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ABSTRACT Corrosion of test assets and other structures used by the Missile Defense Agency (MDA) and other DOD branches is an ongoing maintenance and reliability issue. The tropical marine environment, such as the Marshall Islands or the Hawaiian Islands, is highly corrosive and improved corrosion protection and control (CPC) methods are needed to protect valuable and critical assets and infrastructure. A solution to this corrosion problem is smart appliquรฉs that provide excellent corrosion protection and health monitoring to alert an inspector if the appliquรฉ has been damaged or has deteriorated. These smart appliquรฉs are peel-and-stick fluoropolymer films with a sensor electrode and pressure sensitive adhesive. Aluminum and steel panels with smart appliquรฉs were exposed to 2000 hours of salt fog. No corrosion was observed on any of the defect-free specimens. On the scribed aluminum panels, no undercutting of the appliquรฉ was seen at the scribe except when a copper electrode induced galvanic attack. On the scribed steel panels, undercutting did not exceed 1-2 mm. Electrochemical impedance spectroscopy (EIS) measurements using the embedded sensors allowed health monitoring. The sensors easily detected the early stages of corrosion resulting from a scribe in the appliquรฉ and from a backside defect. For the backside defects, the sensor measurements correlated with the amount of corrosion present. These sensors would easily detect any damage to the appliquรฉ or poor appliquรฉ installation before any damage to the structure occurred. INTRODUCTION Corrosion of test assets and other structures used by the Missile Defense Agency (MDA) and other DOD branches is an ongoing maintenance and reliability issue. Corrosion is estimated to cost DOD over $20B per year ? the greatest factor in lifecycle costs.1 The cost of repairs, maintenance, and replacement is a direct cost. The loss of lives and readiness are additional indirect costs, which cannot be assessed in dollar amounts, especially in time of a national emergency or wartime. Corrosion is aggravated by the need to operate in some of the most corrosive environments. MDA, for example, must station test assets at remote locations such as the Kwajalein Atoll in the Marshall Islands and the Pacific Missile Range Facility at Kauai, Hawaii. These facilities include critical test assets such as radars, as well as civil and base infrastructure (e.g. buildings, water and fuel systems, power plants, etc.). Marine or coastal locations, especially those in hot or equatorial climates, are particularly corrosive. Remoteness of facilities further exacerbates the situation by limiting the staff available to perform frequent maintenance of structures and systems. As an example of the aggressive environment, corrosion made a half-million-dollar boom truck unsafe and useless at Kwajalein Atoll after only 3 years. The constant salt spray from the Pacific Ocean corrodes all structures and equipment and dramatically reduces operational lifetime and increases life-cycle costs.
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- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
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INTRODUCTION ABSTRACT Field experiments designed to evaluate deoxygenation of natural seawater as a corrosion control measure for unprotected seawater ballast tanks demonstrated decreased corrosion in hypoxic (<0.2 ppm 02) seawater using weight loss and linear polarization measurements. The experiments also demonstrated the difficulty of maintaining hypoxic seawater. Using a gas mixture it was possible to displace dissolved oxygen in natural seawater. However, aerobic respiration and corrosion reactions consumed oxygen and produced totally anaerobic conditions within the first days of hypoxia. When gaskets and seals failed oxygen was inadvertently introduced. The impact on corrosion depended on the amount of dissolved oxygen in the system at the time of the inadvertent oxygen introduction. Steels exposed to cycles of hypoxic seawater and oxygenated atmosphere had the highest corrosion rate and severity. Deoxygenation of seawater has been demonstrated as an environmentally friendly ballast water treatment to control introduction of non-native aquatic species. 1 Investigators have proposed that the same treatment provides a low-cost, effective corrosion control measure for uncoated carbon steel ballast tanks based on the concept that reducing oxygen fromthe ballast tanks will limit oxidation. 1' 2 Matsuda et al. 2 conducted shipboard trials by sealing a ballast tank at the deck and installing vertical pipes into the headspace. They reported that pumping pure nitrogen gas into the headspace for 1.5 hr reduced oxygen levels in the seawater to approximately 0.2 mg/L and decreased the rate of uniform corrosion of carbon steel by 90%, as determined by weight loss. Matsuda et al. 2 did not include the normal ballast tank operational practice of cycling between filled and emptied tanks nor did they investigate the consequences of introducing additional oxygen. Furthermore, there was no evaluation of localized corrosion. . . . . ? ~1 ! r ' ~ : r ' Previous laboratory experiments 3' 4 comparing corrosion resulting from stagnant aerobic natural seawater with corrosion resulting from stagnant anaerobic natural seawater over a one-year period demonstrated the following: (1) corrosion was more aggressive under totally anaerobic conditions as measured by instantaneous corrosion rates (1/Rp) and weight loss, (2) under aerobic conditions corrosion was uniform and the surface was covered with iron oxides (lepidocrocite and goethite) and (3) under anaerobic conditions the corrosion was localized pitting and the corrosion products were mackinawite and pyrrothite. Several investigators 57 have suggested that the most corrosive operating condition is one in which carbon steel is exposed to alternating oxygenated/deoxygenated seawater.
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ABSTRACT The interference bond is now a commonplace cathodic protection (CP) system feature. It is designed to mitigate cathodic protection interference and allow the transfer of CP currents between pipelines. This circulation of current from multiple sources often precludes the possibility of recording true polarized off potentials at a time when higher degrees of accuracy are demanded (e.g. Direct Assessment). Why have the standard cathodic protection interference testing procedures remained basically unchanged for the past four decades? Did we get it right the first time? How do you explain all of the many inconsistencies and our selective approach to interference? Let us question the accuracy of the testing procedures, the effects of reference electrode placement, the effects of voltage gradients, the erroneous interference test methods, the validity of the measured data, the inappropriate solutions often applied, and some of the many cases which just do not fit the accepted norm. INTRODUCTION Interference bonds, either resistance or direct, have been commonly installed to mitigate cathodic protection interference for more than forty years. In that time period, there appears to have been minimal evidence of major problems with the historical approach and remedy to CP interference.
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- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (0.98)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Drillstem/well testing (0.91)
ABSTRACT The Hanford Site near Richland, Washington has 177 underground waste tanks that store approximately 253 million liters of radioactive waste from 50 years of plutonium production. No online corrosion monitoring systems have ever been used at Hanford to facilitate the early detection of the onset of localized corrosion should it occur in a waste tank. Because of this, a program was started in 1995 to develop an electrochemical noise (EN) corrosion monitoring system to improve Hanford?s corrosion monitoring strategy. Three systems are now installed and operating at Hanford. System design, performance history, data and the results of a recent analysis of tank vapor space data are presented. INTRODUCTION The Hanford Site has 177 underground waste tanks that store approximately 253 million liters of radioactive waste from 50 years of plutonium production. Twenty-eight tanks have a double shell and are constructed of welded ASTM A537-Class 1 (UNS K02400), ASTM A515-Grade 60 (UNS K02401), or ASTM A516-Grade 60 (UNS K02100) material. The inner tanks of the double-shell tanks (DSTs) were stress relieved following fabrication. One hundred and forty-nine tanks have a single shell, also constructed of welded mild steel, but not stress relieved following fabrication. Tank waste is in liquid, solid, and sludge forms. Tanks also contain a vapor space above the solid and liquid waste regions. The composition of the waste varies from tank to tank but generally has a high pH (>12) and contains sodium nitrate, sodium hydroxide, sodium nitrite, and other minor radioactive and non-radioactive constituents resulting from plutonium separation processes. Leaks began to appear in the single-shell tanks (SSTs) shortly after the introduction of nitrate-based wastes in the 1950s. Leaks are now confirmed or suspected to be present in a number of SSTs.1 The probable modes of corrosion failures for the SSTs are nitrate induced stress corrosion cracking (SCC) and pitting.2 No leaks have ever been confirmed in the DSTs, but a study in 1996 identified SCC and pitting as the greatest potential threats to the long-term integrity of these tanks.3 Corrosion monitoring and control of the DSTs at Hanford has historically been provided through a waste chemistry sampling and analysis program. In this program, waste tank corrosion is inferred by comparing waste chemistry samples taken periodically from the DSTs with the results from a series of laboratory tests done on tank steels immersed in a wide range of normal and off-normal waste chemistries.4 This method has been effective, but is expensive, time consuming, and does not yield realtime data. In 1996, the Department of Energy Tanks Focus Area launched an effort to improve Hanford?s DST corrosion monitoring strategy and to help address questions concerning the remaining useful life of these tanks. Several new methods of on-line localized corrosion monitoring were evaluated. The EN technique was selected for further study based on numerous reports that showed this technique to be the most appropriate for monitoring and identifying the onset of localized corrosion.
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Hydrogen Embrittlement Of Prestressed Concrete Cylinder Pipes
Reiner, Lisa (California State University) | Santos, Pablo (California State University) | Herrera, Guillermo (California State University) | Cervantes, Octavio (California State University) | Bavarain, Behzad (California State University)
ABSTRACT Extensive research was conducted on prestressed ASTM A648 Class II steel wire to identify the fracture morphology. Hydrogen embrittlement results when this prestressed steel wire, embedded in concrete cylinder pipe, is cathodically overprotected. From this study, a correlation was established between the environmental variables (pH, cathodic potential) and the type of failure. These experiments demonstrated that hydrogen embrittlement occurred in both environments (pH 2 and pH 12) and affected the fracture behavior of the wires. The wires subjected to cathodic potentials above-1.2 VSCE showed moresusceptibility to hydrogen embrittlement than the other samples. The SEM fractographic analyses showed a specific fracture morphology for the hydrogen embrittled regions of the charged samples. The SEM analysis of the fracture surface showed a thin rim (about 20-50 microns in thickness) on the outer surface that contrasts with the rest of the fracture morphology. In summary, the ASTM A648 steel / prestressed wire showed high susceptibility to hydrogen embrittlement at cathodic potentials above -1.2 VSCE, resulting in severe loss of toughness and catastrophic failure under sudden action of force (water hammering). Therefore, it is extremely important to avoid overprotecting these prestressed wires when using a cathodic protection system to improve life expectancy. INTRODUCTION Prestressed concrete cylinder pipes (PCCP) distribute water to industrial, agricultural and residential areas. Thousands of miles of PCCP network throughout major cities of the United States. These durable concrete pipes combine the compressive strength and corrosion inhibiting properties of concrete with the tensile strength of prestressing wire. The alkalinity of concrete generally provides sufficient resistance to corrosion for the prestressed pipe. But in high chloride environments, the passivating abilities of concrete may be compromised, increasing the risk of steel rebar corrosion and rupturing of the pipes. PCCP can suffer accelerated corrosion where the cement mortar cover is damaged, the pipe is in contact with chloride contaminated or low pH soils or is influenced by stray DC currents. These occurrences can result in sudden catastrophic failure of the pipe [1]. One means of reducing the corrosion rate is by applying a negative voltage to the prestressed wire through cathodic protection. The voltage that is most commonly used in the field is - 0.85 volts. Constant voltage throughout the pipeline is necessary, but with thousands of miles of piping, it is difficult to uniformly protect them. Higher voltages close to the rectifier are used to compensate for the voltage drop resulting from pipeline resistance. Most of the prestressed wires utilized in these pipes are high strength steel and when cathodically overprotected may become vulnerable to a phenomenon known as hydrogen embrittlement (HE) or hydrogen induced cracking (HIC) [2].
Corrosion Protection of Carbon Steel in Natural Sea Water, Using New 4 Phosphonopiperazione-1-yl Phosphonic Acid Inhibitor
Braisaz, Thierry (Centre de Corrosion Marine et Biologique) | Rousseau, Christelle (Corrodys Centre de Corrosion Marine et Biologique) | Villemin, Didier (Ecole Nationale Supeneure) | Benzakour, Jaouad (Laboratory Electro Chimie Analytique) | Amar, Hassan (Laboratory Electro Chimie Analytique) | Derja, Ahmed (Laboratory Electro Chimie Analytique)
ABSTRACT The potential use of new aminomethylene phosphonic acids as corrosion inhibitors for pure iron in 3% (w/v) NaCI has been previously investigated by Amar et al. ~ in 2003. In order to evaluate this new class of inhibitors in an industrial context, corrosion of carbon steel in natural seawater was investigated using electrochemical analytical techniques (i.e. steady-state current-voltage curves and Linear Polarisation Resistance method). An optimisation of the experimental key parameters has been carried out using a D-Optimal design methodology (response surface). Nevertheless, the obtained results point out that inhibition efficiency is low (about 10% to 46%) compared to that obtained in 3% (w/v) NaCI solution. Several hypotheses are suggested in order to understand the difference between natural seawater and 3% (w/v) NaCI electrolyte. INTRODUCTION The development of new inhibitor systems for industrial applications presents a constant challenge as products are optimised and screened with regard to performance, environmental and economic viability. In recent years, exhaustive practical experience has highlighted the importance of the organic corrosion 2'3 inhibitors in water. Since, many researchers 47 have studied the corrosion of iron and its alloys and their inhibition by organic phosphorus inhibitors in neutral solutions. Phosphonic acid derivatives alone or with other additives such as bivalent cations exhibit a great efficiency. In this case, the inhibition properties depend on the number of phosphono functional groups in a molecule and also on different substituents. Several mechanisms, such as hydroxide precipitation or chelate formation may influence inhibition characteristics ~'4-~. Some authors proposed that the ability of the inhibitor to form complexes with dissolved ferrous or ferric ions plays a key role in the inhibition mechanism 6'8. In a previous work ~, 4 phosphonopiperazine-l-yl phosphonic acid (PPPA) was used as an inhibitor for the corrosion of pure iron in 3% (w/v) NaCI solution. For chloride ion concentrations roughly equivalent to that of seawater (3.0-3.6% w/v NaCI), it was shown that a concentration of 5.10 .3 mol.dm 3 drifted Ecorr potential to more negative values. In this case, the inhibitor efficiency, calculated from potentiodynamic polarisation curves and Linear Polarisation Resistance (LPR), was more than 90%. Careful examination of the literature reveals that the studied aminomethylene phosphonic acid has not yet been studied as corrosion inhibitor in natural seawater. The aim of the present work was to measure and optimise the efficiency of a new inhibitor of corrosion of carbon steel in natural seawater. For this purpose, in order to get the most information from each experiment perform, an experimental design methodology and electrochemical techniques (i.e. potentiodynamic polarisation curves and Linear Polarisation Resistance) have been used. Values obtained previously for pure iron in 3% (w/v) NaCI have been compared to the present results.
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ABSTRACT Laboratory experiments were designed to determine the influence of polarization (ยฑ175 mV vs. saturated calomel electrode) in natural fresh water and in dilute microbiological media (1:100 Luria- Bertani broth) on biofilm formation on 316L stainless steel. Biofilms formed on all polarized and unpolarized surfaces within 120 hours. Variability among the surfaces was detected with environmental scanning electron microscopy. Polarization influenced microbial settlement in both media. Biofilm formation on polarized surfaces may not represent natural biofilms formed in the absence of polarization. INTRODUCTION Physical separation of anodes and cathodes and subsequent measurement of some electrochemical parameter have been used to detect biofilm formation and to evaluate the electrochemical impact of biofilms.1-3 In some cases polarization has been used.1, 2 Angell et al.1 used a concentric ring 304 stainless steel electrode to demonstrate that a consortium of sulfate-reducing bacteria and a Vibrio sp. maintained a galvanic current between the anode and cathode. In their electrode design, pitting was induced by passage of a 11 ยตA cm-2 current density to a small (0.031 cm2) anode. The anode was concentric to, and separated from, the cathode (4.87 cm2) by a Teflonยฎ (polytetrafluoroethylene) spacer. Current was applied for seventy-two hours either during or after microbial colonization. Once the applied current was removed the resultant galvanic current flowing between the anode and the cathode was monitored by a zero resistance ammeter. They found that a current was maintained in the presence of a microbial consortium. No current was measured in a sterile control. Licina and Nekoksa2 developed a probe consisting of ten 316 stainless steel concentric rings separated by epoxy. A potential (which varies according to experimental conditions) is imposed for 1 hour each day between the electrodes so that the electrodes are alternately anodes and cathodes. The metal discs are polarized to produce an environment conducive to biofilm formation. The applied current, required to achieve a pre-set potential between electrodes, remains stable until a biofilm forms. Once a biofilm is established, current increases consistent with a decrease in the polarization resistance. The generated current, current that continues to flow between the electrodes after the external polarization has been removed, is another indication of biofilm development. In the absence of a biofilm the generated current is expected to be zero. In the presence of a biofilm some current is expected to flow. While the Angell et al.1 and the Licina and Nekoksa2 probes are similar in that both rely on separation of anode and cathode regions for detection of microbial presence, there are significant differences. The concentric ring electrode1 provides a technique by which microbiologically influenced corrosion (MIC) can be studied and is not intended to represent any natural situation. The commercial probe2 is intended to provide information about an operating system (such as a flowing cooling water piping) that can be used to make decisions about cleaning or treatment. The probe designs also differ in the motivation for polarization. Angell et al.1 induced pitting in the anode. Franklin et al.4 and Little et al.5 were among the first to demonstrate that bacteria are attracted to anodic sites. The spatial relationship between corroding ferrous materials and bacteria has been demonstrated using several techniques and electrolytes.6-8 There is general agreement among investigators that bacteria are attracted to anodic sites on ferrous materials. Polarization of the multiple ring probe does not cause localized corrosion and is designed to encourage biofilm
- Materials > Metals & Mining > Steel (0.77)
- Energy > Oil & Gas > Upstream (0.49)
- Water & Waste Management > Water Management > Constituents > Bacteria (0.49)
ABSTRACT Corrosion of pipes made of stainless steel in the process water distribution system of a leather processing plant was investigated by various analytical and electrochemical methods. The attack was identified as MIC by manganese oxidizing microorganisms. The preferential attack at the heat tinted welds is explained by the potential shift caused by biomineralized MnO2, preventing repassivation. INTRODUCTION Stainless steel (SS) is the material of choice in many systems carrying fresh water. In the passive state, the material exhibits practically no corrosion rate, resulting in a virtually unlimited lifetime, eliminating the need for further corrosion protection and keeping the water free of undesired corrosion products. However, passivity is vulnerable to breakdown by chloride ions, possibly inducing phenomena like pitting or crevice corrosion. Besides the chloride concentration, the corrosion potential determines the probability of corrosion initiation and repassivation, respectively. Normally, the corrosion potential is determined by the oxygen dissolved in the water. However, additional redox systems may influence the potential. Biofilms at the metals surface may provide such redox systems and a potential shift in the anodic direction is frequently denoted .Ennoblement.. In particular, manganese oxidizing microorganisms (MOMOs) have been identified as a group of organisms that may cause .Ennoblement. by biomineralizing dissolved Mn2+ as manganese oxides and hydroxides in a higher oxidation state, i.e. MnO2 and related compounds1,2. In the present view3, the role of such biomineralized MnO2 in corrosion processes is governed by its well known abiotic _ electrochemical properties. It may act as a strong oxidant by itself and, moreover, serve as a catalyst for oxygen reduction. A number of case histories related to MIC by MOMOs have been reported so far4-8. In continuation of our work, a recent case from a leather processing plant is presented here. The results of various investigations will be reported and discussed below with respect to the practical consequences.
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ABSTRACT A mixed culture of D. gabonensis and D. capillatus, in synthetic seawater supplemented with nutrients formed a biofilm combined with ferrous sulfide corrosion products that largely covered carbon steel electrodes (SAE-1020). Electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP) measurements were carried out for this study. Electrochemical impedance results indicated the formation of three films: an inner corrosion products film, an outer corrosion products film and the biofilm or organic film in abiotic media. After one month of batch culture, it was observed that during biofilm formation there are two different controlled processes. During the first period activation-diffusion controlled corrosion was observed. The second period showed diffusion controlled corrosion due to biofilm establishment. Impedance spectra denote an increase in R~t (charge transfer resistance) with time in the presence of biofilm. Magnitudes of the phase angle contributions are indicative of biofilm and corrosion products interphases heterogeneity during primary formation stages. INTRODUCTION Aqueous environment promote metals surface oxidation. Furthermore, under bacterial presence, biofilm formation also occurs, which might influence corrosion phenomena. Biofilms have been identified as heterogeneous aggregates, which are built in communities over materials surfaces or they are associated with interphases by a self-produced extrapolymeric matrix [1-5]. Biofilms might affect corrosion by changing the nature of the physicochemical interactions between metallic materials and their environment or the rate controlling step, thus accelerating or inhibiting the corrosion process [6, 7]. Sulfate-reducing bacteria (SRB) are able to form biofilms over carbon steel surfaces in poorly oxygenated areas. Thus, these bacteria are frequently involved in corrosion under anaerobic conditions and they act to transform sulfurs in hydrogen sulfide which, in the presence of ferrous ionic compounds tend to form ferrous sulfides [8, 9]. Different species of SRB have different influence on the corrosion process [9]; therefore experiments were conducted to study the effects of lately discovered SRB strains. D. gabonensis [10] and D. capillatus [11] are halophilic, hydrogenase positive sulfate-reducing bacteria, recently isolated from oil industry marine installations affected by corrosion. The role of these bacteria in corrosion phenomena has not been entirely documented. Complexity of biocorrosi6n processes requires the utilization of an extensive variety of techniques for various analyses. Since biofilm development, metabolic activity and corrosion can be approached as electrochemical- nature based processes [7], electrochemical measurements can be used to study them. When open circuit potential (OCP) measurements have been carried out, an increase of this value through time has been shown due to iron protecting biofilms [12]; however, when iron passivation occurs this behavior is also exhibited, even in the presence of SRB, which can lead to localized corrosion phenomena [13]. Electrochemical impedance spectroscopy (EIS) has been used in the study of biocorrosion [14, 15], for monitoring corrosion rates [12], SRB influence in corrosion of buried pipelines [16], SRB influence in corrosion of reinforced concrete [17], bacterial corrosion inhibition [ 18], biofilm formation and influence in corrosion [ 19, 20, 21 ], etc. EIS provides quantitative and mechanistic information for biocorrosion processes [22].
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ABSTRACT Effects of a variety of water chemistry conditions on the corrosion behavior of Type 304 stainless steel (SS) in a simulated boiling water reactor (BWR) environment are described. In particular, the effects of dissolved oxygen (02), hydrogen (H2), and hydrogen peroxide (H202), and various impurities on the electrochemical corrosion potential (ECP) and oxide structure of 304 SS are considered. It has been shown that the presence of H202, water flow rate, and corrosion rate and oxide chemistry of 304 SS significantly affected the 304 SS ECP and also observed that the presence of Cu in the water increased the 304 SS ECP in HWC, but no significant of Zn effect was observed. It is also interesting to note that in the presence of both H202 and H2, Pt ECP is lower than 304 SS ECP, mainly due to possible catalytic nature of Pt and/or low chemical potential of OH radicals. INTRODUCTION The degradation of structural materials in nuclear power plants has been well addressed in previous papers ~-2. It is well understood that when the ECP of stainless steel (SS) in high temperature water is decreased, the intergranular stress corrosion cracking (IGSCC) susceptibility of sensitized SS in BWRs can be decreased. By lowering the ECP of SS below a critical potential {-230 mV vs. the standard hydrogen electrode (SHE)}, the susceptibility to IGSCC in BWRs is markedly reduced. The ECP is controlled by the amounts of oxidizing and reducing species and the hydrodynamic water flow conditions and can also be affected by the electronic/ionic conductivity of oxide films formed on metal surfaces in aqueous environments. H 2 is added to the feed water of BWR to mitigate IGSCC of structural components by reducing the dissolved oxidant concentration. This process is referred to as hydrogen water chemistry (HWC). Large amounts of H2 addition are normally required to sufficiently lower the dissolved 02 and H202 concentrations so that the IGSCC protection potential (-230 mVshe) is attained. Although IGSCC can be sufficiently suppressed by the HWC process, it is not an optimum process from an operating viewpoint. The disadvantages of HWC include high " 16 60 operating dose rates due to increased N release to the turbine, high H 2 gas cost, and higher Co contribution to shut down dose rates, etc. The IGSCC protection potential is also difficult to achieve in the highly oxidizing and high water flow regions. In order to improve the effectiveness of HWC, the noble metal technology (NMT) was developed as a new tool to mitigate the IGSCC of BWR components. This approach involves improving the catalytic recombination of 02 and H202 with H2 to form H20 on the metal surface, and thereby achieving the low ECP values and low crack initiation/growth rates at much lower H2 addition rates and with minimal negative impact on BWR operation. This process thus requires only a stoichiometric amount of H2 in water (i.e. >2:1 H:O molar ratio, >1:8 H:O weight ratio) 3-8. Layers of very high catalyst concentration have been produced by electro- and electro- less plating, vapor deposition, sputtering, etc. of pure or mixed noble metals. A system-wide approach which relies on electroless reduction of very dilute noble metal compounds added to the BWR coolant for a limited time period, has been termed "noble metal chemical addition" [NMCA], and shows great promise as a technique to provide a noble metal coating on all wetted components. This catalytic effect has been demonstrated for a broad range of iron, nickel, and cobalt-based noble metal alloys, materials coated with individual or mixtures of noble metals. A wide variety of approaches to apply noble metals to BWR components have been developed for creating a catalytically a
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