Susceptibilities to stress corrosion cracking （SCC） of X80 pipeline steel in high pH solutions with various concentrations of HC03 at a passive potential of-0.2 V vs. SCE were investigated by slow strain rate tensi...Susceptibilities to stress corrosion cracking （SCC） of X80 pipeline steel in high pH solutions with various concentrations of HC03 at a passive potential of-0.2 V vs. SCE were investigated by slow strain rate tensile （SSRT） test. The SCC mechanism and the effect of HC03 were discussed with the aid of electrochemical techniques. It is indicated that X80 steel shows enhunced susceptibility to SCC with the concentration of HCO3 increasing from 0.15 to 1.00 mol/L, and the susceptibility can be evaluated in terms of current density at -0.2 V vs. SCE. The SCC behavior is controlled by the dissolution-based mechanism in these circumstances. Increasing the concentration of HCO3 not only increases the risk of rupture of passive films but also promotes the anodic dissolution of crack tips. Besides, little susceptibility to SCC is found in dilute solution containing 0.05 mol/L HCO3 for X80 steel. This can be attributed to the inhibited repassivation of passive films, manifesting as a more intensive dissolution in the non-crack tip areas than at the crack tips.展开更多
Susceptibilities to stress corrosion cracking（SCC） of X80 pipeline steel in relatively concentrated carbonate/bicarbonate solutions with different chloride ion concentrations or p H value at a passive potential of-2...Susceptibilities to stress corrosion cracking（SCC） of X80 pipeline steel in relatively concentrated carbonate/bicarbonate solutions with different chloride ion concentrations or p H value at a passive potential of-200 m V vs SCE were investigated by slow strain rate tensile test.In order to explore the SCC mechanism and the evaluation criterion for the SCC susceptibility of the steel in passive state,electrochemical measurements were taken.Potentiodynamic polarization curves were obtained at different potential sweep rates,and electrochemical impedance spectroscopy measurements were taken after fast polarization to the passive potential.The effects of chloride ion and p H on SCC behaviors of X80 steel at the passive potential were also discussed.The results showed that the SCC mechanism of X80 pipeline steel was greatly influenced by the passive film formed in these solutions.The SCC behaviors followed the film suppressed anodic dissolution mechanism in these circumstances,because the filming process accounted for a considerable proportion of the overall electrode process.The criteria for evaluating the SCC susceptibility of the steel at passive potential were proposed and validated.Decreasing in the concentration of chloride ion or increasing in p H value resulted in the reduction in SCC susceptibility.The existence of chloride ion greatly lowered the passivation tendency and the film stability,while its concentration determined the dissolution rate of the steel matrix.Higher p H value was responsible for the stable and tenacious passive films and the high repassivation capability.It was also inclined to lower the anodic dissolution rate at crack tips by retarding the cathodic oxygen reduction.展开更多
This study aims to disclose the thermo-oxidative degradation behaviors and kinetics of a carbon fiber reinforced polyimide(CFRPI)composite for modeling of the Iong-term degradation process.The degradation behaviors we...This study aims to disclose the thermo-oxidative degradation behaviors and kinetics of a carbon fiber reinforced polyimide(CFRPI)composite for modeling of the Iong-term degradation process.The degradation behaviors were revealed through off-gas products analysis,and the overall kinetic interpretation was achieved from study of the mass-loss curves recorded under dynamic conditions.It was found that thermooxidative degradati on of the CFRPI composite was a multistep process,which in eluded four main reaction steps.Since most kinetic an alysis methods were derived from simple reactions described by a single kinetic triplet,they cannot be applied reliably to such a process.Therefore,we firstly separated the four overlapped reaction steps by peak fitting of derivative thermogravimetric curves using Fraser-Suzuki equation consider!ng the asymmetrical n ature of kin etic curves,and subsequently an a lyzed each in dividual reaction employing Friedma n method and experimental master-plots method.Four sets of kinetic triplets were determined to characterize the entire degradation process.The validity of four corresponding kinetic triplets was confirmed by perfect simulation of mass-loss curves recorded at both dynamic conditions used in kinetic analysis and entirely different isothermal conditions.Finally,modeling of Iong-term aging at 400°C of the CFRPI composite was successfully achieved based on these kinetic triplets.The predicted mass loss and flexural property correlated well with experimental results.This study can serve as a basis for rapid evaluation of the long-term durability of the CFRPI composite in various application environments.展开更多
Based on the analysis of the mechanism of train slippage, this paper discusses the availability judgment threshold of wheel diameter calibration with examples, and puts forward corresponding feasible suggestions accor...Based on the analysis of the mechanism of train slippage, this paper discusses the availability judgment threshold of wheel diameter calibration with examples, and puts forward corresponding feasible suggestions according to the discussion results.展开更多
This paper reviews the current state of knowledge and advances on the stress-corrosion cracking(SCC)of Ti alloys subject to harsh corrosive environments in the deep sea,and presents the knowledge gaps and future direc...This paper reviews the current state of knowledge and advances on the stress-corrosion cracking(SCC)of Ti alloys subject to harsh corrosive environments in the deep sea,and presents the knowledge gaps and future directions.A comprehensive review of classifications and applications of Ti alloys for deep-sea engineering indicates that the near-αandα+βTi alloys with high strength and great weldability are the primary selection for deep-sea equipment.The role of residual stress,microstructure types,alloying elements and corrosive environmental factors on SCC performance of Ti alloys are also summarised.It is revealed that the Ti alloys with Widmanstatten structure show the lowest SCC susceptibility,and alloying of Nb,Mo and Al elements plays a positive role in the boost corrosion resistance of passive film.Syn-ergistic effects of environmental deep-sea factors include high hydrostatic pressure,low dissolved oxy-gen content,low temperature and decreasing pH levels intensify the SCC of Ti alloys by inducing local dissolution of the passive film and facilitating hydrogen-induced cracking at crack tip.The study also highlights future research requirements in SCC of Ti alloys in deep sea:including the set-up of unified and suitable methods of in-situ and simulated experiments,modeling and predicting of SCC behaviour in real situations,and exploring practical protective strategies specifically.These findings provide a refer-ence for further SCC mechanisms research and promote the microstructure optimisation and performance improvement of the advanced Ti alloy-based material systems for deep-sea engineering.展开更多
文摘Susceptibilities to stress corrosion cracking （SCC） of X80 pipeline steel in high pH solutions with various concentrations of HC03 at a passive potential of-0.2 V vs. SCE were investigated by slow strain rate tensile （SSRT） test. The SCC mechanism and the effect of HC03 were discussed with the aid of electrochemical techniques. It is indicated that X80 steel shows enhunced susceptibility to SCC with the concentration of HCO3 increasing from 0.15 to 1.00 mol/L, and the susceptibility can be evaluated in terms of current density at -0.2 V vs. SCE. The SCC behavior is controlled by the dissolution-based mechanism in these circumstances. Increasing the concentration of HCO3 not only increases the risk of rupture of passive films but also promotes the anodic dissolution of crack tips. Besides, little susceptibility to SCC is found in dilute solution containing 0.05 mol/L HCO3 for X80 steel. This can be attributed to the inhibited repassivation of passive films, manifesting as a more intensive dissolution in the non-crack tip areas than at the crack tips.
基金supported by the National Natural Science Foundation of China (Nos.51471034,51131001 and 51171025)
文摘Susceptibilities to stress corrosion cracking（SCC） of X80 pipeline steel in relatively concentrated carbonate/bicarbonate solutions with different chloride ion concentrations or p H value at a passive potential of-200 m V vs SCE were investigated by slow strain rate tensile test.In order to explore the SCC mechanism and the evaluation criterion for the SCC susceptibility of the steel in passive state,electrochemical measurements were taken.Potentiodynamic polarization curves were obtained at different potential sweep rates,and electrochemical impedance spectroscopy measurements were taken after fast polarization to the passive potential.The effects of chloride ion and p H on SCC behaviors of X80 steel at the passive potential were also discussed.The results showed that the SCC mechanism of X80 pipeline steel was greatly influenced by the passive film formed in these solutions.The SCC behaviors followed the film suppressed anodic dissolution mechanism in these circumstances,because the filming process accounted for a considerable proportion of the overall electrode process.The criteria for evaluating the SCC susceptibility of the steel at passive potential were proposed and validated.Decreasing in the concentration of chloride ion or increasing in p H value resulted in the reduction in SCC susceptibility.The existence of chloride ion greatly lowered the passivation tendency and the film stability,while its concentration determined the dissolution rate of the steel matrix.Higher p H value was responsible for the stable and tenacious passive films and the high repassivation capability.It was also inclined to lower the anodic dissolution rate at crack tips by retarding the cathodic oxygen reduction.
文摘This study aims to disclose the thermo-oxidative degradation behaviors and kinetics of a carbon fiber reinforced polyimide(CFRPI)composite for modeling of the Iong-term degradation process.The degradation behaviors were revealed through off-gas products analysis,and the overall kinetic interpretation was achieved from study of the mass-loss curves recorded under dynamic conditions.It was found that thermooxidative degradati on of the CFRPI composite was a multistep process,which in eluded four main reaction steps.Since most kinetic an alysis methods were derived from simple reactions described by a single kinetic triplet,they cannot be applied reliably to such a process.Therefore,we firstly separated the four overlapped reaction steps by peak fitting of derivative thermogravimetric curves using Fraser-Suzuki equation consider!ng the asymmetrical n ature of kin etic curves,and subsequently an a lyzed each in dividual reaction employing Friedma n method and experimental master-plots method.Four sets of kinetic triplets were determined to characterize the entire degradation process.The validity of four corresponding kinetic triplets was confirmed by perfect simulation of mass-loss curves recorded at both dynamic conditions used in kinetic analysis and entirely different isothermal conditions.Finally,modeling of Iong-term aging at 400°C of the CFRPI composite was successfully achieved based on these kinetic triplets.The predicted mass loss and flexural property correlated well with experimental results.This study can serve as a basis for rapid evaluation of the long-term durability of the CFRPI composite in various application environments.
文摘Based on the analysis of the mechanism of train slippage, this paper discusses the availability judgment threshold of wheel diameter calibration with examples, and puts forward corresponding feasible suggestions according to the discussion results.
基金supported by the National Natural Science Foundation of China(Nos.51931008 and 52201090).
文摘This paper reviews the current state of knowledge and advances on the stress-corrosion cracking(SCC)of Ti alloys subject to harsh corrosive environments in the deep sea,and presents the knowledge gaps and future directions.A comprehensive review of classifications and applications of Ti alloys for deep-sea engineering indicates that the near-αandα+βTi alloys with high strength and great weldability are the primary selection for deep-sea equipment.The role of residual stress,microstructure types,alloying elements and corrosive environmental factors on SCC performance of Ti alloys are also summarised.It is revealed that the Ti alloys with Widmanstatten structure show the lowest SCC susceptibility,and alloying of Nb,Mo and Al elements plays a positive role in the boost corrosion resistance of passive film.Syn-ergistic effects of environmental deep-sea factors include high hydrostatic pressure,low dissolved oxy-gen content,low temperature and decreasing pH levels intensify the SCC of Ti alloys by inducing local dissolution of the passive film and facilitating hydrogen-induced cracking at crack tip.The study also highlights future research requirements in SCC of Ti alloys in deep sea:including the set-up of unified and suitable methods of in-situ and simulated experiments,modeling and predicting of SCC behaviour in real situations,and exploring practical protective strategies specifically.These findings provide a refer-ence for further SCC mechanisms research and promote the microstructure optimisation and performance improvement of the advanced Ti alloy-based material systems for deep-sea engineering.
