A variety of techniques are available for monitoring metal corrosion in electrolytes. However, only some of them can be applied in the atmosphere, in which case a thin discontinuous electrolyte film forms on a surface. Traditional and state-of-the-art real-time corrosion monitoring techniques include atmospheric corrosion monitor (ACM), electrochemical impedance spectroscopy (EIS), electrochemical noise (EN), electrical resistance (ER) probes, quartz crystal microbalance (QCM), radio-frequency identification sensors (RFID), fibre optic corrosion sensors (FOCS) and respirometry.
1. Introduction
The atmospheric corrosion of metallic materials has huge financial, environmental and cultural implications. In 2016, the Association for Material Protection and Performance (AMPP) published the International Measures of Prevention, Application, and Economics of Corrosion Technologies (IMPACT) report, which estimated the global cost of corrosion to be equivalent to 3.4% of the global Gross Domestic Product. They calculated that by using the available corrosion control techniques, it would be possible to save between 15 and 35% of the total corrosion cost [
1]. Alongside financial losses, undetected corrosion can cause sudden industrial and transport failures that may result in environmental catastrophes and hazards that endanger health and lives. Furthermore, corrosion is known to induce irreversible damage in, or even destruction of, unique cultural artefacts.
Atmospheric corrosion is a complex process of interaction between materials and the environment. Environmental corrosivity is dependent on various parameters, including relative humidity (RH), temperature (T) and air pollutant concentrations. Thus, understanding the corrosion of metallic materials requires detailed knowledge of these parameters and their effect on the underlying corrosion processes [
2]. The main tools used to assess environmental corrosiveness, corrosion progression, material corrosion behaviour and the effects of coatings and inhibitors, involve cumulative or real-time monitoring of corrosion rates and environmental parameters, and frequent equipment inspections. This review is focused on real-time corrosion monitoring, which we define as a long-term instantaneous measuring of parameters directly linked to corrosion loss.
Many real-time corrosion monitoring techniques have been developed for monitoring of metal corrosion in electrolytes. However, their applicability is limited under atmospheric conditions, under which a thin electrolyte layer is formed on a metallic surface. This limitation particularly relates to electrochemical methods that require a conductive connection between the electrodes. Modified electrochemical and non-electrochemical real-time corrosion monitoring techniques have been developed for use in both indoor and outdoor atmospheres. Such techniques are designed to meet the requirements of easy measurement and data interpretation, direct corrosion rate determination, rapid responses to changes in corrosivity and wide applicability in environments with different influences on corrosivity [
3]. In the last decade, these techniques have evolved, but no paper summarizing the developments has been published.
2. Comparison of Atmospheric Corrosion Monitoring Techniques
Studies applying the real-time atmospheric corrosion monitoring techniques described in the previous sections are summarised in Table 1 in terms of environments, sensing materials, ranges of detected corrosion rates and suitability for localised corrosion detection.
This entry is adapted from the peer-reviewed paper 10.3390/met12020171