Effect of Material Factors on FAC Rate and Characteristics of Oxide Layer

2010 ◽  
Author(s):  
Yutaka Watanabe ◽  
Hiroshi Abe ◽  
Takamichi Miyazaki
Keyword(s):  
Oxide Layer ◽  
Defect Density ◽  
Carbon Steels ◽  
Metal Interface ◽  
Accelerated Corrosion ◽  
Cr Content ◽  
Transmission Electron ◽  
Scale Characteristics ◽  
Cr Concentration ◽  
Flow Accelerated Corrosion

Combined effects of Cr content and pH on corrosion rate of carbon steels due to flow accelerated corrosion have been examined by experiments and their relation to oxide scale characteristics based on detailed oxide layer characterizations using transmission electron microscope with X-ray analyzer have been discussed. Effect of Cr content on FAC mitigation decrease continuously as pH is increased from neutral to 10.4 and effect of pH on that increase significantly from pH 9.1 to 9.4. Obvious Cr enrichment has been observed in the oxide layer of 1.01 wt% Cr content steel regardless pH condition. Cr concentration is highest at top surface of oxide layer, and that decrease from surface to oxide / metal interface gradually. It has been suggested that Cr enrichment stabilize oxide layer (decrease solubility and defect density of oxide layer), as a result, FAC suppressed.

Effects of Cr Content and Environmental Factors on FAC Rate of Carbon Steels

2009 ◽  
Author(s):  
Yutaka Watanabe ◽  
Kiwamu Sue ◽  
Hiroshi Abe
Keyword(s):  
Environmental Factors ◽  
Removal Rate ◽  
Carbon Steels ◽  
Strong Impact ◽  
Oxide Compound ◽  
Accelerated Corrosion ◽  
Cr Content ◽  
Ph Dependency ◽  
Order Of Magnitude ◽  
Flow Accelerated Corrosion

Combined effects of Cr content and environmental factors, pH and dissolved oxygen concentration, on removal rate of carbon steels due to flow accelerated corrosion have been examined by experiments. The effects of environmental factors on FAC rate have been attempted to interpret based on oxide solubility, which has been precisely evaluated by separate experiments and numerical estimations. pH dependency of the FAC rate has been found to be directly related to solubility of magnetite. Cr content holds a strong impact on the FAC rate regardless of pH values from 6.84 to 10.4. Addition of 1% Cr to a carbon steel reduces the FAC rate by one order of magnitude under the environmental conditions, where magnetite forms. Addition of oxygen up to 1200ppb changes the oxide from magnetite to hematite, resulting in significant improvement in corrosion resistance. Oxide film characteristics, e.g. compositional distributions and types of oxide compound, have been also examined and their correlation to the FAC rate has been discussed.

Evaluation of Wall Thinning Rate Due to Flow Accelerated Corrosion With the Coupled Models of Electrochemical Analysis and Double Oxide Layer Analysis

2009 ◽  
Author(s):  
Masanori Naitoh ◽  
Shunsuke Uchida ◽  
Yasushi Uehara ◽  
Hidetoshi Okada ◽  
Seiichi Koshizuka
Keyword(s):  
Oxide Layer ◽  
Electrochemical Analysis ◽  
Anodic Current Density ◽  
Coupled Models ◽  
Accelerated Corrosion ◽  
Double Oxide ◽  
Wall Thinning ◽  
Layer Analysis ◽  
Flow Accelerated Corrosion ◽  
Thinning Rate

Systematic approaches for evaluating flow accelerated corrosion (FAC) are desired before discussing application of countermeasures for FAC. Future FAC occurrence should be evaluated to identify locations where a higher possibility of FAC occurrence exists, and then, wall thinning rate at the identified FAC occurrence zone should be evaluated to obtain the preparation time for applying countermeasures. Wall thinning rates were calculated with the coupled models of static electrochemical analysis and dynamic double oxide layer analysis. Anodic current density and electrochemical corrosion potential (ECP) were calculated with the electrochemistry model based on an Evans diagram and ferrous ion release rate determined by the anodic current density was applied as input for the double oxide layer model. The thickness of oxide layer was calculated with the double oxide layer model. The dependences of mass transfer coefficients, oxygen concentrations ([O2]), pH and temperature on wall thinning rates were calculated with the coupled model. It was confirmed that the calculated results of the coupled models resulted good agreement with the measured ones. The effects of candidates for countermeasures, e.g., optimization of N2H4 injection point into the feed water system, on FAC mitigation was demonstrated as a result of applying the model.

scholarly journals Effect of Drum Pressure on Flow Accelerated Corrosion in Gas Fired Combined Cycle Power Plant: A Case Study and Literature Review

2019 ◽  
Vol 2 ◽  
pp. 17-27
Author(s):  
Ujjal Kumar ◽  
Chamely Khatun ◽  
Md Sakinul Islam ◽  
Nhol Kao ◽  
Fazle Rabbi ◽  
...  
Keyword(s):  
Power Plant ◽  
Oxide Layer ◽  
Control Valve ◽  
Combined Cycle ◽  
Protective Oxide ◽  
Accelerated Corrosion ◽  
Protective Oxide Layer ◽  
Flow Accelerated Corrosion ◽  
Water Turbulence

The dissolution of ferrous ions from the protective oxide layer and/or base metal by corrosion with the assistance of turbulent flow is called flow accelerated corrosion (FAC). Flow accelerated corrosion is the most common and continuous corrosion reaction in combined cycle power plants (CCPP). Heat recovery steam generator (HRSG) drum pressure fluctuation and/or turbulent drum water greatly influences the FAC of drum and economizer. This kind of FAC was investigated in the low-pressure drum (LPD) and low-pressure economizer (LPE) of a 210 MW gas-fired combined cycle power plant (Four-unit HRSG & GT) with an air-cooled condenser (ACC). Severe FAC was observed due to the fluctuation of pressure in the LPD with respect to time. As a result, huge amounts of soluble iron (Fe2+) and insoluble (Fe3+) was found in all running HRSG’s LPD water. Due to pressure fluctuations in the LPD, a protective oxide layer (mostly magnetite), as well as the base metal, were corroded from the LPD and LPE even after carefully maintaining recently developed water cycle chemistry in this CCPP. Severe leakage was found in the LPE due to corrosion. The actual reason for the problem was found to be a malfunctioning steam-control valve in the turbine unit’s LP system. This valve was malfunctioning by suddenly opening to 100% and then closing to around 10% continuously. This malfunction creates enormous pressure drops in both the LPD and LPE units. It is understood that water turbulence is the main cause of FAC affecting the LDP and LPE. This assessment is based on chemical laboratory analysis and physical inspection. There was no non-destructive testing (NDT) performed in this study. The severe FAC happened in four days and for this reason, HRSG and steam turbines were shut down. Maintenance work on the control valve and flushing of the LPD and LPE successfully resolved the FAC problem. One week later, LPE leakage was found on the unit-3 HRSG and as reported in this study this was also found to be the result of FAC. From this case study, it is concluded that not only water quality but also water turbulence can create severe FAC problem.

A233 Relationship between thinning rate of carbon steels due to flow-accelerated corrosion and characteristics of oxide films formed

2015 ◽  
Vol 2015.20 (0) ◽  
pp. 205-208
Author(s):  
Takuma YANO ◽  
Hiroshi ABE ◽  
TAKAMICHI Miyazaki ◽  
Yutaka WATANABE ◽  
Kazutoshi FUJIWARA ◽  
...  
Keyword(s):  
Oxide Films ◽  
Carbon Steels ◽  
Accelerated Corrosion ◽  
Flow Accelerated Corrosion ◽  
Thinning Rate

Flow Accelerated Corrosion of Carbon Steel with Droplet Impingement Using a Modified Rotating Cylinder Electrode Experiment

CORROSION ◽  
10.5006/3345 ◽  
2020 ◽  
Vol 76 (2) ◽  
pp. 202-209 ◽  
Author(s):  
Amna Esayah ◽  
Madison Kelley ◽  
Andrew Howell ◽  
Stephen J. Shulder ◽  
Brajendra Mishra ◽  
...  
Keyword(s):  
Electrochemical Impedance ◽  
Rotating Cylinder ◽  
Liquid Films ◽  
Electrode System ◽  
Carbon Steels ◽  
Protective Oxide ◽  
Droplet Impingement ◽  
Accelerated Corrosion ◽  
Rotating Cylinder Electrode ◽  
Flow Accelerated Corrosion

In power plant cooling systems, water droplets and condensate films form due to heat transfer through cooling tube walls. Condensate films are known to cause flow accelerated corrosion on carbon steels used in air-cooled condensers. Corrosion is further accelerated by droplets suspended in the accelerating steam that impinge on walls, T-joints, or valves, further damaging protective oxide layers on pipe walls. Droplet impingement and flow accelerated corrosion were studied using a modified rotating cylinder electrode system coupled with electrochemical impedance spectroscopy. Surface liquid films caused by droplet impingement were found to correlate directly with flow accelerated corrosion caused by condensate films. In the absence of a stable liquid film, droplet impingement increased corrosion rates and resulted in pit formation. Select corrosion inhibitors were found to be ineffective under flow accelerated corrosion or droplet impingement.

scholarly journals Predicting and Preventing Flow Accelerated Corrosion in Nuclear Power Plant

2014 ◽  
Vol 2014 ◽  
pp. 1-23 ◽  
Author(s):  
Bryan Poulson
Keyword(s):  
Mass Transfer ◽  
Nuclear Power ◽  
Mass Transfer Rate ◽  
Environmental Parameters ◽  
Theoretical Models ◽  
Carbon Steels ◽  
Accelerated Corrosion ◽  
Material Factor ◽  
Flow Accelerated Corrosion ◽  
Over 40 Years

Flow accelerated corrosion (FAC) of carbon steels in water has been a concern in nuclear power production for over 40 years. Many theoretical models or empirical approaches have been developed to predict the possible occurrence, position, and rate of FAC. There are a number of parameters, which need to be incorporated into any model. Firstly there is a measure defining the hydrodynamic severity of the flow; this is usually the mass transfer rate. The development of roughness due to FAC and its effect on mass transfer need to be considered. Then most critically there is the derived or assumed functional relationship between the chosen hydrodynamic parameter and the rate of FAC. Environmental parameters that are required, at the relevant temperature and pH, are the solubility of magnetite and the diffusion coefficient of the relevant iron species. The chromium content of the steel is the most important material factor.

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