Papers by Keyword: Pitting Corrosion

Abstract: The electrochemical behaviour of the rehealing oxide scales on the K52 nanocrystalline coatings had been studied by polarization curves. The results indicated that the oxide scales formed on the nano-coating exhibited rehealing ability after pitting corrosion, and the coating still had excellent corrosion resistance. The rehealing ability was enhanced with prolonged re-oxidation time. EDX analyses revealed that the oxide scales within the pits were composed of mixed-oxides (Cr2O3, Al2O3 and TiO2). The mixed-oxides were made up of two layers: the external oxide layer was composed of Cr2O3 and TiO2 and the internal oxide layer was Al2O3.

Abstract: TWIP steels are high Mn (17-35%) austenitic steels having strength and ductility concurrently. This makes them suitable for applications that need high strength and ductility like gas tanks and oil platforms. To these applications corrosion resistance of these steel is also of paramount importance and needs to be noticed. This was achieved by two usual methods of weight loss and potentiodynamic polarization of the samples, after that they casted and hot rolled in experimental scale. The observed corrosion pits are related to the chemical composition. It is connected with the high dissolution rate of Mn and Fe atoms in NaCl solution. Fractographic analyses of samples revealed corrosion products on their surface in a form of pits with diversified size.

Abstract: The NiTi shape memory alloy passivated for 90 min by autoclaving has been studied towards corrosion performance in the Tyrode’s simulated body fluid using open circuit potential and EIS measurements. The surface morphology and thickness of the oxide layer was determined by XRR. The HREM was used to observe the cross-section of the thin foil and to confirm the amorphous state of the TiO₂ layer and its thickness. Electrochemical measurements revealed a good corrosion resistance at the beginning of long-term (20 days) immersion. It was found that with the increase of immersion time, the corrosion resistance of the surface deteriorated after nearly 1 day of immersion due to occurence of pitting corrosion. The EIS method was used to detailed study on the electrolyte | passive layer interfacial properties. Equivalent electrical circuit for the pitting corrosion on the passivated NiTi alloy has been applied.

Abstract: 0.04C-16Cr and 0.04C-16Cr containing 26ppm B ferritic stainless steels were smelted by using a vacuum induction furnace. Then 65% boiling nitric acid method and the electrochemical potentiokinetic reactivation method (EPR) were used to research their intergranular corrosion sensitivity. Meanwhile, electrochemical test method (Tafel polarization curve method, the anode circular polarization curve method) and chemical immersion method were used to research their pitting corrosion resistance. The results showed that the corrosion rate of 0.04 C-16Cr stainless steel containing 26ppm B in 65% boiling nitric acid is lower than that of 0.04 C-16Cr stainless steel. The reactivation rate of 0.04C-16Cr containing 26ppm B in dilute sulphuric acid medium significantly reduced compared with that of 0.04C-16Cr. The pitting corrosion potential, self-corrosion potential and the value of (Eb-Ep) of the stainless steel containing with 26ppm B in chlorideions medium reduced, while the corrosion rate increased compared with the stainless steel without B addition. It indicates that trace boron addition improves the intergranular corrosion resistance and repair ability of the passive film of the 0.04C-16Cr ferritic stainless steel after pitting corrosion process in chloride ions medium, but it also promotes the pitting corrosion tendency of the steel. Besides, introduction B to 0.04C-16Cr ferritic stainless steel reduces the steel’s corrosion resistance in active dissolved zone and promotes its intergranular corrosion tendency in chloride ions medium. The electrochemical characteristics of local corrosion are consistent with the results of chemical immersion test.

Abstract: Corrosion perforation in the oil-tank bottom is one of the most damaging mechanisms in oil-tanks. This paper presents a two-dimentional cellular automata model which simulates the corrosion perforation in the oil-tank bottom. According to the mechanism of metal corrosion in the oil-tank bottom, the CA model which simulates the electrochemical reactions and diffusion steps of pitting corrosion is proposed. With a series of simulation, the results show that CA is a powerful approach to model corrosion perforation in the oil-tank bottom, which could be of practical importance in predicting the security of oil-tanks.

Abstract: Monel 400 is nickel-copper alloy being widely in thermal and nuclear power plants, marine environments because to its outstanding properties include high ductility, good weldability and good corrosion resistance. In the present investigation, an attempt was made to evaluate the mechanical properties of gas tungsten arc welded Monel 400 weldments. Also Monel 400 weldment was studied for the pitting corrosion behavior.

Abstract: We report the tensile behavior of corroded steel plates with huge corrosion pit. The behavior of corroded steel plates is not easy to predict because of its surface roughness. We therefore conducted tensile tests first to understand the behavior experimentally using the corroded steel plates taken from plate girder bridge. Before the testing, a 3D laser prove system was employed to measure the surface irregularity. In addition, finite element model was developed here to predict the behavior numerically. The model was validated by the tensile test results so that the finite element model can be reliably used for the parametric study. It is found from the parametric study that the location of huge corrosion pit affects the tensile strength, at most 15%.

Abstract: Hysteretic loops were used to study the influence of several ions in sedimentary water of oil tank on local corrosion at the bottom of crude oil tank, which were measured by the electrochemical station CHI660. The results indicated that the pitting increased firstly and then decreased with the increasing of the concentrations of each ion. The most serious pitting corrosion occurred under the following condition: the concentration of Cl-, SO42-, HCO3-, Mg2+, Ca2+ were 10.0 g/L, 1.0 g/L, 0.75 g/L, 0.35 g/L, 0.2 g/L, respectively.

Abstract: Supermartensitic stainless steel grades are widely used in oil and gas industries to substitute duplex and super duplex stainless steels these years. In this paper the corrosion behavior of supermartensitic stainless steels with different chemical compositions, S-165 and HP, was investigated in Cl^- environment. All the samples were treated by quenching at 1000 °C followed by tempering at 630 °C for 2h. After heat treatment, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) were determined on both kinds of samples. Polarization curves shows that the metastable pitting nucleuses were formed in passive area and the Cr content is the most important factor leading to the differences of pitting potential. The potentiodynamic polarization curves were conducted at various NaCl contents (5000, 15000 and 35000 ppm) and emphasized the need to account for the Cl^- sensitivity of samples under corrosion environment. The results show that, the pitting potential decrease with the increase of chloride contents. The behavior of passive film was analyzed by electrochemical impedance spectroscopy.

Abstract: The pre-corrosion damage tests of LC4 aluminum alloy with the shot peening surface treatment and un-shot peening surface treatment are performed under two different time levels: 12h and 24h. Based on the observation of the corrosion morphology of aluminum alloy, the corrosion damage mechanism of shot peening aluminum alloy can be divided into three stages: intergranular corrosion occurs first, and then denudation generates, at last pitting corrosion occurs as denudation depth reaches a certain degree. For shot peening aluminum alloy, the denudation depth, mass loss and the total depth of corrosion damage are used to represent the corrosion characteristics. With the corrosion time increase, the three parameters all increase correspondingly.