Atmospheric Corrosion Modeling and Corrosivity Categorization of 1008 Carbon Steel in Alaska

Atmospheric corrosion continues to be a significant monetary problem. Particularly in colder climates, such as Alaska, the complexity of atmospheric corrosion increases and additional factors make it difficult to estimate the corrosive phenomena. Despite the topic's significance, there exists a noticeable knowledge gap regarding the corrosivity of metals in cold regions in general. This lack of data stands in stark contrast to Alaska's growing importance on the global stage, particularly its potential as a pivotal point for cargo, strategic military location, refueling hub, and location for aerospace applications. Multi-angle corrosion test racks were deployed at four test sites across Alaska, each distinct in their environment, equipped with weather sensors and chloride candles. The principal weather parameters recorded were the ambient air temperature, relative humidity, time of wetness at exposure angles of 0°, 30°, and 45°, total rainfall, and aerosol chloride and sulfate deposition. Once coupon exposure was complete, coupon mass loss was measured and the corrosion rates were calculated as a function of the surface exposure angle. Comprehensive analyses, including weather correlation, mass loss analysis, SEM/EDXA, and optical profilometry, were used to determine corrosion rates and classify the corrosivity of the four sites against well-recognized standards.

Atmospheric corrosion is a process that is heavily dependent on weather parameters. Heavy snowfall and dramatic freeze-thaw cycles observed in Arctic conditions further complicate the atmospheric corrosion mechanisms. The main purpose of this paper is to monitor and measure weather parameters, aerosol chlorides, and sulfates in the atmosphere and correlate it to the degradation of carbon steel alloys widely used in land, sea, aerospace transportation, oil and gas, fisheries, and mining applications. Carbon steel alloys (UNS G10060) were exposed to four atmospheric test sites in Alaska, representing distinct environments. Multi-angle test racks were designed, equipped with chloride candles and weather stations, and deployed to each site. The parameters recorded were Time of Wetness (TOW), relative humidity (RH), temperature, and aerosol chloride and sulfate deposition rates. The corrosion rate of carbon steel was calculated from the mass loss data. Accelerated laboratory tests were conducted in cyclic corrosion test chambers (CCTC) following the modified GM9540P standard for correlation studies.

In colder climates, factors like substantial snowfall, frequent freeze-thaw cycles, the use of de-icing salts, and increasing global temperatures add complexities to the established paradigms governing atmospheric corrosion. To elucidate the mechanisms of atmospheric corrosion under colder temperatures, four distinct test sites were established in the state of Alaska, USA. Each site was equipped with a modern, multi-angle exposure test rack coupled with an auxiliary weather station. Within these setups, five commonly used metal alloys were exposed at 0-, 30-, and 45 degrees from the horizontal over 6- and 12-month periods. Weather correlation analysis, mass loss analysis, SEM/EDXA, and optical profilometry studies were conducted following the exposure of the metal specimens to determine corrosion rates (CR) and damage. The measured CR, exposure angle, and accompanying meteorological data—specifically, temperature, relative humidity, time of wetness, precipitation, chlorides, and sulfates—were benchmarked against ISO standards to classify and categorize the corrosivity of the four test sites in Alaska. The PSCA test site (Kodiak, AK) was the most aggressive environment regarding all weather parameters. UAF (Fairbanks, AK) was the least aggressive, and test sites PAA (Port of Anchorage, AK) and UAA (University of Anchorage, AK) showed mild to moderate aggressiveness. Samples exposed at 0° consistently showed higher corrosion rates than those exposed at 30° and 45° across all instances. At the more aggressive PSCA site, a distinct correlation was observed between the exposure angle and CR with samples exposed at 0° showing the highest CR, followed by 30°, then 45°. Optical profilometry studies revealed that the comparison of surface roughness between the exposed samples followed an extremely similar pattern to that of CR. Corrosivity categorization based on CR from experimental mass loss data varied from the estimation of CR through existing dose-response functions and weather parameters. Newer standardized models involving more weather parameters are required to better estimate and predict corrosivity in colder climates. Alaska's growing role as a critical military, cargo, shipping, and refueling hub enhances its importance as an ideal natural laboratory for studying atmospheric corrosion in cold regions, as demonstrated by the developed test sites discussed in this paper.

Vietnam is situated in the wet tropical zone; thus, atmospheric conditions are characterized by high temperatures and a long time of wetness (TOW). In addition, the salt air coming in from the sea causes a high chloride concentration in coastal areas. Furthermore, Vietnam is a developing country, which means that air pollution is increasing with the development of industry. These factors result in significant damage to materials by atmospheric corrosion. In this report, the results of a recent study on the corrosion of carbon steel and zinc-galvanized steel at 6–8 testing sites in Vietnam over 10 recent years (1995–2005) are focused on as well as the effects of environmental factors on atmospheric corrosion. The results showed that the corrosion of carbon steel is dominated by TOW, whereas zinc-galvanized-steel corrosion strongly depends on the chloride ion concentration in the air. The corrosion losses of both carbon- and zinc-galvanized steel fit the power model well with high correlation coefficients. In addition, the characteristics of the Vietnamese climate are introduced in the form of distribution maps of temperature (T), relative humidity (RH), total rainfall and TOW. A relationship between TOW, T and RH was found that enabled the calculation of TOW from T and RH data, which are available at meteorological stations. Finally, atmospheric corrosivity is determined on the basis of data on TOW, Cl– and SO2 concentrations, and the carbon steel corrosion rate. It is shown that in Vietnam, TOW is so long that the corrosion rate of carbon steel is in the C3 category; nevertheless, Cl– and SO2 concentrations in the atmosphere are not high.

Atmospheric corrosion is a complex process, which involves chemical, electrochemical, and physical changes to the metal exposed. Atmospheric corrosion occurs when a metal surface is under a thin layer of moisture, but not completely immersed, and the metal surface corrodes while exposed to environmental factors. The arctic and sub-arctic region identified by the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) has an average temperature of -18oC or less during winter. It is commonly assumed that there is very little to no corrosion in cold environments. However, previous studies in the Antarctic and Arctic regions have shown significant corrosion damage when exposed to cold conditions. Studies in the sub-arctic region of Canada, Norway, and Russia show extensive atmospheric corrosion rates (when compared to Antarctica) due to human developments and the resulting increase in mining and metallurgical industries. Experimental and theoretical work has shown that the electrochemical process proceeds at temperatures as low as -25oC to -20oC . Moreover, very little corrosion data are available for metal alloys exposed to cold arctic and sub-arctic conditions. The two important factors that affect atmospheric corrosion rates are aerosol chlorides (or salt-laden snow from the marine environment or deicing salts on roads) and time of wetness (TOW) along with other climatic parameters such as rainfall, temperature, humidity. Factors that drive the atmospheric corrosion in cold climates are winds that can bring in salt-laden snow from the marine environment and the use of de-icing salts can also contribute to high levels of chlorides. The eutectic point or the freezing point of de-icing salts can be lowered to -50oC, melting the ice/snow layer on top of metal samples. This phenomenon keeps metal samples moist for much longer periods, thus increasing the TOW. In the presence of chlorides and moisture, extensive atmospheric corrosion damages can be observed on metal samples. Another contributing factor to high corrosion rates is low rainfall, which in turn cannot periodically wash off the deposited chlorides and SO2 on top of the samples. In addition, ever-increasing ambient temperatures due to climate change in recent years affect the snow presence on top of the metal samples. The temperature of the samples is not too high to evaporate the snow/ice deposited, but high enough to cause melt and sustain moisture for longer periods of time. This leads to the formation of varying thickness of wet ice/snow layers on the metal surface. Long hours of sunlight in the summer also increase the surface temperature of metal samples beyond the ambient temperatures, causing dew formation and condensation, which in turn results in higher TOW. The atmospheric corrosion damage in cold environments is close to the main human activity, which is concentrated near the coastal areas. The substantial human growth and climate change in the arctic and sub-arctic region pushes for a renewed better understanding of the atmospheric corrosion mechanisms that can lead to good choice of materials selection and better design practices for infrastructure and other applications. The combination of urbanization and proximity to marine environments make arctic and sub-arctic regions in North America, particularly Alaska, an important natural laboratory to study atmospheric corrosion in cold regions. Design and establishment of modular corrosion test racks equipped with weather stations will be discussed. The angle of exposure can be changed to 0, 30 and 45-degrees to the horizontal (see the attached figure). This will allow us to test the metals alloys exposed to different angles for the same exposure period and study the effect of snow/ice retention on top of the metal surface. Figure 1

Based on analysis of data from field exposure programs within, e.g., UN ECE and ISO CORRAG a model describing atmospheric corrosion of common technical metals has been developed. The model uses environmental parameters that are easily available on different geographical scales. The combination of temperature and relative humidity can be used to express the time of wetness based on a probability model for the prediction of time of wetness from annual temperature and relative humidity data. The sulfur dioxide air concentration and the chloride deposition are included in different parts of the model and these two parts contain separate expressions for the combination of temperature and relative humidity (or temperature and time of wetness). This makes it possible to apply the model in marine areas with different deposition of chlorides and different pollution levels. The development of the model has contributed to a better understanding of the conditions for atmospheric corrosion, including tropical regions. The individual terms of the model have been adapted using physical and chemical principles. This makes the model useful for predictions also in regions outside those defining the original data set. Examples of independent data from field exposures not included in the model development are shown and discussed.

Atmospheric corrosion is an essential problem to industrial and infrastructure engineering. The abundant concerned of the problem is the lifetime service of metal structure and equipment which result in the safety operation and economic loss. Atmospheric corrosion is a very complicated process that causes deterioration of metallic materials by chemical or electrochemical reaction between the metal and its environment. The corrosion parameters like relative humidity, time of wetness, and numerous pollutant substances which involve species deposited from atmosphere and species from the metal resulting from corrosion itself, affect to the atmospheric corrosion. A common method for atmospheric corrosion investigation is the long-term exposure test under natural environment, but this method requires time-consuming and high-cost expanse. To investigate the corrosivity of atmosphere, in this research, several chemical species such as NaCl, KCl, Na2SO4, NaNO3, KNO3, MgCl2.6H2O, and Mg(NO3)2.6H2O were used as artificial rainfall solution with the variation of concentration. Four types of ACM sensors which consist of Fe-Ag, Zn-Ag, Al-Ag, and Cu-Ag galvanic couple were used to define the correlation between sensor output and Corrosion Rate (CR), which affected by the chemical concentration of individual and mixed solutions. The 1 mm thick of low-carbon steel sheet specimens, with the size of 70 × 150 mm, were exposed to the artificial rainfall test. The CRs were calculated by measuring weight loss after removing corrosion products, or rust layer, by immersing the samples into Hydrochloric Acid (HCl) solution ( ISO/DIS 8403.3). In water, the molecules of the species are separated into cation and anion. The results reveal that the corrosivity of the cation is negligible compared to the anion. In term of the concentration, the SO4 2- anion is more corrosive than Cl- and NO3 - anion respectively. For a low chemical concentration, the CRs affected by each ion are small and similar to the CR of Deionize-water. This is the result of the spontaneously formed of the oxide film which provides some degree of protection, and the breakdown of the film is usually required higher aggressivity of the electrolyte. For further increasing the molar concentration, the CR raises up to reach a steady state. The signal output of Fe-Ag and Zn-Ag couple give a good relation for determining the corrosion rate in both individual and mixed solutions. Al-Ag couple, however, is unable to forecast the CR in the unknown pollution species, especially the mixed solution, because it is more sensitive with Cl- and NO3 - ions and less so with SO4 2- ions. Nonetheless, Al-Ag galvanic sensor offers a great advantage to predict the chemical species in the environment. For instance, if the CR is high, and the Al-Ag sensor output is low, the SO4 2- ions is assumed as the major contain in the solution or the environment. The lifetime service of Fe-Ag galvanic sensor is much lower than those of Zn-Ag, Al-Ag, and Cu-Ag, respectively. The results of the research indicate that the ACM sensors are capable of estimating corrosivity of the atmosphere; the research methods discussed in this paper proves that the CRs are dependent on the atmospheric composition and can be forecasted through ACM sensors.

Atmospheric corrosion of structural metals including aluminum, copper, carbon steel and galvanized steel has been investigated in various areas in Iran based on meteorological data and test coupon mass loss. Using annual average temperature and relative humidity (RH), the time of wetness (TOW, τ) of 51 cities in Iran was obtained in 2012. Coincidentally, sulfur dioxide (SO2) and chloride ion (Cl−) concentrations were measured in these cities; then, according to ISO 9223, the predicted corrosion rate (rcorr) of aluminum, copper, carbon steel and galvanized steel was calculated. Geographical information system (GIS) modeling of TOW, air pollutants (sulfur dioxide and chloride ion) and estimated rcorr were extracted. The mentioned metallic coupons were exposed to the outdoor atmosphere of 15 test sites for up to 12 months to measure the actual corrosion rate of metals. The corrosion products were characterized using scanning electron microscopy and an X-ray diffractometer. The results show that the atmospheric corrosivity of Iran as a developing country is mainly affected by the air temperature, RH and Cl− deposition rate. The atmosphere at shorelines is much more aggressive. Predicting the corrosion loss, the northern coastlines show a more corrosive atmosphere. On the contrary, coupons fixed at the southern coastlines are severely corroded compared with those fixed at the northern shorelines. Chabahar has the most corrosive atmosphere for carbon steel, galvanized steel and copper coupons where their actual corrosion rates (CRs) are 514.68, 10.25 and 11.01 μm/year, respectively. Aluminum coupons presented the best corrosion resistance at all test sites, and their CR were approximately nil. The result shows that models developed by ISO 9223 are not appropriate for predicting the atmospheric corrosion of aluminum, copper, galvanized steel and carbon steel in most areas in Iran.

Atmospheric corrosion is a complex process, which involves chemical, electrochemical, and physical changes to the metal exposed. Atmospheric corrosion occurs when a metal surface is under a thin layer of moisture, but not completely immersed, and the metal surface corrodes while exposed to environmental factors. Atmospheric corrosion of metal alloys in cold environments is assumed to be negligible and limited corrosion data are available in cold climates. However, studies in the Arctic and Antarctic regions have shown significant corrosion damages when exposed to cold conditions. The rate of atmospheric corrosion on various alloys is affected by environmental parameters that include temperature, rainfall, humidity, chloride-ion deposition rate, and time of wetness (TOW). Two important factors that affect atmospheric corrosion rates are aerosol chlorides and TOW. The main goal of this research is to monitor and measure the aerosols chlorides in the atmosphere, measure TOW and correlate the degradation of carbon steel alloys that are widely used in land, sea, and aerospace transportation, the oil and gas, fisheries, and mining applications. The main objectives achieved are design of Combined Chloride and Corrosion Portable Racks (C3PR) and deployment of C3PR racks in four different Alaskan environments. Chloride deposition rate measured using ASTM standards for three different exposure periods along with TOW, ambient temperature and RH data are correlated to the atmospheric corrosion rate of carbon steel to understand the underlying atmospheric corrosion mechanisms. The results from this research work will give a better understanding on the atmospheric corrosion studies in cold arctic/sub-arctic environment and lead to more externally funded projects.

The atmospheric corrosion has been shown to be an electrochemical process, the atmospheric corrosion behavior of Q235 stell evaluated with ACM (Atmospheric corrosion monitor) electrochemical technique was investigated in the study. The experimental results showed that there existed a close relation between electrochemical data and climatic parameters was confirmed. Taking into consideration accuracy and sensitivity of electrochemical technique, the ISO-standardized time of wetness (TOW) seems to be too conservative. SO2 seems to be more aggressive than chloride on metal corrosion in the early stage of atmospheric corrosion but the complexion reverses in the final stage of atmospheric corrosion. The ratio of corrosion rate from integration of ACM current to corrosion rate from weight loss of test specimens, that is, cell factor is fairly constant at the same test site but varied greatly between test sites. Based on constant cell factors and close relation between electrochemical data and climatic parameters in all test sites, ACM electrochemical technique can evaluate and classify the short-term atmospheric corrosivity as a substitute for gravimetric method, and the verification shows that atmospheric corrosivity classifications according to integration of ACM current and especially to cell factor coincide with the specifications of ISO Standard.

The marine atmospheric test site at Kure Beach, North Carolina, has long been recognized for its corrosion severity. It represents a benchmark for testing materials' resistance to marine atmospheric corrosion. The two test areas at the site have often been referred to as the 80-foot and 800-foot test lots (or the 25-meter and 250-meter lots), respectively. For over 38 years the amount of airborne chlorides from the sea spray have been monitored monthly. Chloride deposition is only one of several environmental factors which can contribute to atmospheric corrosion. Some of the other important factors include relative humidity, time of wetness, temperature, prevailing wind direction, and rainfall—which are all also monitored routinely. Corrosivity is monitored more directly by determination of mass loss for two reference materials, carbon steel and zinc. Because of a number of recent changes, the 25- and 250-meter test locations have now been designated as the “oceanfront” and the “near-ocean” lots. Continued monitoring of these sites will benefit existing and future marine atmospheric test programs, including those of various ASTM subcommittees. Examples of materials on continuous exposure in the “museum areas” of the oceanfront and the near-ocean lots are reviewed for the purpose of educating new corrosion engineers on the importance of long-term testing in natural environments.

A series of regression analyses was made on the multi-year corrosion losses of panels of steel, zinc, copper, and aluminum in the ISO CORRAG program. In every case, the only sites selected for the analyses were sites with all four exposures reported and complete data sets on the time of wetness, sulfur dioxide, and chloride deposition. The regressions with significant R values were then selected for further analyses. The time exponent and one-year corrosion coefficient were regressed against the environmental variables. None of the exponent regressions showed large environmental effects. The steel exponent was increased by chloride deposition and time of wetness. The copper exponent was increased by increasing time of wetness and decreased by increasing chloride. Neither zinc nor aluminum exponents showed significant effects from the environmental data. The best environmental regressions were only able to predict the measured corrosion losses to within a factor of two for steel, zinc, and copper. The aluminum loss predictions were worse. Some other environmental variables will need to be found to improve this approach to predicting atmospheric corrosion.

In order to classify the corrosivity of the different Colombian atmospheres, as part of an extensive research project [1], plates of carbon steel were placed in 21 stations spread along the country electrical infrastructure (transmission lines and substations). There were measured among others at these stations, the time of wetness and deposition of sulfates and chlorides for 12 months, in addition steel plates were taken bimonthly to the laboratory in order to measure the mass loss suffered by these during the time of exposure. The classification of the 21 stations was done in 4 groups, considering the time of moisture, content of chlorides and sulfates, height above sea level and the plates exposure time; these are considered linearly independent variables according to the implemented technique of decomposition unique values (DPS). The criterion used for classification was the similarity of the variables using the Euclidean rule considered in the Kohonen unsupervised neural network. Additionally, models were implemented for the steel mass loss for each one of the groups using feed forward neural networks (RN), defining the above variables as inputs and the mass loss as the output. Besides, the comparison between the RN model for the group 1, with other models using genetic algorithms (GA) and the Simplex method is presented.

Atmospheric corrosion and chloride deposition on metal surfaces was studied at an unpolluted coastal (marine) site, an unpolluted rural inland site, and a polluted urban site. Chloride deposition by both wet (precipitation) and dry deposition processes over a multi-year period was measured using ion chromatography analysis of incident precipitation and precipitation runoff from the surface of metal samples. Chloride deposition was measured on zinc, copper, lead, mild steel, and non-reactive blank panels, as well as two panels coated with thermal-sprayed zinc alloys. Chloride deposition measured by runoff chemistry was compared with chloride deposition measurements made by the ASTM wet candle technique. Corrosion mass loss as a function of distance from the ocean is presented for copper and mild steel in bold exposures on the west coast.

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.