Field Test Site for Environmental Corrosion of Steel Materials

Abstract: This paper introduces the current status of developments in environmental corrosion testing technologies for steel materials both domestically and internationally. It summarizes various experimental methods required in the research and development of new corrosion-resistant steel materials, and analyzes the key research areas and emerging trends in outdoor exposure tests, indoor accelerated simulation tests, online corrosion monitoring and detection, and big data evaluation techniques. Given that natural environment corrosion testing of steel materials is crucial for ensuring their safety and reliability during service, establishing a standardized and normalized environmental corrosion testing technology system represents an important task for enhancing the quality of China’s steel materials.

As the most important structural material, steel is used in nearly every industry. With the development of the energy industry, marine resources, and the shipbuilding industry, the demand for high-performance, corrosion-resistant steels is becoming increasingly urgent. However, under environmental conditions, steel materials are prone to corrosion. According to data from the major consulting project "Research on China's Corrosion Status and Control Strategies," in 2014, the total cost of corrosion across all industries in China accounted for approximately 3.34% of the country's Gross Domestic Product (GDP), reaching 2.13 trillion RMB. Moreover, corrosion products and failed materials and components also cause severe environmental pollution and have far-reaching impacts. Given that corrosion data for steel in natural environments such as the atmosphere, soil, and water possess characteristics of being non-transferable, public-benefit oriented, long-term, and continuously collected, it is critically important to establish a foundation for enhancing the quality of China's steel materials by systematically accumulating and sharing scientific data on material environmental corrosion, as well as by standardizing and normalizing environmental corrosion testing techniques.

For a long time, research on environmental corrosion of steel materials has focused primarily on experimental equipment, technologies, methodologies, and standards. With the advent of the information age, data science has also come to play a significant role in corrosion testing research. Whether it’s natural environment corrosion tests conducted under atmospheric, aquatic, soil, and microbial conditions, or localized corrosion tests such as stress corrosion cracking, pitting corrosion, and galvanic corrosion—including assessments of the overall corrosion resistance of components or equipment—both domestically and internationally, considerable data have already been accumulated. As high-throughput testing technologies and methods continue to be adopted, the volume of such data will grow rapidly. At the same time, data analysis and modeling techniques—including data mining, support vector machines, and Bayesian models—have provided powerful support for corrosion science research. These data and data-analysis methods are critically important for gaining deeper insights into corrosion mechanisms, tracking corrosion patterns over the long term, developing new corrosion-resistant alloys, identifying effective corrosion-control technologies, and guiding material selection for engineering design. The demand from corrosion science for data and information research has become the driving force behind the emergence and development of corrosion informatics.

Based on this, the article provides a comprehensive review of environmental corrosion testing technologies for steel materials and the current state of overseas research, offering foundational information for their further application in China. It also serves as a reference for the design, R&D, and manufacturing of steel materials, providing a theoretical basis for material selection for equipment operating under various environmental conditions, thereby enhancing the reliability and durability of China’s steel products and equipment.

1. Natural Environment Exposure Corrosion Testing Technology

From the mid-18th century to the 21st century, humanity’s understanding of metal corrosion has evolved from an empirical stage to a systematic, discipline-based research phase. Modern studies on environmental corrosion of materials have a history of nearly a century. Taking atmospheric corrosion as an example, the accumulation of corrosion data for metals exposed to outdoor natural environments began in 1906, when the American Society for Testing and Materials (ASTM) established an atmospheric corrosion testing site and conducted corrosion tests on a variety of materials under atmospheric conditions. In the 1920s, Vernon in the United Kingdom cleaned metal specimens thoroughly and then exposed them to outdoor natural environments to measure corrosion rates and identify major corrosion products. Vernon’s experimental research methodology has been continuously adopted ever since, though the instruments used for observation and characterization have undergone substantial improvements. It was thanks to Vernon’s experimental studies that the field of corrosion science transitioned from what might be called an “artistic” domain into a true scientific discipline. Based on extensive data collected from natural environment corrosion experiments, researchers have conducted in-depth studies on the mechanisms underlying metal corrosion in the atmosphere.

Countries around the world attach great importance to research on the environmental adaptability of steel and its products throughout their production, transportation, and service life. They are actively engaged in accumulating corrosion data and conducting experimental studies on materials exposed to typical natural environments, aiming to understand the corrosion patterns of various materials under real-world conditions. This research is of paramount significance for controlling environmental corrosion of materials and reducing economic losses. The study of the natural environmental adaptability of steel materials is highly complex, involving numerous influencing factors that are difficult to replicate in laboratory settings. Therefore, only through field trials and observations at outdoor test sites can we obtain accurate and realistic data on material environmental adaptability. The establishment of networks of natural environment testing stations and the accumulation of relevant data have a history spanning over a century. Given the significant differences in natural environmental conditions among countries, these networks reflect those unique local characteristics.

Our country boasts a vast territory and a complex natural environment. With its distribution across seven climatic zones from north to south, it has given rise to seven typical atmospheric environments (rural, urban, industrial, marine, plateau, desert, and tropical rainforest), five major river systems (the Yellow River, the Yangtze River, the Pearl River, the Songhua River, and the Huai River), four maritime regions (the Bohai Sea, the Yellow Sea, the East China Sea, and the South China Sea), and more than 40 different soil types.

The corrosion rates of materials can vary by a factor of several times, or even dozens of times, depending on the environmental conditions; therefore, it is impossible to simply substitute these rates with data from developed countries. Only through long-term data accumulation and experimental research can we obtain accurate corrosion data and understand the underlying patterns specific to our country’s natural environmental conditions.

Corrosion testing in China’s natural environments began in the 1950s. After decades of construction and development, based on the existing infrastructure of China’s material-environment corrosion test stations, a national field station planning initiative was established in collaboration with the Ministry of Science and Technology. This initiative brought together more than ten institutions from various industries, departments, and regions to jointly build a national material-environment corrosion platform consisting of 31 field test stations and one central hub, as shown in Figure 1. The platform includes 16 atmospheric corrosion test stations, 8 soil corrosion test stations, and 7 water corrosion test stations, stretching from Kurle in the west to Zhoushan Island in the east, from Mohe in the north to the Xisha Islands in the south—covering all typical natural environmental zones in China. Field sites for environmental corrosion testing have been established, and a comprehensive set of environmental corrosion testing procedures and technologies has been developed. These environmental corrosion testing procedures have now evolved into 28 industry standards for corrosion testing. In addition, a resource-sharing service platform for material-environment corrosion information—the China Corrosion and Protection Network—has been established. www.ecorr.org ), providing physical and informational resources on material corrosion (aging) to all sectors of society.

Figure 1: Distribution Map of Test Stations in the National Materials Environmental Corrosion Platform System

Outdoor environmental exposure testing is the most commonly used method in natural environment testing. According to the exposure mode, it can be categorized into three types: direct exposure, semi-enclosed exposure, and fully enclosed exposure. The selection of exposure sites should primarily take into account a comprehensive evaluation of various environmental factors and their effects on steel products, as well as the representativeness and accuracy of test results, and the nature and rate of performance changes. Currently, China's existing natural environment corrosion testing stations can adequately represent the typical natural environmental zones across the country. By studying the impact of environmental factors on the corrosion of steel materials and continuously accumulating data, we have established the corrosion patterns of steel materials under China's typical environmental conditions. In the research and development of corrosion-resistant steels and in assessing the environmental adaptability of equipment, China has developed a complete set of field testing technologies that meet international standards and have been widely adopted. The National Materials Environmental Corrosion Platform has completed the largest-scale materials environmental corrosion testing program in China, covering more than 100 types of materials—including carbon steel, weathering steel, stainless steel, and coated/镀层 materials. Given China's vast territory and complex natural environments, a systematic exposure testing program lasting up to 16 years has been conducted, involving stratified modeling studies on atmospheric, soil, and seawater corrosion, as shown in Figure 2.

(a) Atmospheric environment (b) Aquatic environment (c) Soil environment (d) Deep-sea environment

Figure 2: Natural Corrosion Tests of Steel in Atmospheric, Aquatic, Soil, and Deep-Sea Environments

With the implementation of the nation’s “Belt and Road” initiative, the National Materials Environmental Corrosion Platform has been conducting environmental corrosion tests and accumulating data on steel materials in Southeast Asia since 2015. Natural environment corrosion tests have been carried out in Thailand, Indonesia, Singapore, Malaysia, and other regions. These efforts will guide material selection for major construction projects and application demonstrations in areas such as port development, marine engineering, and high-speed railways.

Under the global trend of material environmental corrosion observation and testing research, in order to enhance the adaptability of materials to their environments and ensure the comparability of environmental corrosivity, observation and testing studies aimed primarily at accumulating material corrosion data have adopted unified specifications and standards—from exposure methods to detection techniques. In developed countries, the standardization of material environmental corrosion testing has already received widespread attention. In recent years, the United States, Japan, Germany, and other NATO countries have invested substantial human and material resources into extensive experimental research and data accumulation in the field of material environmental corrosion, actively promoting the standardization of material environmental corrosion observation and testing. Internationally, standardization organizations represented by ISO have established relatively mature and comprehensive systems for the standardization of material corrosion observation and testing; currently, more than 60 standards have been publicly published. Developed countries such as the United States have all established detailed material environmental corrosion testing standardization systems tailored to their own national conditions. Taking the United States as an example, organizations including the National Institute of Standards and Technology, the American Society for Testing and Materials (ASTM), the National Association of Corrosion Engineers (NACE), the American Society for Metals (ASM), and the Society of Petroleum Engineers (SPE) have jointly researched and formulated thousands of standards and specifications related to material corrosion and protection, creating a highly specific and well-developed standard system. Currently, there are over 800 active standards for atmospheric corrosion observation and testing of materials alone. All material environmental corrosion tests conducted by the U.S.-based Atlas Climate Services Group are carried out in accordance with standards set by ASTM, SAE, MIL, DIN, JIS, Nissan, and others. Therefore, through scientific and systematic management and the establishment and operation of various standard systems, natural environment exposure testing research can further enhance the authority and scientific rigor of environmental corrosion data for steel materials and their products.

2 Indoor Environmental Accelerated Corrosion Testing Technology

In natural environments, due to the long evaluation cycles required for assessing the failure of steel materials and the complex and variable influencing factors in field tests, relying solely on field testing methods cannot meet the demands of developing new steel materials or evaluating and predicting the corrosion life of these materials. Therefore, it is essential to establish accelerated corrosion testing techniques for steel materials, enabling the prediction of the long-term service behavior and service life of steel and its components under actual environmental conditions.

Both domestically and internationally, it is widely recognized that accelerated corrosion tests conducted in indoor environments cannot simply serve as a substitute for corrosion exposure tests conducted in natural environments. The evaluation criteria for laboratory-accelerated corrosion tests depend on the correlation between indoor and outdoor corrosion tests.

Due to its strong theoretical foundation, diverse environmental conditions, numerous influencing factors, and insufficient accumulation of data and case studies, the accelerated corrosion testing technology—with its good correlation between indoor and outdoor environments—has long been hindered in its development. Therefore, the development of new theories and technologies for the systematic evaluation of material environmental accelerated corrosion holds significant practical value and scientific importance, and represents one of the key research areas in the field of environmental testing technologies for steel materials. Below, we will introduce the development of indoor accelerated testing technologies for simulating corrosion in atmospheric, seawater, and soil environments, respectively.

Early indoor accelerated simulation methods for atmospheric corrosion primarily employed wet-heat testing, including the introduction of SO₂. ₂ , H ₂ S, CO ₂ Then, accelerated corrosion tests using simulated corrosive gases are conducted. In 1962, ASTM established three salt-spray test standards: the neutral salt-spray test, the acetate salt-spray test, and the copper chloride-acetate salt-spray test. Currently, the salt-spray test remains the most commonly used method for accelerating the simulation of atmospheric corrosion in marine environments. However, numerous experimental studies have demonstrated that the salt-spray test method can only serve as an artificial accelerated corrosion testing technique and does not adequately simulate environments containing chloride ions, such as marine atmospheres. Various single salt-spray tests exhibit poor simulative accuracy for atmospheric exposure, primarily because they lack a “wet-dry” cycling process. Under natural atmospheric conditions, the liquid film formed on specimens due to rain, fog, and other factors undergoes a periodic cycle of thickening and thinning, as well as wetting and drying. Therefore, some researchers have proposed a composite salt-spray test method incorporating periodic saltwater spraying with a drying phase. In 1980, Japanese researchers introduced a cyclic immersion-composite test method, which demonstrates excellent reproducibility in its accelerated simulation approach. Pourbaix employed this method to study atmospheric corrosion, subjecting specimens to periodic immersion in distilled water and NaHSO. ₃ or NaCl solution, respectively simulating atmospheric corrosion under accelerated rural, industrial, and marine conditions. The study shows that experiments lasting several weeks can be correlated with natural exposure lasting one year or longer.

In recent years, foreign scholars have combined tests such as cyclic spraying and cyclic immersion, giving rise to a variety of cyclic composite corrosion tests that incorporate multiple environmental factors. These tests not only enable the simultaneous control of temperature, relative humidity, dry-wet frequency, dry/wet alternation, and pollutants like SO₂, but also provide a more comprehensive assessment of material degradation under complex environmental conditions. ₂ , CO ₂ By controlling environmental factors such as pollutant concentration and wind speed, it is possible to simulate atmospheric corrosion under a variety of meteorological conditions and obtain data that closely resembles results from real-world atmospheric exposure tests. Currently, internationally, research on accelerated atmospheric corrosion simulation has shifted from focusing on single or a few environmental factors toward multi-factor, composite acceleration of corrosion. When conducting accelerated testing, the goal is not merely to mimic atmospheric corrosion phenomena per se, but rather to replicate the underlying mechanisms and fundamental principles governing atmospheric corrosion. For many years, the study of equivalent accelerated test environments for materials exposed to atmospheric conditions has received considerable attention from both academic and engineering communities at home and abroad. In particular, developed countries have carried out numerous highly effective studies on topics such as the impact of corrosive environments on the service life of equipment—including aircraft structures—methods for predicting service life in corrosive environments, corrosion control strategies for structural components, and laboratory techniques for accelerated corrosion testing using structural simulation specimens along with corresponding environmental spectra.

Using an indoor accelerated simulation test method and building on an extensive accumulation of corrosion data, the National Materials Environmental Corrosion Platform Comprehensive Research Center has, in light of actual field conditions—particularly the high-temperature, high-humidity, and high-salt-mist marine atmosphere of the Xisha Islands—developed a simulated solution that accurately reflects the atmospheric characteristics of the Xisha region. Based on this, the center designed a comprehensive indoor accelerated test method featuring cyclic immersion combined with salt-spray corrosion environments. Furthermore, it developed a series of atmospheric corrosion accelerated testing devices, including cyclic immersion corrosion chambers and micro-scale corrosive gas environment chambers, as well as simple and rapid electrochemical testing equipment and an electrolytic cell device capable of automatically controlling thin-film liquid thickness. The center also developed reference electrodes and other testing technologies suitable for electrochemical measurements in thin-layer solutions, thereby advancing research into atmospheric corrosion mechanisms. Building upon this systematic series of atmospheric corrosion accelerated testing technologies, the center conducted a comprehensive study on the real-world conditions of outdoor-exposed materials, influencing factors, grey relational analysis, environmental spectrum development, and indoor accelerated testing. As a result, a relatively systematic and reliable environmental spectrum-based accelerated testing methodology and a theoretical framework for life assessment have been established. These methods have since been widely adopted across various industries, including aerospace, aviation, electronics, and automotive.

The marine environment is one of the harshest natural settings for material corrosion. The real-sea corrosion coupon test is a reliable method for evaluating corrosion in marine environments; however, this test is time-consuming and costly. To obtain large amounts of experimental data in a shorter period, researchers have developed indoor simulated accelerated corrosion testing methods and evaluation techniques for marine environments. The author’s team has developed a series of new indoor simulated accelerated corrosion testing devices as well as accelerated testing devices that simulate the corrosive performance of materials in deep-sea environments, as shown in Figure 3. Furthermore, the team has conducted research on accelerated corrosion tests of materials under both shallow-sea and deep-sea environmental conditions.

Figure 3: Marine Corrosion Simulation Accelerated Testing Technology and Related Equipment Series

The indoor simulated accelerated corrosion testing apparatus for marine corrosion enables functions such as alternating dry and wet conditions, control of various corrosive gas environments, and simulation of different marine corrosion zones (marine atmospheric zone, splash zone, tidal zone, and fully immersed zone). It can simultaneously conduct indoor simulated/accelerated corrosion tests and electrochemical measurements under complex marine environmental conditions involving multiple factors, making it suitable for carrying out accelerated corrosion simulations of various metallic materials in marine environments within a laboratory setting.

Experiments have shown that the accelerated simulation test apparatus can replicate both multi-zone corrosion and marine erosion-corrosion behaviors in the ocean. As illustrated in Figure 3, the material corrosion-performance testing device for deep-sea environments utilizes a flow-circulation system to precisely control the physicochemical parameters of seawater, such as dissolved oxygen, temperature, pressure, and salinity. The pressure can be increased to over 50 MPa—equivalent to a depth of 5,000 meters when converted solely based on pressure. This apparatus realistically simulates the low-temperature and high-pressure conditions experienced by steel materials in actual deep-sea environments, thereby addressing several limitations of existing deep-sea testing methods, including long experimental data acquisition times, limited data types, and the inability of static高压釜 to accurately mimic real deep-sea environmental conditions. By using this apparatus, it is possible to gain insights into the corrosion behavior of typical metallic materials under various simulated deep-sea environmental conditions, such as different pressures and media characteristics. Figure 4 shows the surface corrosion behavior of X70 pipeline steel in simulated seawater environments at different depths.

(a) 0 m surface (b) 0 m inner rust (c) 860 m (d) 1,200 m

Figure 4: Macroscopic morphology photographs of X70 steel U-bend specimens after immersion under different simulated depth conditions.

The environmental factors influencing soil corrosion of steel materials are complex. Predicting the long-term corrosion behavior and service life of steel materials based on short-term accelerated corrosion test results has consistently been one of the major challenges in environmental corrosion testing and evaluation technologies. Currently, China has developed a series of equipment and evaluation methods for steel soil corrosion testing, including a soil corrosion simulation accelerated testing chamber as well as techniques for assessing and testing the susceptibility of grooves to corrosion. These methods and associated standards have been widely adopted in industry, thereby promoting the evaluation and development of new high-strength pipeline steels with enhanced corrosion resistance.

The National Materials and Environmental Corrosion Platform has selected representative soils from the Yingtan area and the Korla region as primary research objects. Additionally, soils from six other typical regions across China were chosen for comparative analysis, enabling an examination of the types of corrosion experienced by steel pipelines in these typical soil environments. By analyzing corrosion data from materials including Q235 steel, X70 steel, and X120 steel, corrosion evaluation indices for soils were established and differentiated from three perspectives: uniform corrosion, pitting corrosion, and stress corrosion. Utilizing the gray relational analysis model, combined with data correlation analysis techniques such as genetic algorithms, the following soil characteristics were identified as key indicators: soil resistivity, moisture content, soil pH value, soil texture, redox potential, pipe-to-soil potential, salt content, and Cl⁻ concentration. ^- As key environmental parameters influencing soil corrosivity, the content levels were used to establish a comprehensive evaluation method for soil corrosivity of buried steel pipelines based on these eight soil property indicators. Verified against existing data from eight national soil stations, the proposed method shows a high degree of correlation with actual data. Compared with foreign methods (DIN-50929 and ANSI A21.5), this method not only adopts an internationally recognized multi-indicator approach for assessing soil corrosivity but also addresses the shortcomings of practicality inherent in mainstream international standards, thereby enhancing both the practicality and accuracy of the multi-indicator approach for comprehensive soil corrosivity assessment.

3 Online Corrosion Monitoring and Big Data Evaluation Technologies

With the development of information technology, the United States proposed the “Materials Genome Initiative” in 2011. The concept of data sharing and the development of computational tools align closely with the material corrosion platform’s longstanding commitment to data sharing and its continuous advancement in simulation-based computational research. The book “Materials Corrosion Informatics,” published in 2014, along with related work, pointed out that the goal of the Materials Genome Initiative is to shorten the current materials development cycle from 20–30 years to just 2–3 years. This goal necessitates innovative breakthroughs in materials corrosion research—leveraging simulation computing and cross-data sharing to develop new, efficient, and reliable corrosion testing methods; establish new standards for classifying environmental severity; formulate novel multi-scale theories of corrosion behavior; and create advanced life-prediction models. Taking the monitoring, detection, and assessment of atmospheric corrosion of steel as an example, we briefly illustrate the research progress and applications of corrosion testing techniques combined with big-data evaluation technologies.

The corrosive degradation of metallic materials in the atmosphere is primarily caused by the alternating cycles of humid and dry climates. The corrosion process occurs because metals undergo electrochemical corrosion under thin liquid films. Thus, atmospheric corrosion not only follows the general principles of electrochemical corrosion but also exhibits its own unique characteristics. Currently, Atmospheric Corrosion Monitoring (ACM) instruments remain an important tool for studying atmospheric corrosion. These ACM instruments reflect the strength of atmospheric corrosivity based on the current signals generated by thin-film electrochemical cells. Among them, the ACM cell—a crucial component of the monitoring device—is designed according to the principle of galvanic corrosion, which is rooted in the fundamentals of corrosion electrochemistry.

The author has developed a multi-channel atmospheric corrosion monitoring device suitable for high-throughput data acquisition, as shown in Figure 5. This monitor can select multiple typical atmospheric environments to perform online monitoring of the corrosion degree of steel materials under different spatial and temporal conditions. The atmospheric corrosion probe reflects the intensity of atmospheric corrosion by measuring the current signal generated by an electrochemical cell beneath a thin liquid film. Based on the data obtained, a preliminary analysis is conducted to identify the primary environmental factors influencing atmospheric corrosion in different regions as well as the specific characteristics of their corrosive environments. The atmospheric corrosion probe can be customized in specifications according to the monitored space and operating conditions, making it particularly well-suited for tracking trends in changes in atmospheric corrosion levels.

Figure 5: ACM Detection Device

The ACM device application system adopts a B/S architecture and the Java language, supports cross-platform operation, and enables GIS map visualization. It can display and store real-time data on the overall environmental climate. The interface features dynamic, graphical instruments that visually present data from microclimate monitoring stations. Additionally, this device offers historical data query, chart-based output, and analytical capabilities for monitoring stations.

ACM monitoring technology based on big data from the internet enables intelligent monitoring of corrosion-related big data, addressing the shortcomings of traditional coupon testing—such as long design cycles, fragmented data, instability caused by the coupling of multiple environmental factors during data accumulation, and delays in data monitoring. This technology facilitates the comprehensive analysis of big data on corrosion environments (including temperature, humidity, chloride ion concentration, SO₂, etc.). ₂ Real-time intelligent and automated data collection—including parameters such as concentration and particulate matter content—as well as high-throughput computation and analysis in materials informatics, and real-time intelligent monitoring of corrosion processes—all these capabilities ultimately give rise to a steel-material service-data-sharing platform endowed with the characteristics of “corrosion big data.” Through this platform, online collection of corrosion data during the service life of steel materials, data analysis, processing, mining, and information management are realized, providing a new approach for the safe and healthy diagnosis of steel materials and their components, and further advancing corrosion protection technologies for steels used in island and reef environments.

4 Conclusion

Focusing on the urgent needs of national economic development and strategic planning, we continuously improve the methods for testing the environmental corrosion of steel materials under natural conditions. We also persistently collect corrosion data on steel materials and products in typical domestic and international natural environments, as well as in harsh and extreme environments (such as deep and distant seas, the Xisha and Nansha Islands, and the Arctic and Antarctic regions), thereby enriching and refining the database of environmental corrosion for steel products. Building on multi-cycle and long-term datasets, we further promote the integrated application and practical implementation of information technologies—including modeling, simulation, and knowledge discovery—to gain a deeper understanding and reveal the scientific laws and mechanisms underlying the environmental corrosion of steel materials. We are also working to refine and enhance the system of environmental corrosion evaluation standards for steel materials, aligning domestic research on natural environment corrosion testing with international practices. In doing so, we aim to contribute to improving the quality of steel products and strengthening China’s international competitiveness in the steel industry.