Flow-assisted Corrosion Research Articles

Blanket test facility for mockup testing on water cooled ceramic breeder blanket system

Intensive research and development activities have been conducted for designing a water-cooled ceramic breeder (WCCB) blanket system. In this system 325 °C/15.5 MPa of pressurized water removes heat injected and accumulated in blanket containers made of a reduced activation ferritic/martensitic steel, F82H. The container has lithium ceramics and beryllium pebbles as tritium breeder and neutron multiplier, respectively. In order to demonstrate performance of the system, especially for high-temperature pressurized water coolant, experimental apparatus have been installed in Rokkasho Fusion Institute, National Institutes for Quantum Science and Technology, Japan. These apparatuses enable to conduct the following experiment on full-scale mockups: 1) high heat flux (HHF) test to demonstrate heat removal of surface heat flux by electron beam gun simulating plasma, 2) flow assisted corrosion, 3) coolant ingress into dummy pebble beds, and 4) beryllium-water reaction between the coolant and the pebbles. In this paper, overviews, specifications, early results of these apparatus are reported.

Flow-Assisted Corrosion of API 5L X56 Steel: Effect of Flow Velocity and Dissolved Oxygen

Flow-Assisted Corrosion of API 5L X56 Steel: Effect of Flow Velocity and Dissolved Oxygen

Flow-Assisted Corrosion of Carbon Steel in Simulated Nuclear Plant Steam Generator Conditions

Flow-assisted corrosion occurs via increased dissolution and/or mechanical degradation of protective oxide formed on the surface of construction materials in direct contact with coolant liquids. In the present paper, this phenomenon is studied on carbon steel in an ammonia-ethanolamine-hydrazine electrolyte by in situ electrochemical impedance spectroscopy in conditions that closely simulate those that prevail in nuclear plant steam generators. Based on the obtained results, a quantitative kinetic model of the process is proposed and parameterized by nonlinear regression of experimental data to the respective transfer function. On the basis of the experimental and calculational results, it is concluded that flow-assisted corrosion of carbon steel is limited by oxide dissolution and cation ejection processes and the protective layer–coolant interface. Expressions for the film growth and corrosion release processes are proposed and successfully compared to operational data.

Assessment of flow-assisted corrosion rate of copper alloy cooling tube for application in fusion reactors

In-vessel plasma facing components in fusion reactors such as ITER and DEMO experience high thermal loads and require active cooling, for which water is one possible coolant. The solution where plasma facing components utilise tungsten blocks as sacrificial armour has a joint internal structure of cooling tubes made from the copper base (∼99 % Cu) alloy CuCrZr. This paper concerns the testing of CuCrZr tubes with respect to flow-assisted corrosion (FAC) at water velocity in the range 8–10 m/s and temperature in the range 150 °C–250 °C. The FAC rate was evaluated by gravimetry, microscopy, and sampling of the water from the re-circulating test system. When the electrochemical potential of the CuCrZr specimens was kept in the reducing range where Cu is thermodynamically stable as a metal, no FAC could be observed on the specimens. At electrochemical potentials that promotes oxidation of Cu through presence of an oxidizer the FAC rate of a straight CuCrZr tube was estimated to be in the order of 400 µm per full power year.

Surface analyses of corrosion products formed on API X-70 steel in sour brine after testing in a pipe loop

Flow assisted corrosion (FAC) is a problem of pipeline systems that handle high flow rates and strong direction changes. In the present investigation, FAC was tested on carbon steel exposed to the NACE 1D-196 environment by means an experimental pipe loop. As the exposure time increased, corrosion products formed a mixture of oxides, sulfides, and an apparent sulfate (rhombohedral mikasaite Fe2 (SO4)3), which was found in greater proportion and appeared to have a significant effect on decreasing corrosion rate. Transmission electron microscopy and x ray diffraction patterns seemed to confirm the presence of a sulfate and some oxides as the major chemical species contained in the corrosion products.

CFD-Based Erosion and Corrosion Modeling of a Pipeline with CO2-Containing Gas–Water Two-Phase Flow

A natural gas transportation pipeline with a gas–water two-phase flow containing CO2 is prone to severe flow-assisted corrosion (FAC). The accumulation location of the water phase in the pipeline and the wall shear stress distribution are important factors affecting the severity of this phenomenon. In this work, computational fluid dynamics (CFD) simulations were performed using the realizable k-ε model and volume of fluid (VOF) model to determine the gas–water volume fraction distribution and wall shear stress in a gas–water two-phase pipeline and established a pipeline corrosion prediction model. By determining where the water phase accumulates in the pipeline, the potential corrosion area could be predicted. By alleviating the phenomena of excessive local wall shear stress and bubble cavitation, the FAC due to the formation of stress and acid gas can be controlled. The simulation results lay a certain foundation for the corrosion research of gas–liquid two-phase flow pipelines.

Application of artificial intelligence to predict flow assisted corrosion in nuclear/thermal power plant

Flow assisted corrosion (FAC) is a wall-thinning phenomena of carbon steel pipe in nuclear and thermal power plant. Due to FAC, many accidents have taken place in nuclear plants resulting in casualties. In FAC, dissolution of iron from the iron-oxide fluid interface at pipe wall takes place and it is affected by pH, oxygen concentration, flow rate, temperature and chromium content of piping material. Due to complex interaction of these parameters, FAC prediction is difficult using conventional modeling tools and experimental evaluation is time consuming and costly. In this work, artificial neural network (ANN) has been used for FAC prediction using 320 data points collected from published literature. The neural network training was carried out using Lavender-Marquardt back-propagation algorithm in Matlab. The results show that ANN is a powerful tool for predicting FAC rate with regression coefficient above 90% and hence it can be very useful by regular training of the model with actual operational data in safety management and long term planning in nuclear/thermal power plant. A sensitivity analysis with respect to each parameter has been carried out using ANN model. It is observed that FAC rate is lower under alkaline conditions and goes through a maxima in a temperature range of 140 to 150°C.

Probabilistic analysis of electromagnetic acoustic resonance signals for the detection of pipe wall thinning

ABSTRACT This study proposes a probability of detection (POD) model for the probabilistic analysis of the detectability of electromagnetic acoustic resonance (EMAR) method for the detection and evaluation of pipe wall thinning. Forty-one carbon steel plate samples with an artificially corroded groove were prepared to simulate pipe wall thinning caused by flow-assisted corrosion. Experiments were performed to gather EMAR signals from the samples, and subsequently the depths of the grooves were evaluated based on the fundamental frequency of the measured signals. The results of the experiments showed that the error in evaluating the depth of a groove tended to increase with the depth. The results also confirmed that the surface roughness of the groove would contribute to the error, and the thickness of a plate without corrosion can be quite accurately evaluated. Analysing the measured EMAR signals using the proposed POD model, which takes these characteristics into consideration, and a conventional one confirmed that the proposed model can more reasonably evaluate the probability of detection against small wall thinning, as well as the false-positive rate.

Under Deposit Corrosion in Steam Generators: Towards Understanding Critical Deposit Thresholds

Most significant industrial facilities operate large steam systems, including multiple steam generators. The steam produced may be used for power generation by steam turbines or for heating various equipment items and is usually critical to the overall operation of the plant. Each steam generator will typically contain hundreds of carbon steel tubes: the failure of such tubes by unpredicted corrosion represents a common cause of plant downtime, significant lost production, and an ongoing safety risk. The mechanism of UDC in these systems is not well-understood, and this is in part because of the experimental challenges of studying such systems [1-3]. However, some clear parametric observations have been made and it is now established that very low (ppb) levels of dissolved ferrous ions and micro-scale particles of magnetite are produced by flow-assisted corrosion in the steam generator feed-water systems, and that these are then deposited on to the heat transfer surfaces. Together with the presence of only trace (ppb) levels of bulk chloride contamination, these deposits can lead to extraordinarily rapid corrosion. Characteristic features of the damaged material include: the porous structure of the deposit layer; the presence of high local chloride concentrations within the deposits; and formation of a complex ‘multi-duplex’ layer of corrosion product that exhibits approximately linear growth kinetics. According to EPRI guidelines [4], 35 mg.cm-2 represents a critical threshold for deposit thickness after which interventional maintenance should be initiated. This nominal thickness is not based on mechanistic understanding and is often achieved in boilers within only a few years of operation, resulting in the need for expensive and time-consuming chemical cleaning to remove the deposits. Hence, it is necessary to better understand the various stages in the formation of these layers to improve prediction of UDC and help reduce conservatism in maintenance without compromising on safety. In this presentation, we will present a study of field-retrieved samples that were examined with optical and electron microscopy techniques, coupled with phase and chemical analyses. This will be compared with model experiments where deposits are formed under laboratory-controlled conditions [1], including both new and literature data. We will discuss these data in terms of a model for UDC in steam generators, with emphasis on the critical deposit thickness and the particular role of chloride in the formation of the characteristic multi-duplex scales. References Robertson, J. and Forrest, J.E., 1991, Corrosion Science, 32(5/6), 521-540.Howell, A.G., 2006, NACE – 06458, NACE international publication.Dooley, R.B. and Bursik, A., 2010, Boiler and HRSG tube failures - Hydrogen Damage, 12(2), 122-127.Dooley, R.B., 2005, EPRI Technical Report, 1-154.

Study of flow-assisted corrosion (FAC) in a API 5L X-70 steel in a brine-H2S–CO2 system using the rotating cylindrical electrode

Corrosion caused by the mixture CO2/H2S in the transport of hydrocarbons is one of the most important research areas in the energy industry due to the severe problems it produces during the wear and tear of the pipes. Based in previous studies, in the present investigation the corrosion of API 5L X-70 steel in media with CO2 and H2S is studied as well as mixtures of both media, by means of a rotating cylindrical electrode due to the need to know the behavior of corrosion products in metals. The corrosion rate is evaluated at different pressures of H2S and CO2 and at 30 and 60 °C using the potentiodynamic polarization resistance measurements. From the results, it is observed that steel at the conditions of 0.8 bar H2S + 0.2 bar CO2 at 30 °C, yielded the lowest corrosion rate. This behavior is attributed to the fact that when H2S predominates it allows the formation of a greater number of protective layers comprised by a mixture of oxides, sulfides, sulfates and carbonates as corrosion products.

The Effect of Jet Flow Impingement on the Corrosion Products Formed on a Pipeline Steel in Naturally Aerated Sour Brine

Corrosion was generated by the action of a jet impingement flow of sour brine on pipeline steel samples of X70. Flow-assisted corrosion affected nature, number and peak intensity of the chemical species formed as corrosion products. Iron sulfides predominated in static and low flow rate conditions (1.1 m/s), whereas at 2.4 m/s iron oxides were mainly formed, which led to higher corrosion rates and suggested that oxides are less protective than sulfides. On inhibition, imidazoline seems to mitigate oxide formation and support sulfide formation balancing both species on steel surface. Ferrite phase in laminar pearlite was preferentially dissolved with/without inhibitor, and mackinawite (FeS2) was formed at every flow rate, angle with and without inhibitor. Theoretical stresses determined by computational flow dynamics for corrosion product removal showed a fair approximation to those proposed in the literature.

Evaluation of Corrosion in YA-Type ATR Fuel Element During Reactor PALM Cycle 153B

Two types of flow-assisted corrosion were observed at advanced test reactor (ATR) during PALM Cycle 153B-1 (April 2013): pitting corrosion and flow-assisted erosion corrosion. In this paper, a description of the corrosion is provided along with the results of thermodynamic, kinetic, neutronic, and thermohydraulic modeling. Together, these results provide a plausible explanation and means of corrosion remediation in the future. Cycle 153B-1 was a typical operating cycle for the ATR and did not result in any unusual plant transients. However, when the fuel elements were removed from the core and inspected, several thousand flow-assisted corrosion pits and “horseshoeing” defects (erosion corrosion) were readily observed on the surface of the several YA-type fuel elements. A thermohydraulic model of coolant in channel 20 (near a YA fuel element and the Be neutron reflector) was generated and helped to establish that the horizontal saw cuts in the Be neutron reflector had a significant effect on the temperature of the coolant. Horizontal cuts in the beryllium reflector block were created to arrest the propagation of large vertical crack(s) in Be. The flow was turbulent, rather than varying linearly with gradual heating of the coolant as it passed through the channel. The temperature rise was represented by a series of “humps,” which occurred at each horizontal saw cut in the beryllium reflector block. Each of the 13 saw cuts had a chamfered edge which resulted in the coolant flow being redirected as a jet across the coolant channel into the surface of the EE (i.e., a plate without nuclear fuel) plate. This explained the temperature rise and the observed scalloping and pitting degradation on the YA-M fuel elements. In the case of scalloping (horseshoeing), a surprising similarity of this defect to those appearing on aluminum plates rolled in overlubrication conditions was established. The neutronics data for modeling were provided using advanced irradiation simulations (MCNP, HELIOS). The following corrective measures were proposed based upon the results of JMatPro v.8.2 modeling (TTT and CCT diagrams): change the fabrication process by adding blister anneal before program anneal immediately after cold rolling of AA6061 plate. This step allows achieving complete recrystallization and eliminates strengthening due to metastable precipitates.

Effect of a nano-sized TiC particle addition on the flow-assisted corrosion resistance of SA 106B carbon steel

Carbon steel with dispersed nano-sized TiC ceramic particles was fabricated by the ex-situ introduction of the particles into the melt, with the flow-assisted corrosion (FAC) resistance then investigated in the presence and absence of TiC nanoparticles using a once-through type of FAC loop test. From the potentiodynamic polarization curves, the current density at any given anodic potential was decreased and the open-circuit potential was increased by the addition of TiC nanoparticles. In addition, when the nano-sized TiC particles were added, the FAC rate was 1.38 times lower than that of carbon steel without TiC nanoparticles, indicating an improvement of the FAC resistance due to the homogeneous distribution of the TiC reinforcing nanoparticles.

Simulations and Experiments for the Detection of Flow-Assisted Corrosion in Pipes

Flow-accelerated corrosion (FAC) is a phenomenon which causes wall thinning of pipes, fittings, vessels, and other components in the metal based piping systems that carry water or water-steam mixture in power plants and refineries. Currently used nondestructive techniques, such as radiographic testing (RT), ultrasonic testing (UT), and pulsed eddy current (PEC) testing in order to determine the remaining wall thickness, are time consuming and not economical. Hence, in this work, the use of the fundamental torsional mode ultrasonic guided wave to detect FAC was investigated using the finite element method (FEM) simulations and that were validated with experiments. The torsional wave was generated by the magnetostriction principle using surface mounted strips made of magnetostrictive Hyperco (FeCo) material that provided the source for the surface tractions required to generate the ultrasonic guided wave. The transient electric field was provided through a solenoid coil wound over the strips and permanent magnets were employed to provide the bias magnetic field. From this work, it was observed that the pulse-echo method is not suitable for the FAC detection because of the insignificant reflections from FAC defect region that could not be effectively detected. The through-transmission method was found to be more suitable for the FAC detection because the amplitude of transmitted signal decreased with increase in radial depth of FAC in both the simulation and experiment.

Study of Flow-Assisted Corrosion of AZ91D Magnesium Alloy in Loop System Based on Array Electrode Technology

A loop system was used to investigate flow-assisted corrosion (FAC) of AZ91D magnesium alloy at an elbow based on array electrode technology by potentiodynamic polarization, computational fluid dynamics, simulation and surface analysis. The experimental results demonstrate the fluid hydrodynamics plays a significant role in the FAC of AZ91D magnesium alloy. The corrosion rate increases from the outer wall to the inner wall of the elbow, with the higher corrosion rate corresponding to the higher flow velocity and larger shear stress at the elbow. The maximum corrosion rate appears at the innermost wall of the elbow, the location with the maximum flow velocity and shear stress.

Rotary Dynamic System Which Corrosion Test Simulates Conditions In Sea WaterFlow

The study of flow-assisted corrosion (FAC) involves the development of equipment capable of exposing metallic materials at different flow rates. The main aim of this work is to present a new equipment that allows evaluate the effect of corrosion by marine flow. This new device was built in carbon steel and it’s capable of exposing up to 162 specimens generating three different speeds in each test. Unlike other existing field devices such as rotating drum using curved specimens and only generates a flow rate per test (1,2), the device presented here uses simple machining specimens and higher flow rates.

The Design and Analysis of a Feeder Pipe Inspection Robot With an Automatic Pipe Tracking System

The feeder pipes in a pressurized heavy water reactor (PHWR) suffer from flow-assisted corrosion (FAC), which makes the wall thickness of the pipes thin. This effect is a well-known degradation mechanism of a carbon pipe with high pressure and high flow rate. Therefore, the weak parts of the pipe should be measured to guarantee the safety. This paper describes a mobile out-pipe inspection robot with an automatic pipe tracking system for a feeder pipe inspection in a PHWR. The robot is composed of dual inch worm mechanisms. One is for a longitudinal motion along a pipe, and the other is for a rotational motion in a circumferential direction to access all of the outer surfaces of a pipe. A design method for a gripper actuator is proposed by using a kinematic and force analysis. The proposed mechanism shows a more stable gripping capability than the conventional ones. An automatic pipe tracking system is proposed based on machine vision techniques to make the mobile robot follow the exact outer circumference of a curved feeder pipe as closely as possible, which is one of the requirements of a thickness measurement system for a feeder pipe. The proposed sensing technique is analyzed to verify its feasibility and to develop a calibration method for an accurate measurement. A mobile robot and control system are developed, and the automatic pipe tracking system is tested in a mockup of a feeder pipe.

Electrochemical characterization of sintered magnetite electrode in LiOH solution

In relation to the mitigation of flow assisted corrosion (FAC) occurring at the carbon steel materials at power plants, magnetite powder was sintered into pellets and used to construct electrodes for electrochemical property measurements in LiOH solutions at ambient conditions. Measurements indicated adsorption of hydroxide ions on the magnetite surface. Slow cathodic scanning removed the adsorbed OH − and returned the electrode surface to its original state. It is proposed that the cause of cyclic voltammetric (CV) peaks is the reduction of H 2O involving the conduction band edge ( E C) and valence band edge ( E V) of the magnetite. Negative polarization by the CV produced hydrogen atoms and injected them into the magnetite body; these were oxidized when the sweep was reversed and then dissipated at the magnetite surface by contact with OH − ions. Results support the interaction of magnetite energy levels with adsorbed species, rather than the dissolution of magnetite.

Effect of fluid hydrodynamics on flow-assisted corrosion of aluminum alloy in ethylene glycol–water solution studied by a microelectrode technique

Aluminum (Al) alloy microelectrodes were designed and installed in an impingement jet system to investigate the effect of fluid hydrodynamics on Al alloy corrosion in a flowing ethylene glycol–water solution by electrochemical measurements and computational fluid dynamics simulation. Results demonstrate that fluid hydrodynamics, in particular, the fluid flow velocity and shear stress, play an essential role in corrosion of Al alloy. The microelectrode located at the center of the sample holder is associated with the most stable state, while the one at the edge of the holder has the most active state. The electrochemical activity of the Al alloy microelectrode, indicated by the anodic dissolution current density, is directly related to the velocity of fluid flow and the shear stress.

Cathodic reaction kinetics and its implication on flow-assisted corrosion of aluminum alloy in aqueous ethylene glycol solution

The cathodic reaction kinetics and anodic behavior of Al alloy 3003 in aerated ethylene glycol–water solution, under well-controlled hydrodynamic conditions, were investigated by various measurements using a rotating disk electrode (RDE). The transport and electrochemical parameters for cathodic oxygen reduction were fitted and determined. The results demonstrate that the cathodic reaction is a purely diffusion-controlled process within a certain potential region. The experimentally fitted value of diffusion coefficient of oxygen is 3.0 × 10−8 cm2 s−1. The dependence of cathodic current on rotation speed was in quantitative agreement with Levich equation. At potentials more positive than the diffusion controlled region, the cathodic process was controlled by both diffusion and electrochemical kinetics. The electrochemical reaction rate constant, k 0, was determined to be 1.1 × 10−9 cm s−1. There is little effect of electrode rotation on anodic behavior of Al alloy during stable pitting. However, fluid hydrodynamics play a significant role in formation of the oxide film and the Al alloy passivity. An enhanced electrode rotation would increase the mass-transfer rate of solution, and thus the oxygen diffusion towards the electrode surface for reduction reaction. The generated hydroxide ions are favorable to the formation of Al oxide film on electrode surface.