Flow Accelerated Corrosion Rate Research Articles

Effects of fluid dynamics parameters on flow-accelerated corrosion at elbow of carbon steel pipeline

Flow-accelerated corrosion (FAC) has always posed a significant threat to the safe operation of the secondary circuit in nuclear power units. In this study, we investigated typical carbon steel elbow pipe sections susceptible to FAC failure using fluid dynamics software to analyze the hydrodynamic characteristics at varying inlet velocities (2 m s−1, 4 m s−1, and 6 m s−1). The distribution of the FAC rate was monitored in real time using an array electrode. The results revealed that the outermost side of the elbow pipe section was the most susceptible location to FAC. By comparing different fluid dynamic parameters with the FAC rate, we identified radial velocity as an effective parameter for characterizing the FAC rate. Additionally, we established an empirical formula for predicting flow-accelerated corrosion in elbow pipe sections using the least squares method. The implications of this research are pertinent to the design and operation of pipelines in nuclear power plants.

Assessment of flow-accelerated corrosion-induced wall thinning in SA106 pipes with elbow sections

A combination of flow-accelerated corrosion (FAC) tests and corresponding computational fluid dynamics (CFD) tests were performed to determine the hydrodynamic parameters that could help predict the highly susceptible location to FAC in the elbow section. The accelerated FAC tests were performed on a specimen containing elbow sections fabricated using commercial 2-inch carbon steel pipe. The tests were conducted at flow rates of 9 m/s under the following conditions: water temperature of 150 °C, dissolved oxygen <5 ppb, and pH 7. Thickness reduction of the specimen pipe due to FAC was measured using ultrasonic testing. CFD was conducted on the FAC test specimen, and the turbulence intensity, and shear stress were analyzed. Notably, the location of the maximum hydrodynamic parameters, that is, the wall shear stress and turbulent intensity, is also the same location with maximum FAC rate. Therefore, the shear stress and turbulence intensity can be used as hydrodynamic parameters that help predict the FAC-induced wall-thinning rate. The results provide a method to identify locations susceptible to FAC and can be useful for determining inspection priority in piping systems.

Effects of Cr and Mo contents on the flow-accelerated corrosion behavior of low alloy steels in the secondary side of pressurized water reactors

Carbon steels have been extensively used as structural materials in the secondary side of pressurized water reactors, which are susceptible to flow-accelerated corrosion (FAC). To overcome this issue, low-alloy steels containing 2.25Cr-1Mo (P22) have been introduced, as Cr and Mo are effective alloying elements in mitigating FAC. However, the behavior of these alloying elements in the secondary water chemistry is not well-understood, and therefore, there is a need to explore alternative materials that can address the issue of FAC. In this study, three model alloys were manufactured based on Ducreux's model on FAC rate to examine the effects of Cr and Mo on the corrosion behavior of low-alloy steels compared to that of commercial P22. Microstructure of P22 was ferritic/pearlite structure while the model alloys was ferritic/tempered bainite structure due to the existence of Mn and Si. The difference in microstructure led to the difference in hardness values, and elimination of Mo from the model alloys resulted in reduction in strain. The FAC rate was mainly influenced by the Cr content in the oxide layer rather than Mo. The passive film layer hinders the exposure of the inner layer to H2O in the solution, resulting in Cr3+ dissolution into the Fe oxide layer. The continuous passivation leads to the formation of two compact layers, one amorphous and one crystalline Cr, creating Fe oxide substitutes. It is also revealed that the solubility of Cr species is much lower than that of Fe species resulting in the enrichment of Cr in the outer layer, and thus the higher Cr content reinforces the passivity of the steels. The Fe-Cr alloy exhibited promising corrosion resistance, suggesting that it could be a potential substitute for Fe-Cr-Mo alloy.

The effect of flow velocity and material microstructure on FAC behavior and mechanism in simulated PWR conditions

In this study, combined with room-temperature electrochemical and hydrodynamic numerical simulation techniques, rotating disc tests in a high-temperature, high-pressure water environment were conducted to investigate the mechanisms of flow velocity and microstructure of SA106B on Flow Accelerated Corrosion (FAC). It has been demonstrated that the microstructure of SA106B influenced the corrosion potential and consequently the corrosion resistance. The normalization treatment changed the pearlite morphology from a segregated band to a diffuse island, which shifted the corrosion potential of SA106B in a positive direction, increased the polarization resistance, greatly reduced the local corrosion degree, increased the corrosion resistance, and noticeably slowed down the FAC rate of SA106B. On the other hand, the FAC rate increased linearly with an increase in flow rate, and its slope was related to the corrosion potential. The difference between the FAC rates of the as-received and normalized SA106B strongly depended on the flow velocity, and became more pronounced as the flow rate increased. When the flow velocity approached 4.34 m/s, the decrease degree of FAC rate of normalized SA106B compared to that of as-received SA106B increased dramatically, which may be related to the thickening and cracking reduction of Fe3O4 film on the normalized SA106B.

Flow accelerated corrosion and erosion\u2212corrosion behavior of marine carbon steel in natural seawater

In this work, flow accelerated corrosion (FAC) and erosion−corrosion of marine carbon steel in natural seawater were electrochemically studied using a submerged impingement jet system. Results show that the formation of a relatively compact rust layer in flowing natural seawater would lead to the FAC pattern change from ‘flow marks’ to pits. The increase of the flow velocity was found to have a negligible influence on the FAC rate at velocities of 5−8 m s−1. The synergy of mechanical erosion and electrochemical corrosion is the main contributor to the total steel loss under erosion−corrosion. The increase of the sand impact energy could induce the pitting damage and accelerate the steel degradation. The accumulation of the rust inside the pits could facilitate the longitudinal growth of the pits, however, the accumulated rusts retard the erosion of the pit bottom. The erosion and corrosion could work together to cause the steel peeling at the pit boundary. The steel degradation would gradually change from corrosion-dominated to erosion-dominated along with the impact energy increasing.

Flow-accelerated corrosion assessment for SA106 and SA335 pipes with elbows and welds

A FAC (flow-accelerated corrosion) test was performed for a straight pipe composed of the SA335 Gr P22 and SA106 Gr B (SA106-SA335-SA106) types of steel with welds as a function of the flow rate in the range of 7–12 m/s at 150 °C and with DO < 5 ppb at pH levels ranging from 7 to 9.5 up to a cumulative test time of 7200 h using the FAC demonstration test facility. Afterward, the experimental pipe was examined destructively to investigate opposite effects as well as entrance effects. In addition, the FAC rate obtained using a pipe specimen with a 50 mm inner diameter was compared with the rate obtained from a rotating cylindrical electrode. The effects of the complicated fluid flows at the elbow and orifice of the pipeline were also evaluated using another test section designed to examine the independent effects of the orifice and the elbow depending on the distance and the combined effects on orifice and elbow. The tests were performed under the following conditions: 130–150 °C, DO < 5 ppb, pH 7 and a flow rate of 3 m/s. The FAC rate was determined using the thickness change obtained from commercial room-temperature ultrasonic testing (UT).

Flow accelerated corrosion rate on carbon steel pipe bend by thin layer activation technique and computational modeling: Under PHWR operating conditions

Carbon Steel (CS) piping plays a vital role in the heat transport circuits of power plants. These pipes undergo excessive degradation in some of the specific locations due to the flow dynamics variation and such corrosion is termed as the flow accelerated corrosion (FAC). The corrosion rate is usually estimated at a specific location based on one of the best available technique known as the Think Layer Activation (TLA) method. In the present study this method was adopted for the estimation of CS pipe corrosion with 50NB Sch 160, bend angle of 58° and 4D bend radius (D-pipe diameter). Irradiated location was chosen based on the turbulence patterns in the bend as mapped by CFD analysis. At the specified location the corrosion rate to be monitored was irradiated with the proton beam of 13.3 MeV energy aiming for the nuclear reaction of Fe56(p,n) Co56. This irradiated specimen was welded to the High Temperature High Pressure (HTHP) loop and operated at 290 °C/87 bar. The chemistry parameters like pH (10.2) and DO (< 5 ppb) in the loop were maintained by suitably adding LiOH and N2H4. Corrosion rate was assessed by measuring the radioactivity decrease due to corrosion. Throughout the experimental duration the radioactivity measurement was carried on the CS pipe surface at the fixed distance locations. The flow structure in the considered geometry is simulated using CFD. The flow field, velocity, is used to calculate the wall shear stress and mass transfer coefficient. The corrosion rate is calculated with the help of Chilton-Calbourn Equation. It is observed that the computed corrosion rate for this CS pipe under this chemistry and geometry conditions was 400um/y which coincides with that of the TLA method.

The Roles of Fluid Hydrodynamics, Mass Transfer, Rust Layer and Macro-Cell Current on Flow Accelerated Corrosion of Carbon Steel in Oxygen Containing Electrolyte

The flow accelerated corrosion (FAC) of EH 36 carbon steel in the oxygen containing flowing electrolyte is studied using multi-electrode array arranged in a jet rig system. The FAC of the working electrodes (WEs) under both uncoupled and coupled conditions are investigated in conjunction with computational fluid dynamics (CFD) simulation. Results show that a higher mass transfer rate would lead to a higher FAC rate when the WEs are uncoupled. The rust layer could retard the oxygen diffusion, resulting in the FAC rate decreasing. The mass transfer process and the distribution of the rust layer are significantly influenced by the fluid hydrodynamics. However, when the WEs are coupled together, serious FAC damage would occur on the WEs where lower mass transfer rates are registered. The macro-cell currents would become the main lead of FAC propagation at coupled conditions.

The Effect of Heat-and-Mass Transfer and Flow Hydrodynamics on the Flow Accelerated Corrosion Rate in Evaporators of Combined-Cycle Unit Heat-Recovery Steam Generators

Flow accelerated corrosion (FAC) is considered one of the major causes of damage to heat-recovery steam generators (HRSG) of combined-cycle units. In the last few decades, a great number of papers devoted to this problem have been published in many countries around the world. The results of investigations were analyzed as a rule, on the basis of the flow-averaged thermochemical parameters of the flow, while the features of the near-wall liquid film determining the FAC rate were not taken into account. The indicators in the near-wall region depends on the heat-and-mass transfer conditions, flow hydrodynamics, and the specific of chemicals used to correct the water chemistry (WC). For ammonia and oxygen water treatment chemistries, an equilibrium model is proposed and its validity for HRSG evaporators is substantiated. The rate of the exchange of gas reagents between steam and water is determined by the distribution coefficient Kd. To simplify calculations, simple approximating correlations of Kd for ammonia and oxygen is recommended. For the water chemistry with solid reagents, a diffusion model has been developed to calculate mass transfer on the basis of data on heat transfer in steam-generating tubes. The concentration of reagents near the wall is determined by both the turbulent transport of the liquid between the flow core and the near-wall layer and the coefficient of reagent distribution between the phases. Simple approximating correlations of distribution coefficients for Na3PO4, NaOH, and 90H Turb helamine are proposed. An approximate correlation between the hydraulic resistance coefficient Kh and the geometric parameter Kс of the FAC process has been established. The hydrodynamic fundamentals of the standard HRSG structural members have been studied in more detail than FAC. To estimate Kс, one can use the known value of Kh and the correlation between them. However, this correlation should be used with care since it has been obtained for certain conditions of unambiguity (i.e., specific construction material, water chemistry, flow history, etc.). Under other conditions, this correlation will change somewhat; therefore, it can only be used for rough estimation.

Investigation of corrosion behavior at elbow by array electrode and computational fluid dynamics simulation

AbstractThe present study focuses on the flow‐accelerated corrosion (FAC) behavior of A106Gr.B steel at 90° elbow by electrochemical measurement and computational fluid dynamics (CFD) simulation. The FAC rates under turbulent flows with a velocity of 3 and 1.5 m/s were measured by an array electrode technique in a loop system. The experimental results reveal that the maximum FAC rate appears at the extrados of 90° elbow, consistent with the locations from the rupture of the carbon steel piping in the worst cases at elbows. In addition, an effective mass transfer coefficient in consideration of the geometric factor was used to evaluate the FAC rate at intrados and extrados of the 90° elbow by CFD simulation. The predicted results are in good agreement with the experimental values.

Local Flow-Accelerated Corrosion of Welds in NPP Power Unit Pipelines: Phenomenon Mechanism Features and Measures to Prevent Damage

Flow-accelerated corrosion of metal caused by single- or two-phase flow of working fluid leads to thinning and destruction of welds in NPP power unit pipelines. Field experience gained from the operation of Russian and foreign nuclear power plants testifies that there have been many cases of damages inflicted to welds due to local flow-accelerated corrosion, the number of which tends to grow with the time for which the power units have been in operation. The article gives examples of the most typical places and characteristic features pertinent to the way in which the flow-accelerated corrosion of weld elements' metal takes place. The role and influence of the chemical composition of the weld metal and heat-affected zone metal on the location and rate of local flow-accelerated corrosion thinning in welds are determined. The flow hydrodynamic characteristics having an essential effect on the rate of flow-accelerated corrosion processes and the local thinning occurrence places are determined. Results from numerical modeling of the flow-accelerated corrosion weld thinning development process for different contents of chromium in the weld and heat-affected zone metal are given. The possibility of increasing the flow-accelerated corrosion rate in pipelines downstream of a weld with a preceding extended straight pipeline segment made of metal not prone to flow-accelerated corrosion is analyzed. Methods aimed at preventing the occurrence of damage to pipelines of NPP power units due to flow-accelerated corrosion are discussed. The article gives information on the results of activities for modifying the standard programs for in-service inspection of pipelines at VVER-based NPPs and also on the use, at Russian NPPs, of software systems providing support to the personnel on optimizing the arrangement and scheduling of in-service monitoring of flow-accelerated corrosion wear of heat-affected zones in welds of the pipelines used at NPP power units equipped with VVER-440, VVER-1000, and BN-600 reactors. It can be expected that the application of regularly updated software systems for supporting the personnel will make it possible to timely prevent inadmissible thinning and abrupt flow-accelerated corrosion-induced failures of pipeline welds in the power units of Russian nuclear power plants.

Influence of flow velocity and temperature on flow accelerated corrosion rate at an elbow pipe

Abstract Flow accelerated corrosion (FAC) is one of the important issues that must be considered for aging fossil and nuclear power plants. To understand the effect of thermal flow field on FAC, FAC rates at an elbow pipe were measured under different flow velocity and temperature conditions. The elbow test section was made of stainless steel (diameter D = 49.5 mm) and FAC rates were measured using corrosion sensors made of carbon steel. The dissolved oxygen concentration was kept under 0.1 μg/kg, and pH was nearly neutral (about 7.0) at room temperature. The mean cross-sectional velocity was changed from 0.39 to 5.74 m/s (Reynolds number, about 1.0e6). When the water temperature was about 150 °C, the FAC rate was smaller at the intrados of the elbow pipe than at other circumferential locations. This tendency continued downstream. The FAC rates at the elbow pipe were larger than those upstream and downstream from the elbow pipe and the FAC rates downstream from the elbow pipe decreased along the flow direction. FAC rates increased as flow velocity increased and their relationship was not linear. The ratios of the maximum FAC rate at the elbow to the FAC rate in the upstream straight pipe ranged from about 1.7 to 2.9. When temperature decreased to 100 °C, FAC rate at the intrados became the largest of the other circumferential sensors. When temperature decreased further to 50 °C, FAC rate also decreased, but the value was not negligible. The influence of flow velocity was negligibly small at 50 °C and remarkable at 100 °C and 150 °C. The combination effect of flow velocity and temperature was different from place to place and particularly strong at the elbow.

Effects of local velocity components on flow-accelerated corrosion at 90° elbow

Experimental and numerical studies are conducted to investigate the effects of turbulent parameters on flow-accelerated corrosion (FAC) behavior of low carbon steel at 90° elbow. The experimental testing of flow-accelerated corrosion behavior was carried out by the array electrode technique in a circulating loop system. The measurement of electrochemical corrosion test shows that the maximum corrosion current density is located in the extrados side of test section while the minimum value appears at the intrados side, consistent with the typical flow-accelerated corrosion induced failures of turbine plant pipelines and equipment. In addition, the flow behavior inside piping components of the loop system were sufficiently simulated by computational fluid dynamics (CFD) simulation and turbulent parameters were compared with flow-accelerated corrosion rate. With respect to the comparison of the results, the radius direction local velocity component (vr) is in good accordance with the configuration of corrosion current density. Therefore, the present results reveal the radius direction local velocity component is a major parameter for predicting the pipe-wall thinning of the 90° elbow due to flow-accelerated corrosion.

Flow-accelerated corrosion rate and residual life time estimation for the components of pipeline systems at nuclear power plants based on control data

As of today, large volumes of data related to non-destructive operational control are accumulated on NPPs. For ensuring safe operation of power units, optimization of scope and scheduling operational control it is necessary to continue development of guidance documents, software products, methodological guidance and operational documentation (Baranenko et al. 1998, Gulina et al. 2013, Recommendation (NSAC-202L-R4) 2013). Approaches are examined to assessment of the rate of erosion-corrosion wear (flow-accelerated corrosion - FAC) according to the data of operational control. The present study was performed based on the data of thickness gauging of different elements of pipelines of NPPs with different types of reactor. Further development of ideas exposed in (Baranenko et al. 2016) allowed revealing specific features of ECW processes on straight sections, bends and in the zones adjacent to weld joints of pipelines of NPPs equipped with VVER and RBMK reactors. Presence of the process of deposition of corrosion products on internal surfaces of pipeline walls results in the fact that residual lifetime of elements nominally increases due to deposition. However, real wall thickness under the layer of deposits is unknown just as the initial wall thickness is unknown as well. Investigation implemented in the present study is aimed at the substantiation of the methodology of calculation of FAC rate according to the data of operational control for the purpose of drawing calculation results closer to the reality keeping conservatism. Uniform approach to the assessment of FAC rate in the examined elements of pipelines was developed. Methodologies for evaluation of correction coefficients taking into account dimensional technological tolerances, special features of geometry of the element, as well as effect of deposits on the results of thickness measurements were suggested based on the data of operational control and industry standards. The implemented studies demonstrated efficiency of the developed procedures for pipeline welding zones. Analysis of known and newly developed procedures was performed for bends and ranking of these procedures according to the criterion of “conservatism of evaluation of residual lifetime” was executed. Introduction of correction coefficients allows enhancing conservatism of calculations of lifetime characteristics as compared with calculations performed on the basis of nominal values of thicknesses; the result depends on the type and dimensions of the element, its geometry, as well as on the type of reactor.

Prediction of Flow Accelerated Corrosion of NPP Pipeline Elements by Network Simulation Method

Based on a comprehensive approach that uses the computer simulation of the process of destroying structural materials and technology of self-learning neural networks, a methodology has been developed for predicting the rate of flow accelerated corrosion (FAC) of pipeline elements with a single-phase medium of the second circuit of nuclear power plants (NPPs). The neural network model has been implemented in the Delphi Integrated Development Environment. The neural network consists of an input layer containing seven elements and an output layer with two elements. As the input variables of the neural network, the parameters that have the greatest influence on FAC process are chosen. These are the medium temperature, the pipeline internal diameter, the oxygen content in the medium, the coolant flow velocity, the hydrogen index, the time of monitoring (or the start of operation), and the time for which the prediction is performed. For each of the network input parameters, intervals of possible values were chosen. At that, the factors that affect FAC rate, but not included in the feasible model (chromium, copper and molybdenum content in the pipeline material, amine type) are assumed to be permanent. As the output parameters of the neural network, FAC rate and the variation of the pipeline element wall thickness within the predicted time interval have been selected. As the activation function of the neural network the sigmoid function is used. As a method of training the neural network, the error back propagation method has been chosen, which assumes both a forward and reverse passage through the network layers. As the learning algorithm of the neural network, the one with a teacher has been chosen. As a test sample for the neural network, it is proposed, along with operational control data, to use the results of calculations based on a statistical model created in the framework of a special calculation-experimental method. The application of the developed methodology makes it possible to improve the prediction accuracy of FAC rate without determining all the dependencies between the many factors that influence FAC process. The low errors of the constructed models make it possible to use the results of calculations both to determine the resource characteristics of NPP pipelines and optimize operational control.

Hydrodynamic effects on flow accelerated corrosion at 120 °C and neutral pH conditions

Abstract The objective of present study is to investigate the influence of bend geometry and the resulting flow phenomenon on the rate of metal loss due to Flow Accelerated Corrosion (FAC). Experiments were carried out with an aggressive chemistry of neutral pH (6.5–7.0) and at a temperature of 120 °C to minimize the time duration required to make unambiguous measurement of the change of wall thickness due to FAC. Measurement of FAC rate was carried out by installing a stainless steel FAC specimen holder, in which the bend pipe was assembled by stacking carbon steel rings to simulate a bend of 10 mm bore with 58o bend angle and twice the bend diameter. The flow rate was adjusted to maintain a velocity of 7 m/s in the test section. The corrosion rate was experimentally quantified by the weight loss method, over an exposure period of two months at 120 °C in single phase of de-mineralized water. During this experiment, the value for the average thickness loss was found to be 0.9 mm. The turbulence patterns in the bend specimen holder were mapped by Computational Fluid Dynamics (CFD) parameters such as the wall shear stress and turbulent kinetic energy. The simulated mass transfer co-efficient and the corresponding corrosion rate correlated well with those of the measured values in various regions of the bend. The CFD studies showed that the intrados of the bend corrodes at a faster rate as compared to other regions of the bend. The change in temperature at a constant volumetric flow rate and in liquid phase does not significantly affect the velocity profile in the bend geometry.

Flow-Accelerated Corrosion Wear of Power-Generating Equipment: Investigations, Prediction, and Prevention: 2. Prediction and Prevention of General and Local Flow-Accelerated Corrosion

The second part of this review considers physicochemical models and computer codes used for predicting flow-accelerated corrosion wear of power generating equipment. Approaches used to prevent the occurrence of general and local flow-accelerated corrosion that are based on selecting metals resistant to flow-accelerated corrosion and adjusting the water chemistry of power units are also discussed. The existing computer codes use physicochemical models of flow-accelerated corrosion and statistical data on damages inflicted to power units due to flow-accelerated corrosion processes. Advantages and drawbacks of different analytical physicochemical models describing the flow-accelerated corrosion process are pointed out together with the specific features of using them in elaborating flow-accelerated corrosion computing codes. It is shown that the processes lying at the heart of the flow-accelerated corrosion mechanism include, on the one hand, the occurrence of a protective oxide layer on the metal surface and, on the other hand, the dissolution of this layer and carryover of dissolution products in the flow. Differences between the processes through which metal undergoes flow-accelerated corrosion in a single-phase water flow and in a two-phase wet steam flow are analyzed. Thus, the redistribution of admixtures and gases between the phases that takes place in two-phase media may cause a change in the pH values, thereby significantly influencing the flow-accelerated corrosion rate. In addition, the rate with which flow-accelerated corrosion products are carried over into a two-phase stream depends on the liquid film flow mode on the streamlined surface. The flow-accelerated corrosion rate computing codes most widely known around the world, including the COMSY code (Germany), CHECWORKS SFA code (United States), BRT-CICEROTM code (France), and RAMEK code (Russia) are considered. Their specific features and application limits are pointed out. Information on the effect the content of chromium, molybdenum, and copper has on the flow-accelerated corrosion rate is given. It is shown that the choice of metals resistant to flow-accelerated corrosion is a combined technical and economic problem, and the way in which it is solved has an effect on the safety and reliability of power unit operation. It is pointed out that the liquid phase pH value is essentially affected by the steam wetness degree if the latter exceeds 20%.

Flow-Accelerated Corrosion Wear of Power-Generating Equipment: Investigations, Prediction, and Prevention: 1. Flow-Accelerated Corrosion Processes and Regularities

The first part of this review considers the prerequisites and scales of damage inflicted to the equipment and pipelines of power plant units as a consequence of flow-accelerated corrosion, and examples of accidents involving lethal outcomes that occurred at nuclear power plants as a result of pipeline ruptures caused by flow-accelerated corrosion are given. It is shown that the scope of items susceptible to flow-accelerated corrosion includes components of condensate–feedwater and wet steam path equipment and pipelines made of carbon and low-alloy steels. The main negative consequences caused by flow-accelerated corrosion are local metal thinning spots that can lead to abrupt failures and depressurization of the process circuit and contamination of working fluid with iron containing products of flow-accelerated corrosion. Sedimentation of these products in a steam generator is one of factors causing damage to and failure of its heat transfer tubes. It is proposed to draw a distinction between general and local flow-accelerated corrosion. General flow-accelerated corrosion causes ingress of iron-containing compounds into the working fluid and is characterized by a moderate metal thinning rate that does not lead to destructions or occurrence of wormholes involving loss of process circuit leak tightness. The effects of local flow-accelerated corrosion manifest themselves in small parts of intricately shaped channels and are characterized by a significant metal thinning rate with possible occurrence of wormholes or abrupt destruction of the pipeline and power-generating equipment components. Typical cases of and statistical data on damages inflicted to nuclear power plant components due to flow-accelerated corrosion are presented. The physicochemical fundamentals and regularities relating to flow-accelerated corrosion of metal occurring in one- and two-phase flows are considered. It is pointed out that the hydrodynamic factor plays the determining role in the occurrence of zones and rate of local thinning caused by flow-accelerated corrosion. The key hydrodynamic characteristics influencing the local flow-accelerated corrosion rate are determined. Fundamental differences between the mechanisms governing flow-accelerated corrosion in two-phase medium and single-phase water flow are shown. These differences stem from the specific features of hydrodynamics pertinent to the motion of liquid film and interphase redistribution of admixtures and gases that gives rise to a change in the pH value of liquid. The results from experiments aimed at studying the effect of temperature on the flow-accelerated corrosion rate of different metals in a two-phase wet steam flow and the effect of steam wetness degree on the liquid film flow mode are presented.

Mathematical modeling of orifice downstream flow under flow-accelerated corrosion

The main objective of this paper is to establish an analytical model to evaluate the rate of corrosion in a horizontal pipe downstream of an orifice under flow-accelerated corrosion (FAC). FAC is a major issue causing the wall thinning of carbon steel piping in power plants. In this work, the dimensional analysis was employed using the method of repeating variables and the Buckingham Pi Theorem. It was found that the Sherwood number and the relative distance from orifice are the main dimensionless parameters influencing FAC downstream of an orifice. Concerning the available experimental data, two different cases considered; orifice ratio (OR) of 0.25 and 0.5. The result of mathematical modeling agreed with the experimental data. The maximum value of the FAC rate could be well-predicted for the OR of 0.25, while the location of the maximum FAC rate could be well predicted for the OR of 0.5. It was found that the maximum value of FAC rate increases with decreasing orifice ratio and also the maximum value will be located between 1 and 4dp downstream of the orifice in both cases. This work could be useful for professionals in industry and researchers in the field and could be the starting point for a new way of evaluating the FAC rate downstream of a flow’s singularity.

Расчет скорости коррозии и остаточного ресурса элементов трубопроводов АЭС по данным контроля

Расчет скорости коррозии и остаточного ресурса элементов трубопроводов АЭС по данным контроля