High Corrosive Environments Research Articles

Comparative Study on Intergranular Corrosion Characteristics of Cast Duplex Stainless Steel Stabilized with Zirconium

Intergranular corrosion of duplex stainless steel is a major concern in high corrosive environments. Interstitial stabilization of alloy is a possible technique for susceptibility to intergranular corrosion. In this paper, zirconium addition was made to 5A grade cast duplex stainless steel in order to achieve the stabilization. Addition of zirconium forms a mixture of zirconium carbides and nitrides which suppress the chromium depletion and thus increase the intergranular corrosion resistance. The metallurgical characterization was carried out on the specimens by means of optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy, and x-ray diffractometry. Corrosion behavior investigation using oxalic acid etch test and double-loop electrochemical potentiokinetic reactivation technique results underline the superior corrosion-resistant property of zirconium-added cast duplex stainless steel.

Highly Flexible and Transparent Ag Nanowire Electrode Encapsulated with Ultra-Thin Al2O3: Thermal, Ambient, and Mechanical Stabilities

There is an increasing demand in the flexible electronics industry for highly robust flexible/transparent conductors that can withstand high temperatures and corrosive environments. In this work, outstanding thermal and ambient stability is demonstrated for a highly transparent Ag nanowire electrode with a low electrical resistivity, by encapsulating it with an ultra-thin Al2O3 film (around 5.3 nm) via low-temperature (100 °C) atomic layer deposition. The Al2O3-encapsulated Ag nanowire (Al2O3/Ag) electrodes are stable even after annealing at 380 °C for 100 min and maintain their electrical and optical properties. The Al2O3 encapsulation layer also effectively blocks the permeation of H2O molecules and thereby enhances the ambient stability to greater than 1,080 h in an atmosphere with a relative humidity of 85% at 85 °C. Results from the cyclic bending test of up to 500,000 cycles (under an effective strain of 2.5%) confirm that the Al2O3/Ag nanowire electrode has a superior mechanical reliability to that of the conventional indium tin oxide film electrode. Moreover, the Al2O3 encapsulation significantly improves the mechanical durability of the Ag nanowire electrode, as confirmed by performing wiping tests using isopropyl alcohol.

Analytical analysis of vibration characteristics for the hard-coating cantilever laminated plate

For laminated plate served in high temperature and high corrosion environment, hard coating can be applied to suppress destructive vibration. While the creation of the dynamic model of hard-coating laminated plate is the premise of the research on vibration reduction. This study was focused on analyzing vibration characteristics of the hard-coating cantilever laminated plate under base excitation. Orthogonal polynomials were used as admissible displacement functions to formulate the displacement field, Lagrange’s equation was used to build the governing equations of both free vibration and forced vibration for the composite plate, and methods of solving the natural characteristics and the harmonic response were presented. A T300/QY89l1 laminated plate with NiCoCrAlY+YSZ hard coating was chosen to demonstrate the proposed method and obtained results were compared with the ones gotten by ANSYS software with the purpose of assessing the rationality of the developed analytical model. Finally, based on the established model, the influences of hard-coating parameters, including thickness, Young’s modulus, and loss factor, on the vibration characteristics of the laminated plate were studied. The results show that increasing the thickness, Young’s modulus and loss factor of hard coating are beneficial to vibration reduction of laminated plate.

Elevated Temperature Properties of Extruded Aluminium Matrix Composites Reinforced with Nickel Coated Silicon Carbide Particles

The superior mechanical properties of Aluminium Matrix Composites (AMC) together with the weight saving makes them attractive for a variety of engineering applications. They also have improved mechanical properties at the operating conditions, such as high temperature, corrosive or wear environment, etc. This paper deals with the study of high temperature tensile properties of Al 2014-10 wt.% SiC composites prepared using stir casting method. The cast billets were extruded at 450°C with ram speed of 2 mm/s and extrusion ratio of 8:1. The optical microscopy and scanning electron microscopy analysis were carried out on the as-cast and extruded base alloy and the composites. The room temperature and high temperature tensile properties were evaluated. The results of this study show that the extrusion process improves both the room temperature and high temperature strength of the base alloy and composites. The percentage increase is more in the case of base alloy than the composites.

Guided Wave Propagation and Damage Detection in Composite Pipes Using Piezoelectric Sensors

Composite materials have many attractive properties, e.g. light-weight combined with high mechanical strength, and are recognized as an enabling technology for deep-water high pressure high temperature (HPHT) and corrosive environment applications. However, composite still has a barrier to entry in relation to steel due to limited field experience and lack of systematic failure prediction and assurance of in-service performance. Advances in such areas would enable the use of composites in a wider range of applications. Evaluation of in-service prototypes offers a partial solution but is costly. Thus a method that allows constant health monitoring of the composite in real-time and in-situ would be extremely useful. Ultrasonic guided wave-based structural health monitoring (SHM) technology is one of the most prominent options in non-destructive evaluation and testing (NDE/NDT) techniques. To investigate the feasibility of guided wave-based SHM for composite pipes, propagation characteristics of guided waves in an epoxy hybrid carbon/glass fibres pipe are systematically studied using finite element (FE) simulation and experiments. Both axisymmetric modes of propagation, the longitudinal L(0,n) and torsional T(0,n) modes are considered in the simulation process, however only the longitudinal modes can be captured by the piezoelectric sensors. Additionally, the tuning curves experimentally plotted are used to obtain the frequency with the maximum amplitude of each guided mode. Finally, guided waves in the composite pipe are tested with artificial defects (gel coupled coins) to understand the behaviour of guided waves after interaction with the defects. The different condition of artificial defects, e.g., the defect size and defect location are studied to find out the proper condition and limitation of using guided waves to monitor and inspect composite pipes.

Radiation endurance in Al2O3 nanoceramics

The lack of suitable materials solutions stands as a major challenge for the development of advanced nuclear systems. Most issues are related to the simultaneous action of high temperatures, corrosive environments and radiation damage. Oxide nanoceramics are a promising class of materials which may benefit from the radiation tolerance of nanomaterials and the chemical compatibility of ceramics with many highly corrosive environments. Here, using thin films as a model system, we provide new insights into the radiation tolerance of oxide nanoceramics exposed to increasing damage levels at 600 °C –namely 20, 40 and 150 displacements per atom. Specifically, we investigate the evolution of the structural features, the mechanical properties, and the response to impact loading of Al2O3 thin films. Initially, the thin films contain a homogeneous dispersion of nanocrystals in an amorphous matrix. Irradiation induces crystallization of the amorphous phase, followed by grain growth. Crystallization brings along an enhancement of hardness, while grain growth induces softening according to the Hall-Petch effect. During grain growth, the excess mechanical energy is dissipated by twinning. The main energy dissipation mechanisms available upon impact loading are lattice plasticity and localized amorphization. These mechanisms are available in the irradiated material, but not in the as-deposited films.

Effect of Heat Treatment and Surface Condition on Inter-Granular Corrosion of Alloy 800

Abstract The alloy 800 is being used for steam generator tubings for pressurized heavy-water reactors (PHWRs). This material is susceptible to degradation because of severe operating conditions, like high temperature, stress, and corrosive environment. These degradation mechanisms include primary water stress corrosion cracking (PWSCC), secondary side or outer diameter stress corrosion cracking (ODSCC), inter-granular corrosion (IGC), fretting, wear, denting, high cycle fatigue, corrosion fatigue, etc. The present study was conducted to analyze the effect of solution annealing temperatures, sensitization treatments, and surface conditions on the corrosion rate. The alloy 800 tubular samples were investigated by means of a conventional corrosion test (according to ASTM G28-02) and an electrochemical potentiokinetic reactivation (EPR) test. Susceptibility to inter-granular corrosion under various experimental parameters was examined by using both the test methods and the results are compared. The observed trends in corrosion rate obtained by using conventional method and EPR test were found to be similar. These results were used to obtain most optimum heat-treatment parameters and surface condition, which will yield best corrosion resistance.

The use of experimental bending tests to more accurate numerical description of TBC damage process

Thermal barrier coatings (TBCs) have been extensively used in aircraft engines to protect critical engine parts such as blades and combustion chambers, which are exposed to high temperatures and corrosive environment. The blades of turbine engines are additionally exposed to high mechanical loads. These loads are created by the high rotational speed of the rotor (30 000 rot/min), causing the tensile and bending stresses. Therefore, experimental testing of coated samples is necessary in order to determine strength properties of TBCs. Beam samples with dimensions 50×10×2 mm were used in those studies. The TBC system consisted of 150 μm thick bond coat (NiCoCrAlY) and 300 μm thick top coat (YSZ) made by APS (air plasma spray) process. Samples were tested by three-point bending test with various loads. After bending tests, the samples were subjected to microscopic observation to determine the quantity of cracks and their depth. The above mentioned results were used to build numerical model and calibrate material data in Abaqus program. Brittle cracking damage model was applied for the TBC layer, which allows to remove elements after reaching criterion. Surface based cohesive behavior was used to model the delamination which may occur at the boundary between bond coat and top coat.

Development of a Composite Technique for Preconditioning of 41Cr4 Steel Used as Gear Material: Examination of Its Microstructural Characteristics and Properties

Commercial 41Cr4 (ISO standard) steel was treated by a composite technique. An intermediate layer was introduced firstly at the 41Cr4 steel surface by traditional carburizing and nitriding. Then a hard Cr coating was brush-plated on the intermediate layer. Finally, the coating layer was modified by high current pulsed electron beam (HCPEB), followed by quenching and subsequent tempering treatment. The microstructure, mechanical properties, and fracture behavior were characterized. The results show that a nanocrystalline Cr coating is formed at the 41Cr4 steel surface by the treatment of the new composite technique. Such nanocrystalline Cr coating has acceptable hardness and high corrosion resistance performance, which satisfies the demands of the gears working under high speed and corrosive environment. The composite process proposed in this study is considered as a new prospect method due to the multifunction layer design on the gear surface.

Design of Korean Standard Modular Buoy Body Using Polyethylene Polymer Material for Ship Safety

Buoy is the structure which is floated on sea surface in order to indicate the presenting obstacle such as reef and shallow sea and to show the direction of sea route to ship during sailing. Generally, the conventional material of buoy is steel and it has some problems. Firstly this steel light buoy has safety risk in case of collision between ship and steel buoy. Secondly steel buoy revealed high corrosion environment of salted water and oxide and corrosion of steel can lead to marine pollution. Thirdly it needs too much maintain cost because of its heavy weight. In this study, in order to overcome these problems we changed the buoy material from conventional steel body to polyethylene body. Polymer buoy body was designed with module type part and it can reduce total weight up to 43.12%. To evaluate the strength of that part, the structure analysis simulation was carried out with respect to stress, displacement, and strain. Maximum stress was 1.667 × 107 N/m2 and it was 25% of yielding stress of base material. Maximum displacement and strain were 3.164 mm and 0.00433353 and they are too small value and in safe range with comparing to total length of body. The stability of polymer buoy body was compared with conventional buoy with respect to center of gravity, center of buoyancy, metacenter, oscillation period, and tilt angle by wind, tidal current, and wave. Every value was improved comparing conventional one and we can get more stable buoy. Therefore the new polymer buoy body could prove its safety and stability.

Ultraviolet light irradiation on pitting corrosion of Cu-based bulk metallic glasses

We report the observation that UV irradiation substantially improves pitting corrosion resistance of Cu-based bulk metallic glasses. Specifically, two Cu-based bulk metallic glasses in this study showed more stable passive films under UV irradiation than under irradiation-free condition when polarized in 3.5 wt.% NaCl aqueous solution. This finding indicates that Cu-based bulk metallic glasses are promising to serve in high UV irradiation and corrosive environments.

Temperature measurements using a lithium niobate (LiNbO3) pyroelectric ceramic

Temperature measurements from a power generation system could improve its overall safety and efficiency. In addition, real time temperature measurement could lead to a qualitative assessment of the health of the energy system. The challenge of real time temperature measurement inside of a power generation unit lies in the sustainability and the reliability of sensing materials in high temperature and corrosive environments. In this paper, a pyroelectric ceramic material (lithium niobate, LiNbO3) capable of sustaining high temperatures, is considered as the temperature sensing material. LiNbO3 is a pyroelectric material that generates current proportional to the rate of temperature change with time. This property is sustained by LiNbO3 until it reaches its Curie temperature (1210°C). The generated current could be used for many applications including temperature sensing and energy harvesting from waste heat recovery. This paper presents the temperature measurement results using a LiNbO3 pyroelectric ceramic. Ceramics with dimensions of 1cm×1cm with two different thicknesses, 2mm and 1mm, were used as the temperature measurement sensors. Two samples were heated by a 14.5W/cm2 heat flux and cooled with natural convection. Electrodes were made on both surfaces of the samples with high purity silver paint and two electrical leads were connected to a picoammeter to measure the generated current with respect to the rate of temperature change of the material during heating and natural cooling. A K-type surface thermocouple was attached on top of LiNbO3 to compare the temperature measurements and maximum 8% and 6.7% differences were found for 2mm and 1mm thick samples, respectively.

Copper Nanoparticles Effect on the Corrosion Behavior of Different Types of Nickel-Based Super Alloys

Nickel-based alloys are usually used for a wide range of applications like petrochemical processing, oil and gas extraction, marine engineering and high temperature applications in power generation industry e.g., heat exchangers or turbine blades due to their excellent corrosion resistance and good mechanical properties. Nickel-based alloys are designed to resist high loading and severe corrosive environments during operations. The aim of this study is to investigate the effect of depositing copper nanoparticles of different sizes on top of the surface of different nickel-based alloys (e.g.alloys 825, 625 and 276) on their corrosion behavior in different electrolytes of different pH values and chloride and sulfide ions concentrations. The study included, electrochemical and non-electrochemical characterization techniques. Also, the surfaces of the corroded alloys were checked using optical and scanning electron microscopy, energy dispersive x-ray and atomic force microscopy.

Copper Nanoparticles Effect on the Corrosion Behavior of Different Types of Nickel-Based Super Alloys

Nickel-based alloys are usually used for a wide range of applications like petrochemical processing, oil and gas extraction, marine engineering and high temperature applications in power generation industry e.g., heat exchangers or turbine blades due to their excellent corrosion resistance and good mechanical properties. Nickel-based alloys are designed to resist high loading and severe corrosive environments during operations. The aim of this study is to investigate the effect of depositing copper nanoparticles of different sizes on top of the surface of different nickel-based alloys (e.g.alloys 825, 625 and 276) on their corrosion behavior in different electrolytes of different pH values and chloride and sulfide ions concentrations. The study included, electrochemical and non-electrochemical characterization techniques. Also, the surfaces of the corroded alloys were checked using optical and scanning electron microscopy, energy dispersive x-ray and atomic force microscopy.

Microstructure of Cast Ni-Cr-Al-C Alloy

Abstract Nickel based alloys, especially nickel based superalloys have gained the advantage over other alloys in the field of high temperature applications, and thus become irreplaceable at high temperature creep and aggressive corrosion environments, such as jet engines and steam turbines. However, the wear resistance of these alloys is insufficient at high temperatures. This work describes a microstructure of a new cast alloy. The microstructure consists of γ matrix strengthened by γ’ fine precipitates (dendrites) improving the high temperature strength and of Chromium Cr7C3 primary carbides (in interdendritic eutectics) which are designed to improve wear resistance as well as the high temperature strength.

Permeability test and fuzzy orthogonal analysis of hydrogenated nitrile O-ring

Abstract In the high temperature, high pressure and high corrosive environment of the oil and gas drilling downhole, the weatherability of rubber sealing material has a great influence on the production safety. In order to study the important degree of every key environmental factor in downhole influencing the sealing performance of rubber sealing material, a new device of simulating downhole environment is designed to test the permeability of O-ring. The sample is hydrogenated nitrile O-ring and orthogonal experiment method is used to do nine tests by getting three levels from temperature, pressure and CO 2 volume fraction. Test adopts fuzzy orthogonal method to analyze the main effects and the interaction between two factors, taking tensile strength, diameter variety rate and pH value of indicator as evaluation index. The results show that: the environmental factor influencing the sealing performance of hydrogenated nitrile O-ring from high to low by turns is temperature, pressure and CO 2 volume fraction, while the interaction between temperature and pressure is the most significant. It provides a new way to study the influence of downhole complex environment on the performance of rubber sealing material. Moreover, the results have important reference value to further study the failure mechanism of rubber sealing ring in many environmental factors and the rational use in engineering.

Experimental Study of the Crack Growth in Stainless Steels Using Thermal Methods

Martensitic steels are used in the engineering fields where high temperatures, corrosive environments and high mechanical stress are required. In this work,theThermoelastic Stress Analysis (TSA) technique was used to characterize the fracture mechanics behaviour of twomartensitic stainless steels.TSA technique is proposed both for the monitoring in continuous way the crack position and for evaluatingthe stress intensity factor (SIF). An automatic procedure was developed capable to process very quickly the thermoelastic data acquired during the test. In this way, the Paris’ Law can be assessed reducing significantly the testing time.

Synthesis and characterization of tungsten nitride (W2N) from WO3 and H2WO4 to be used in the electrode of electrochemical devices

Tungsten nitride was synthesized from commercial WO3 and H2WO4, two precursors with different specific surface areas: 1.0m2/g and 14.7m2/g. The material was prepared by nitridation method by a thermal treatment at 873K under NH3 flow. The W2N single phase was obtained with a crystal size of 15nm and 11nm, respectively, and with specific surface areas of 7.3m2/g (from WO3) and 27.8m2/g (from H2WO4). Both W2N exhibited high stability after a phosphoric acid attack. The W2N (WO3) powders show a high conductivity with a low activation energy (0.02eV) measured by Electrochemical Impedance Spectroscopy. Those properties, that is, stability, high electronic conductivity and low activation energy make W2N a promising candidate to be used in the electrode of electrochemical devices in high corrosive environments.

Pitting Corrosion Damage for Prediction Useful Life of Geothermal Turbine Blade

In the last years, the power industry in Mexico has suffered the consequences of some mechanisms of damage that reduce the efficiency in power generation. These mechanisms of damage originate problems in main components as rotors, nozzle blades and others due to losses of pressure, high vibrations, erosion and corrosion. By the type of work fluid, mixture of water-steam and brine rich in salts, geothermal turbines are in a high corrosion environment. The main forms of damage caused by corrosion in a geothermal turbine are crevice corrosion and pitting corrosion. The latter is a damage mechanism through which the useful life is affected. The blades of the last stage in low pressure (LP) in the geothermal turbines are exposed to corrosion by environment and high load cycles which cause failures by corrosion fatigue, crack initiation and crack propagations. In this work, a methodology for the analysis of the failure by pitting corrosion and its consequences in its useful life was obtained. From the results, it is possible to conclude that this corrosion may influence a mechanism of pitting corrosion, which precedence to stress corrosion cracking and corrosion fatigue.

Joining of Oxide Dispersion Strengthened Steels for Advanced Reactors

The design, manufacture, and experimental analysis of structural materials capable of operation in the high temperatures, corrosive environments, and radiation damage spectra of future reactor designs remain one of the key pacing items for advanced reactor designs. The most promising candidate structural materials are vanadium-based refractory alloys, silicon carbide composites and oxide dispersion strengthened steels. Of these, oxide dispersion strengthened steels are a likely near-term candidate to meet required demands. This paper reviews different variants of oxide dispersion strengthened steels and discusses their capability with regard to high-temperature strength, corrosion resistance, and radiation damage resistance. Additionally, joining of oxide dispersion strengthened steels, which has been cited as a limiting factor preventing their use, is addressed and reviewed. Specifically, friction stir welding of these steels is reviewed as a promising joining method for oxide dispersion strengthened steels.