declined. The protective property of the oxide films was DO-independent. The related mechanism was discussed.Highlights► An experimental E-pH diagram for 304SS at 300 °C was constructed. ► The safe E-pH zone of 304SS enlarged in high-pH deaerated solution. ► Increasing pH value improved the protective property of the oxide film on 304SS. ► The protective property of the oxide film on 304SS was DO-independent.

The evolution of electrochemical behaviour and oxide film properties of 304 stainless steel in high temperature aqueous environment have been studied by polarization curves, electrochemical impedance spectra (EIS) and X-ray photoelectron spectroscopy (XPS). The electrochemical data indicate that the corrosion resistance of the steel increases with immersion time. The EIS and XPS analyses show that the oxide films are a duplex structure and the corrosion rate is dominated mainly by the Cr-rich inner layer. The correlation between the evolution of the electrochemical behaviour and the changes of the oxide film properties is discussed.Highlights► Both of the EIS data and XPS data indicate the oxide film has a duplex structure. ► The resistance of the inner layer increases faster than that of the outer layer. ► The currents for oxide formation are controlled by different mechanisms.

The characteristic of oxide scales on T91 superheater tube after long-term service in an ultra-supercritical coal power plant was investigated using light optical microscopy, stereomicroscope, X-ray diffraction, electron probe micro-analyzer, scanning electron microscopy and energy-dispersive X-ray spectroscopy. It was found that the oxide scale formed on the inner wall of the tube was a multi-layer structure. The outer layer consisted of Fe3O4 and Fe2O3 with some pores and tended to exfoliate. The inner layer consisted of Cr-rich spinel. The Cr-rich oxide was observed as striations parallel to the oxide/metal interface. The possible mechanisms of oxidation and exfoliation are also discussed.Graphical abstractHighlights► Corrosion of a T91 superheater tube after long-term service was investigated. ► The oxide has a structure with Fe-rich outer layer and Cr-rich inner layer. ► The Cr-rich oxide was observed as striations parallel to the oxide/metal interface. ► The exfoliation of the oxide scale can be explained by a buckling mode.

Oxide films formed on Alloy 690 exposed to 290 °C water containing 3 ppm O2 were investigated. It was found that Cr rich oxides form initially through solid-state reactions. Ni–Fe spinels gradually develop on surface layer by precipitation with increasing immersion time. Initially formed Cr rich oxides react with outwards diffusing Ni and Fe to form small spinel particles which then vanish gradually. An inner layer develops from oxide/matrix interface through inward diffusion of oxidant. Cr is preferentially oxidized and tends to dissolve into solution. The resultant inner layer consists of predominant NiO which cannot serve as a protective barrier layer.Highlights► The oxide film is initially Cr enriched, but loses Cr as immersion time increases. ► The oxide film mainly consists of outer Ni–Fe spinel particles and inner NiO layer. ► The inner NiO layer forms as Cr dissolves and is not a protective barrier layer.

Characteristics of oxide films formed on 304 stainless steel under alternately changing Ni2+ concentrations in oxygenated high temperature water were examined. Oxides preformed under low Ni2+ concentration evolve from hematite to spinel after subsequent immersion under high Ni2+ concentration. Meanwhile, Ni content in the surface layer of oxide rises up while Fe content drops. Oxide films preformed under high Ni2+ concentration show little change in phase composition after subsequent immersion under low Ni2+ concentration. Fe contents in surface layer rise up while the change of Ni contents depends on the original phase composition and whether residual Ni2+ is present.Highlights► Hematite preformed under low Ni2+ level evolves into spinel under high Ni2+ level. ► Oxide films maintain in phase composition when Ni2+ level changes from high to low. ► Oxide film preformed under high Ni2+ level could consume trace Ni2+ in solution.

Characteristics of the oxide films formed on 304 stainless steel exposed to 290 °C oxygenated water in a nickel-lined autoclave were examined. The oxides evolve from dominating irregularly shaped hematite to faceted spinels with increasing immersion time. The surface layer of oxide film is first Cr-enriched and then Ni-enriched as immersion time increases. The oxides nucleate by solid-state reactions with selective dissolution of Fe and Ni, and then grow up through precipitation of cations from solution. Nickel ions dissolved from the nickel lining could promote the stability of NiFe2O4 spinel and influence the oxidation behaviour of 304 stainless steel significantly.Research highlights► Oxides formed evolve from dominating hematite to spinel as immersion time extends. ► Oxides nucleate by solid-state reactions and then develop through precipitation. ► Ni2+ can stabilize NiFe2O4 and influence the oxidation behaviour of 304 SS notably.

The role of nitrogen on the passivation of nickel-free high nitrogen and manganese stainless steels was investigated in 0.5 M H2SO4, 3.5% NaCl and 0.5 M H2SO4 + 0.5 M NaCl solutions using potentiodynamic polarization, electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy techniques. The passive film stability was enhanced in 0.5 M H2SO4 and the pitting resistance was improved in 3.5% NaCl solution by more nitrogen addition. The influence of nitrogen extended the whole anodic polarization region in 0.5 M H2SO4 + 0.5 M NaCl solution, as demonstrated by the enhanced dissolution resistance, promoted adsorption and passivation process, improved film protection and pitting resistance with increasing nitrogen content. Possible mechanisms relating to the role of nitrogen in different potential regions were discussed.

The effects of cold work and sensitization treatment on the microstructure and corrosion resistance of a nickel-free high nitrogen stainless steel (HNSS) in 0.5 M H2SO4 + 0.5 M NaCl, 3.5% NaCl and 0.5 M NaOH + 0.5 M NaCl solutions have been investigated by microscopic observations, electrochemical tests and surface chemical analysis. Cold work introduced a high defect density into the matrix, resulting in a less protective passive film as well as reduced corrosion resistance for heavily cold worked HNSS in a 3.5% NaCl solution. No obvious degradation in corrosion resistance took place in a 0.5 M H2SO4 + 0.5 M NaCl solution, possibly due to the stability of the passive film in this solution. Sensitized HNSSs showed reduced corrosion resistance with increasing cold work level in both 3.5% NaCl and 0.5 M H2SO4 + 0.5 M NaCl solutions due to a reduction in the anti-corrosion elements in the matrix during the cold work-accelerated precipitation process. The cold work and sensitization treatment had no influence on the corrosion resistance of the HNSS in the 0.5 M NaOH + 0.5 M NaCl solution even though the property of the passive film changed. The effects of cold work and sensitization treatment on the characteristics of passive films formed in the three solutions are discussed.

Pitting corrosion behavior of three kinds of nickel-free and manganese-alloyed high-nitrogen (N) stainless steels (HNSSs) was investigated using electrochemical and immersion testing methods. Type 316L stainless steel (316L SS) was also included for comparison purpose. Both solution-annealed and sensitization-treated steels were examined. The solution-annealed HNSSs showed much better resistance to pitting corrosion than the 316L SS in both neutral and acidic sodium chloride solutions. The addition of molybdenum (Mo) had no further improvement on the pitting corrosion resistance of the solution-annealed HNSSs. The sensitization treatment resulted in significant degradation of the pitting corrosion resistance of the HNSSs, but not for the 316L SS. Typical large size of corrosion pits was observed on the surface of solution-annealed 316L SS, while small and dispersed corrosion pits on the surfaces of solution-annealed HNSSs. The sensitization-treated HNSSs suffered very severe pitting corrosion, accompanying the intergranular attack. The addition of Mo significantly improved the resistance of the sensitization-treated HNSSs to pitting corrosion, particularly in acidic solution. The good resistance of the solution-annealed HNSSs to pitting corrosion could be attributed to the passive film contributed by N, Cr, and Mo. The sensitization treatment degraded the passive film by decreasing anti-corrosion elements and Cr-bearing oxides in the passive film.

Morphologies, microstructures and chemical composition of oxide films grown on Alloy 625 at 400 °C, 450 °C and 500 °C in oxidizing supercritical water containing 2.0% H2O2 were investigated using weight measurement, grazing incidence X-ray diffractometry, scanning electron microscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. It was found that the mass gain of the alloy in oxidizing supercritical water increased with exposure time. The smallest mass gain was obtained at 450 °C, agreeing well with the smallest oxide film thickness at this temperature. The average thickness of the oxide films was 1.28 μm, 0.72 μm and 1.42 μm at 400 °C, 450 °C and 500 °C, respectively after 250 h exposure. The size of oxide crystals on the alloy surface gradually grew with increasing exposure temperature. A discontinuous and thin Cr2O3 layer was formed at 400 °C in oxidizing supercritical water as a result of leaching of Cr3+ as Cr6+, while a continuous Cr2O3 layer was formed at 450 °C and 500 °C. Duplex oxide layer structure was observed at all three temperatures, which was identified to consist of Ni(OH)2/NiO/NiCr2O4/Cr2O3/Alloy 625 from outer to inner layer. The growth mechanism of oxide films on Alloy 625 in oxidizing supercritical water seems to be similar to that in high temperature water, namely the Ni(OH)2/NiO outer layer growth by dissolution and precipitation mechanism and the Cr2O3 inner layer formation by oxygen diffusing inward and reacting with the retained Cr.

This paper presents corrosion failure analysis on a commercial pure nickel thermocouple sheath used in BaTiO3 hydrothermal synthesis reactor. Detailed investigations of the corrosion products have been performed using stereomicroscope, X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. It was found that the corrosion failure of the sheath was mainly due to general corrosion and crevice corrosion of pure nickel, and the main corrosion products were Ni(OH)2. Many cracks were observed inside the corrosion products and along the interfaces between the corrosion products and metal matrix. BaTiO3 particles were deposited as parallel white bands along the above cracks inside the corrosion products. Chloride ions also entered the cracks or crevices, resulting in the acidification inside the crevice and aggravated the attack of nickel matrix. Some recommendations to prevent/minimize future similar corrosion failures were proposed.