Assessing the corrosion protection property of coatings loaded with corrosion inhibitors using the real-time atmospheric corrosion monitoring technique

The atmospheric corrosion monitoring(ACM)technique has been widely employed to track the real-time corrosion behavior of metal materials.However,limited studies have applied ACM to the corrosion protection properties of organic coatings.This study compared a bare epoxy coating with one containing zinc phosphate corrosion inhibitors,both applied on ACM sensors,to observe their corrosion protection properties over time.Coatings with artificial damage via scratches were exposed to immersion and alternating dry and wet environments,which allowed for monitoring galvanic corrosion currents in real-time.Throughout the corrosion tests,the ACM currents of the zinc phosphate/epoxy coating were considerably lower than those of the blank epoxy coating.The trend in ACM current variations closely matched the results obtained from regular electrochemical tests and surface analysis.This alignment highlights the potential of the ACM technique in evaluating the corrosion protection capabilities of organic coatings.Compared with the blank epoxy coating,the zinc phosphate/epoxy coating showed much-decreased ACM current values that confirmed the effective inhibition of zinc phosphate against steel corrosion beneath the damaged coating.

Preparation and Properties of Embeddable Ag/Ag Cl Gelling Reference Electrode for Rebars Corrosion Monitoring in Concrete

Reference electrodes are a key part for corrosion monitoring and measurement of rebars in concrete. A reference electrode that can be buried in concrete is fabricated by using Ag/Ag Cl electrode and methyl cellulose gelling electrolyte. The stability, repeatability and anti-polarization of the reference electrode are investigated; the influences of the inner electrolyte loss, exterior OH- contamination, and temperature on the potential of the reference electrode are also investigated in this paper. The results show that the reference electrode has good stability, repeatability, and antipolarization. The influences of inner electrolyte loss, exterior OH- contamination, and temperature on the potential of the reference electrode are minimal. Therefore, it can be used for corrosion monitoring and measurement of rebars in concrete.

Atmospheric Corrosion Monitoring of Field-exposed Q235B and T91 Steels in Zhoushan Offshore Environment Using Electrochemical Probes

This work aimed to in-situ monitor the atmospheric corrosion of steels exposed to Zhoushan offshore environment by using electrochemical noise（EN） technique. A portable EN monitoring system was established and two electrochemical probes（named as Q235 B and T91） were designed. Experimental results indicated that the noise resistance of T91 steel was higher than that of Q235 B steel, revealing that the corrosion resistance of T91 was higher than that of Q235 B. A 60-day monitoring result indicated that the noise resistance was well correlated with the weight loss data. Wavelet analyses results of EN data indicated that Q235 B underwent uniform corrosion and T91 suffered from localized corrosion, which was further confirmed by the surface observation. It is concluded that EN can be used as a new method to identify the corrosion form and corrosion resistance in atmospheric conditions.

Understanding environmental impacts on initial atmospheric corrosion based on corrosion monitoring sensors

Atmospheric corrosion monitoring(ACM)sensors were employed to study the initial atmospheric corrosion of carbon steels over a one-month period in six outdoor dynamic atmospheric environments in China.Based on the~250,000 corrosion data sets collected,the environmental impacts of relative humidity,temperature and rainfall on the initial corrosion behavior of carbon steels were investigated.The results showed that rainfall was the strongest environmental factor influencing the initial atmospheric corrosion rate.Relative humidity significantly influenced the corrosion of carbon steels in low-precipitation environments and non-rainfall period.

Long-term Field Corrosion Monitoring in Supporting Structures of China Xiamen Xiangan Subsea Tunnel

Xiamen Xiangan Subsea Tunnel is the first undersea tunnel constructed in China. It has become the major undersea pathway connecting Xiamen Island and Xiangan District since its operation in 2010. The total length is 6.05 km with the undersea length of 4.2 km. In an effort to onsite-monitor reinforcement corrosion in concrete structures, the commercially available CorroWatch multiprobe sensors and ERE-20 reference electrodes were pre-embedded in the selected locations and positions of supporting structures during the tunnel constructions. The real-time data have been collected annually by onsite measurements for 6 years. In this paper, the feasibility of the onsite corrosion monitoring system and suitability of the measured parameters including corrosion current, potential and temperature are discussed based on the preliminary results. The measured typical cyclic-type variations in corrosion current and temperature with monitoring time might be related to the seasonal changes during the annual routine measurements. The widely scattered corrosion potentials that are fluctuated complicatedly reflected localized differences in the vicinity of rebar and concrete. These findings, along with the progressively ongoing research, will provide valuable information in structural durability for service life prediction of reinforced concrete structures exposed to marine environments.

Comparative investigation on copper atmospheric corrosion by electrochemical impedance and electrical resistance sensors

Electrochemical impedance(EIS)and thin electrical resistance(ER)sensors were invented for atmospheric corrosion measurement of copper(Cu)during cyclic wetting−drying/high−low temperature tests and field exposure tests.Three-month field exposure results showed that average corrosion rate of Cu measured by ER sensor was well in accordance with that by weight loss method.During cyclic wetting−drying test,EIS was proven to reflect sensitively time of wetting and drying on the surface of sensor.Although corrosion rate obtained from EIS had a similar tendency to that obtained from ER sensors,the former was more dependent on environmental humidity than the latter.When relative humidity was low than 60%,corrosion rate of Cu measured by EIS was much lower than that by weight loss method,mainly attributing to the fact that impedance sensor failed to detect corrosion current of interlaced Cu electrodes due to the breakdown of conductive passage composed of absorbed thin liquid film under low humidity condition.Promisingly,ER sensor was proven to be more suitable for atmospheric corrosion monitoring than electrochemical techniques because it could sensitively monitor thickness loss of Cu foil according to the Ohmic law,no matter how dry or wet the sensor surface is.

On-line Monitoring of Epoxy Resin Exposed to Acid Solution

In this study, a new on-line health monitoring technology for the determination of the penetration of environment solution into epoxy resin was pursued. A corrosion sensor including plastic optical fiber and pH indicator was fabricated. The color-change layer of this sensor appeared after immersion in sulfuric acid solution, which could be examined by using optical fiber and spectrophotometer. The results showed that the penetration of sulfuric acid was detected by adding bromophenol blue （BPB） in the corrosion sensor. This system could be applied to on-line health monitoring of chemical equipment structures.

Portable 4-Channel Electrochemical Noise Test System

A portable 4-channel electrochemical noise(EN) test system with high precision was developed.The modular instrument cRIO was used as its core and the signal conditioning module included zero resistance ammeter(ZRA),fly line,screening box and shielded wire.The EN data were acquired from two Q235 carbon steel specimens placed in 0.5 mol/L H2SO4 solution and 0.1 mol/L NaCl solution.The experimental result shows that this system can achieve an accuracy of 10 pA and 10 μV,and it can be applied to on-site multi-channel EN test.

Research on acoustic emission monitoring of pitting corrosion on 304 stainless steel

In order to study acoustic emission （AE） characteristics of pitting corrosion on 304 stainless steel under higher than normal temperature, pitting corrosion process of 304 stainless steel in 6° ferric chloride solution at 70° was monitored by AE technology. Conventional parameter-based approach and signal-based analysis were combined to deal with recorded AE signals, and micrographic observation was performed for further verification. The results showed that AE hit and energy increased gradually with time and reached the peak at certain time, and then declined and maintained a stable condition. Signal waveform was mainly composed of low-frequency （〈 100 kHz） flexural wave with larger amplitude and energy and high-frequency （〉 100 kHz） expansion wave with lower amplitude and energy. The research results have some certain significance for AE monitoring of pitting corrosion on 304 stainless steel under higher than normal temperature.

Electrochemical measurements used for assessment of corrosion and protection of metallic materials in the field:A critical review

Corrosion degradation is detrimental to metal structures as it shortens their lifetime and leads to huge economic losses and unexpected disasters.Therefore,the detection and monitoring of corrosion degradation is of great importance.Herein,we briefly review the state-of-the-art electrochemical methods,instrumentation(based on virtual instrumentation),and advanced sensor/probes that are used in the field for the assessment of corrosion damage.Typical corrosion monitoring results,some of which have been obtained at Tianjin University in the past 30 years,for metallic materials and organic coating/metal systems in atmospheric,marine,and soil conditions in the field are presented.Detection methods,data analysis,and theoretical and mathematical models regarding each corrosion system are discussed,and the challenges,problems and possible solutions for each case are suggested.Lastly,future developments,such as wireless,intelligent,and automatic electrochemical measurement,that will augment the present electrochemical methods of evaluating corrosion degradation are summarized.

Experimental and finite element analyses on the corrosion of underground pipelines

Underground pipelines, on which a city relies for survival and development, have become an important part of lifeline engineering. Underground pipelines are utilized for conveying liquid, gas or loose solid, pipeline leakage and damage occasionally resulting from corrosion. Corrosion monitoring of underground pipelines is aimed at ensuring their normal operation and preventing loss of life and property. In this paper, a new method to monitor corrosion of pipelines has been proposed to solve the mentioned problem. Under the influence of internal pressure and corrosion, the pipeline wall becomes thinner and the circumferential deformation increases. The method is to indirectly investigate pipeline corrosion by monitoring the circumferential deformation. Numerical simulation confirms that the circumferential strain curve of the pipeline wall measured by using the proposed method to describe the corrosion is feasible. The proposed method provides a new way for real-time and long-term monitoring and management of underground pipelines.