Physicochemical studies of mild steel corrosion and atmospheric corrosivity mapping of Karachi: An important harbor city of modern Maritime Silk Route

This paper has reported physicochemical features of mild steel's corrosion products and provided atmospheric corrosivity maps of Karachi harbor city, drafted on the basis of spatial distribution of corrosion data from July 2018 to June 2019 at 10 different urban, industrial, and marine test sites. Exposure tests have been performed to study atmospheric corrosivity, corrosion products, and corrodants including chloride, sulfur dioxide, time of wetness (TOW), and corrosion rate as per ISO and ASTM standards. Scanning electron microscope, Fourier-transform infrared spectroscopy, and X-ray diffraction have corroborated the presence of lepidocrocite, goethite, magnetite, and quartz phases at almost all the test sites, with slight variations in their morphologies and quantities. The data analysis has revealed that TOW is a major detrimental factor to accelerate corrosion of mild steel at Karachi city. The corrosivity category of all urban and marine test sites is found in C₄–C₅ range, whereas for industrial test sites, it is found in C₃–C₅ range. Resultant corrosivity maps have shown that the prevailing atmosphere is significantly corrosive at Karachi harbor city. This study has furnished a novel product of atmospheric corrosivity map, which is the first-ever corrosivity map for Pakistan.     

Atmospheric corrosion kinetics and dynamics of electrogalvanized mild steel in southeastern coastal area of China–Pakistan Economic Corridor

This study aims to examine atmospheric corrosivity, corrodants, and corrosion products of southeastern coastal area of China–Pakistan Economic Corridor as per ISO protocols 9223 and 9225, and ASTM standards G1, G50, G140-02, D4458-94, and D2010. Test sites are located at National Institute of Oceanography (NIO) and Karachi Port Trust (KPT) at the banks of the Arabian Sea. Electrogalvanized mild steel test coupons were exposed, and levels of corrodants (sulfur dioxide, chloride, and time of wetness) were measured for a period of 24 months, from May 2014 to May 2016. Corrosivity category C5+ is established in terms of the corrosion rate for both NIO and KPT test stations, which does not coincide with the corrosivity category C5 ascertained by employing environmental characteristics and atmospheric corrodants. Corrosion kinetic parameter “n” and correlation coefficient (R²) are 0.71 and 0.97 for NIO and 0.96 and 0.97 for KPT, respectively. Scanning electron microscopy/energy-dispersive spectroscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction spectroscopy have corroborated the presence of simonkolleite and hydrozincite, zinc oxide, zinc hydroxychloride, and zinc in corrosion products at both test sites.     

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.     

Effect of height on the corrosion of steel and galvanized steel in nontropical coastal marine environments

In this study, the behavior of carbon steel and galvanized steel in nontropical coastal marine environments was evaluated. Evaluation was carried out with specimens with dimensions of 10 cm × 10 cm × 0.3 cm. These specimens were exposed to four testing stations (Iquique, Mejillones, Los Vilos, and San Vicente), where racks were installed both at ground level (ground), as well as in the upper zone of electrical transmission towers (tower). In each station, 24 specimens of A36 carbon steel and galvanized steel were placed (12 each). The corrosivity of the environment was measured using the ISO 9223, 9225, and 9226 standards. The specimens were evaluated on-site, monthly, through visual inspection and photographic record. Once withdrawn, the corrosion rate was determined and the corrosion products were analyzed through Raman and Fourier-transform infrared. The results show that, in all cases, the corrosion rate is greater in the tower than on the ground. However, even though the Los Vilos station is located farther from the sea (3,500 vs. ≈500 m), the corrosion rate of steel in the tower is the highest. This is caused by the generation of HCl from the transformation of lepidocrocite into goethite, in the presence of low chloride content, which acidifies the steel/corrosion product interface. In the case of galvanized steel, the corrosion rate is a function of the chloride content in the atmosphere, obtaining an excellent correlation between both parameters.     

Pitting of zinc: Observations on atmospheric corrosion in tropical countries

A five-nation study has investigated the mechanisms and rates of the atmospheric corrosion of zinc and steel in tropical regions in Australia, Thailand, Indonesia, Vietnam and The Philippines. For the study, 18 exposure sites encompassing severe marine, marine, severe industrial, industrial, marine/industrial, urban and highland environments were established across the countries. At each location, zinc and steel plates were exposed for periods of three months and one year, and measurements were taken of a wide range of surface-response and climatic parameters, including gaseous SO_x and NO_x, airborne salinity, relative humidity (RH) and temperature, rainwater composition, surface temperature and time of wetness (TOW). Exposed plates were used to determine mass loss, the nature of corrosion products (using FTIR and SEM-EDS) and the morphologies of corrosion layers (via SEM-EDS). Regression analysis indicated that the prime factors controlling zinc corrosion rate were climate (temperature and rainfall) and surface-response (TOW), and surprisingly not pollutant levels, despite significant variation in SO_x levels across the sites. SEM studies indicated the presence of pitting below the oxide layers on zinc, particularly those plates exposed at marine and other sites with relatively low SO_x levels. In contrast, no pitting was observed (or pits had very low aspect ratios) in the specimens exposed at sites with high SO_x levels. The possible processes leading to the observed damage patterns are discussed.     

Long‐term atmospheric corrosion monitoring

The paper presents the analysis of corrosion rates of carbon steel, zinc, aluminium and copper after long‐term exposition as a function of time and environmental parameters. All experimental methodologies on the test sites were carried out according to ISO standards. The analysis of trends of environmental pollution and corrosion rates was performed for one year exposition of metals on three sites (urban/industrial, urban and rural atmosphere) in Poland. The corrosivity changes as a result of a reduction of corrosion rates of metals used are relatively smaller then the reduction of pollution. By using the equation C = Atⁿ, where C – corrosion rate after t years, A – corrosion rate after the first year of exposition, and results of long‐term corrosion rates, exponent n was determined for the different metals and sites from log‐log plots.     

Atmospheric corrosion of carbon steels in tropical and subtropical climates in Southern China

Q235 and Q345 carbon steels were exposed for up to 24 months at three test sites of tropical and subtropical climate. The atmospheric corrosion kinetics of Q235 and Q345 was studied by weight-loss measurement. The results show that the ranking of the atmospheric corrosivity from weak to strong of the three test sites is Xishuangbanna, Guangzhou, and Wanning. The kinetics of the atmospheric corrosion process presents two stages with an accelerated second stage in marine environments of high chloride ion content and high relative humidity, whereas no second stage appears in the kinetics curves in rural and industrial urban environments. The corrosion acceleration stage in the marine environment of the Wanning site is attributed mainly to the high chloride ion concentration and loose rust layer structure.     

Corrosion Protection of Steel Highway Bridges: II Characterisation of bridge locations by corrosion and environmental measurements

Abstract

Climatological and air pollution factors greatly affect the corrosion damage to steel highway bridges. This paper gives first results of a programme to define quantitative criteria by which the potential corrosivity of a prospective bridge location can be assessed.

At seven sites throughout the country, the corrosion rates of a special mild steel, a low alloy steel and zinc are being measured under both open and sheltered exposure conditions. Meteorological and air pollution data are also being collected.

To eliminate the considerable delays which can occur in negotiating the building of permanent test compounds, a mobile test rig has been developed, which can be easily transported to any prospective bridge location.From the first year's results, it is apparent that sheltered test specimens give a much closer indication of the corrosivity under a bridge deck than do open exposure specimens. Of the environmental factors, atmospheric chlorides and sulphur compounds are the major factors influencing corrosion rate. It was not possible, at this stage of the work, to produce a correlation between corrosion rates and meteorological data.     

Comparability and accuracy of time of wetness sensing methods relevant for atmospheric corrosion

The performance of three time of wetness (TOW) determination methods during outdoor exposure was examined. Two impedance-based TOW sensor types, RH, and temperature sensors were exposed to coastal marine and laboratory environments for up to three months. The sensor and ISO 9223 methods examined provided incomparable estimates. Inaccuracy of the ISO method originated from a humidity threshold well above the drying point of deposited aerosols and differences between surface and ambient RH. TOW sensor accuracy was linked to electrode configuration. Small electrode spacing was demonstrated to be required to capture the range of wetting events of importance to atmospheric corrosion.     

接触网部件材料在模拟典型大气环境介质中的腐蚀——热浸镀锌材料的腐蚀(I)

采用腐蚀失重法与显微镜技术,研究了电气化铁路接触网热浸镀锌部件材料在模拟典型大气环境(海洋环境、工业环境、城市环境)介质中的腐蚀及其形貌。结果表明,热浸镀锌材料在模拟城市大气环境介质中的腐蚀最为严重,工业环境次之,海洋环境腐蚀最轻。二次加工与成型会引起镀锌层局部破损致使基材局部暴露与镀锌层形成电偶对,会加重热浸镀锌部件的腐蚀,且破损面积越大腐蚀越严重。同样,热浸镀锌部件与不锈钢紧固件耦接会形成电偶腐蚀,也会加重热浸镀锌部件的腐蚀。建议针对电气化铁路各段不同的大气环境,选择不同的接触网零部件材料、或者采用相应的防腐措施。在接触网构件加工和装配过程中,建议改进加工工艺程序,避免热浸镀锌部件的二次加工或者成型;建议采用绝缘措施,以达到热浸镀锌部件与不锈钢紧固件之间的绝缘耦接,避免电偶腐蚀发生。     

Kinetics of atmospheric corrosion of mild steel, zinc, galvanized iron and aluminium at 10 exposure stations in India

As a part of updating Corrosion Map of India project, atmospheric corrosion behaviour of commercially available engineering materials such as mild steel, galvanized iron, zinc and aluminium metals was studied in marine, industrial, urban, and rural environments by weight loss method at 10 exposure stations in India over a period of 5 years. The results of these studies demonstrated that galvanized iron, zinc and aluminium metals were several times more durable than mild steel. Compared to galvanized iron and zinc, aluminium provided superior protection in industrial and marine environment except at Mormugao Port Trust (MPT). It also offered much better resistance to corrosion in rural environments. At certain places, galvanized iron proved to be more durable than aluminium. The results obeyed well with the empirical kinetics equation of the form C = Ktⁿ, where K and C are the corrosion losses in μm after 1 and ‘t’ years of the exposure, respectively, and ‘n’ is a constant. Based on ‘n’ values, the corrosion mechanisms of these metals are predicted. The corrosion products formed on the metal samples in Chennai marine atmosphere were identified by X-ray diffraction analysis.     

Atmospheric corrosion in Mauritius

Abstract

Carbon steel is commonly used in Mauritius, and information related to its atmospheric corrosion behaviour in the Mauritian atmosphere is not readily available. Hence, the present study was performed to obtain relevant data and to develop a model for predicting the atmospheric corrosion degradation of carbon steel in Mauritius. Carbon steel samples were exposed outdoors at several sites, according to BS EN ISO 8565. They were removed after specific time periods, and their mass loss was determined. At the same time, the sites’ environmental parameters were monitored. From the mass loss measurements and the environmental parameters considered, it was found that the corrosivity of the Mauritian atmosphere falls in category C3 to C4, according to ISO 9223. A model was developed using the SPSS software, and it was found that the atmospheric corrosion in Mauritius depends mainly on the time of exposure and the carbon content of carbon steel.     

不锈钢的大气腐蚀研究—12年暴露试验总结

总结了５种不锈钢在我国７个试验点的１２年大气腐蚀试验结果,材料中包括了最常用的不锈钢,环境中包括了亚热带,温带,工业性,海洋性,干燥环境及湿热环境等各种典型环境。不锈钢在大气中是耐蚀的。当含Ｃｒ量达到１８％以上时耐蚀性很好,钼能明显提高不锈钢的耐蚀性,超低碳也能提高其耐蚀性。     

Atmospheric corrosion of mild steel. Part II – Marine atmospheres

This paper summarizes the results obtained in the MICAT project for mild steel specimens exposed for 1 to 4 years in 47 marine atmospheres in the Ibero‐American region. All these atmospheres were characterized for climatology, pollution and corrosion rates according to ISO standards. Complementary morphological and chemical characterization of the steel corrosion product layers (SCPLs) formed in these atmospheres was carried out. The overall analysis of results contributes to understanding, in a systematic way, how atmospheric corrosivity categories can be correlated with corrosion mechanisms. Special aspects of the atmospheres, from pure to mixed marine, were considered.     

Corrosivity category maps of a humid tropical atmosphere: the Yucatán Peninsula,México

Fourteen test sites were established in the tropical humid atmosphere of the Yucatán Peninsula and the Mexican Caribbean area. In each environment sulfur dioxide and chloride deposition rates were measured and the corrosion rates of flat plate samples (low carbon steel, copper and zinc) determined. In selected locations open helix samples of copper, and low carbon steel were also tested. In two typical test sites (a rural-urban and a marine-coastal) the time-of wetness and temperature were registered, then their influence on the metallic corrosion rates discussed. The obtained data were used for classification of atmospheric aggressivity, according to ISO 9223. It was observed that the aggressivity categories of marine coastal zones are C5, the highest one, while the rural and rural-urban sites classify as C2, C3 and C4. No appreciable difference in category classification is observed, when flat plates or open helix samples are used.     

Towards the development of a corrosion map for Abu Dhabi

Infrastructure development in the United Arab Emirates continues to escalate, yet very few corrosion studies have been performed in the region. In a step to address this situation, this paper reports on a study of zinc and steel corrosion and salt deposition rates at five sites in the Emirate of Abu Dhabi. The sites are classified as either urban/marine, marine, inland or mountainous. The study found that zinc corrosion rates range from 15 µm/year on the coast to 0.6 µm/year inland, while steel corrosion rates are 56 and 10 µm/year, respectively, at the same locations. While the salt deposition rate ranges from 5 to 18 mg/m²/day, it is not directly related to distance from the coast. Although the salt deposition rates observed are consistent with those at locations at similar latitudes, the corrosion rates are higher than in locations with comparable salt deposition rates. However, when the data were analysed along with relevant local meteorological data, it was found to be consistent with the basic assumptions of the holistic model of atmospheric corrosion developed by Cole et al. In particular, it is suggested that the relatively high corrosion rates observed here are associated with a greater accumulation of salt, which can occur in Abu Dhabi because rainfall, and thus rain washing, is extremely low compared to similar exposure locations in Australia and South‐East Asia.     

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.     

Atmospheric corrosion of ASTM A-242 and ASTM A-588 weathering steels in different types of atmosphere

The work analyses the atmospheric corrosion resistance of two widely used weathering steels: ASTM A-242 and ASTM A-588. The steels were exposed for up to 5 years in different types of atmosphere: rural, urban, industrial and marine. The atmospheric corrosion resistance of the steels was evaluated and the rust layers formed on them were characterised by X-ray diffraction, optical microscopy and scanning electron microscopy. The most relevant conclusions reached include the following: (a) the visual appearance (colouring) of the rust, rust texture, nature of the corrosion products and compactness of the rust layers formed are similar in both types of weathering steel. (b) No great differences are observed in the corrosion resistance. Slight differences occur in the industrial atmosphere, where ASTM A-242 presents 10–13% less corrosion than ASTM A-588. (c) In the C2-C3 ISO corrosivity atmosphere both types of weathering steels are adequate for unpainted use. However are not suitable in higher ISO corrosivity atmosphere.     

Atmospheric corrosion of galvanized steel and aluminium in marine and marine‐industrial environments of Saudi Arabia

Three‐year exposure programme was carried out in Saudi Arabia at nine test stations with different climatic and pollution conditions. The aim of this study was to evaluate the joint effect of atmospheric pollutants (Cl^? and SO₂), relative humidity (RH) and temperature (T) on the atmospheric corrosion of galvanized steel (GS) and aluminium (Al). Corrosion rates of the two metals have been obtained by loss of weight after 1, 2 and 3 years exposure. The composition of the corrosion products formed on the specimens was identified by X‐ray diffraction analysis. A classification of the atmospheric corrosion aggressivity of the test sites based both on environmental data and corrosion rate measurements was made according to ISO 9223. In some regions, it can be found that corrosion rate values exceed those established by the ISO standard.     

Comparative analysis for the corrosion susceptibility of Cu,Al, Al–Cu and C‐steel in soil solution

Corrosion of different materials (Cu, Al, Al–Cu and C‐steel) in soil solution was evaluated at ambient temperature using various techniques. The weight loss of the studied materials varied exponentially with time. Kinetic data revealed that the corrosion of Cu and Al–Cu are diffusion controlled while Al and C‐steel show gradual change from diffusion control to charge transfer control. Nonferrous materials have better durability factors than C‐steel. Good consistency between the data obtained from EIS and PDP measurements was observed. SEM showed a biogenic corrosion layer with density that depends on the metal type. Correlation between corrosion rates and the estimated soil solution corrosivity was obtained.