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Production Chemistry, Metallurgy and Biology
Life Evaluation of ZrO2/Ni Base Alloy Plasma Jet Coating Systems in High Efficiency WTE Boiler Superheaters
Kawahara, Yuuzou (Mitsubishi Heavy Industries Ltd.) | Nakagawa, Yuji (Mitsubishi Heavy Industries Ltd.) | Sakurada, Toshio (Mitsubishi Heavy Industries Ltd) | Kamakura, Hiroki (Mitsubishi Heavy Industries Ltd.) | Kira, Masaharu (Mitsubishi Heavy Industries Ltd.) | Imaizumi, Yukio (Kyusyu Electric Power Co. Ltd.)
ABSTRACT In order to improve the durability and cost performance of superheater in high efficiency WTE boiler, new Ni base alloy/YSZ dual coating systems using plasma-jet spray technology has been developed, and then the life of these coatings sprayed on 500°C/9.8MPa high-efficiency WTE boiler superheater was evaluated by the long term field corrosion test. Three kinds of coating layer of alloy 625/YSZ, NiCrSiB alloy/YSZ and Cr3C 2 ? NiCr sprayed by 100kW plasma-jet system both on site and on shop were installed in tertialy and secondary superheater having high metal temperature of 450 ~ 500°C, and exposed for more than 1.3 years. As the results of the field corrosion test, alloy 625/YSZ and NiCrSiB alloy/YSZ coatings with inorganic sealant showed excellent durability more than 1.5 years compaired with conventional NiCrSiB alloy HVOF system in tertialy superheater. Based on the detail investigation of cut-off tube samples, A durability of each coatings reduce with increase in corrosivity of combustion gas. YSZ and inorganic sealant were clarified to work as a penetration bar- rier for corrosive components in deposits to coating/base metal interface. Especially, in soot blower affected position, Cr3C 2 ? NiCr layer sprayed in secondary superheater peeled off by thermal cyclic factor after four months exposure, while large corrosion prevention effect was observed in Ni base alloy/YSZ layer regardless of partial peeling-off of YSZ layer. An application of Ni base alloy/YSZ coatings for actual boiler is expected in the future. INTRODUCTION The realization of high efficiency WTE boilers has been making progress in Japan recently with steam condi- tions of 400°C and 3.9 MPa becoming common for both conventional stoker type and pyrolysis gasification ash melt- ing type plants. In addition, a 500°C 9.8 MPa high-efficiency WTE plant, which started operation in 1998, has also continued stable operation for about six years. On the other hand, 450 to 540°C and 5.9 to 9.8 MPa electric power generation plants with fluidized bed boilers that bum industrial waste, such as biomass and scrap tires, have recently been constructed and put into operation. In order to improve the durability of high-temperature high-pressure boiler materials which bum such waste fuels, it is considered necessary to apply optimum boiler designs that prevent high-temperature corrosion and erosion- corrosion of superheaters and waterwall tubes, given economic conditions that require the total cost of plant opera- tions to be reduced. Further, high-temperature corrosion-resistant materials and coatings need to be used that are low in cost and excellent in terms of maintainability. At present, thermal spray coating with Ni-base alloys (80Ni20Cr, NiCrSiB alloys, etc.), clad composite tubes, and weld overlays made of Alloy 625, amongst other measures, are used in various countries around the world to prevent the corrosion of waterwall tubes. In Japan, high-temperature combustion is being implemented in which the furnace outlet combustion gas tem- perature is set at more than 850°C in order to prevent the formation of dioxins, as well as to realize reduced NOx (Low 0 2) operation., In addition, there are high expectations for the development of:coating systems that are highly durable against severely corrosive environments. Corrosion-resistant tube materials, such as 310S type stainless steel and alloy 825, are also used for superheaters, as well. Furthermore, there is a strong need for low cost materials of improved durability that can be used to prevent partial corrosion damage caused by the impact of soot blowers and that can also facilitate the realization of further increases and improvements in high-
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ABSTRACT Industrial cooling water systems will undergo more and more environmental constraints and the recycling of these waters will increase the risks of scale deposition and corrosion. The use of environmentally friendly chemical additives to inhibit these phenomena is necessary. Polyaspartates (PASP) have been proposed as potential green multifunctional inhibitors. Their inhibition efficiency on both the nucleation and growth of calcium carbonate (CaCO3) deposits and on the formation of corrosion products has been studied, under hydrodynamic conditions, by electrochemical techniques such as the use of the quartz crystal microbalance and impedance spectroscopy. Nucleation and growth of CaCO3 crystals have also been viewed in situ in a flow cell fitted with a specially designed microvision device. PASP are found to act as multifunctional green inhibitors with a threshold effect for cooling water systems. These polymers decrease the mass of calcium carbonate deposited: the corrosion rate is lower in the presence of both PASP and calcium than in their absence. The morphologies of calcium carbonate and corrosion products obtained in these assays are also greatly modified in the presence of PASP. The mechanism of action of polyaspartates combines adsorption, dispersion, complexation (with both iron and calcium ions) and insertion in the crystal lattice. Models for the mechanisms of action of polyaspartates are proposed. A first one deals with the inhibition of calcite in combination with enhancement of vaterite and a second with the inhibition of corrosion. INTRODUCTION Cooling water systems will undergo severe environmental constraints. The recycling of water will also increase the risks of both calcium scale deposition and metal corrosion in the circuit. These risks may compromise the overall plant performance1. At the present time organic phosphonates with metallic additives (Zn, Mo) are mostly used to avoid formation of both scale and corrosion. In the future, rejects of phosphorous and metallic ions will be limited for ecological reasons. Biodegradable polyaspartates (PASP) have recently been proposed as potential green multifunctional inhibitors2-4. This work deals with the mechanisms of inhibition of PASP on both carbonate scale deposition and metal corrosion. Under different hydrodynamic conditions, their inhibition efficiency on the nucleation and growth of calcium carbonate (CaCO3) and on corrosion has been studied by electrochemical techniques such as the use of both the quartz crystal microbalance and the impedance spectroscopy. Different authors5-8 have shown that inhibition of scale depends on the characteristics of the polymeric chain (molecular weight, linearity). Polyaspartates seem to act also as corrosion inhibitors7,9,10 but for others11-13 they accelerate this phenomenon. In this paper, we will review the effect of polyaspartate on the scale and corrosion inhibition and the influence of the polymer characteristics on their inhibiting efficiency. Mechanisms of action will be proposed discussed. EXPERIMENTAL Synthesis and biodegradability of polyaspartates Polyaspartates were prepared from L-aspartic acid by three different ways of synthesis that are based on intermolecular dehydration : thermal polycondensations without or with an acid catalyst and bulk polycondensations with catalyst. The formula of polyaspartate is given in figure 1. The experimental procedures for their synthesis and the characterization of their biodegradability have been described in another publication2. Scale Inhibition Evaluation The inhibition efficiency of scale deposition by polyaspartates has been evaluated by an electrochemical technique14. The
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- Water & Waste Management > Water Management > Constituents > Salts/Sulphates/Scales (0.36)
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- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Inhibition and remediation of hydrates, scale, paraffin / wax and asphaltene (1.00)
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ABSTRACT Many alloys exposed in high-temperature process equipment corrode by sulfidation corrosion in the presence of steam or other oxidizing gases. This paper discusses the latest results of an extensive testing program for a diverse group of about 50 commercial alloys exposed to temperatures of 573 ? 1273 K with exposure times up to 6,000 hours for a total data compilation of nearly 4 million hr. The data compilation now allows engineering corrosion assessments for sulfidation and sulfidation in the presence of oxidizing gases and predictions for wide ranges of conditions. The effects of gas composition, temperature, exposure time and alloy type have all been analyzed and compiled to allow prediction of corrosion for wide ranges of conditions to allow engineering predictions of corrosionlimited lifetimes. Applications for this technology are found in industries such as oil refining, petrochemicals production, pulp/paper production, and power generation. BACKGROUND This paper discusses the potential of high-temperature gases to corrode metals by sulfidation in the presence of oxidizing gases and recommends how to predict sound metal losses for a wide range of conditions. Corrosion of metals and alloys used in equipment handling high-temperature, corrosive, sulfidizing gases is a potential concern in processes used in petroleum refining, gas processing, fired equipment, process heaters, thermocouples, instrumentation, hydrocracking, coking, vacuum flashing, hydrotreating, coal/coke/oil gasifying, petrochemical production, catalytic reforming and gasification of black liquor in pulp/paper production. Corrosion can often define the maximum allowable temperature or maximum allowable gas species concentrations for metals and alloys in equipment, although mechanical properties or other considerations may also define the maximum allowable temperature. Determining the extent of sound metal loss by corrosion should allow assessment of the remaining useful load-bearing thickness of components as equipment corrodes. It is therefore important to review how the characteristics of the exposure conditions and the alloys can combine to influence the rate of corrosion. Most corrosion data for alloys exposed to high-temperature gases are reported in terms of weight change/area for relatively short exposures and inadequately defined exposure conditions. Unfortunately, the weight change/area information is not directly related to the thickness (penetration) of corroded metal, as illustrated in Figure 1 and is often needed in assessing the strength of process equipment components. Corrosion is best reported in penetration units, which indicate the sound metal loss, as discussed earlier1-2. Corrosion in high-temperature gases is affected by key parameters of the corrosive environments such as temperature, alloy composition, time, and gas composition. Summaries of metal penetrations for some typical conditions are shown in this presentation, which extends beyond the traditional corrosion weight change data by reporting total metal penetration for an extensive number of alloys over a wide range of conditions. Compositions of some of the alloys discussed in this paper are shown in Table 1. SULFIDATION CORROSION MECHANISM To better understand sulfidation in the presence of oxidizing gases, the corrosion mechanism of sulfidation in the absence of oxidizing gases will first be reviewed. Sulfidation is corrosion, which forms sulfide corrosion products, leads to metal loss (penetration), and occurs upon exposure of metals to gases containing H2S. The first step in determining the potential for equipment to sulfidize is to determine that sulfidation is the dominant corrosion mechanism. The key indicator
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- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
ABSTRACT Model austenitic alloys are being studied as part of an alloy development program for high temperature (¡Ý650°C) recuperators for small gas turbine engines. In many cases, the recuperator design requires an alloy foil with both high temperature strength and corrosion resistance in an exhaust gas environment. Previous work showed that type 347 stainless steel would not have sufficient corrosion resistance for this application. Long-term testing is being conducted to better understand the effect of composition on corrosion resistance in humid air at 650°-800°C. Current results show that Fe-20Cr-20Ni with additions of Mn and Si has excellent corrosion resistance in humid air for more than 5,000h at 650° and 700°C. Increasing the Ni content of the alloy is critical to improving corrosion resistance. INTRODUCTION The August 2003 blackout in the United States has bolstered the case for distributed generation as a solution for overloaded transmission lines and improved reliability. One element in the distributed generation portfolio are small (30-250 kW) single-shaft, gas turbine engines or microturbines.1-2 With a footprint of approximately 3m x 4m, these engines could be sited at the user?s facility and provide base or peak load electricity while delivering waste heat for climate control or heating water. One potential market uses methane from landfills and sewage plants as fuel.3 Microturbines are environmentally attractive because of their low NOx emissions. However, one of the drawbacks of current microturbines is their relatively low electrical generation efficiency (¡Ö30%) compared to large gas turbines. (An overall efficiency increase is obtained by using the waste heat for other uses.) Thus, one goal of the Department of Energy?s Distributed Energy Resources program is to improve the efficiency of next-generation microturbines.4 Increasing the turbine inlet temperature is a primary method for increasing engine efficiency. Higher operating temperatures require the selection or development of cost-competitive materials for advanced microturbines. One of the most critical areas is the recuperator or heat exchanger, which significantly boosts the efficiency of small turbine engines.5 Increasing the temperature of the recuperator while maintaining durability requirements has proven to be a critical problem. Most recuperator designs have used type 347 stainless steel because of its combination of creep and corrosion resistance. However, it has been well documented that increasing the exposure temperature to ¡Ý650°C has resulted in accelerated attack of type 347 stainless steel due to the presence of water vapor in the exhaust gas.6-10 Accelerated attack due to water vapor has been observed for both ferritic and austenitic alloys in the 600°-900°C range11-16 and is currently being investigated by a number of research groups. An increase in the corrosion rate is a particular concern for recuperators because most designs employ thin-walled alloy components having a limited Cr reservoir. The Cr reservoir is an important factor in determining corrosion lifetime because, as Cr is depleted from the foil, at some critical Cr content the foil will no longer be able to form a protective Cr-rich surface oxide. In order to meet recuperator durability goals of ¡Ö40,000h, a stainless steel must be identified with a low Cr consumption rate and which will make it resistant to accelerated attack. As described in previous papers,9,10 the goal of this program is to develop a low-cost alternative to type 347 stainless steel by (1) identifying the base Cr and Ni contents needed for resistance in these environments; (2) identifying beneficial minor alloying additions and (3) combining
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Performance of Weld Overlay Materials in a Simulated Coal Fired Combustion Environment
Clark, Arnold (Thyssen Krupp VDM GmbH) | Eckhardt, Eckhardt (Thyssen Krupp VDM GmbH) | Dupont, John N. (Lehigh University) | Deacon, Ryan (Lehigh University) | Marder, Arnold R. (Lehigh University) | Paul, Larry D.I. (Thyssen Krupp VDM GmbH)
ABSTRACT A new alloy with high chromium has shown excellent resistance to corrosion in combustion atmospheres like those produced in low NOx coal-fired power boilers. This new material is Alloy 33 (UNS R20033) and contains approximately 33% chromium. Chromium is well known as a key alloy addition to improve resistance to sulfidation, which is the major corrosion mechanism in coal-fired boilers using low NOx combustion technologies. In addition, the alloy 33 shows less segregation of alloying elements than currently used materials when in the welded condition; segregation in welds has been suggested as playing a contributing role in boiler tube corrosion and corrosion assisted cracking mechanisms. The improved corrosion resistance of Alloy 33 demonstrated in this study is expected to result in longer life of the weld overlay used to protect boiler tubes. Because of the complex nature of boiler environments, a field test is now being perused to demonstrate the benefit of alloy 33 under actual service conditions. INTRODUCTION In order to reduce emissions, special burners that limit NOx production have been installed in many coal-fired utility boilers. A reducing combustion region is created in the furnace to prevent thermal NOx formation; the highest temperature regions are starved of oxygen and therefore limit the reaction between nitrogen and oxygen to form the undesirable NOx. However, these conditions also reduce the naturally occurring sulphur in the coal to H2S, which accelerates corrosion rates on the water cooled boiler tubes in the lower furnace region. In addition, ash deposits and slag on the tubes can further accelerate corrosion. Accelerated corrosion of waterwall tubes resulting from low NOx burners was recognized as a problem early in the use of these pollution control devices1 Corrosion rates of up to 80mpy (2mm/y) were predicted. More recently, boiler tube corrosion rates in plants operating with low NOx burners have been reported to be between 30 to 80 mpy (0.8 to 2.0 mm/y)2-3. The use of weld overlays was considered an attractive means to solve this corrosion problem, particularly since it does not require pressure part modifications4. In addition to corrosion, there have also been reported problems with cracking of boiler tubes. This has been reported on many different types of boiler tubes, including: bare alloy boiler tubes5, 309 stainless steel weld clad boiler tubes6, and Alloy 625 weld clad boiler tubes4. This phenomenon is generally referred to as circumferential cracking and is mostly limited to supercritical boilers. The thermal fluctuations that occur as a result of slag sheds and operating changes create alternating stresses in the boiler tubes that lead to cracking. In addition, there appears to an environmental aspect to this cracking, as a sulphur spine appears down the center of these cracks4. Therefore, materials with increased corrosion resistance should also be more resistant to this type of cracking. EXPERIMENTAL Three new alloys were selected for testing as weld overlay materials. Alloy 622 (UNS N06022) produced as a weld overlay was also included as a reference sample. These alloys and the reasons for considering these materials for a weld overlay in a low NOx coal fired power boiler are as follows: Alloy 50- Nicrofer 5020* (UNS N06650) ? A Nb-free weld metal with slightly lower molybdenum and lower tungsten levels than the Alloy 22 currently being used; this results in less segregation and also reduces the tendency to form intermetallic mu phase in the weldment. Also Alloy 50 has a low thermal expansion coefficient that could reduce circumferential cracking.
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ABSTRACT This paper discusses automatic gas-metal-arc-welding (GMAW) overlay cladding for fireside corrosion and erosion/corrosion protection of the waterwall in coal-fired boilers equipped with a low NOx burner system. In addition, the use of overlay cladding for protection against steam soot blower erosion is discussed. Also discussed is the use of the cladding method for protection against damages from water lancing used to remove slag deposits from the waterwall. The overall success of this surface cladding technology for waterwall protection in coal-fired boilers is described. INTRODUCTION In a coal-fired boiler, the furnace wall (often referred to as waterwall) is constructed of tubes connected by membranes, surrounding the furnace enclosure for extracting heat for generation of steam. The material for waterwall construction is typically carbon or Cr-Mo steel. The waterwall is subject to high heat flux, fireside corrosion and fly ash erosion/corrosion attack. In general, the fireside corrosion is in a form of oxidation. However, recent installations of low NOx burner systems in boilers for reducing NOx emissions have caused the combustion conditions to change from oxidizing to reducing in the lower furnace. This causes the waterwall corrosion to change from oxidation to sulfidation, thus resulting in a significant increase in tube wall metal wastage rates 1-5. Wastage rates in many boilers have been observed to increase from 0.25 mm/y (10 mpy) or less to up to 2.5 mm/y (100 mpy) or more. The waterwall is also subject to fly ash erosion/corrosion because of dynamic combustion conditions. In addition, constant removal of slag deposits from the waterwall tubes may be needed for maintaining the required heat transfer. Some of the slag removal methods include steam sootblowing and water injection using water lances or water canons. The latter approach utilizes thermal shock to achieve the slag removal. This method can potentially cause the tube to develop thermal fatigue cracking. In trying to deal with these waterwall materials degradation issues, the industry has been trying to find a cost-effective, long-term solution. Among several corrosion and erosion/corrosion protection methods tried, weld overlay technology involving automatic GMAW overlay cladding has become the most common waterwall protection method for solving the severe tube wastage problems in the boiler 5-10. The automatic GMAW overlay cladding has been applied successfully to mitigate the tube wall thinning problems in both subcritical and supercritical units equipped with low NOx burners. The cladding has also been successfully used for restoring the structural integrity of the waterwalls of many subcritical boilers that have operated for 20 plus years. It generally is more cost-effective to overhaul and restore the existing waterwall on-site by applying a corrosion-resistant weld overlay to prevent further tube wall thinning than replacement with new fabricated waterwall panels. When the thickness of the badly corroded waterwall has been reduced to below the ASME Code allowable, a weld metal build-up using a matching filler metal to that of the tube material can be performed to increase the tube wall thickness to meet the ASME Code before applying a corrosion-resistant overlay. Furthermore, an increasing number of boilers have to resort to water injection with either water lances or water cannons in order to remove slag deposits from boiler tube surfaces due to the use of powder river basin (PRB) coal for reducing emissions and lowering fuel cost. Accordingly, the tubes are more prone to thermal fatigue cracking. The overlay cladding may be an effective protection method against damages from the use of water lances or
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- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
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INTRODUCTION ABSTRACT This review article provides a summary of recent literature published on the subject of corrosion inhibitor developments and testing for application in offshore oil and gas producing systems. The paper is split into two sections. Section 1 reviews inhibitor development and testing pertaining to offshore 'shallow water' production systems and Section 2 summarizes developments and testing related to offshore 'deep water' production systems. Corrosion inhibitor developments for managing corrosion within wet oil and gas production pipelines and production equipment are well documented through out the NACE literature. Chemical vendors research and development efforts producing chemistries that provide mitigating benefits aqainst corrosion in land based, wet sweet [~-~8] (acid gas is CO2) and wet sour [~9-49] (acid gas is H2S and CO2) oil and gas production systems are well documented. The land based pipeline systems are generally constructed by linking carbon steel sections of pipe wrapped with some form of external insulation and burying the asset in the soil a few meters beneath the surface. Corrosion inhibitors have also been developed for managing internal corrosion in wet oxygenated production environments [so:] and for providing mitigating benefits against hydrogen induced cracking (HIC) and sulfide stress cracking [51] (SSC) corrosion. SECTION 1" OFFSHORE SHALLOW WATER OIL AND GAS PRODUCTION SYSTEMS Offshore shallow water is considered to represent water depths less than 1,000 feet (ft) (305 m). Corrosion Control Consideration for Topside Offshore Oil and Gas Processing Systems There is a general acceptance by the offshore oil and gas industry that corrosion is an important safety issue. Detailed studies addressing the development of a high level risked based corrosion strategy for topside offshore processing facilities are available from Capsis [52] Gravity Based Structures Corrosion control, corrosion monitoring, chemical treatments, materials selection, criticality analysis for offshore oil & gas production gravity base structure are important. Haddon and Monahan [53:] provide a brief overview of the various techniques that are used to detect, monitor and control corrosion on the Hibernia installations and up dates this general background with four years of operational experience. The Hibernia platform is a concrete gravity base, oil & gas production facility that sits on the Grand Banks of Newfoundland in approximately 80 meters (m) of water. The methods and tools used for inspection management, corrosion control, and corrosion monitoring are discussed in detail. Although the examples presented here relate specifically to the Hibernia asset, similar corrosion engineering practices are common throughout the oil and gas industry. Floating Production Structures Garner and Gill [~] provide corrosion control information pertaining to a floating production, storage and offloading (FPSO) oil production processing facility. This account highlights the main differences between the approaches to corrosion control on a ship compared with an FPSO and provides an overview of the overall corrosion strategy adopted for the Terra Nova FPSO development, offshore Newfoundland. Corrosion Control for Wet Sub Sea Carbon Steel Pipeline Systems Hannah, Joosten, and Koltz [ss] provide an account of evaluation criteria used for developing and selecting corrosion inhibitors for severe high pressure high temperature gas production environments. Ahn and Dougherty [s6] provide another account for development of corrosion inhibitors for use in artic and subsea high velocity flowlines. Corrosion Inhibitor Design Conside
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ABSTRACT Since the early 1980?s cathodic protection technology has been increasingly applied to reinforced concrete structures. Various anode materials in various configurations have been used. In this study an effort was made to document the long-term field performance of nineteen impressed current systems installed on fourteen bridge structures and one tunnel located in ten states of the United States of America and one Province of Canada over a period of five years. The cathodic protection systems evaluated in this study utilized zinc, titanium with mixed metal oxide coating, conductive coating, conductive polymer, and coke asphalt based anode materials. These systems were installed on bridge decks, super and substructure elements of bridge structures and a deck of a tunnel in various environmental conditions. At the end of the study the age of the systems varied from thirteen months to twelve years. As the ability of the cathodic protection system to stop corrosion is well established, the focus of this effort was to ascertain the effectiveness of each anode material and configuration to serve as a cathodic protection anode on reinforced concrete structures. This paper documents the findings of this study. INTRODUCTION Cathodic protection (CP) is a technology used to mitigate corrosion of metals and has been used on ships and pipelines for many decades. The first use of this technology on a bridge deck dates back to 19731. Based on extensive government and private industry research, the Federal Highway Administration (FHWA) concluded that CP is the only rehabilitation technique that has proven to stop corrosion in salt-contaminated bridge decks regardless of the chloride content in the concrete2. This technology is based on the principle of applying an external source of current to counteract the internal corrosion current produced in reinforced concrete components. During cathodic protection, current flows from an auxiliary anode material through the electrolyte (concrete) to the surface of the reinforcing steel. Various materials in various configurations are used as auxiliary anodes for cathodic protection resulting in various types of cathodic protection systems. The selection of the anode material and its configuration is paramount to the success of the system. The primary objective of this study was to determine the effectiveness of various materials and configurations when used as auxiliary anodes on highway structures through a long-term evaluation. A total of fifteen highway structures (fourteen bridges and one tunnel) protected by one or more CP system(s) were included in this study. The structures were located in ten states of the United States of America and one Province of Canada. These structures were protected by a total of nineteen impressed current CP systems using the following anode materials and were monitored for a period of five years: a) Arc Sprayed Zinc b) Zinc Stripes c) Titanium Mesh Coated With Precious Metal Oxide d) Titanium Ribbon Coated With Precious Metal Oxide e) Arch Sprayed Titanium followed by an Application of Precious Metal Oxide f) Conductive Coating g) Conductive Polymer Placed in slots h) Conductive Polymer Placed in mounds i) Conductive Coke Asphalt Based on the age of the system, two to six evaluations were conducted. Most of the structures were selected by FHWA based on previous studies performed under the Strategic Highway Research Program (SHRP). Additional structures were added to the program as they became known to the research team. Structures that could not be properly evaluated were deleted from the study. During each evaluation, visual and delamination surveys were
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- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
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ABSTRACT In October of 2000 work was started on a project to develop a temporary electrochemical noise (EN) based corrosion monitoring system for Bethel Valley Evaporator Storage Tank (BVEST) W-23 at Oak Ridge National Laboratory (ORNL). The project was undertaken to assess the corrosivity of the waste in the tank and to assist in the overall development program for nuclear waste tank corrosion monitoring at the Hanford Site and other DOE facilities. Prior to the fabrication and deployment of the Tank W-23 system, laboratory testing was performed at ORNL to characterize the behavior of 304L (UNS $30403) stainless steel in simulated Tank W-23 waste solutions. Following the laboratory work a system was deployed in Tank W-23 in June of 2001. Data collection was terminated in June of 2002. Both laboratory data from the development effort and field data from system operation in Tank W-23 are presented herein. INTRODUCTION Underground storage tanks made of mild steels or stainless steels are used to contain radioactive wastes generated by facility operations at numerous Department of Energy (DOE) sites. Most of these sites are now involved to varying degrees in environmental restoration and site cleanup. Because corrosion-related failures of waste tank walls could lead to the leakage of radioactive contaminants to the soil and groundwater, it has become essential to monitor corrosion conditions of the tank walls as tanks approach their design life. In October of 2000 work was started on a project to develop an EN based corrosion monitoring system for BVEST W-23 at ORNL. The project was undertaken to assess the corrosivity of the waste on welds in the tank and to assist in the overall development program for nuclear waste tank corrosion monitoring at the Hanford Site and other DOE facilities. Prior to the fabrication and deployment of the Tank W-23 system, laboratory testing was performed at ORNL to characterize the behavior of 304L (UNS $30403) stainless steel in simulated Tank W-23 waste solutions. Following the laboratory work a system was deployed in Tank W-23 in June of 2001. Data collection was terminated in June of 2002. This paper describes the laboratory development effort, final system design, and operational history of the Tank W-23 system. BACKGROUND Tank W-23 is a 50,000 gallon (189,270 L) waste tank fabricated from ½ inch thick (1.27 cm) welded 304L (UNS $30403) stainless steel plates. The tank measures approximately 12 feet (3.6 m) in diameter and 61 feet (18.6 m) in length. It is housed in a concrete vault lined with stainless steel in the BVEST facility near the center of the ORNL campus. 1 The BVEST facility is used to collect liquid low- level waste (LLLW) from waste stream producers at ORNL. The LLLW is reduced in volume through processing at an evaporator prior to being moved to the BVEST facility. Tank W-23 is primarily used as a storage tank but can also serve as a feed tank for the evaporator. Because of its role as a storage tank that could see waste streams of varying composition, Tank W-23 was selected as an ideal tank for the application of on-line corrosion monitoring. Prior to 1995, only a small number of traditional electrochemical techniques had been tried within the DOE complex to determine the corrosivity of nuclear waste stored in underground tanks. Coupon exposure programs, linear polarization resistance (LPR), and electrical resistance (ER) techniques have all been tried with limited degrees of success. 25 These techniques are most effective for monitoring uniform corrosion, but are not well suited for early detection of localized forms of corrosion such as pitting and stress corrosion cracking (SCC). Over the last ~20 years, EN b
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- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
ABSTRACT A new approach for estimating whether a present condition satisfies a critical one for initiating propagating corrosion cracks was developed. A change in potential fluctuation (potential noise) of a stressed specimen was measured in a chloride solution, with stepwise increase in temperature up to 80ºC. A fully sensitized UNS30400 (type-304) stainless steel was used for the specimen. Under the employed conditions, the potential fluctuations are regarded as resulting from the initiation and repassivation of non-propagating stress corrosion cracks. The charge in each event was calculated from the amplitude of the potential fluctuation. The frequency distribution of the occurrence rate of the potential fluctuation was examined as a function of the charge. Propagating cracks occurred at a temperature of 80ºC and stress levels of 341 or 440 MPa. At this temperature and these stress levels, the histograms of charge frequency had significantly higher amplitude in the range 0.25 to 2.5 µC, in comparison with conditions where propagating cracks did not appear. It is considered that this approach would be a promising method for monitoring the initiation of stress corrosion cracking at actual plants. INTRODUCTION The electrochemical noise measurement (ENM) is establishing a place as a method 1 for measuring polarization resistance, following the linear polarization method and electrochemical impedance spectroscopy (EIS). In general, it might be said that the polarization resistance is not a tool for localized corrosion but for general corrosion monitoring. However, the electrochemical noise (EN) itself has a potential for assessing localized corrosion activity, because the primary source of the EN on a Copyright passivated electrode is a transient current resulting from the initiation and repassivation of metastable localized corrosion. Pioneer attempts 2-11 on the application of the ENM for localized corrosion activity were the use of spectrum analysis. The spectrum analyses of the EN have revealed some interesting probabilistic features in the initial process of localized corrosion. However, it may be said that comprehensive results that encourage the application of the spectrum analysis to a monitoring method at actual plants seem not to be shown. A method using localization index (LI)1,12 might be a representative approach for monitoring the localized corrosion activity. However, as it has been pointed out 13, the LI has the disadvantage that it is sensitive not only to the degree of the localization of corrosion activity but also to changes in the value of the mean current. Recently, a new method that might be immune to the change in the mean current was proposed 14; this method used the average charge from individual local dissolution for the analysis; the quantity was calculated with an equation delivered from the shot-noise theory. This method is unique but it seems not to be widely applied yet. Stress corrosion cracking (SCC) is considered as the most serious corrosion damage in chemical plant, especially those for processing halide fluids. SCC is characterized by its high propagation rate in the cross-sectional direction relative to other localized corrosion phenomena, and it happens extensively on corrosion resistant materials, which are usually used in small thickness. Thus, the occurrence of the crack must be detected during the initiation stage or at a very initial stage of propagation, in order to monitor SCC successfully. Also, when we apply the ENM or other electrochemical method for localized corrosion monitoring, it must be kept in mind that we have to estimate a change happened on the huge area of structural material using information from the small area of working electr
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- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)