LCH Corrosion Sensors for CUI in Storage Tanks and Marine Applications
Corrosion can be caused by electrochemical changes (such as wall thinning, pitting, crevice corrosion, and galvanic corrosion), fluid erosion (such as impingement and erosion-corrosion), environmentally induced cracking (such as intergranular cracking, transgranular cracking, stress corrosion cracking [SCC], and hydrogen-induced cracking [HIC]), high temperatures, microorganisms, and mechanical loads (such as fretting and fatigue).
Prioritizing corrosion prevention followed by continuous monitoring of the interface region helps avoid economic losses. Monitoring systems for corrosion and insulation-layer leakage primarily utilize electrochemical detection technologies.
Electrochemical Noise (EN) is a passive technique used to detect localized corrosion behavior and assess corrosion rates at the interface under low-humidity conditions. (Note: This monitoring technology is not currently in use.)
Electrochemical Impedance Spectroscopy (EIS) is a powerful technique for studying a system's complex impedance; it is sensitive to changes in both surface phenomena and bulk material properties. Tafel polarization is an electrochemical technique used to investigate corrosion processes and rates.
The Electrical Resistance (ER) method is used to detect metal loss; it operates on the principle that corrosion causes an increase in electrical resistance.
Corrosion under insulation (CUI) involves reactions occurring beneath the insulation layer. Pipelines may be bare or protected by coatings (such as epoxy or metallic coatings). The primary causes of CUI include moisture ingress, differences in material potential, temperature gradients, and the presence of chlorides or other compounds at the pipe-insulation interface. Depending on insulation properties and environmental conditions, moisture may diffuse or become trapped, triggering corrosion reactions. The deposition of chlorides and other compounds on or near the pipe surface accelerates the corrosion process at the interface. Temperature gradients significantly influence corrosion under insulation; moisture tends to accumulate near the pipe when its temperature is low, whereas it migrates toward the outer layer of the insulation as the pipe temperature rises. Such temperature-cycling conditions degrade the performance of coating and insulation layers, thereby reducing overall thermal efficiency. We employ thin, multi-channel, flexible electrical resistance (ER) corrosion probes (insulated at the base with materials such as silicone or PTFE-graphite). To compensate for temperature-induced resistance variations, metal electrodes (e.g., carbon steel, aluminum) are arranged on a single plane; one side is covered with a corrosion-resistant material to prevent corrosion on that face, while the degree of corrosion is determined by the ratio of resistance values.
Storage tanks (whether underground or above-ground) are used globally to store various chemical compounds under suitable environmental conditions. Underground environments—including factors like soil resistivity—can initiate and accelerate corrosion processes. External corrosion occurs on the tank surface when the protective coating begins to deteriorate. We monitor coating degradation using Electrochemical Impedance Spectroscopy (EIS) and a dual-electrode ring sensor designed to simulate soil salinity-induced corrosion (dual-capacitance method).
Marine Vessels: Corrosion and corrosion fatigue are major causes of significant hull damage. Seawater properties—such as temperature, oxygen content, pH, corrosive minerals, and chloride levels—vary by location and depth. Atmospheric corrosion affects hull components not submerged in seawater, as the steel's passive layer cannot withstand these conditions. Seawater flow accelerates hull corrosion, and the distribution of cracks and corrosion depends on various environmental phenomena. Proper monitoring and repair of all damage and cracks are essential to prevent catastrophic failures; corrosion and fatigue monitoring are particularly critical for the structural integrity of bulk carriers and oil tankers. We utilize multi-channel EIS-based atmospheric corrosion sensors for monitoring.
