Atmospheric corrosion in tropical and subtropical climate zones: 3. Modeling corrosion and dose-response function for structural metals

The results of statistical analysis of a corrosion-climate database are presented. New dose-response functions have been obtained by methods of multiple and nonlinear analysis for evaluating corrosion-related weight losses of structural metals in the regions with humid tropical and subtropical climate. Original Russian Text ? A.A. Mikhailov, P.V. Strekalov, Yu.M. Panchenko, 2007, published in Korroziya: Materialy, Zashchita, 2006, No. 7, pp. 2–10. For part 2, see [1].     

3种有色金属在沈阳地区的大气腐蚀规律

通过Cu，Zn，A1在沈阳地区的大气暴露实验，总结了3种金属的大气腐蚀规律，并讨论了干沉降和湿沉降对金属的大气腐蚀影响。结果表明：Cu，Zn的腐蚀深度与暴露时间呈线性关系；A1的腐蚀深度与暴露时间呈幂指数关系。利用X射线衍射仪和扫描电镜对腐蚀产物的结构和形貌进行分析，并讨论了3种金属大气腐蚀产物的形成过程。     

Artificial neural network corrosion modeling for metals in an equatorial climate

The majority of the metals used in the distribution and transmission electric energy lines, such as cables, towers and accessories are susceptible to the corrosion degradation process. For that reason, studying the factors that influence the atmospheric corrosion is an important issue. In this paper, an artificial neural network model was developed with linear and sigmoidal functions, aiming to predict low-carbon steel, copper and aluminum corrosion rates according to environmental parameters in the area of São Luis – Maranhão, Brazil. The area along the “702 – São Luis II –Presidente Dutra” 500 kV transmission line, located in an equatorial region, is employed for this purpose. A specific methodology was developed to determine the local corrosivity rate for these metals. Five atmospheric corrosion stations (ACS) were installed along the 702 transmission line in an extension of 200 km. Along with the meteorological data, local pollutants were collected and analyzed during a period of two years. In the same period, specimens were exposed to this atmosphere and periodically collected for corrosion evaluation. The obtained results indicate that the neural network can be used as a good corrosion estimator.     

Atmospheric corrosion of hot and cold rolled carbon steel under field exposure in Saudi Arabia

Carbon steel (hot and cold rolled) specimens have been exposed to the action of different atmospheres at 20 test sites distributed in Saudi Arabia and was investigated in terms of environmental factors such as average temperature, average relative humidity and deposition rates of atmospheric pollutants (Cl⁻ and SO₂). Applying the standard ISO 9223 norm aggressiveness of the atmospheres corresponding to 0the different test sites has been determined. Calculations of corrosion rates were made via loss of weight and characterization of the corrosion products formed on samples has been carried out by means of X-ray diffraction (XRD). The major constituent of the rust formed in marine and marine-industrial environment is goethite (α-FeOOH). These samples also show the presence of a large proportion of lepidocrocite (γ-FeOOH) and small amounts of ferrihydrite and maghemite (γ-Fe₂O₃). In the case of urban and rural samples goethite is the major constituent of corrosion layers. The rust formed under the urban environment also contains large amounts of ferrihydrite and in a lesser proportion, of goethite and maghemite.     

Long-term forecast of corrosion mass losses of technically important metals in various world regions using a power function

An analysis of the results of corrosion tests on flat and helix specimens made of technically important metals carried out within the ISO CORRAG program is given. Stochastic relationships between coefficient n in the power function, which characterizes the protective properties of the corrosion products, and the limiting corrosion rate α, with the corrosivity of each type of atmosphere were found. A forecast of corrosion losses for a period of up to 50 years was given using the linear function in the stationary stage, a power function, and limiting corrosion rate values α. The reliability of the forecasts was estimated.     

The science of pipe corrosion: A review of the literature on the corrosion of ferrous metals in soils

The paper reviews the literature that may assist in forming a multiscale model of corrosion in soils. This model should take into account macro-environmental processes (rainfall, etc.), soils processes (water movement, oxygen transport, etc.), processes within the oxides, and the electrochemical activity occurring at the metal surface. The literature reviewed includes traditional corrosion research such as surveys and historical analysis of buried pipelines, scientific exposures of buried metal, results from buried sensors, and laboratory studies aimed to duplicate soil exposures. Also included are wider studies on water and solute movement in soils, and oxygen transport through soils.     

Atmospheric corrosion of carbon steel in Colombia

The corrosion behaviour of carbon steel at six test sites in Colombia and its relationship with exposure time and environmental characteristics of each site were investigated. The corrosion products were characterized by XRD, SEM and EDS. It was found that in Barranquilla, the most aggressive site, corrosion depends mainly on chlorides. Furthermore, in the more aggressive environments there was a greater tendency to formation of protective corrosion products. Lepidocrocite and goethite were found as major constituents of rust. A structure not reported in the literature was found, corresponding to strings of several hundred micrometers long and consisting of lepidocrocite plates.     

Modification of metals and alloys by electron beam treatment (review)

Conclusion Investigations of methods of surface treatment of metals and alloys by a concentrated electron stream are being ever more widely developed. Such action causes a significant change in the structure and properties of materials, which in turn causes a significant improvement in the service properties of the treated parts.Electron beam treatment promotes obtaining of fundamental and practical information on phase and structural transformations in cooling at different rates of materials widely used at present in industry and those having promise of use in the near future. In a number of cases the action of an electron stream provides necessary and unexpected properties of materials.Electron beam heating is used most widely for processes of refining of the surface of metal blanks, hardening of alloys from the liquid and solid states, surfacing and surface alloying, and treatment of previously applied coatings. Methods of amorphisation and shock hardening of thin surface layers are in the study stage.Physicotechnical Institute, Academy of Sciences of the Belorussian SSR. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 42–47, July, 1990.     

Synthesis and evaluation of Tris-hydroxymethyl-(2-hydroxybenzylidenamino)-methane as a corrosion inhibitor for cold rolled steel in hydrochloric acid

Tris-hydroxymethyl-(2-hydroxybenzylidenamino)-methane (THHM) was synthesized. The effect of THHM on the corrosion of cold rolled steel (CRS) in 0.1 M hydrochloric acid was then investigated by Tafel polarization curve and electrochemical impedance spectroscopy (EIS). Polarization curve results clearly reveal the fact that THHM is a good cathodic type inhibitor. EIS results confirm its corrosion inhibition ability. The inhibition efficiency increases with increasing THHM concentration but decreases with immersion time. Atomic force microscopy (AFM) reveals that a protective film forms on the surface of the inhibited sample. The adsorption of this inhibitor is found to follow the Langmuir adsorption isotherm. THHM adsorbs on the sample probably by chemisorption.     

极寒环境下厚规格船舶用钢的发展

北极地区能源和贸易航线潜力、南极地区科考行动等受到越来越多的关注,促进了大型高技术极寒环境下服役船舶的需求和发展,同时对满足极寒环境服役条件船舶用低温钢的各项性能提出了更高的要求,厚规格、具有优异低温韧性和易焊接的更高强度级别的极寒环境下船舶用低温钢是今后的发展趋势。介绍了国内外船舶用低温钢的发展状况和低温钢的成分、生产工艺特点,建议采用低碳当量成分设计的新TMCP工艺技术路线,应用纳米相强韧化理论并控制其组织构成,从而实现优异的低温强韧性和止裂性能。     

Atmospheric corrosion of nickel in various outdoor environments

As part of a field exposure program in the north-west of France on atmospheric corrosion of metal and alloys, this study presents the results of the behaviour of nickel panels exposed in industrial, urban and rural atmospheres. Mass measurements were investigated during the exposure and adherent corrosion layers were followed by means of several methods of analysis: Fourier transform infrared reflection-absorption spectroscopy, X-ray diffraction and scanning electron microscopy with X-ray microanalysis. In order to determine all the chemical species formed in the corrosion layers, corrosion products released from the surface by rainfall were also studied by collecting the streaming water from the nickel surfaces. Anionic and cationic quantities in the streaming water were determined respectively with ionic chromatography and polarography. The nickel attack appears as a pitting corrosion process accompanied by the formation of soluble corrosion products in dry exposure periods, these being regularly dissolved by rainfall events. Pits are associated with the formation of nickel salts, mainly sulphates and chlorides with small amounts of nitrate, and surrounded by carbonate species. The corrosion rate increases from rural to industrial areas.     

A review of impedance plot methods used for corrosion performance analysis of painted metals

Modern impedance measuring instrumentation has made testing and data acquisition of the corrosion degradation behaviour of painted metal systems a relatively simple matter, compared to methods used in past decades. However, the analysis of such data is not so simple and requires considerable future work input. This paper reviews some of the various methods available for impedance analysis and discusses their applicability to painted metals. A small library of Bode and Nyquist plot shapes is presented, based on increasingly more complex equivalent electrical circuit models, along with methods for obtaining equivalent circuit component values. Other plotting methods are also reviewed, as well as limitations of impedance plot methods for painted metals.     

Atmospheric corrosion of field-exposed AZ31 magnesium in a tropical marine environment

Corrosion behavior of AZ31 magnesium in tropical marine atmosphere was investigated. Chloride ions deposition rate played an important role in the corrosion process, which resulted in an obvious fluctuation of the corrosion rate. The corrosion was initiated from pitting corrosion and then evolved into general corrosion as the exposure time extended. Mg₅(CO₃)₄(OH)₂·xH₂O was the dominate products during the whole exposure periods. The products on the specimens weathered for 1, 6 and 12 months slightly suppressed the corrosion process, while that generated after 24 months of exposure exhibited good protective ability against further corrosion attacks.     

Outdoor-indoor corrosion of metals in tropical coastal atmospheres

Results of indoor and outdoor atmospheric corrosion tests conducted during a long period of time at Cuba and Campeche (Mexico) indicated very high corrosion rates at both sites which have humid-tropical marine climate. We found that the outdoor corrosivity ranges from C3 to >C5 according to ISO 9223 nevertheless metals exposed to sheltered conditions presented higher corrosion rates compared to outdoors, whereas in closed (indoor) environments the corrosion rate significantly decreased. It is recommended to define an additional level of corrosivity for tropical coastal atmospheres in outdoor and sheltered conditions as corrosion depends on the geographical position and exposure conditions.     

Atmospheric corrosion of field-exposed AZ91D Mg alloys in a polluted environment

The atmospheric corrosion behaviour of cast and high pressure die-cast AZ91D alloy in a polluted environment were investigated by SEM, XRD and FTIR. The atmospheric corrosion rate of the ingot was higher than that of the die-cast specimen. SO₂ gas played an important role in atmospheric corrosion. The effects of dew condensation on the ingot were greater than that on the die-cast specimen. The corrosion was initiated in the less noble α phase of the samples. The β phase, on the other hand, remained and acted as a barrier to corrosion.     

Atmospheric corrosion in subtropical areas: XRD and electrochemical study of zinc atmospheric corrosion products in the province of Santa Cruz de Tenerife (Canary Islands, Spain)

In the present paper, zinc sheets have been exposed for 4 years to the action of different atmospheres in 35 test sites located in the province of Santa Cruz de Tenerife, Canary Islands, Spain. Corrosion products formed on the surface of the samples have been identified by means of X-ray diffraction (XRD) for the first and second year of exposure. Zincite, hydrozincite, simonkolleite, zinc chlorohydroxysulphate, zinc oxysulphate and zinc hydroxysulphate have been identified in the test sheets. Preliminary results of an electrochemical study of the breakdown potential of zinc samples are also presented in order to test the protective effect of the film formed on the surface of the samples. It was found that the protective effect of this film increases linearly with exposure time.     

Detection of corrosion degradation using electrochemical noise (EN): review of signal processing methods for identifying corrosion forms

Electrochemical noise (EN), as one of the most promising in situ electrochemical methods in corrosion and electrochemical science, has been developing rapidly in recent years with the advancements in instrumentation and signal processing methods. One advantage of EN is its application in long-term or early stage corrosion process monitoring because it instantly detects corrosion rate and corrosion forms. Investigators have applied various mathematical methods to extract characteristic parameters from EN. In this paper, identifying corrosion forms using parameters obtained from time domain, frequency domain and time–frequency domain is reviewed, and the correlation between parameters and corrosion forms is discussed. Finally, other in situ techniques are recommended to be employed synchronously with EN measurement in order to obtain reliable analyses.