Calculation Of Corrosion Rate Research Articles

PERILAKU DISTORSI, KEKERASAN DAN KOROSI HASIL HARDFACING PADA PERMUKAAN BAJA KARBON MENGGUNAKAN ELEKTRODA HV-800 DENGAN BERBAGAI KETEBALAN

This research aims to look at the hardness and corrosion of the weld layer. In addition, distortions were also observed in the post-welding specimens. Weld layers were made with variations of one, two and three layers of welding using HV-800 electrodes. The first step in this research is a literature study, followed by preparing tools and materials, heating electrodes, welding process, observing distortion, cutting specimens for testing followed by hardness and corrosion testing, and data analysis and conclusions. From the results of observing the distortion, it can be seen that the thicker the weld layer, the greater the distortion that will occur. Distortions in specimens welded with one, two and three layers are 1.5, 4 and 6° respectively. Furthermore, based on the results of the hardness test, it can be seen that the thicker the weld layer, the greater the hardness. The hardness of the one, two and three layer welded specimens was 550.2, 632.82 and 650.68 HV respectively. Then, based on the weighing results, it can be seen that the longer the immersion time, the greater the reduction in mass during 120 hours of immersing. Finally, from the results of the corrosion rate calculation it can be seen that the thicker the weld layer, the lower the corrosion rate that will occur. The corrosion rates for specimens welded with one, two and three layers were 13.23, 11.02 and 10.29 mpy, respectively. All three specimens have good corrosion resistance because they fall into the "good" criteria.

PENGARUH QUENCHING SETELAH PENGELASAN TERHADAP KOROSI DI BAWAH INSULASI MEDIA AIR LAUT PADA BAJA A36

Corrosion in low-carbon steel is a significant issue in the industrial world, particularly in the oil, gas, refining, and chemical industries, as it leads to substantial financial losses. The total losses experienced by companies in Indonesia are estimated to reach 2-5% of the country's GDP. Corrosion arising from insulation damage, known as Corrosion Under Insulation (CUI), is challenging to detect but has a profound impact on industrial processes. Welding quality and corrosion resistance can be improved through post-weld heat treatment (PWHT). This research aims to investigate the influence of rapid cooling after welding low-carbon ASTM A36 steel on corrosion events under insulation using the "Water Immersion" method with seawater from the Muntok area, Bangka Belitung Islands Province, for 7 and 14 days. The welding process is performed using shielded metal arc welding (SMAW). Heat treatment is applied at 880°C for 60 minutes, as determined by the carbon equivalent calculation, followed by rapid cooling in seawater. Testing includes chemical composition analysis, non-destructive testing with dye penetrant on the welds, Brinell hardness testing, corrosion rate calculations, charpy impact testing, and metallography observations. The research results indicate that quenching enhances hardness and toughness while affecting the corrosion rate of the material after corrosion immersion, both with and without insulation. Material immersion exhibits a corrosion rate inhibition on the 14th day due to the formation of an oxide layer that hinders further degradation. Metallography observations reveal that after welding, phases formed include pearlite, acicular ferrite, and widmanstatten structures.

Corrosion Effect of Biodiesel-Diesel Blend on Different Metals/Alloy as Automotive Components Materials

Biodiesel has emerged as a progressively widespread and significant alternative to traditional diesel fuel within the transportation sector. Despite its growing popularity, the issue of corrosive tendencies upon interaction with both moving and static components of diesel engines and fuel systems poses a serious concern. This research endeavors to assess the corrosion characteristics of materials commonly found in automotive fuel systems when exposed to various blends of rapeseed oil biodiesel and diesel. The study involved static immersion tests, lasting 3360 h at room temperature, using B0, B20, B40, B60, B80, and B100 fuels. Copper, brass, aluminum, zinc, and stainless steel plate samples were subjected to these tests. The evaluation at the conclusion of the study included weight loss measurements, corrosion rate calculations, and observation of changes in the exposed metal surfaces. Surface morphology was scrutinized using a Bresser LCD MICRO 5MP digital microscope. Additionally, the total acid number (TAN) was employed to assess alterations in fuel acidity before and after the immersion tests.

The Corrosion Behavior of Cnidoscolus aconitifolius (Chaya) Leaf Extract on Mild Steel in H2SO4 and Brine (NaCl Solution) Environments

The inhibition efficacies of extracts of Cnidoscolus aconitifolius (Chaya) leaves in the corrosion of mild steel were investigated in H2SO4, and NaCl media. Weight loss method was employed to determine corrosion rate. The ribbed mild steel rod was cut into forty (40) coupons, each measuring 16 mm (diameter) by 8 mm (length) and their initial weights taken and noted. Twenty (20) beakers containing 0.5M and 1.0M each of H2SO4 and NaCl solution separately with varying volumes of the extracts ranging from 5ml to 20ml were set up with four (4) coupons in each beaker fully immersed using nylon strings. The set up was allowed to stand for an exposure time of 672hrs with a coupon withdrawn from each beaker every 168 hours and processed using standard procedures before being reweighed using digital weighing balance. The weight difference for each coupon was obtained and used for corrosion rate calculation using the formula, CPR= K∆W/ρAt. Other corrosion parameters were also obtained using the relevant formulae: inhibition efficiency, IE%=(〖CR〗_c-〖CR〗_i)/〖CR〗_c ×100 and surface coverage, , θ=(〖CR〗_c-〖CR〗_i)/〖CR〗_c .The results obtained indicated that the normal corrosion rate profile for passivating metals was followed with the weight loss by the coupons being higher in the control media than those ones in the inhibited media. It was also observed that increase in volumes of these extracts from 5ml to 20ml decreased the corrosion rate of mild steel in the media. We found that in both media Cnidoscolus aconitifolius (Chaya) exhibited high inhibition efficiencies of 78.14% in H2SO4 and 64.15% in NaCl at extract concentration of 20 ml. Plots of the Langmuir adsorption isotherms suggest uniform surface covering of the adsorbent molecules at equilibrium state of the adsorbate–adsorbent system, with very strong adsorption forces. Based on these findings, the results suggest that Cnidoscolus aconitifolius (Chaya) leaves extract is a veritable green inhibitor for both acidic and salt media and can be a suitable alternative to the synthetic inhibitors widely used in the oil and gas industry.

Electrochemical corrosion study of carbon steel in bio-oil environments

Comprehensive corrosion risk assessments are essential for ensuring the safe and efficient utilization of bio-oil (BO) in industrial applications. In this study, electrochemical measurements (EMs) such as potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) were conducted for carbon steel (CS) at BO storage temperatures of 20 and 50 °C. Different electrolytes were used, including BO, BO+10 wt% methanol (10 ME), BO+20 wt% methanol (20 ME), and 0.1 M acetic acid (0.1AC). To improve data quality in low-conductive environments, various techniques were employed for EMs. Concurrent immersion experiments (IEs) were performed to validate corrosion rate (CR) calculations obtained from EMs. The PDP results revealed uniform corrosion as the prevalent form of CS corrosion in BO environments, while EIS measurements indicated the involvement of adsorption/chelation processes. A well-fit equivalent circuit model was proposed for EIS data. The ratios between CRs obtained from EMs and IEs were around 4.3 and 0.9 at 20 and 50 °C, respectively, for all electrolytes, confirming the reliability of EMs for evaluating CS corrosion in BO environments. This study provides valuable insights into corrosion assessments of structural alloys in BO environments using reliable yet inexpensive EM techniques.

Laju Korosi Logam Baja Karbon Rendah di Larutan Garam pada Berbagai Konsentrasi Inhibitor Korosi dari Ekstrak Daun Pepaya

Papaya leaf extract could be used as an organic corrosion inhibitor. Corrosion inhibitors were used as a method to reduce corrosion rate. The most corrosive environment was the marine environment. The purpose of this study was to determine the best concentration of papaya (Carica papaya) leaf extract inhibitor which could reduce the corrosion rate of low carbon steel in a 3.56% NaCl solution environment. The maceration process was carried out for 24 hours with 70% ethanol solvent with a solute:solvent ratio of 1:8 (w/v) at room temperature. Inhibitor extracts were analyzed qualitatively with the phytochemical method. The addition of FeCl3 was carried out on the inhibitor extract from papaya leaves. The color change occurred from blackish brown to greenish black which indicated the presence of tannin compounds in the papaya leaf extract. Corrosion testing was carried out with hot stream temperature setting at 45⁰C to 55⁰C and concentrations of inhibitor extracts at 300, 600, and 900 ppm. The test was conducted for 36 hours with a span of metal mass every 6 hours. Corrosion rate calculation is done by weight loss method. The results showed that papaya leaf extract inhibitors positive contained corrosion inhibitor and could reduce the corrosion rate in 3.56% NaCl solution. The corrosion rate without inhibitor is 1.023 mmpy. Corrosion rates with inhibitor concentrations of 300, 600, and 900 ppm were 0.755, 0.585, and 0.438 mmpy, respectively.

Enhanced adhesion and corrosion resistance of reduced graphene oxide coated-steel with iron oxide nanoparticles

Despite its potential for use in coating applications, graphene can promote corrosion at exposed graphene-metal interfaces because it presents cathodic properties when exposed to most metals. Moreover, such exposed areas can accelerate localized corrosion, which may lead to serious damage of the coated metal. This study describes a method for preparing reduced graphene oxide (RGO) coatings with iron oxide nanoparticles (Fex−1Ox), which exhibit improved adhesion strength and oxidation resistance on steel substrates. A suspension that contained a mixture of graphene oxide (GO) and graphene oxide with Fex−1Ox (GO/Fex−1Ox) was formulated and applied to a large area on a steel substrate using electrophoretic deposition. Mechanical and electrochemical characterizations of the RGO and RGO/Fex−1Ox coatings were conducted after thermal reduction at 810 °C in a 10 % Ar/H2 atmosphere. A 138 % improvement in adhesion tensile strength was measured using a mechanical test derived from the standard pull-out test. Moreover, the enhanced oxidation resistances of RGO and RGO/Fex−1Ox coatings were confirmed after thermal reduction using electrochemical impedance spectroscopy and the potentiodynamic polarization method. From calculation of corrosion rate, RGO/Fex−1Ox coatings were corroded by 4 and 13 times slower than RGO coatings and bare steel, respectively. These results suggest that graphene coatings with iron oxide nanoparticles could serve as effective adhesion-promoting intermediary layers that retard steel corrosion in certain applications.

Corrosion inhibition of carbon steel by acridine orange in HCl solution: Electrochemical and weight loss studies

The inhibition effect of acridine orange (AO) on the corrosion of A105 carbon steel in 0.5 M hydrochloric acid has been investigated using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and weight loss tests. Using polarization plots and corrosion rate calculations, it has been revealed that AO acts as an effective inhibitor. The results have showed that the inhibition efficiency increases with increasing inhibitor concentration and A behaves as a mixed type inhibitor in HCl solution. Based on the data obtained from the EIS tests, it has been determined that the charge transfer resistance increased from 74.20 Ω.cm2 for blank solution to 250 Ω.cm2for 100 ppm of AO. Comparison of the results obtained from the three methods, have shown that the methods are in acceptable agreement. Investigation the effect of temperature in the range of 20-60 °C has indicated that the inhibition efficiency increased with temperature, so that at 40 and 60 °C, the inhibition efficiency would reach 90%. The thermodynamic parameters of steel dissolution including activation energy, standard enthalpy and entropy of activation have been calculated and discussed. It was also found, that the adsorption of AO on the steel surface has obeyed Langmuir isotherm and adsorption has been performed spontaneously.

Environmental aspects of metal corrosion at oil and gas chemical enterprises

Metal corrosion of technological equipment not only has a significant impact on industry, but also has serious consequences for the environment, being one of the causes of environmental problems. The object of research in this paper is the issue of corrosion damage to the metal of technological equipment, types of corrosion and corrosion damage, and methods of protection against corrosion. On the example of a shell and tube heat exchanger with the help of nondestructive methods of control (external and internal inspection, ultrasonic thickness measurement) the research of corrosion rate of its main elements has been carried out. According to the results of researches the calculation of corrosion rate of the main elements of the heat exchanger was carried out. The corrosion rate for the heat exchanger shell was found to be 0.37 mm/year, which exceeds the value of 0.1 mm/year, which is accepted in the design of this heat exchanger. The obtained results allowed to identify the most vulnerable places of the research object and to choose the most effective ways to protect the base metal of the heat exchanger from corrosion.

Durability of latent heat storage systems

Latent heat storage represents technology with significantly higher energy storage density. The thermal energy storage capacity of building structures and storage units integrated into building services contribute to the energy flexibility of buildings. This paper presents results from laboratory experiments focused on the compatibility of heat storage media represented by phase change materials (PCMs) with materials of container. Material compatibility of selected PCMs with the plastics and metals were tested by a long-term experiment. Two organic-based and two inorganic-based phase change materials were selected for tests of compatibility with selected metals (aluminium, copper and brass) and plastics (PP-H, PE-HD, and PVC-U). Plastic-PCM compatibility was determined by gravimetric method. For evaluation of metal-PCM compatibility, calculation of corrosion rate was applied. The less mass changes and lower penetration of PCMs to the matrix was observed for inorganic-based PCMs compared to organic-based PCMs. In case of compatibility between metals and PCMs, the highest values of corrosion rate were calculated for copper immersed in inorganic-based PCMs Rubitherm SP25.

Effect of Co and Al Contents on Hot Corrosion Resistance of Powder Metallurgy Aeroengine Disk Superalloys

Hot corrosion behavior of a powder metallurgy superalloy (Alloy 1) in molten 95% Na2SO4+5%NaCl salts at 800 °C are investigated with average corrosion rate calculation, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy spectrum analyzer (EDS). Meanwhile, the hot corrosion tests of Alloy 2 at 800°C were also carried out for comparison. Experimental results show that the corrosion layers obtained after 100h of hot corrosion were mainly composed of Cr2O3, Al2O3 , NiO , Ni3S2 , NiCr2O4 and Cr2S3 at 800 °C. The cross-sectional morphologies and corresponding elemental maps indicate that a large amount of sulfides and oxides appeared in internal substrate. According to these results, the cooperating mechanism of oxidation and sulfuration in Na2SO4-NaCl salts for Alloy 1 is confirmed. Compared with Alloy 2, the increased Co and Al content in Alloy 1 with better hot corrosion resistance at 800 °C promoted the rapid formation of continuous Cr2O3 and Al2O3 protective films on the alloy surface in which Co inhibited internal oxidation of Al and reduced internal diffusion of S through the third element effect. Key words: powder metallurgy superalloy; hot corrosion; oxidation; molten Na2SO4-NaCl salts; sulfuration

Hot Corrosion Behavior of a New Powder Metallurgy Superalloy in Molten Na<sub>2</sub>SO<sub>4</sub>-NaСl Salts

Hot corrosion behavior of a powder metallurgy superalloy (Alloy 1) in molten 95% Na2SO4+5%NaCl salts at 700 °C, 750 °C and 800 °C are investigated with average corrosion rate calculation, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy spectrum analyzer (EDS). Experimental results show that the average corrosion rate of Alloy 1 increases as the temperature elevates. The corrosion layers obtained after 100h of hot corrosion were mainly composed of Cr2O3, TiO2, Al2O3 , NiO and Ni3S2 at each temperature, meanwhile NiCr2O4 and Cr2S3 appeared at 750 °C and 800 °C respectively. The cross-sectional morphologies and corresponding elemental maps indicate that lots of Ni-Ni3S2 eutectic appeared in corrosion layers and a large amount of sulfides and oxides appeared in internal substrate. According to these results, the combined mechanism of oxidation and sulfuration in Na2SO4-NaCl salts for Alloy 1 is confirmed. Compared to Alloy 2, the increased Co and Al content in Alloy 1 with better hot corrosion resistance at 800 °C promoted the rapid formation of continuous Cr2O3 and Al2O3 protective films on the alloy surface in which Co inhibited internal oxidation of Al and reduced internal diffusion of S through the third element effect.

Integrated Design and Analysis of Corrosion Rate Model on Tubular Pipe of Oil and Gas Production Well

Corrosion occurrence in the oil and gas production system is an example of an unavoidable problem. This problem is caused by the presence of water and corrosive material fraction along with the produced hydrocarbon. On the way from the reservoir to the surface, the mixture between water fraction and the corrosive substance might adhere to the wall of conduit steel pipe (e.g. tubing, casing, and flowline) and can lead to corrosion on the wall. The corrosion problem can have a major impact on the economics of the production because the cost of production equipment is relatively expensive and workover operation is very costly. Therefore, planning and mitigation for a better production system need to be performed, so that the rate of corrosion can be controlled, and its economic impacts can be minimized. The purpose of this study was to create an integrated model of the corrosion rate calculation on the tubing by the Petroleum Engineering Study Program of Bandung Institute of Technology (ITB). Several terms related to the production process were considered in this model: the characteristics of the produced fluid, flow regimes, pressure and temperature conditions along the tubing, the trajectory of the well, the type of tubing material used, and the use of inhibitors. The model was developed from the model developed by C. de Waard, Liane Smith, and Mike Billingham. The corrosion rate calculation model was then validated using field data and the results were compared with the result from industrial commercial software, Electronic Corrosion Engineer (ECE®). The corrosion rate calculation model were able to predict the rate of corrosion in oil and gas wells accurately. A software-based system was created based on this integrated and accurate proven model. By using this software, the production system can be simulated and tested for various conditions, and then the result can be compared with each other to obtain the optimum fluid production rate with minimum corrosion rate. In addition, this software is capable to determine the most suitable tubing material which will be used in a given production environment and condition.

Exact calculation of corrosion rates by the weight-loss method

Abstract Corrosion is an important problem that engineers and scientists must overcome to avoid the collapse of structures, chemical processing plants, and metallic objects, which can lead to not only economic loss but also environmental and human losses. One of the simplest and most widely used methods to quantify corrosion rates (CRs) is the immersion test. The usual approach that has been used to date, to quantify the CR by this method, is to assume that the initial surface area of the corroding object remains constant over time. It is shown that such approximations underestimate the true CR and that they may lead to significant errors. A formula to calculate the CR considering changes in the area is presented in this work. The formula herein can be used to accurately quantify the CR by the immersion test and improve the quality of experimental data and the analysis and modeling of corrosion phenomena.

Impact of 20% Ethanol-blended Gasoline (E20) on Metals and Non-metals used in Fuel-system Components of Vehicles

Ethanol is considered as a potential biofuel for blending with gasoline and, in India, it is planned to increase the ethanol content to 20 percent in gasoline by year 2025 from present allowable limit of maximum 10 percent. It is important to evaluate the impact of E20 fuel on the materials used in fuel-system components. An evaluation of 8 metals, 6 elastomers and 4 plastics used in various fuel-system components was conducted through systematic exercise of laboratory immersion following standard methods like SAE J1747 and SAE J 1748 with all the quality and quality assurance measures. The study was conducted with E20 as test fuel and commercial gasoline (BS IV) as a baseline fuel for comparative assessment. Impact of E20 on metals was evaluated through calculation of corrosion rates in mm/year based on data obtained for change in mass post-immersion in above fuels. Similarly, impact of elastomers and plastics was evaluated through observed changes in properties like mass, volume, tensile strength, elongation, impact strength and hardness. Impact of E20 on metals tested was found to be insignificant based on the corrosion rates. Polychloroprene, SBR, HNBR and Fluoroelastomer were found to perform similar or better in most of the properties with E20. Impact of E20 on NBR-PVC and Epichlorohydrin was more as compared to commercial gasoline. Similar changes in properties of PA12, PBT and Acetal were observed in both the fuels. Impact of E20 on tensile strength and volume change properties of PA66 was found to be more than commercial gasoline. The vital information generated can be utilised by design engineers for selection, modification of materials for various components of fuel-system of vehicles

Corrosion Product Film of a Medium-Mn Steel Exposed to Simulated Marine Splash Zone Environment.

The corrosion behavior of a medium-Mn steel in a simulated marine splash zone was studied by a dry–wet cyclic corrosion experiment and electrochemical experiment. The corrosion products were characterized by corrosion rate calculation, composition detection, morphology observation, element distribution detection, valence analysis, polarization curve, and electrochemical impedance test. The results show that the corrosion products of the sample mainly include γ-FeOOH, FexOy, MnxOy, and a small amount of (Fe,Mn)xOy, and the valence state of iron compounds and manganese compounds in different corrosion stages changed obviously. In the initial corrosion products, Mn is enriched significantly and facilitates the electrochemical reaction of corrosion process. The content of Ni in the inner rust layer is high. The semi-quantitative analysis of the corrosion product elements shows that the atomic concentrations of Cr and Mo increase significantly in later corrosion products, indicating that the dense isolation layer formed by alloy element compounds in the corroded layer is the main factor to improve the protection ability of the rust layer at the end corrosion stage of the sample. With the corrosion durations, the corrosion current density of the sample with the corrosion product film first increases and then decreases, and the corrosion potential first moves negative and then shifts in a positive direction subsequently, indicating that the protective effect of the corrosion product film is gradually significant.

Compatibility Tests between Three Commercially Available Organic PCMs and Metals Typically Used in Fin-and-Tube Heat Exchangers.

Energy storage is one of the most effective ways to increase energy savings and efficiency of heating and air conditioning systems. Phase change materials (PCMs) are increasingly used in latent heat thermal energy storage (LHTES) systems to increase their capacity. In such systems, costs are a very important factor of viability so the typical heat transfer elements like fin-and-tube heat exchangers are used to construct the LHTES. The problem of this approach is a possibility of corrosion of metals in contact with PCM that shortens the life cycle of LHTES. Therefore, the main objective of this work is an experimental study of the compatibility of metals typically used in fin-and-tube heat exchangers (copper and aluminum) with three commercially available organic PCMs (RT15, RT18HC, and RT22HC). Compatibility of PCMs with copper and aluminum was tested for a period of approximately two months, during which a total of 35 heating and cooling cycles were carried out, each with a complete phase transition of the tested materials. In the course of the tests it was assessed whether the PCM caused corrosion of the tested metals. The evaluation was based on the gravimetric method, calculation of corrosion rate, and visual observations and measurements of the features on the metal sample’s surface using optical microscope. It was determined that RT15, RT18 HC, and RT22 HC show low corrosion rates for aluminum and copper samples. The visual tests indicate that there was no change in the PCM solutions during the tests, only a sediment was observed for the samples with the combination of copper and aluminum. Microscopic examination of the surface of the samples did not show any significant surface changes, except for the aluminum samples, on the surface of which local microdefects were observed. It follows from the present results that copper and aluminum can be used to design the heat transfer surface in contact with the chosen PCMs.

Mapping Corrosivity Steel Construction at Atmospheric Conditions in Langsa Town Center and Palm Oil Mill Industry

Corrosion is one of the main causes of early failure of infrastructure both for public housing facilities and public facilities in downtown Langsa. This corrosion is caused by air pollution generated from motor vehicle and household industry exhaust fumes and exhaust smoke from the nearest palm oil mill industry from the city of Langsa. Related to air pollution, its sustainability should be a concern regarding environmental impacts that occur, one of which is atmospheric corrosion. This study aims to analyze the impact of the effects of pollution on infrastructure corrosion on construction steel which is often used on infrastructure in the city of Langsa and the palm oil mill industry. There are five types of steel model infrastructure consisting of strips of plate steel, elbow steel, cylinder steel, plate steel, and low carbon steel market have become specimens. Calculation of corrosion rate using the method of mass loss by reference to ASTM standard G50, the location selected above buildings in downtown Langsa and palm oil mill industry. The results of the study for one year showed the level of corrosion rate that occurred in 5 types of steel construction is still relatively safe or its relative corrosion resistance can be classified in the outstanding category (<1 mil per year). The conclusion is that 5 types of construction steel that have been tested, are resistant to corrosion, and are suitable for use as the main construction material in Langsa City and the palm oil mill industrial environment.

Investigation of corrosion products formed on the surface of carbon steel exposed in Banda Aceh's atmosphere

This research aims to study the corrosion rate and characteristics of corrosion products of carbon steel due to exposure in the environment of Banda Aceh, Indonesia. The ASTM G50 was used as the basis for the specifications of the specimens for corrosion rate calculation. The corrosion rate was calculated based on ASTM G1. The features of corrosion products studied are morphological features, types, and chemical compounds of the rust. These characteristics were identified using scanning electron microscopy (SEM) and x-ray diffractometer (XRD). The corrosion rate of carbon steel was obtained using the weight-loss method. The study was conducted for twelve months, i.e. January to December of 2018. After one year of exposure, it was found that the highest corrosion rate occurred in the March–April period which was 0.024 mpy and falls into outstanding category of relative corrosion resistance. Various morphological features of corrosion products found during the period of exposure, including worm nest, bird's nest, globular, cotton ball, laminar, lath, bar, needle-shaped, and whisker structures. These structures were lepidocrocite (γ-FeOOH) and goethite (α-FeOOH). During twelve months of exposure, corrosion products formed were dominantly lepidocrocite and goethite. It was found that the lepidocrocite might transform into goethite through prolonged exposure time.

Analysis and calculation of corrosion rate of aluminum alloy in nitric acid solution

In this paper, the polarization curve and corrosion amount of aluminum alloy 1050 in 30 mass% nitric acid solution were measured as the corrosion potential under natural corrosion. it was found that the surface corrosion of aluminum alloy was uniformed and the corrosion rate calculated according to the weight loss-time curve was 0.25 mA·cm−2 by observing the corrosion morphology. The polarization resistance curve was obtained by differentiating the polarization curve. The corrosion rate calculated by analyzing the characteristics of the polarization resistance curve was 0.29 mA·cm−2, which was close to the actual corrosion rate obtained by chemical erosion.