74 research outputs found
Effect of SO2 content on SCC behavior of E690 high-strength steel in SO2-polluted marine atmosphere
No full textSlow strain rate tensile (SSRT) test in a simulated device was employed to investigate the effect of SO2 on stress corrosion cracking (SCC) behavior of E690 steel in SO2-polluted marine atmosphere. Results revealed that SO2 can greatly enhance the SCC susceptibility of E690 steel in marine atmosphere and the SCC mechanism in this environment is a combination of anodic dissolution (AD) and hydrogen embrittlement (HE). The increase of SCC susceptibility was attributed to the formation of a compact rust layer on steel surface that SCC microcracks can initiate from the bottom of cracks in the rust layer consequently. Moreover, hydrogen evolution was greatly enhanced with the increase of SO2 content, and SCC susceptibility increased rapidly as a result
Effect of Alternating Current on Corrosion Behavior of X80 Pipeline Steel in Near-Neutral Environment
No full textThe rapid development of energy, electricity, and transportation industries has created a market for steel pipes; however, buried steel pipelines near high-voltage transmission lines and electrified railways often experience alternating current (AC) corrosion at the damaged coating of pipelines; such phenomenon is mostly due to the resistance between the capacitance and inductance coupling, especially for long-distance pipelines in parallel operation. AC corrosion can cause pipeline corrosion perforation and stress corrosion cracking (SCC) in some cases, which has been a vital threat to the pipeline safety. In this work, the influence of AC on corrosion behavior of X80 pipeline steel was investigated in NS4 near-neutral solution by data acquisition technique, electrochemical test, immersion tests and surface analysis techniques. Results show that with the increasing of AC density, corrosion morphology changed from uniform corrosion to localized corrosion with many pits. Under the full AC interference, X80 steel occurred cathodic and anodic polarization which resulted in iron dissolution and hydrogen precipitation. The negative half wave AC would lead to hydrogen evolution and hydrogen induced anodic dissolution, the pits in X80 steel surface present sharp. However, under disturbance of positive half-wave AC, only anodic dissolution occurred and the pitting appeared spill shape and smoothly. Under various AC waveform interference, the corrosion products of X80 steel surface were different. Under full AC wave and positive half-wave interference, the corrosion products were loose, had have no alpha-FeOOH and occurred cracks; however, under negative half-wave AC interference, the corrosion products were denser and contained alpha-FeOOH which has protective effect on substrates
Influence of sea mud state on the anodic behavior of Al-Zn-In-Mg-Ti sacrificial anode
No full textThe influence of sea mud state on the anodic behavior of Al-Zn-In-Mg-Ti sacrificial anode was investigated by the methods of electrochemical, immersion and surface analysis techniques. In this work, the simulated seawater, sea mud and seawater/sea mud transition region systems were set up in laboratory, it can measure the galvanic corrosion of sacrificial anode in seawater/sea mud transition environment. Results show that the corrosion rate of Al-Zn-In-Mg-Ti sacrificial anode in simulated seawater is higher than that in simulated sea mud. And the corrosion rate increased with the increasing size of sea mud. When the Al-Zn-In-Mg-Ti sacrificial anode and Q235 joint together at the ratio of cathode and anode area of 50:1, the mix potential shift negative with the increasing size of sea mud and the mixed current density is highest in seawater and increase with the increasing size of sea mud. The corrosion rate is determined by the conductivity and dissolved oxygen in various mud size. In simulated seawater environment, Al-Zn-In-Mg-Ti sacrificial anode present relatively uniform dissolution; however, in simulated sea mud environment, due to the different dissolved oxygen in various mud size, Al-Zn-In-Mg-Ti sacrificial anode present nonuniform dissolving, especially in simulated lager particles sea mud
Effect of Hydrogen Charging on the Stress Corrosion Behavior of 2205 Duplex Stainless Steel Under 3.5 wt.% NaCl Thin Electrolyte Layer
No full textThe effect of hydrogen charging on the stress corrosion cracking (SCC) behavior of 2205 duplex stainless steel (DSS) under 3.5 wt.% NaCl thin electrolyte layer was investigated on precharged samples through hydrogen determination, electrochemical measurement, and slow strain rate tensile test. Results show that hydrogen charging weakens the passive film without inducing any obvious trace of localized anodic dissolution. Therefore, hydrogen charging increases the SCC susceptibility of 2205 DSS mainly through mechanism of hydrogen embrittlement rather than mechanism of localized anodic dissolution. 2205 DSS shows a more susceptibility to hydrogen under the TEL when hydrogen charging current density (HCCD) is between 20 and 50 mA cm(-2). The increasing trend is remarkable when hydrogen charging current density increases from 20 to 50 mA cm(-2) and fades after 50 mA cm(-2)
Corrosion effect of Bacillus cereus on X80 pipeline steel in a Beijing soil environment
No full textThe corrosion of X80 pipeline steel in the presence of Bacillus cereus (B. cereus) was studied through electrochemical and surface analyses and live/dead staining. Scanning electron microscopy and live/dead straining results showed that a number of B. cereus adhered to the X80 steel. Electrochemical impedance spectroscopy showed that B. cereus could accelerate the corrosion of X80 steel. In addition, surface morphology observations indicated that B. cereus could accelerate pitting corrosion in X80 steel. The depth of the largest pits due to B. cereus was approximately 11.23 mu m. Many pits were found on the U-shaped bents and cracks formed under stress after 60 days of immersion in the presence of B. cereus. These indicate that pitting corrosion can be accelerated by B. cereus. X-ray photoelectron spectroscopy results revealed that NH4+ existed on the surface of X80 steel. B. cereus is a type of nitrate-reducing bacteria and hence the corrosion mechanism of B. cereus may involve nitrate reduction on the X80 steel. (C) 2018 Elsevier B.V. All rights reserved
Corrosion effect of Bacillus cereus on X80 pipeline steel in a Beijing soil environment
No full textThe corrosion of X80 pipeline steel in the presence of Bacillus cereus (B. cereus) was studied through electrochemical and surface analyses and live/dead staining. Scanning electron microscopy and live/dead straining results showed that a number of B. cereus adhered to the X80 steel. Electrochemical impedance spectroscopy showed that B. cereus could accelerate the corrosion of X80 steel. In addition, surface morphology observations indicated that B. cereus could accelerate pitting corrosion in X80 steel. The depth of the largest pits due to B. cereus was approximately 11.23 mu m. Many pits were found on the U-shaped bents and cracks formed under stress after 60 days of immersion in the presence of B. cereus. These indicate that pitting corrosion can be accelerated by B. cereus. X-ray photoelectron spectroscopy results revealed that NH4+ existed on the surface of X80 steel. B. cereus is a type of nitrate-reducing bacteria and hence the corrosion mechanism of B. cereus may involve nitrate reduction on the X80 steel. (C) 2018 Elsevier B.V. All rights reserved
Modeling for corrosion fatigue crack initiation life based on corrosion kinetics and equivalent initial flaw size theory
No full textIn present paper, a novel, effective and economical model based on corrosion kinetics and equivalent initial flaw size theory was proposed to predict the corrosion fatigue crack initiation (CFCI) life of E690 steel in simulated seawater. Comparison between the predicted S-N curves and the measured data showed that this model was of nice accuracy under high peak stresses, while non-negligible deviation existed under low peak stresses due to lack of enough measured data or consideration for the stress effect on corrosion rate. Despite of that, thought of this model still has a good practicability in predicting CFCI life of steels
STRESS CORROSION BEHAVIORS OF E690 HIGH-STRENGTH STEEL IN SO2-POLLUTED MARINE ATMOSPHERE
No full textWith the development of industry, the atmosphere in many cities along the coastal lines such as Qingdao in China has been polluted with SO2, and has been changed to coastal-industrial atmosphere with the coexistence of SO2 and Cl-. The corrosion and stress corrosion cracking (SCC) behavior and mechanism of steel in this environment is different from that in the coastal atmosphere containing only Cl- or the industrial atmosphere containing only SO2. Previous study have indicated that SO2 in the marine atmosphere can greatly promote the stress corrosion cracking of high-strength steel due to acidification of thin electrolyte layer and reproduction of H+ through FeSO4. E690 steel, as a newly-developed high strength steel, is very promising to be widely used in offshore platform in the near future for its excellent performance. However, there is few research about its SCC behavfor in marine atmosphere, especially in SO2-polluted atmosphere. Therefore, it's of great importance to investigate the SCC behavior and mechanism of E690 steel in this environment. In this work, U-bend specimen corrosion test under dry/wet cyclic condition, electrochemical measurements, crack morphology observation and rust layer analysis, were conducted to investigate the effect of SO2 on SCC behavior of E690 steel in simulated SO2-polluted marine atmosphere. The results indicated that E690 steel has a high SCC susceptibility in SO2-polluted marine atmosphere with a combined mechanism of anodic dissolution (AD) and hydrogen embrittlement (HE). SO2 in the atmosphere can facilitate the densification of inner rust layer by promoting the formation of alpha-FeOOH and enrichment of Ni and Cr in the inner rust layer, leading to the concentration of Cl- under the rust layer, which may result in the initiation and propagation of SCC cracks significantly and therefore enhance the SCC susceptibility
Corrosion fatigue crack initiation and initial propagation mechanism of E690 steel in simulated seawater
No full textIn the present paper, the corrosion fatigue crack initiation and initial propagation mechanism of E690 steel in simulated seawater were studied by stress-controlled fatigue tests and a series of subsequent characterizations on the fracture surface, microstructure and secondary cracks. Results show that the corrosion fatigue crack initiation and initial propagation mechanism evolves with elevated peak stress level in simulated seawater. When peak stress is far below the proof stress, cracks preferentially initiate at the parent austenite grain boundaries (PAGBs) with 68.4% probability and at the ferrite lath boundaries (FLBs) with 31.6% probability. Meanwhile, the cracks also preferentially propagate along the PAGBs and FLBs. Upon the peak stress close to or above the proof stress, cracks turn to initiate from the emerging corrosion pits and propagate without zigzag detour but by splitting the ferrite laths which transversely block its propagation way
Shape memory composite (SMC) self-healing coatings for corrosion protection
No full textA shape memory composite (SMC) coating with a self-healing ability was prepared by a facile method based on a thermoresponsive shape memory polymer (SMP) that utilized carnauba wax microparticles as the healing agent. Damages to the SMC coating was healed via heating, which triggered a two-step healing mechanism consisting of defect closure through a shape memory effect at 65 degrees C and then defect sealing by molten wax at 90 degrees C. The surface morphologies of the scratched and healed coatings as well as a wax-free SMP coating were first studied by optical stereomicroscopy and scanning electron microscopy (SEM). To assess the recovery of the coating's barrier properties, macroscopic and localized information was obtained by electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM), respectively. The healing performance was also evaluated by comparing the macroscopic morphologies of the intact, damaged and healed coatings after long-term immersion. The results from both tests were in agreement and confirmed the key roles of carnauba wax microparticles in the complete recovery of the barrier properties of initially damaged coatings upon thermally assisted self-healing. (C) 2016 Elsevier B.V. All rights reserved
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