Corrosion Mechanism of L360 Pipeline Steel Coated with S8 in CO2-Cl− System at Different pH Values

The corrosion behavior of L360 pipeline steel coated with or without elemental sulfur (S8) in CO2–Cl− medium at different pH was studied. An autoclave was used to simulate the working conditions for forming the corrosion scale, and an electrochemical workstation with a three-electrode cell was used to analyze the electrochemical characterization of the corrosion scale. A wire beam electrode was used to determine the potential and current distribution, and scanning electron microscopy and X-ray diffraction were used to characterize the morphology and composition of the corrosion scale. The results showed that the deposition of S8 on the surface of the electrodes caused serious localized corrosion, especially under acidic conditions. The morphology and localized corrosion intensity index further proved that the deposition of S8 significantly promoted corrosion, especially pitting corrosion. Finally, a novel corrosion mechanism of L360 pipeline steel coated with S8 in a CO2-Cl− environment under acidic conditions was proposed, and we then modeled the theoretical mechanisms that explained the experimental results.

Effect of Alternating Stray Current Density on Corrosion Behavior of X80 Steel under Disbonded Coating

In this paper, the effect of alternating stray current (AC) density on the corrosion behavior of X80 steel under disbonded coating was studied by electrochemical methods, wire beam electrode (WBE) technology, and surface observation technology. The results showed that under the interference of different AC densities, the corrosion potential of X80 steel under disbonded coating underwent negative deviation, and the degree of negative deviation increased with the increase of AC density. The corrosion current density of X80 steel under disbonded coating with the action of 0~100 A/m2 AC density had few differences. While the corrosion current density of X80 steel with the action of 200~300 A/m2 AC density increased and the corrosion current density was higher than that under low AC density. The cathode area of the wire beam electrode under disbonded coating is mainly distributed outside and the edge of the gap between disbonded coating and X80 steel, while the anode area is mainly distributed inside the gap.

EFFECTS OF TEMPERATURE ON MILD STEEL GRADIENT-DISTRIBUTED WBE IMMERSED IN 3.5 wt.% NaCl SOLUTION

To study the corrosion behavior of carbon steel in seawater at different temperatures, a novel electrochemical method called gradient-distributed wire beam electrode technique with high temporal and spatial resolution has been employed. This new wire beam electrode was prepared by three kinds of carbon steel with different carbon contents so that it can evaluate three materials simultaneously in the same corrosion medium (3.5[Formula: see text]wt.% NaCl solution) and improve the accuracy of tests results. After the gradient-distributed wire beam electrode soaked in 3.5[Formula: see text]wt.% NaCl solution for 8[Formula: see text]h, compared with measured at room temperature, the corrosion rate was accelerated greatly and polarity reversal of potential-current was also observed.

Chloride Diffusion and Induced Reinforcement Corrosion in Concrete with Fly Ash and Ground-Granulated Blast-Furnace Slag Exposed to Marine Submerged Zone1

This paper investigates the influence of mineral admixtures fly ash (FA) and ground-granulated blast-furnace slag (GGBS), the byproducts of industry, on chloride ions migration and corrosion resistance performance. A novel preparation method of wire beam electrode (WEB) was also introduced to explore the excellent corrosion-resistant capacity of concrete with mineral admixtures. By comparing concrete specimens with and without FA and GGBS, the test result of wire beam electrode, rapid chloride migration (RCM), and electrochemical tests highlight the positive impact of fly ash and GGBS against chloride ions migration, respectively. Concrete with fly ash and GGBS supplies an advanced protection effect of ordinary Portland cement; meanwhile, CO2 emission amount can be significantly reduced. Moreover, homemade wire beam electrode was proved to be a novel and reliable test method against corrosion, which has agreement with the test result of an electrochemical device.

USING WIRE BEAM ELECTRODE (WBE) TO EVALUATE THE CORROSION BEHAVIOR OF ND STEEL IN ACID MEDIUM

In this article, wire beam electrode (WBE) was used to evaluate the corrosion behavior of ND steel in environmental acid atmosphere with different partial pressure of CO2. Meanwhile, corrosion products and surface morphology analysis also used to support this research. The results showed that the corrosion behavior began from the edge of droplet in dew point corrosion, and gradually spread to the center of it. The spread speed would be increasing with CO2 partial pressure enhance, which was 24h in 5% CO2 and 4h in 50% CO2. Corrosion current density in the edge of droplet can form the “cathode-anode-cathode ring” structure and disappears gradually as the corrosion time was going. Corrosion morphology observation results showed three ring shapes region and different elemental composition of different corrosion products, which is correspondence with the “cathode-anode We-cathode ring” structure measured in WBE experiments. The results showed that the reaction gradually transferred to the uniform corrosion on electrode surface when the dew point corrosion reaction reaching the late stage. It comes from the dissolution, diffusion and reaction of gaseous corrosion medium of CO2 and O2.

NOVEL TYPE OF GRADIENT-DISTRIBUTED WIRE BEAM ELECTRODE MEASURED IN 3.5 wt.% NaCl AND ITS APPLICATION IN FAST DETECTION TECHNIQUE

In this paper, the electrochemical performance of a novel gradient-distributed wire beam electrode (WBE) is measured in different corrosion medium. This electrode contains three kinds of carbon steel with different carbon content. WBE was consisted of 100 carbon steel wires and regularly prepared into a [Formula: see text] matrix. The carbon steel wires for each row is the same, but the adjacent rows are different. The electrochemical corrosion behavior of regions with different carbon steel wires can be tested clearly. The results revealed that the heterogeneity of local corrosion of metal, which can be well studied by WBE, meanwhile, the phenomenon of polarity reversal can also be detected. Corrosion potential–current distribution map of the novel WBE showed obvious striped features when immersed in 3.5[Formula: see text]wt.% NaCl solution with different pH (pH[Formula: see text]2, 6 and 12). Corrosion firstly occurred in the high carbon steel region in the acidic conditions, and then quickly spreads to other areas, eventually causing the entire surface of the WBE to be corroded. While in the neutral salt solution, only the regions of high carbon steel and some part of medium carbon steel area appeared obvious anode currents during a long time testing. When the pH of corrosive solution reached to 12, the corrosion rate is greatly reduced and then corrosion process is suppressed. This new method can evaluate the corrosion resistance of materials more accurately.