Changes In Corrosion Rate Research Articles

Effect of Alloying Elements on the Corrosion Behavior of Carbon Steel in CO2 Environments

The objective of the present study was to evaluate the effect of alloying elements (Cr, Mo, and Cu) on the corrosion behavior of low carbon steel in CO2 environments. Six samples were prepared with varying Cr content from 0 wt% to 2 wt% and with added 0.5 wt% of Mo and Cu; the specimens had ferritic/pearlitic microstructures. Steel samples were exposed to a CO2-saturated 1 wt% NaCl solution with different combinations of pH and temperature (pH 4.0 at 25°C, pH 6.6 at 80°C, and pH 5.9 at 70°C). Changes in corrosion rate with time were determined by linear polarization resistance measurements. The surface morphology and the composition of the corrosion product layers were analyzed by surface analysis techniques (scanning electron microscopy and energy dispersive x-ray spectroscopy). Results showed that the presence of Cr and Cu showed a slight positive effect on the corrosion resistance at pH 4.0 and 25°C. At pH 6.6 and 80°C, regardless of the alloying elements, the trend of corrosion rate with time was similar, i.e., the corrosion rate of all specimens decreased with time resulting from the formation of protective FeCO3. A beneficial effect of Cr presence was clearly seen at “gray zone” conditions: pH 5.9 and 70°C, where steel sample without Cr showed no decrease in corrosion rate with time. The presence of Cr in the steel promoted the formation of protective FeCO3 with Cr enrichment and it decreased the corrosion rate.

Corrosion of Q235 carbon steel influenced by the introduction of aerogenic and aerobic bacteria

Corrosion of carbon steel is investigated in the presence of Synechococcus sp. (S. sp., an aerogenic strain) with or without the coexistence of Pseudoalteromonas sp. (P. sp., an aerobic strain). Results of electrochemical and weight loss measurements suggest that the corrosion of carbon steel is continuous in S. sp. containing media while it is inhibited initially and accelerated finally in the coexistence of S. sp. and P. sp. This variation in corrosion rate is believed to be closely related to the difference in the growth and metabolism of two strains in different media. In media containing S. sp. alone, the slow reproduction of S. sp. leads to the relatively stable dissolved oxygen (DO) concentration and the continuous corrosion. In the case of S. sp. + P. sp., P. sp. consume DO and form protective biofilm at the initial stage, and then the death of P. sp. and the rapid reproduction of S. sp. cause the increase of DO concentration and the formation of porous corrosion products, leading to the change of corrosion rate.

Flow cell apparatus for quantitative evaluation of carbon steel corrosion during transitions in fluid composition: Application to transition from inhibited hydrochloric acid to sodium chloride brine

This paper introduces a new flow cell technique that offers the advantage of real-time corrosion rate behaviour acquired as transitions in fluid chemistry occur using in situ electrochemistry. The present study quantifies the corrosion behaviour of a metal surface initially exposed to inhibited acid and subsequently exposed to a model formation brine. The design, optimisation and validation of the flow cell set-up is discussed. Results from initial tests show that inhibition efficiency and steel corrosion rate change significantly during the dilution process as the inhibitor film experiences concomitant changes in the “external” concentrations of acid and propargyl alcohol inhibitor.

INVESTIGATION OF HIGH-ALLOY CHROME-NICKEL STEELS CORROSION RESISTANCE

Background Oil and gas equipment is subjected to intense internal corrosion throughout the entire process of oil and gas production and treatment. Corrosive aggressiveness of the environment is provided by dissolved gases present in the formation and waste waters: oxygen, hydrogen sulphide, carbon dioxide, as well as the vital activity of bacteria and high mineralization. The most dangerous consequence of these factors is the development of local corrosion on the metal. Highly significant equipment in the oil and gas fields are the tubing and casing pipes. One of the ways to improve their durability is to use corrosion-resistant steels that are highly resistant to acidic and alkaline environments, as well as aggressive salt solutions. High-alloy chromium-nickel steels of 08Kh18N10T and 10X17N13M2T grades are often used for these purposes. Aims and Objectives Study of 08Х18Н10Т and 10Х17Н13М2Т steels to pitting corrodibility. Investigation of the of inhibitor protection influence on the change in corrosion rate of underground equipment and pipelines of producing wells at the fields of Samotlorneftegaz JSC using the simples of 08Х18Н10Т and 10Х17Н13М2Т steels. Metods Gravimetric tests of the steels under investigation were carried out in accordance with State Standard 9.502-82 «Unified system for protection against corrosion and aging. Metal corrosion inhibitors for water systems. Methods of corrosion testing». Tests on pitting corrodibility were carried out in accordance with State Standard 9.912-89 «Steels and alloys are corrosion-resistant. Methods of accelerated tests for resistance to pitting corrosion». Polarization studies were performed on the Field Machine potentiostat in a three-electrode clamp electrochemical cell. Corrosive media for polarization studies was a model fluid simulating the composition of the reservoir water of the Samotlor field. Results As a result of gravimetric tests, it is established that in highly aggressive chlorine-containing media steels 08Х18Н10Т and 10Х17Н13М2Т are subjected to local pitting corrosion, and the corrosion resistance of steel 10Х17Н13М2Т is higher than that of 08Х18Н10Т steel. Based on the results of polarization studies, it has been established that the application of the corrosion inhibitor SONKOR-9011 at a concentration of 30 ppm provides a shift in the corrosion potential of the steels to be investigated in the positive range, with a protective effect of 66 %.

Surface characterization of titanium implant healing abutments before and after placement.

Implant healing abutments (IHA) have a vital role in soft tissue healing after implant placement. Although there is thorough investigation on the implant surface, little is known about the effects potentially damaging oral conditions impose on healing abutments. To characterize the surface of titanium healing abutments before and after clinical placement to understand the effects of the oral environment and time on the device surface. Ten regular Straumann IHA were subjected to characterization pre and postplacement to elucidate the effects of the oral environment on device surfaces. Changes in surface crystallinity, morphology, and elemental composition were monitored with Raman spectroscopy, scanning electron microscopy, optical microscopy, and x-ray photoelectron spectroscopy, respectively. In addition, corrosion rate and polarization resistance were obtained to assess electrochemical device stability after placement. Control analysis indicated the titanium oxide of IHAs was thicker than natural commercially pure titanium and had the structure of crystalline anatase. After removal, the abutments possessed large amounts of biological debris, visible scratches, and discoloration sparsely on the surface. Spectroscopic analysis revealed the titanium oxide on the surface of IHAs was structurally unchanged, with crystalline titanium dioxide still present on the surface. Electrochemical results revealed that implanted healing abutments possessed a significantly higher corrosion rate than controls (change in corrosion rate = 2.34 ± 0.58 nm/year). Healing abutments were stable in the oral environment due to the chemical stability of the oxide, and were likely subjected to abrasions from unintentional loading and oral hygiene techniques.

Corrosion Monitoring of Reinforcing Bar in Concrete Under Different Corrosive Environments

Reinforced concrete structures have been widely used for social infrastructures because of their high strength. However, it currently has been passed over 50 years since many infrastructures constructed, and the deterioration in durability is a problem. The corrosion of reinforcing bars due to neutralization of concrete and adhesion of airborne sea salt, and the concrete cracking by corrosion products is considered as the main cause of deterioration. Therefore, in order to properly maintain and manage the infrastructure structure, it is necessary to understand the corrosion deterioration behavior of the reinforcing bars in the concrete. In this study, wet and dry cyclic corrosion test was conducted using concentric ring type electrodes of carbon steel covered with mortar. The difference in corrosion behavior of reinforcing bars due to covering thickness and corrosion test conditions was investigated by continuously measuring the impedance between two electrodes. Furthermore, the diffusion behavior of water and chloride ions in mortar part was observed, and the correlation with corrosion behavior was investigated The concentric ring type electrodes of carbon steel were used as the monitoring electrodes, and they were covered with the different thickness of mortar (hereinafter, the mortar electrode). The composition of the mortar was coarse aggregate: cement: water = 3: 1: 0.6. 10 kg/m3 NaCl was added to the mortar to accelerate corrosion. The covering thickness was set to 3, 10 mm. The corrosion test was carried out by wet and dry cycle, and the electrochemical impedance at two frequencies of 10 mHz and 10 kHz was continuously measured during the corrosion test. A core having a height of 50 mm and a diameter of 40 mm was prepared with the same composition of mortar. The prepared cores were immersed in 0.1 mol/L NaCl solution for several hours. The permeation state of water and chloride ion was investigated by water leakage test agent and fluorescent X - ray analysis. Changes in the corrosion rate of the mortar electrode prepared by underwater curing in the wet and dry cyclic corrosion process were continuously measured. Although there was some variation, corrosion rate decreased in the immersion process, regardless of the thickness of the mortar. The corrosion rate of the electrode with 3 mm mortar showed higher value than that with 10 mm mortar. The changes in corrosion rate and solution resistance in each cycle of corrosion test were examined. The solution resistance gradually decreases in the wet process, and the value showed a minimum in the drying process. This means that diffusion rate of the solution is slow in the mortar. Since the decrease in solution resistance corresponds to the increase in corrosion rate, it is considered that the increase in corrosion rate is due to wetting by the permeated solution. There was a large fluctuation in the electrode with 3 mm mortar, whereas the electrode with 10 mm mortar always showed a low solution resistance value regardless of process of the corrosion test. This difference in wetting environment can affect the change in corrosion rate and corrosion behavior.

A Study of NiTi Alloy Mechanical and Corrosion Behavior Subjected to Mechanical and Cyclic Thermal Loading in Corrosive Environment

The corrosion behavior of a nickel titanium alloy (NiTi) have been investigated. The NiTi alloy is subjected to cyclic thermal loading in corrosive environments (3.5 wt% NaCl and Ringer solution). Thermogravimetric measurement versus temperature is perfumed to obtain forward and reverse martensitic transformation temperatures. Electrochemical Avesta cell is used to study corrosion behavior of NiTi alloy under thermal cycling in absence of mechanical loading. Electrochemical Impedance Spectroscopy and cyclic voltammetry measurements are used to study corrosion behavior at different temperatures and phases. The change in corrosion rate during phase transformations are being investigated. An equivalent circuit model is used to calculate the electrochemical parameters from EIS measurements for forward and reverse martensitic transformations. The results shows the breakdown of passive oxide film on the surface with martensitic transformation. This breakdown would be an origin for fatigue crack initiation and an explanation for fatigue lifetime reduction of NiTi in corrosive environments.

Corrosion behaviour of S43035 ferritic stainless steel in hot sulphate/chloride solution

The corrosion resistance of S43035 ferritic stainless steel at elevated temperatures of 308K, 328K, 348K and 378K was studied through potentiodynamic polarization test and optical microscopy analysis in 2M H2SO4 at 0%, 1%, 3.5% and 6% NaCl. Results show that increase in temperature and NaCl generally hinders the formation of the passive film. Changes in corrosion rate from 308K to 378K at 0% NaCl was marginal. Metastable pitting was absent until 378K due to increased electrolytic action of SO42− ions. In the presence of chlorides at 308K metastable pitting is visible delaying the formation of stable passive film. Passivation behaviour was absent at temperatures above 308K due to polarization similar to carbon steels and a strong decrease in hydrogen evolution over potential especially at 1% and 3.5% NaCl. Optical images showed mild deterioration at 378K from 0% NaCl and the formation of corrosion pits at 308K and 378K from 6% NaCl. Negative enthalpy value at 0% NaCl implies exothermic nature of the steel corrosion reaction. Addition of chlorides changed the steel corrosion reaction to endothermic. Increase in NaCl concentration caused a decrease in activation energy and increase in entropy values due to decrease in passivation of the alloy and consequently increase in corrosion rate. Statistical analysis through ANOVA at confidence levels of 95% and 97.5% showed the strong influence of temperature variation on corrosion rate with F-values of 5.256 at 50.8% in contrast to the NaCl concentration whose value was below the significance level.

Electrical resistance probe measurements of solid particle erosion in multiphase annular flow

Oil and gas production and transportation facilities have the potential of catastrophic explosions, fire and release of toxic gases due to erosion failures which may lead to loss of lives and properties. Repairs of such a complex system can be very expensive and troublesome. Therefore, control of erosion is a subject of paramount interest in the oil and gas production/transportation industry.Reliable erosion monitoring of the process piping and equipment is required to assess the erosion status of these components. Electrical Resistance (ER) probes are used to determine general metal loss rates which could be a result of erosion and/or corrosion. These probes are able to measure for short term erosion or corrosion rate changes by measuring the change in electrical resistance of the probe element. This study focused on collecting experimental erosion data in a large-scale multiphase flow loop with a 76.2mm (3in.) standard elbow using ER probes under particle-laden annular flow conditions.Experiments were performed with superficial gas velocities ranging from 11m/s to 48m/s and superficial liquid velocities ranging from 0.004m/s to 0.27m/s, for liquid viscosities of 1cP and 10cP. Three different sand sizes (20μm, 150μm, and 300μm) were used for performing tests. Effects of different parameters such as liquid flow rate, liquid viscosity, sand size, ER probe location, and flow orientation on erosion were examined. A few experimental results are also used to evaluate the performance of the ER probe versus a fixed mounted non-intrusive ultrasonic sensor.

Evaluation of SD345 Corrosion Resistance in Simulated Concrete Pore Solution

Reinforced concrete known as high strength material has been used for social infrastructure for a long time. However, the number of infrastructures used for more than 50 years has been increasing year by year, and deterioration of their durability is concerned. It is well known that corrosion of reinforcing steel leads to concrete cracks. It means that understanding for corrosion behavior of reinforcing steel is important in order to properly maintain the social infrastructures. In this study, corrosion resistance of SD345 steel materials is evaluated under simulated concrete environment by electrochemical methods. SD345 steel materials are used as samples, and a saturated Ca(OH)2 solution is used in order to simulate the environment in a concrete. The effect of chloride ion was examined by adding NaCl (0, 0.01, 0.1, 0.2, 0.3, 0.5 M) to the test solution. Electrochemical polarization measurements were conducted after immersing in these solutions for 30 minutes. A three-electrode cell was used for electrochemical measurements. Hg/ HgO/ NaOH and Pt were used as the reference electrode and the counter electrode, respectively. Next, impedance measurements were performed at the open-circuit potential with an AC signal of amplitude 10mV in the frequency range from 105 Hz to 10-2 Hz after immersing electrodes for 1day, 1week and 3weeks, in order to investigate passivation behavior in the test solution. The corrosion rate of SD345 was monitored under cyclic wet–dry environments. The wet–dry cyclic corrosion test was conducted by exposure to alternate conditions of 2 minute-immersion in a 0.1 M NaCl solution and 2h-drying or 7 h-drying at 60% RH. 10 mHz and 10 kHz impedances were continuously measured during the wet-dry cycles by corrosion monitor. The plateau of current density is observed in anodic polarization curve in test solutions, indicating that passive film is formed on the surface. In case of the test solution containing NaCl more than 0.1M, however, the current density rapidly increases, and it occurs at the smaller potential with an increase of amount of Cl-. The corrosion monitoring of the samples with passive film previously formed in saturated Ca(OH)2 solution was conducted under the alternate condition of 2 minute-immersion in a 0.1 M NaCl solution and 8 h-drying at 60% RH. The passive film formed by immersion for longer time gave the smaller increase of corrosion rate. It means the state of passive film affects the change in corrosion rate in an early stage. The corrosion rates in both conditions did not increase after 11 cycle. On the other hand, in case of shorter drying condition, the change in corrosion rate showed almost the same behavior regardless of immersion times. This means there is no influence of state of passive film on corrosion behavior in shorter drying environment. The surface of SD345 steel was passivated in a simulaed concrete pore solution, and the resistance of passive film increased with time. The breakdown potential of passive film shifted to less noble with an increase of Cl⁻ concentration. The corrosion performance in cyclic corrosion test with longer drying period depends on the state of passive film previously formed on the surafce. On the other hand, there was no effect of initial state of passive film under cyclic corrosion environment with short drying process.

Sensitivity of chloride-induced corrosion rate of steel in concrete to cover depth, crack width and concrete quality

This paper presents the results of analyses carried out to assess the sensitivity of chloride-induced corrosion rate to change(s) in cover depth, concrete quality and crack width. An empirical chloride-induced corrosion rate prediction model is used to carry out the sensitivity analyses. The main model input parameters for the model are surface crack width (w cr), cover (c) and concrete quality (characterized by a long-term diffusion coefficient, D 90). A two tier sensitivity analysis is carried out to establish (i) which individual input parameter (D 90, c or w cr) corrosion rate is most sensitive to, and (ii) which combination of two input parameters out of the possible three (D 90, c and w cr) corrosion rate is most sensitive to. The sensitivity analyses results show that in cracked concrete change in corrosion rate is greater if concrete quality is varied than if either crack width or cover depth is varied i.e. concrete quality has a dominating role on the effect of either crack width or cover depth on corrosion rate. Generally, in cracked concrete corrosion rate is more sensitive to change in concrete quality than change in either crack width or cover depth. Even though cover cracking increases corrosion rate, and that it should be minimized, a holistic approach considering the effect of cover depth, crack width, and more importantly, concrete quality on corrosion rate should be adopted.

Electrochemical characterization and in-vitro bio-assessment of AZ31B and AZ91E alloys as biodegradable implant materials.

The degradation of magnesium alloys, AZ31B and AZ91E, are under review due to a their ability to degrade under physiological conditions and successively yield an oxidized biocompatible by-product which can safely be absorbed by the body. By exploiting the biodegradability of magnesium alloys, the prospects of developing an unprecedented class of implant are at hand. To do so however, the rate of corrosion of the alloys must be modified in order to better suit physiological conditions. Therefore, anodization was carried out on AZ31B and AZ91E specimens to alter the surface chemistry to reduce the corrosion rates and improve biocompatibility. Scanning electron microscopy, energy dispersive spectroscopy, atomic force microscopy and contact angle meter, were used to characterize and compare the surfaces of untreated and anodized magnesium alloys. Corrosion behavior was evaluated by electrochemical tests using potentiodynamic polarization and electrochemical impedance spectroscopy, to verify changes in corrosion rates as a result of anodization. Finally, a bio-assessment using MTS assays and fluorescent microscopy were carried out to ensure that the anodization process had no compromise on the biocompatibility of the magnesium alloys. The study indicated that the anodization process did alter the surface chemistry of the alloys, yielding slower corrosion rates, while causing no adverse effects in regards to biocompatibility.

CORROSION INHIBITION OF HEAT TREATED MILD STEEL WITH NEEM LEAVE EXTRACT IN A CHLORIDE MEDIUM

Influence of Neem leave extract on the corrosion inhibition of mild steel in a chloride medium was investigated. It was carried out by immersing as-received and heat treated mild steel coupons in salt water with various concentrations of Neem leave extract ranging from 0-20%. Method of investigation was gravimetric, based on weight loss of coupons in the different solutions. The results show that mild steel samples immersed in salt water without Neem leave extract exhibited a much higher weight loss as compared to those with Neem leave extract. A unique trend observed in these investigations was that weight loss was higher for the as-received than the heat treated samples prior to addition of Neem leave extract into the corrosive medium. On addition of the Neem leave extract, a reversed trend was observed where weight loss of the heat treated became higher than the as-received coupons. Change in corrosion rate was insignificant for the control samples for both as-received and heat treated samples. On the contrary, an evident decreasing trend was observed for the heat treated samples while those of as-received were insignificant with time. However. 5% inhibitor showed best corrosion inhibition with the least corrosion rates. The overall results indicate that Neem leave extract effectively inhibits mild steel corrosion in a chloride medium

Study of the Degradation Behaviour of Biomaterial Mg-4.0Zn-2.0Sr Alloy in SBF

In v itro degradation behaviour and biological properties of Mg-4.0Zn-2.0Sr alloy sheet had been studied. The results indicate that a novel biodegradable Mg-4.0Zn-2.0Sr (wt. %) alloy sheet was successfully produced using a series of metallurgical processes. The corrosion of Mg-4.0Zn-2.0Sr (wt. %) alloy sheet immersed in SBF occurred as a cyclic process: pitting corrosion →extending of pitting corrosion along grain boundary→ localized corrosion → pitting corrosion again at the new exposed surfaces and the corrosion products were found that contain HA, CaCO3 and MgOH. The change of corrosion rate of Mg-4.0Zn-2.0Sr alloy sheets immersed in SBF is unstable until the 17th day and the average corrosion rate of the alloy sheets was 1.244 g/(m2 • h) after 17 days immersing, which is slightly higher than that of Mg-4.0Zn-1.0Sr alloy sheet 1.163 g/(m2 • h). The corrosion resistance property in SBF of Mg-4.0Zn-2.0Sr alloy is slightly lower than that of Mg-4.0Zn-1.0Sr alloy, which is proved by electrochemical measurements.

Modelling of carbon steel corrosion under oxygen depleted environment

In Japan, high level radioactive waste (HLW) produced by reprocessing spent fuels has been planned to be fixed in the glass solid body which is enclosed in the stainless steel canister which is further enclosed in the metal overpack. The overpacks are emplaced in tunnels at a deep underground facility. Carbon steel is the most important candidate material for the overpack, because the corrosion rate of carbon steel is known to be as low as 10 μm/year at an assumed deep underground site which is kept at oxygen depleted condition. The corrosion rate of carbon steel measured in the laboratory was found to be almost 10 μm/year at the initial stage, and decreases to a steady state corrosion rate in the order of 0·1–0·01 μm/year, changing with time according to an inverse parabolic rate law. A corrosion model assuming the diffusion of H2O molecule through the precipitated corrosion film (Fe3O4) has been developed to rationalise the observed corrosion rate law under oxygen depleted environment. In this study, an improved model which takes account of the corrosion film dissolution has been proposed by assuming that the dissolution of precipitated Fe3O4 film is controlled by mass transfer process through adjusting diffusion layer in the solution. Digital simulation based on the improved corrosion model with suitable parameters such as the diffusion constant of H2O in the corrosion film and concentration of dissolved Fe2+ species at the surface of the Fe3O4 corrosion film was found well to simulate the observed corrosion rate change with time at various pH values as a function of partial pressure of hydrogen gas and to predict a low and steady state corrosion rate after long time exposure.

Corrosion performance and mechanical properties of sputter-deposited MgY and MgGd alloys

Films of MgY and MgGd alloys were deposited on silicon wafers by magnetron sputtering. The microstructure, crystal structure and mechanical properties were evaluated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and tensile testing. Corrosion was evaluated for immersion in 3.5% NaCl solution saturated with Mg(OH)2. TEM, SEM and XRD indicated that the alloys were single phase. There was no significant change of corrosion rate with alloy content. The strength increased with alloying content, and ductility decreased concomitantly. Strengthening was consistent with solid solution strengthening or short-range order.

An assessment of climate change effects on atmospheric corrosion rates of steel structures

This paper presents a discussion on assessing the potential impacts of climate change on the atmospheric corrosion rates of exposed steel structures. The effects on atmospheric corrosion due to changes in the environmental temperature, carbon dioxide, relative humidity, wind, rainfall and pollution are considered. The limitations and complexities of these assessments are discussed. To demonstrate the use and limitations of this science to evaluate effects related to climate change, a model developed in Australia to predict corrosion is combined with climate change models to project the change in the corrosion rates of steel components and protective zinc coatings in constructions. The method is applied to constructions located along the coastal areas of two Australian cities: Melbourne and Brisbane. These assessments are made using the A1FI scenario, the highest emission scenario defined by the Intergovernmental Panel on Climate Change, applied to nine general circulation models. The projected changes in corrosion rates were found to be an increase of ∼14% for both zinc and steel in Brisbane and a decrease of ∼14% for steel and 9% for zinc in Melbourne. It was also found that the uncertainties associated with the climate change models were small compared to those involved in modelling corrosion for engineering purposes.

Corrosion rate variation of SS 316 under simultaneous factors considering turbulence effect

Investigation of corrosion rate under the simultaneous effect of parameters is a new and important approach that makes our experimental media closer to real condition and offers more realistic results. In this study, the effect of some important marine factors including temperature, pH, velocity and salinity on the corrosion rate of SS 316 is considered synergistically using two by two graphical curves. Experiments are performed in turbulence condition, and each parameter is applied at three levels. The results of this research are compared with the achievements of a former synergistic study of parameters, which had calculated the contribution percentage and qualitative influence of marine factors in laminar condition. This research presents the critical points in the change of corrosion rate under the synergistic effect of parameters and compares the capability of factors in changing the rate of corrosion and studies their qualitative effect.

Effect of Aging on the Microstructure and the Intergranular Corrosion Resistance of X2CrNiMoN25-7-4 Duplex Stainless Steel

Stainless steels are used widely in many industries. A duplex microstructure offers a combination of advantages, including resistance to crevice and stress corrosion, reduced susceptibility to hot cracking in comparison with fully austenitic structures and excellent tensile strength. The paper discusses the effect of aging on the microstructure and corrosion resistance of X2CrNiMoN25-7-4 super duplex stainless steel. Low and predictable corrosion rate is an important parameter for steels operating in aggressive environments. Resistance to intergranular corrosion expressed by corrosion rate (mm/year) was determined in accordance with standard PN-EN ISO 3651-1. Metallographic studies were carried out to evaluate surface degradation and intergranular corrosion. The results support an evaluation of the impact that phase fraction changes caused by aging have on resistance to intergranular corrosion. The results of the corrosion analysis were used to develop mathematical models describing changes in corrosion rate over time for different phase fractions.

Theoretical Analysis of Reinforcement Tunnel Lining Corrosion

The main cause of ageing damage in reinforced concrete structures is reinforcement corrosion. Damage can be detected visually as coincident cracks along the reinforcement bar, which are significant of both reduction of the re-bar, cross-section and loss of bond strength for reinforced concrete. The reinforced concrete is one of the most widely used engineering materials as final lining of tunnels. The corrosion is common durability problems that have significant effect on the tunnel performance. This study intends to analysis reinforcement concrete corrosion at the tunnel lining by applying temperature expansion theory on steel through numerical simulation process, with expansive force effect. The thickness of concrete cover and the diameter of steel bar have an impact on the stress for reinforcement concrete during propagation of corrosion process. The corrosion cracks appear at the corner of a tunnel lining then in invert and vault because the maximum stress will be in the corner then in invert and vault. The internal force in the concrete lining changes differently when the corrosion rate change.