# Corrosion Monitoring Techniques in Subcritical and Supercritical Water Environments
###### Abstract  
A series of advanced equipment exposed to sub-/supercritical water environments at high temperatures, high pressures, and extreme water chemistry with high salt and dissolved oxygen content faces serious corrosion problems. Obtaining on-site corrosion data for typical materials in harsh environments is crucial for operating and maintaining related equipment and optimizing various corrosion prediction models. First, this article introduces the advantages and disadvantages, usage scenarios, and future development potential of several in situ monitoring technologies, including ultrasonic thickness measurement, the infrared thermography method, microwave imaging, eddy current detection, and acoustic emission. Considering the importance of electrochemical corrosion data in revealing microscale and nanoscale corrosion mechanisms, in situ testing techniques such as electrical resistance probes, electrochemical corrosion potential, electrochemical impedance spectroscopy, and electrochemical noise that can be applied to sub-/supercritical water systems were systematically discussed. The testing platform and typical data obtained were discussed with thick and heavy colors to establish a mechanical prediction model for corrosion behavior. It is of great significance to promote the development of corrosion monitoring techniques, such as breaking through testing temperature limitations and broadening the industrial application scenarios and maturity. corrosion; supercritical water; monitoring techniques; research platform +
Footnote †: journal: Applied Sciences  
participate in charge transfer reactions) [5]. In addition, metal pipelines are subjected to long-term high pressure, and nuclear power plants have been threatened with severe local corrosion damage, such as pitting corrosion and stress corrosion cracking, since their inception [5]. Statistics show that the atomic power events that have occurred globally so far are generally caused by localized corrosion. Additionally, ultra-supercritical plants have gradually replaced low-parameter units and become the primary thermal power plants. Due to the complexity of combustion conditions and gas-solid flow, high-temperature corrosion of water-cooled wall pipes is caused and influenced by various factors [6]. With the improvement of unit parameters and the modification of low NOx burners, the problem of high-temperature corrosion of water-cooled wall pipes has become more serious, which leads to a higher possibility of boiler pipe explosion [7]. On the other hand, corrosion is also a crucial factor affecting the safety of equipment and facilities in the exploration, extraction, transportation, and refining processes of oil and gas [8; 9; 10; 11]. The environment of oil and gas fields is complex and harsh, often characterized by high temperature, high pressure, high salinity, and high mineralization. In harsh subcritical water environments, oil pipes are prone to corrosion and even perforation, seriously affecting oil and gas wells' average production and operation. As an essential transportation system for underwater oil and gas development, the proportion of accidents caused by corrosion can reach 37%. Once oil and gas field pipelines in long-term service rupture or fail due to corrosion, it will cause substantial economic losses and safety hazards [12]. In addition to the energy field, supercritical water oxidation (SCWO) technology can efficiently and thoroughly degrade various high-concentration organic wastes, such as waste fluid, sludge, and hazardous solid waste, with broad application prospects. However, in SCWO treatment systems, the preheating and reaction initiation stages of the initial liquid or slurry materials and the cooling phase of the corresponding reaction products inevitably undergo transcritical water environments due to the predominant electrochemical corrosion [13; 1].