Numerical Analysis of Cold-Formed Thin-Walled Steel Short Columns with Pitting Corrosion during Bridge Construction

Pitting corrosion is harmful during bridge construction,which will lead to uneven roughness of steel surfaces and reduce the thickness of steel.Hence,the effect of pitting corrosion on the mechanical properties of cold-formed thin-walled steel stub columns is studied,and the empirical formulas are established through regression fitting to predict the ultimate load of web and flange under pitting corrosion.In detail,the failure modes and load-displacement curves of specimens with different locations,area ratios,and depths are obtained through a large number of non-linear finite element analysis.As for the specimens with pitting corrosion on the web,all the specimens are subject to local buckling failure,and the failure mode will not change with pitting corrosion,but the failure location will change with pitting corrosion location;the size,location,and area ratio of pitting corrosion have little influence on the ultimate load of cold-formed thin-walled steel short columns,but the loss rate of pitting corrosion section area has a greater impact on the ultimate bearing capacity.As for the specimen with flange pitting corrosion,the location and area ratio of pitting corrosion have less influence on the ultimate load of cold-formed thin-walled steel short columns,and the section area loss rate has greater influence on the ultimate bearing capacity;the impact of web pitting corrosion on the ultimate load is greater than that of flange pitting corrosion under the same condition of pitting corrosion section area.The prediction formulas of limit load which are suitable for pitting corrosion of web and flange are established,which can provide a reference for performance evaluation of corroded cold-formed thin-walled steel.

Effect of surface damage induced by cavitation erosion on pitting and passive behaviors of 304L stainless steel

The corrosion behavior of 304L stainless steel(SS)in 3.5wt%NaCl solution after different cavitation erosion(CE)times was mainly evaluated using electrochemical noise and potentiostatic polarization techniques.It was found that the antagonism effect resulting in the passivation and depassivation of 304L SS had significant distinctions at different CE periods.The passive behavior was predominant during the incubation period of CE where the metastable pitting initiated at the surface of 304L SS.Over the rising period of CE,the 304L SS experienced a transition from passivation to depassivation,leading to the massive growth of metastable pitting and stable pitting.The depassivation of304L SS was found to be dominant at the stable period of CE where serious localized corrosion occurred.

Gear Pitting Measurement by Multi-Scale Splicing Attention U-Net

The judgment of gear failure is based on the pitting area ratio of gear.Traditional gear pitting calculation method mainly rely on manual visual inspection.This method is greatly affected by human factors,and is greatly affected by the working experience,training degree and fatigue degree of the detection personnel,so the detection results may be biased.The non-contact computer vision measurement can carry out non-destructive testing and monitoring under the working condition of the machine,and has high detection accuracy.To improve the measurement accuracy of gear pitting,a novel multi-scale splicing attention U-Net(MSSA U-Net)is explored in this study.An image splicing module is first proposed for concatenating the output feature maps of multiple convolutional layers into a splicing feature map with more semantic information.Then,an attention module is applied to select the key features of the splicing feature map.Given that MSSA U-Net adequately uses multi-scale semantic features,it has better segmentation performance on irregular small objects than U-Net and attention U-Net.On the basis of the designed visual detection platform and MSSA U-Net,a methodology for measuring the area ratio of gear pitting is proposed.With three datasets,experimental results show that MSSA U-Net is superior to existing typical image segmentation methods and can accurately segment different levels of pitting due to its strong segmentation ability.Therefore,the proposed methodology can be effectively applied in measuring the pitting area ratio and determining the level of gear pitting.

Compressive Strength of Tubular Members with Combined Pitting Corrosion and Crack Damage

Tubular members subject to combined pitting corrosion and crack damage were numerically studied to clarify the reduction of ultimate strength and failure behavior,based on numerical models validated against available experi-ments.The effects of length,location and inclined angle of a crack under combined damage were studied to disclose the mechanism of interaction between the crack and corrosion pits.The methods,named as linear superposition directly accumulating the effects of solo crack and solo pitting damage,as well as crack projection transferring an inclined crack to a transverse one,were discussed and verified in the view of assessing ultimate strength of tubular members with combined damage.It was shown that the former is practical but complex while the next always over-estimates the residual strength.Besides,the location and inclined angle of a crack have a subtle effect on the reduction of ultimate strength under combined damage,especially at higher level of pitting damage,due to the synergistic effect between corrosion pits and cracks.Such effect can lead to early occurrence of plasticity and local buckling by inducing stress interaction between crack tips and pits,and causing more significant strength reduction compared with a solo type of damage.A practical method was proposed to determine the loss ratio of cross-sectional area on the equivalent weakest section of a damaged member.Based on the loss ratio,a formula was presented to predict the ultimate strength of damaged members with combined damage,showing good applicability.

Characterization of pitting corrosion of 7A60 aluminum alloy by EN and EIS techniques

The pitting corrosion behaviors of 7A60 aluminum alloy in the retrogression and re-aging （RRA） temper were investigated by electrochemical impedance spectroscopy （EIS） and electrochemical noise （EN） techniques, and the microstructure and the second phase content of the alloy were observed and determined by scanning electron microscopy （SEM） and energy dispersive spectrometer （EDS）. The results show that there exist two different corrosion stages for 7A60 alloy in 3.5%NaCl solution, and the corrosion process can be detected by the appearance of EIS spectrum with two capacitive time constants and the wavelet fractal dimension D extracted from EN. SEM and EDS results also demonstrate that severe pitting corrosion in 7A60 alloy is mainly caused by electrochemical active MgZn2 particles, secondly by Al2MgCu and Mg2Si. Al7Cu2Fe particles make little contribution to the pitting corrosion of 7A60 alloy.

Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels

Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels （HNSS） were investigated by electrochemical and immersion testing methods in chloride solution, respectively. The chemical constitution and composition in the depth of passive films formed on HNSS were analyzed by X-ray photoelectron spectrum （XPS）. HNSS has excellent pitting and crevice corrosion resistance compared to 316L stainless steel. With increasing the nitrogen content in steels, pitting potentials and critical pitting temperature （CPT） increase, and the maximum, average pit depths and average weight loss decrease. The CPT of HNSS is correlated with the alloying element content through the measure of alloying for resistance to corrosion （MARC）. The MARC can be expressed as an equation of CPT=2.55MARC-29. XPS results show that HNSS exhibiting excellent corrosion resistance is attributed to the enrichment of nitrogen on the surface of passive films, which forms ammonium ions increasing the local pH value and facilitating repassivation, and the synergistic effects of molybdenum and nitrogen.

THE RELATIONSHIP BETWEEN PITTING SUSCEPTIBILITY AND INCLUSIONS IN CARBON STEELS IN ARTIFICIAL SEAWATER

The pittings of five carbon steels have been studied by using anodic polarization test and microscope observation. The results show that pitting susceptibilities are related to the types and shapes of inclusions which are the sites of pitting initiation. The pitting initiating at inclusion needs a potential which is defined as pitting potential and the pitting potential is determined by the type and shape of inclusion. The influence of oxygen content in steel on pitting potential is also discussed.

A comparison of the pitting corrosion resistances of the 304 and new 200 series of stainless steels by potential dependent critical pitting corrosion temperatures

This study researched the relationship between the applied potential and the critical pitting temperature （CPT） of the 304 and new 200 series of stainless steels. The fluctuation about the potential dependent CPT for the stainless steels was investigated and the CPT range was obtained. The difference between the potential dependent CPTs of the 304 and 200 series of stainless steels with an applied potential of 100 mV （ vs SCE）, were presented, and by this means the pitting corrosion resistances of them were compared.

Influence of sulfur on inclusion and pitting resistance of 316L stainless steel

The effect of the sulfur content on the microstructure and inclusions of 316 L stainless steel was studied by optical microscopy,scanning electron microscopy,and image analysis,and the effect of sulfur on the pitting corrosion resistance of 316 L stainless steel was studied by conducting ferric chloride immersion test and plotting the electrochemical polarization curves.The results show that the added sulfur is mainly in the form of manganese sulfide inclusions in 316 L stainless steel.With increases in the sulfur content,the grade and percentage of the sulfide in the steel gradually increased,and its distribution became increasingly dense.When the sulfur content exceeded0.1%,the number of sulfide inclusions in the sample increased sharply.When the sulfur content reached 0.199%,the sulfides in the steel were primarily in spindle form,and a large number of spindles were found to refine the grain size of 316 L stainless steel.The pitting corrosion weight loss rate of 316 L stainless steel increased with increases in the sulfur content,while the pitting potential gradually decreased.However,the pitting potential of 316 L stainless steel rebounded when the sulfur content reached 0.199%,which may be related to the grain refinement of the test steel and requires further study.

Comparative study on the corrosion behavior of X52, 3Cr, and 13Cr steel in an O2–H2O–CO2 system: products, reaction kinetics, and pitting sensitivity

The corrosion behaviors of X52, 3Cr low-alloy steel, and 13Cr stainless steel were investigated in an O_2–H2O–CO_2 environment at various temperatures and O_2–CO_2 partial-pressure ratios. The results showed that the corrosion rates of X52, 3Cr, and 13Cr steels increased with increasing temperature. The corrosion rates slowly increased at temperatures less than 100°C and increased sharply when the temperature exceeded 100°C. In the absence of O_2, X52, 3Cr, and 13Cr exhibited uniform corrosion morphology and Fe CO3 was the main corrosion product. When O_2 was introduced into the system, various forms of Fe_2O_3 appeared on the surface of the samples. The Cr content strongly influenced the corrosion resistance. The 3Cr steel with a low Cr content was more sensitive to pitting than the X52 or 13Cr steel. Thus, pitting occurred on the surface of 3Cr when 1.25 MPa of O_2 was added; this phenomenon is related to the non-uniform distribution of Crin 3Cr.

Through-thickness inhomogeneity of precipitate distribution and pitting corrosion behavior of Al-Li alloy thick plate

The thorough-thickness inhomogeneity of precipitate distribution and pitting corrosion behavior of 95 mm-thick 2297 Al-Li alloy rolled plate was investigated using scanning electron microscopy, transmission electron microscopy and electrochemistry method. Precipitate distribution and pit size were statistically analyzed to obtain quantitative information and corresponding correlation. The population density and the size fraction of precipitate on different sections in the thick plate are ranked from high to low in the following order: quarter-section(QS) > surface section(SS) > mid-section(MS). After 300 min potentiostatic polarization, the number and the total volume of pits are ranked from high to low as QS>SS>MS, indicating a higher pitting susceptibility of the plate in QS with more precipitates. The through-thickness inhomogeneity of pitting corrosion in 2297 Al-Li alloy thick plate is mainly ascribed to inhomogeneous precipitate distribution.

Fabrication of high nitrogen austenitic stainless steels with excellent mechanical and pitting corrosion properties

A series of high nitrogen austenitic stainless steels were successfully developed with a pressurized electroslag remelting furnace. Nitride additives and deoxidizer were packed into the stainless steel pipes, and then the stainless steel pipes were welded on the surface of an electrode with low nitrogen content to prepare a compound electrode. Using Si3N4 as a nitrogen alloying source, the silicon contents in the ingots were prone to be out of the specification range, the electric current fluctuated greatly and the surface qualities of the ingots were poor. The surface qualities of the ingots were improved with FeCrN as a nitrogen alloying source. The sound and compact macrostructure ingot with the maximum nitrogen content of 1.21wt% can be obtained. The 18Cr18Mn2Mo0.9N high nitrogen austenitic stainless steel exhibits high strength and good ductility at room temperature. The steel shows typical ductile-brittle transition behavior and excellent pitting corrosion resistance properties.

Effect of Temperature and Cl^- Concentration on Pitting of 2205 Duplex Stainless Steel

The electrochemical behaviors of 2205 duplex stainless steel in NaCl solution with different temperatures and concentrations were studied by gravimetric tests, potentiodynamic polarization, electrochemical impedance spectroscopy and scanning electron microscopy. The experinental results show that temperature and chloride concentration have a great influence on the pitting resistance of 2205 duplex stainless steels. They not only effect the corrosion rate of pitting, but also change the shape of the pits. When NaCl solution was in low concentration and temperature below the critical pitting temperature, pits were very small and scattered with hemisphere-like shape. On the contrary, the pits of 2205 duplex stainless steel were large and sometimes had a lacy cover when the NaCl concentration was higher and the temperature was 70℃.

Effect of Strain and Chloride Concentration on Pitting Susceptibility for Type 304 Austenitic Stainless Steel

The effects of strain and chloride concentration on pitting susceptibility for type 304 stainless steel were studied in situ using the electrochemical technology under constant strain. The impact factor fc was brought forward to value the effect of strain on pitting. The pitting behaviors of type 304 stainless steel in various chloride concentrations under the strain levels 0%, 10%, and 30% were investigated. Potentiostatic polarization technology was used to study how the chloride concentration affected corrosion current density. The results indicated that fc increased substantially and pitting potential varied remarkably when chloride concentration was over 90 mg.L . Under the three levels of strain mentioned above, when chloride concentration was below 463 mg.L^-1,121 mg.L^-1, and 98 mg.L^-1 respectively, the pitting potential shifted towards positivity and, the passive film became more stable. When the strain was below 10%, the pitting susceptibility of type 304 stainless steel varied greatly as strain increased, whereas the susceptibility only changed a little when the strain was over 10%.

EIS Study on Pitting Corrosion of AA5083-H321 Aluminum-Magnesium Alloy in Stagnant 3.5% NaCl Solution

In this research, EIS （electrochemical impedance spectroscopy） technique was utilized to study the pitting corrosion behaviour of AA5083-H321 aluminum-magnesium alloy in 3.5% NaCl solution. Impedance spectra were obtained during 240 h of exposure of the sample to the test solution. The surface and cross-section of the samples were studied by scanning electron microscopy （SEM） and EDAX （energy dispersive analysis of X-ray） analysis. The results indicated that as the resistance of the passive layer on intermetallic particles is very small, this parameter on the sample surface layers is controlled by that of pure passive layer. However, the capacitors in the proposed equivalent circuit are replaced with the constant phase elements （CPE）, due to non-uniformity and occurrence of pitting corrosion on the surface. The outward diffusion of Al^＋3 ions through the passive layer and the thickening of this layer cause the impedance decrease in the first 24 h and increase afterwards. The detachment of intermetallic particles from some of pits and the accumulation of the corrosion products inside some others are factors that prevents the continuation of cathodic reactions on the top of the intermetallic particles.

Study on pitting process of 316L stainless steel by means of staircase potential electrochemical impedance spectroscopy

Pitting corrosion of 316L stainless steel in NaCl solution was investigated by means of staircase potential electrochemical impedance spectroscopy（SPEIS）.The investigation focused on the transition of stainless steel from the passive state to pitting corrosion.Based on the evolution of electrical parameters of the equivalent electrical circuit,it is suggested that the most probable mechanism of pit creation is the film breaking model.The result demonstrates that staircase potential electrochemical impedance spectroscopy is an effective method for the investigation of pitting corrosion.

Evaluation Indicators and Extraction Method for Pitting Corrosion of Structural Steel

A set of evaluation indicators based on corrosion ratio in theory for assessing the extent of pitting corrosion and performance reduction are proposed. In order to quantify the morphology of pitting corrosion and extract the evaluation indicators,the 3D profile data obtained by pitting morphology measurement are imported into a special written program to automatically determine the location of each corrosion pit and distill any desired data pertinent to the pitting morphology. The results show that this method seems to be effective to analyze the corroded surface and characterize the pitting morphology.

Corrosion and pitting behavior of pure aluminum 1060 exposed to Nansha Islands tropical marine atmosphere

The corrosion and pitting behavior of pure aluminum 1060 exposed to Nansha Islands marine atmosphere for 34 months was investigated based on mass loss measurement,scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),X-ray photoelectron spectroscopy(XPS),and electrochemical impedance spectroscopy(EIS).The results indicated that serious pitting corrosion occurred on the surfaces of pure aluminum.The corrosion rate after exposure for 13 months was approximately 1.28 g/(m^(2)·a).The XPS results showed that the corrosion products were Al_(2)O_(3),Al(OH)_(3),and AlCl_(3).Moreover,the corrosion product layer was more protective than the native oxide film,and the protectiveness first increased and then decreased.Finally,the shape of the pits was evaluated using statistical analysis.

Effect of Pulsed Current TIG Welding Parameters on Pitting Corrosion Behaviour of AA6061 Aluminium Alloy

Medium strength aluminium alloy （Al-Mg-Si alloy） has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The preferred welding process for aluminium alloy is frequently TIG （tungsten inert gas） welding due to its comparatively easier applicability and better economy.In the case of single pass TIG welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. The use of pulsed current parameters has been found to improve the mechanical properties of the welds compared to those of continuous current welds of this alloy due to grain refinement occurring in the fusion zone. A mathematical model has been developed to predict pitting corrosion potential of pulsed current TIG welded AA6061 aluminium alloy.Factorial experimental design has been used to optimize the experimental conditions. Analysis of variance technique has been used to find out the significant pulsed current parameters. Regression analysis has been used to develop the model. Using the developed model pitting corrosion potential values have been estimated for different combinations of pulsed current parameters and the results are analyzed in detail.

Serum matrix metalloproteinase 3 in detecting remitting seronegative symmetrical synovitis with pitting edema syndrome: A case report

We report a case of remitting seronegative symmetrical synovitis with pitting edema(RS3 PE) syndrome in a 71-year-old woman. She referred to our hospital with finger stiffness, edema of both hands and feet, pain of bilateral shoulder, wrist, metacarpophalangeal, proximal interphalangeal, and ankle joints. Rheumatoid factor was negative, human leukocyte antigen-B7 antigen was positive. Moreover, matrix metalloproteinase 3(MMP-3) was high. She was diagnosed with RS3 PE syndrome, and treatment with prednisolone(15 mg/d) was started. One week after prednisolone treatment initiation, CRP decreased to negative, and joint pain was almost completely resolved. However, hand stiffness persisted, and MMP-3 level was still high. Thus, prednisolone dose was increased to 20 mg/d, and the stiffness resolved. Twenty days after treatment initiation, MMP-3 was normalized. MMP-3 was more indicative of RS3 PE syndrome symptoms than CRP. Thus, MMP-3 seems to be more sensitive to RS3 PE syndrome symptoms.