Severe General Corrosion Research Articles

Corrosion resistance and corrosion interface characteristics of Cr-alloyed rebar based on accelerated corrosion testing with impressed current

This study investigates corrosion resistance and corrosion interface characteristics of novel Cr-alloyed steel rebar in mortar using electrochemical measurements, X-ray computed tomography (X-CT) scanning, and X-ray photoelectron spectroscope (XPS) analysis. Impressed constant current corrosion (ICCC) test was performed on alloyed steel rebar-mortar (ASRM) sample and carbon-steel rebar-mortar (CSRM) sample in a chloride-contaminated environment. After 5 days of ICCC test, alloyed steel rebar suffered a certain degree of localized corrosion with limited corrosion product, while the carbon-steel rebar presented severe general corrosion. Electrochemical tests demonstrated that the ASRM sample exhibited more than ten times in Rct value of the electrochemical impedance spectroscopy test and only about 0.46% in corrosion current density of the potentiodynamic polarization test compared to the CSRM sample. The above results revealed the excellent passivation performance and corrosion resistance of the ASRM sample, which is attributed to the formation of the stable composite passive film containing Cr/Fe oxides and hydroxides.

Effect of Temperature and Composition on Corrosion Behavior of Medium Cr Steel in a Salt Solution Containing CO2

In this paper, the corrosion behavior of three kinds of medium Cr low C steels in the simulated service environment of the transport pipeline was investigated through accelerated corrosion experiments, and the corrosion resistance mechanism of these experimental steels at different temperatures was investigated by electrochemical means. Finally, the reasons for the difference in corrosion behavior were analyzed from the grain boundary and surface Volta potential. The results show that as the temperature rose, the corrosion rate of the 5Cr specimen increased sharply and the corrosion type developed from slight general corrosion to severe general corrosion. The 7Cr specimen was less sensitive to temperature, and the type of corrosion changed from slight general corrosion to local corrosion. Finally, the 9Cr specimen was not sensitive to temperature, and the type of corrosion was always local corrosion. 5Cr steel could form a protective product film at 30°C. As the temperature rose, the protective ability of the product film decreased, and the matrix dissolved easily. The film of 7Cr and 9Cr samples had not yet precipitated and the matrix was difficult to dissolve at 30°C. However, the matrix dissolved easily at 50°C, and the product film had formed, which played a major role. At 70°C, the protective effect of the product film decreased, and the gap between the 7Cr and 9Cr samples began to appear. The increase of Cr content helped to refine grains and increased the proportion of low-angle grain boundaries. At the same time, the increase of Cr element helped to increase the maximum Volta potential of the experimental steel and increased the Volta potential difference. As a result, the test steel was shown to be resistant to uniform corrosion, but it also increased the risk of pitting corrosion.

Influence of SO2 on the corrosion and stress corrosion cracking susceptibility of supercritical CO2 transportation pipelines

The impacts of SO2 on corrosion and stress corrosion cracking (SCC) of supercritical CO2 (s-CO2) pipeline steels are unclear because of limited field operation experience and somewhat controversial reported results. Comprehensive literature review and corresponding tests in the s-CO2 streams from advanced oxy-fuel plants were performed to fill significant knowledge gaps. The presence of SO2 leads to severe general corrosion but does not initiate SCC of the steels in H2O-saturated s-CO2. SO2 induced corrosion is likely dominated by electrochemical reactions. It is necessary to control H2O% < 2000 ppm and SO2% <100 ppm to avoid potential catastrophic disaster.

Critical water content for corrosion of X65 mild steel in gaseous, liquid and supercritical CO2 stream

CO2 could be transported by pipelines in gaseous, liquid or supercritical phase depending on the operating temperature and pressure. Safety concerns might arise from CO2 transportation pipeline, especially crossing the densely populated areas. Water content is critical to understand corrosion mechanism of CO2 pipeline. Corrosion behavior of API 5L X65 mild steel exposed to CO2 environment with different relative humidity (RH), temperature and pressure was investigated by weight-loss and surface analysis techniques to determine critical water content in gaseous, liquid and supercritical CO2 stream. Surface morphology of coupons and composition of corrosion product layers were analyzed by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). Results showed that general corrosion rates remained steady with the increasing of RH before a separate water phase was observed, and it experienced a remarkable increase in free water for all test conditions. Localized corrosion or severe general corrosion was observed when the relative humidity was beyond 60% at 25 °C and 35 °C, 8 MPa and 80% at 35 °C, 4 MPa. The critical water content in CO2 stream was determined to be 60% RH for liquid and supercritical and 80% RH for gaseous CO2 transportation due to the safety concern of X65 pipeline on the basis of corrosion study.

Corrosion Behavior of X70 Mild Steel during Transportation of Gaseous- and Supercritical-CO2 Fluids

The corrosion behavior of X70 mild steel was investigated in the case of water deposited in CO2 pipeline by means of weight loss method and scanning electron microscopy (SEM). Results showed that general corrosion rate of X70 steel decreased with the increase of CO2 pressure from 4 to 12 MPa at 35 ℃. FeCO3 film and severe general corrosion was observed at 4 MPa, while thin and discontinuous corrosion product and serious pitting corrosion attack were found under other CO2 pressure conditions. It is of great corrosion risk to transport CO2 in gaseous or supercritical sta- tus for X70 mild steel if free water is formed in the pipeline.

Corrosion behaviour of 316L stainless steel and anti-corrosion materials in a high acidified chloride solution

The corrosion behaviour of a type 316L (UNS S31603) stainless steel (SS) expansion joint in a simulated leaching solution of sediment on blast furnace gas pipeline in a power plant is investigated by using dynamic potential polarization curves, electrochemical impedance spectroscopy (EIS), optical microscope, atomic force microscope (AFM) and Scan Kelvin Probe (SKP). Severe general corrosion accompanied by pitting corrosion occurs on the type 316L SS surface in this solution. As the immersion period increases, the charge transfer resistance Rct decreases, the dissolution rate accelerates, the surface roughness increases and the surface potential difference enhances significantly. Then eight corrosion-resistant materials are tested, the corrosion rates of type 254SMo SS, type 2507 SS and TA2 are relatively minor in the solution. The corrosion resistance properties of TA2 is most excellent, indicating it would be the superior material choice for blast furnace gas pipeline.

Degradation of the Mechanical Strength of Al Alloys by Electrochemically Introduced Hydrogen

The high strength Al alloys, 7N01, 6061 and 5083, were examined using slow strain rate testing in chloride-containing acid to neutral solutions under potentiostatic control. Large amounts of hydrogen absorption occurred at potentials above the breakdown potential. In this potential range, the mechanical strength of the alloys is degraded manly by severe general corrosion but hydrogen embrittlement may also occur. On the other hand, polarisation at more negative potentials where there is intense hydrogen evolution does not necessarily lead to a large amount of hydrogen entry except for the case of the alloy 5083, which suffered from hydrogen embrittlement induced by hydride formation around precipitates.

Corrosion behavior of 2195 and 1420 Al-Li alloys in neutral 3.5% NaCl solution under tensile stress

The corrosion behaviors of 1420 and 2195 Al-Li alloys under 308 and 490 MPa tensile stress respectively in neutral 3.5% NaCl solution were investigated using electrochemical impedance spectroscopy(EIS) and scanning electron microscope(SEM). It is found that the unstressed 1420 alloy is featured with large and discrete pits, while general corrosion and localized corrosion including intergranular corrosion and pitting corrosion occur on the unstressed 2195 alloy. As stress is applied to 1420 alloy, the pit becomes denser and its size is decreased. While, for the stressed 2195 alloy, intergranular corrosion is greatly aggravated and severe general corrosion is developed from connected pits. The EIS analysis shows that more severe general corrosion and localized corrosion occur on the stressed 2195 Al-Li alloy than on 1420 Al-Li alloy. It is suggested that tensile stress has greater effect on the corrosion of 2195 Al-Li alloy than on 1420 Al-Li alloy.

ＤＧＡを用いたＣＯ２除去ユニットにおけるＦｅ／Ｎｉ基合金の腐食挙動とその電気化学的解析

The SUS304 stainless steel has experienced severe general corrosion in the CO2 removal units using diglycolamine (DGA), which were located in Niigata prefecture in Japan. For the purpose of selecting suitable corrosion-resistant materials, sample specimens of 15 Fe/Ni-base alloys were installed in the units for about three months. The crrosion behavior of Carpenter, SUS 304, 13Cr alloys and Cr, Cu, Ni was investigated in a 5.0M DGA solution in the laboratory using potentiodynamic polarization and impedance measurements under 4.5MPa CO2 at 100°C. The results of the electrochemical measurements in the laboratory agreed with the test results obtained in the actual units in tendency. The results showed that the corrosion resistance of Fe/Ni-base alloys in the CO2-loaded highly concentrated DGA solution mainly depended on the Cr content of the alloys, because the DGA-carbamate seemed to form soluble chelate compounds with Cu2+, Ni2+ and Fe2+, but not with Cr3+. In the CO2 removal units, a Ni-Cu alloy corroded severely, but the Fe/Ni-base alloys, of which Cr content was higher than 21% or 22%, showed excellent resistance.

Cracking Behavior of a Cu-Mn Weld Alloy in Phosphoric Acid at 288°C

The cracking behavior of a Cu-2Mn weld alloy in concentrated phosphoric acid-alcohol solutions in the temperature range 249 to 304°C has been investigated using the slow strain rate test technique. Moderate amounts of air ingress in the acidic environment was found to produce intergranular cracking in the alloy. Excessive amounts of air produced severe general corrosion and minor cracking. The results have been used to determine the cause of cracking that occurred in the alcohol reactors that were lined with copper and welded with ISA-13 alloy.

Corrosion morphology of copper in dilute sulphate, chloride, and bicarbonate solutions

Abstract The corrosion behaviour of copper was studied in dilute solutions of sulphate, chloride, and bicarbonate anions as well as in solutions containing mixtures of these anions at concentrations similar to those encountered in soft tap water. During potentiostatic anodic polarisation, a relatively large current was produced in the sulphate containing solutions, while a very small current was generated in other environments. The difference in behaviour was attributed to the effect of the anions on the characteristics of the oxide scale and the mode of corrosion attack. A highly porous oxide scale was formed in the sulphate solution. Severe general corrosion, more intensive at grain boundaries, occurred below the scale. The scalesformed in the chloride and bicarbonate solutions were relatively smooth and well compacted. Hemispherical pits developed in the chloride solution underneath a layer of cuprous oxide and chloride crystals. Only bare metal and grain boundaries werefound beneath the scaleformed in...

Electrochemical behavior of some commercial dental amalgams in artificial saliva.

Cathodic, linear anodic, and anodic polarization studies conducted on three commercial dental amalgams, Caulk Fine Cut Alloy, Spheralloy, and Dispersalloy, showed that all amalgams were in a passive state at the corrosion potential in synthetic saliva solution. The corrosion currents at the corrosion potential were therefore small for all the amalgams, in the range 0.08 to 0.30 muA/cm2. However, the Caulk Fine Cut Alloy and Spheralloy amalgams exhibited a breakdown of passivity and high anodic currents at potentials only approximately equal to 100 mV more noble than the corrosion potential whereas Dispersalloy amalgams maintained passivity at potentials up to 700 mV more noble than the corrosion potential. The breakdown of passivity in Caulk Alloy and Spheralloy amalgams is attributed to the presence of the gamma2 phase (Sn7-8Hg) whereas the passive behavior of Dispersalloy amalgam is attributed to the absence of the phase. It is concluded that none of the amalgams will exhibit severe general corrosion in use, but that both Caulk Alloy and Spheralloy amalgams will exhibit pitting corrosion whereas this type of corrosion should be minimal in Dispersalloy amalgams.

Study on the Stainless Steel Used for Fractionator in Crude Oil Distillation Unit

The environment is highly corrosive in the top section of fractionator in the crude oil distillation unit. SUS27 (18-8 steel) was failured due to stress corrosion cracking in 3 months and SUS38 (13Cr-Al steel) due to severe general corrosion. Corrosion resistance of typical austenitic and ferritic stainless steels and the developed 17Cr-Mo steel were compared in such an environment. Then, corrosion resistance of these steels in a few mineral acid solutions and of their weld joints were compared in laboratory.The results were as follows:(a) In the top section of fractionator, 17Cr-Mo steel (containing 0.5-2%Mo) is most resistant to general or pitting corrosion and/or stress corrosion cracking.(b) In laboratory tests, 17Cr-Mo steel shows the lowest corrosion rate in hydrochloric acid solution of 0.1% concentration or less.(c) Austenitic steel containing Mo also shows low corrosion rate in dilute hydrochloric acid solution, but it appears to be susceptible to stress corrosion cracking in dilute hydrochloric acid solution saturated with hydrogen sulfide, judging from test results with SUS27 (18-8).(d) Weld joint of 17Cr-Mo steel is resistant to corrosion as well as the base sheet or plate itself.

沸騰伝熱条件下におけるボイラ蒸発管のアルカリ腐食

Some alkaline solutions were boiled in boiler tubes under heat transfer at 350°C, and corrosion characteristics of the tubes were observed. Local corrosion developed at the lower part of the tubes, and no corrosion was observed in the upper part, owing to the rinsing action of bubbles from the lower part. Sodium hydroxide was the most aggressive among the three reagents tested for the tube surface under the deposit. Corrosion characteristic changed from pitting corrosion to severe general corrosion with increasing thickness of the deposit. Sodium phosphate seemed to be least corrosive if it does not thickly precipitate on the wall. The mill-scale and the rust had almost no influence on corrosion by themselves. It was, however, important for corrosion that they detached from the wall and deposited at the stagnant spots, where local corrosion occurred under the heat transfer. The surface scratch had no effect on corrosion in sodium phosphate solution and also in potassium phosphate solution. In case of sodium hydroxide solution, local corrosion occurred at the scratches under the heat transfer when their depths were more than 0.3mm. The deposit formed by hideout of sodium phosphate solution was also examined.