Localized Corrosion Attack Research Articles

Chemical modification of hydrotalcite coating for enhanced corrosion resistance

This work provided a facile strategy to enhance the corrosion resistance of hydrotalcite coating by the chemical modification of the coating with 8-hydroxyquinolate anions. It shows that the chemical modification treatment induces the phase conversion of hydrotalcite coating by the intercalation of corrosion inhibitor into the coating. The hydrotalcite coating with unique layer micro/nanostructure not only serves as an effective template for the chemical modification of the coating, but also acts as a reservoir for the enhanced corrosion protection performance by releasing the accommodated corrosion inhibitor, when it suffers from local corrosion attack in aggressive environments.

Variability of Local Corrosion Attack Morphology of AISI 316Ti Stainless Steel in Aggressive Chloride Environment

AISI 316Ti is Cr-Ni-Mo austenitic stainless steel stabilized by Ti, recommended for construction of various industrial and medicine devices. In spite of its high Pitting Equivalent Resistance Number (PREN=23.688) it underlies local corrosion namely pitting in aggressive chloride environment. Appearance and extent of AISI 316Ti corrosion damage in a particular chloride solution depends strongly on temperature and surface treatment. One part of tested specimens is surface untreated the second part is treated by nitric acid passivation. Specimens are immersed for 24 hours at the temperatures of 30, 50 and 80 °C in 0.3M FeCl3 solution to induce pitting. Pitting corrosion morphology (shape and size of corrosion pits) is observed viewed from above and in profile as well, by optical metallographic microscope and scanning electrone microscopy SEM. Shape and size of corrosion pits is compared in dependence on temperature and surface finish of specimens.

Electrochemical behavior of hydrophobic silane–zeolite coatings for corrosion protection of aluminum substrate

The anticorrosive properties of a silane–zeolite composite coating applied on a 6061 aluminum substrate was investigated. The composite film, deposited by dip-coating technique, was prepared with different contents of SAPO34 powder (60–90 wt%) with the purpose of evaluating the protective action offered by the zeolite-filled silane matrix. Corrosion protection performance, during immersion in 3.5% NaCl solution, was evaluated by means of a potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS). The coating evidenced good barrier properties and high hydrophobicity. The addition of zeolite in the silane matrix induced, as expected, a reduction of cathodic and anodic current. The zeolite improved the barrier properties of the hybrid sol–gel films, enhancing the resistance to localized corrosion attacks. Better results were observed for the sample with 80 wt% of zeolite filler that evidenced still acceptable protective action after 3 days of immersion in the sodium chloride solution.

Microstructure and corrosion behaviour of A356 aluminium alloy modified with Nd

The microstructure of a gravity-cast A356 aluminium alloy modified with 0.4 wt% Nd and its corrosion behaviour in 3.5 wt% NaCl solution is investigated. The addition of Nd refines the eutectic silicon and results in the formation of Nd-containing intermetallics, which show smaller potential differences relative to the α-Al matrix than the Fe-rich intermetallics in the unmodified alloy. In 3.5 wt% NaCl solution, A356 and A356Nd alloys reveal localized corrosion attack at the Fe-rich/α-Al interfaces, which is then followed by localized corrosion through the eutectic areas. A more refined microstructure and the presence of Nd-rich phases in the A356Nd alloy considerably improves its pitting corrosion resistance compared with the A356 alloy which shows severe pitting corrosion.

Influence of Testing Temperature on the Corrosion Behavior of API 5L X70 Pipeline Steel

Localized corrosion attack is known to take a preponderant role in the onset of stress corrosion cracking of pipeline steels in high pH conditions. Carbonate/bicarbonate solutions can be employed to study the localized corrosion behavior of these materials. In addition to the presence of chloride ions in the electrolyte, the solution temperature is also of prime importance to the onset of pitting corrosion. The aim of this work was to evaluate the influence of the testing temperature on the corrosion behavior of the API 5L X70 pipeline steel which is a standard material for gas pipelines in Brazil. Samples were exposed to a solution consisting of Na2CO3, NaHCO3 and NaCl at three different temperatures: room temperature, 40 oC and 60 oC. The corrosion morphology was observed using scanning electron microscopy. The results showed that pitting corrosion became facilitated when the steel was immersed at higher temperatures.

Corrosion Behavior of Austenitic Stainless Steel in High Sulphate Content

Austenitic stainless steels especially 316L has been used extensively in many sectors including construction, medical and household appliances due to their highly resistance to corrosion attack, reasonable cost and excel in mechanical properties. However, in corrosive media, 316L are susceptible to localised corrosion attack especially in seawater and high temperature. The corrosiveness of media increased as the anions contents increased. This paper presents the corrosion mechanism of 316L exposed to high concentration of sulphate in the salinity of seawater. The solution (media) was prepared according to the same composition as seawater including pH, salinity and dissolved oxygen. The corrosion mechanism were characterized to breakdown potential (Eb) of 316L which are the potential once reaches a sufficiently positive value and also known as pitting potential. This is the most point where localized corrosion susceptibility to evaluate and considered a potential, which could be an appropriate point according to any given combination of material/ambient/testing methods. The Eb value were identified at 4°C, 20°C, 50°C and 80°C and compared with Eb value of 316L in seawater. The Eb value of 316L in high sulphate are higher compared to seawater in every temperature which elucidate that some anions accelerate corrosion attack whereas some anions such as sulphate behaves as inhibiting effect to 316L.

The Effect of Phosphate on the Properties of Copper Drinking Water Pipes Experiencing Localized Corrosion

Extensive localized or pitting corrosion of copper pipes used in household drinking water plumbing can eventually lead to pinhole water leaks that may result in water damage, mold growth, and costly repairs. Water chemistry has been recognized as the cause of some community-wide copper pinhole leak outbreaks. A large drinking water system in Florida recently switched from pH adjustment and orthophosphate addition to a blended ortho-polyphosphate chemical to address this problem. The objective of this study was to examine the impact of phosphates on the morphology and elemental composition of the interior surface of failed copper pipes removed from homes in the community. Scanning electron microscopy (SEM) and energy dispersive spectroscopy analysis of pipe surfaces revealed the build-up of phosphorus over time. Phosphorus was most greatly concentrated over areas of localized corrosion attack. Examination of the corrosion by-product mounds that covered corroding pits showed that phosphorus had migrated to the region adjacent to the copper pipe wall. Distinct copper–phosphorus solids were identified under SEM magnification; however, no crystalline copper–phosphate compound was identified by x-ray diffraction analysis.

Microcapillary polarization measurements of friction stir spot welds made in AZ31B magnesium alloy

Microcapillary polarization procedures were optimized to examine the corrosion characteristics of the various microstructural zones developed during friction stir spot welds made in AZ31 magnesium alloy. Tungsten carbide tracing confirmed the location and shape of the stir zone in the weldment. The stir zone was determined to be the noble region while the base metal and the thermo‐mechanically affected zone were found to be active. The thermo‐mechanically affected zone was found to be most susceptible to localized corrosion attack due to its proximity to the noble stir zone, and the subsequent formation of a macrogalvanic cell. Corrosion rates of individual weld regions were measured.

Selective Dissolution of Retained Austenite in Nanostructured Bainitic Steels

Nanostructured bainitic steels, containing bainitic ferrite laths and retained austenite films, formed at two different isothermal temperatures were compared for corrosion behavior in chloride‐containing solution using electrochemical techniques. The potentiodynamic polarization results suggest that nanostructured bainite formed at 200 °C exhibits marginally higher corrosion resistance compared with that at 350 °C. Post‐corrosion analysis of the galvanostatically polarized samples revealed localized corrosion for both the steels, but the degree of attack was higher in the 350 °C steel than in the 200 °C steel. The localized corrosion attack was due to selective dissolution of the retained austenite phase. The higher volume fraction and larger size of retained austenite in the 350 °C steel as compared to that of the 200 °C steel contributed to the pronounced corrosion attack in the 350 °C steel.

Localised SKP Studies of Cathodic Disbondment on Chromium/Chromium Oxide Coated Steel

Organically coated thin (submicron) chromium PVD coatings have been studied as a means of protecting low carbon sheet steel from localised corrosive attack in the presence of aqueous chloride electrolyte. Novel coating wedges have been utilised to characterise the influence of coating and oxide thickness of chromium coated steel on cathodic disbondment of an applied organic coatings. SKP was used to characterise the delamination kinetics over the wedge and thus identifying optimum coating thicknesses to reduce or even prevent disbondment. It has been demonstrated that the thickness of the metallic coating offered limited influence in altering the disbondment rate with disbondment being limited by cation diffusion. However, through increasing the amount of oxide on the surface it is possible to not only change the limiting mechanism from cation diffusion to electron transfer but also stop the disbondment occurring altogether. Through these experiments it has been demonstrated that the use of wedge coatings and SKP it is possible to quantify optimum coating thicknesses in one single experiment.

Effect of Process Parameters on Clad Quality of Duplex Stainless Steel Using GMAW Process

In recent years, weld cladding are being applied in numerous industries as cost effective engineering solution to use a surface protection layer to protect carbon steel against corrosion attack. The desirable characteristics of cladding alloy are reasonable strength, weldability, resistance to general and localized corrosion attack. The duplex stainless steel having all the desirable characteristic is the candidate material for cladding. However, duplex weld metals have not been studied in detail as duplex stainless steels. Consequently, the properties of duplex weld metals are less well known and only partially understood. In the present study, the properties of duplex weld deposits of the 22 % Cr, 10 % Ni, 3 % Mo, and 0.12 % N type using GMAW process have been investigated. In particular, the influence of welding heat input and shielding gas composition in GMAW process on weld deposit microstructure, impact toughness and resistance to pitting corrosion have been studied. It is observed that concentration of nitrogen of weld deposits influenced by both heat input and shielding gas composition exerted significant effect on microstructure, low temperature toughness and resistance to pitting corrosion.

Effects of Surface Oxide Coating on Corrosion Behavior of Ti-1023/LY12 Galvanic Couple

Galvanic corrosion behavior of Ti-1023 titanium alloy coupled to LY12 aluminum alloy was investigated in 3.5% NaCl solution. Particular attention was given to the effect of anodized coatings on corrosion behaviors of Ti-1023/LY12 galvanic couple. Galvanic test was conducted on the following couples: Ti-1023/LY12, Ti-1023/anodized LY12 and anodized Ti-1023/anodized LY12, respectively. Corrosion properties including open circuit potential (Eoc) of each material, galvanic corrosion potential (Eg) and galvanic corrosion current (Ig) of the couples were monitored. Corrosion morphology was observed by optical microscope (OM) and corrosion mechanisms were analyzed and discussed. It was showed that anodized coatings significantly decreased Eg and Īg of the couples and provide effective protection of the anode from suffering corrosion attack. Only slight localized corrosion was detected on anodized LY12 alloy in the two anodized couples and the LY12 in anodized Ti-1023/anodized LY12 couple was found to be least susceptible to galvanic corrosion. The LY12 alloy in the bare couple: Ti-1023/LY12, was found to be highly susceptible to galvanic corrosion and suffered severe uniform and localized corrosion attack

CORROSION RESISTANCE OF MECHANICALLY ALLOYED 14%Cr ODS FERRITIC STEEL

Abstract The paper presents results of the corrosion resistance of mechanically alloyed oxide dispersion strengthened 14% Cr ferritic stainless. The oxide dispersion strengthened steel was prepared by means of the powder metallurgy route that consists of mechanical alloying of a pre-alloyed argon atomized steel powder (Fe-14Cr-2W-0.3Ti) with 0.3 Y2O3 (wt%), followed by HIPping at 1150°C and annealing at 850°C for 1 h. The density of ODS ferritic steel after consolidation was about 99.0% of theoretical alloy density. The potentiodynamic corrosion tests were performed for 1h and 24 h of material exposure in a physiological saline solution. For comparison the 316 LV austenitic stainless steel was also examined. The obtained results revealed that both materials were in a passive stage, however the lower current corrosion density was measured for 316 LV steel. On the contrary, the austenitic stainless steel exhibited unstable chemical processes at the passive region. On the surface of both materials localized pitting corrosion was observed with different morphology of the cavities. A broken oxide scale with poor adhesion to the ferritic steel matrix with large number of density of localized corrosion attack was observed on the surface of the ODS steel.

Stability of oxide film formed at different temperatures on Alloy 600 in lithiated environment

The nickel base alloys are susceptible to localized corrosion attack and the major contributing factor in these corrosion mechanisms is the oxide film formed on the alloy. The chromium content in the oxide film determines its stability against localized attack that act as precursors for the initiation of stress corrosion cracking (SCC) in the material. The present study aimed at optimizing the hot conditioning parameter by varying the temperature of oxide formation for minimum ion release rate during reactor operation. The surface and in-depth compositional characterization of oxide film formed on Alloy 600 was carried out using micro-laser Raman spectroscopy (MLRS) and glow discharge quadrapole mass spectroscopy (GDQMS) respectively. The relative defect density of oxide films were studied using electrochemical impedance spectroscopy (EIS). The oxide film stability of Alloy 600 in chloride containing environment was correlated to chromium concentration in the film as well as relative defect density.

In-situ characterization of the damage evolution in thin polyelectrolyte films on TWIP steel substrates

Steels showing twinning-induced plasticity (TWIP) are characterized by extraordinary mechanical properties at room temperature, i.e. high strength and ductility. But at the same time these steels are suffering from environmental effects, leading to surface corrosion and hydrogen related effects. Traditional coatings such as zinc layers may not show sufficient formability, so that local failure of these coatings can occur during forming of sheets, e.g. by deep drawing. Local failure of the coating system will eventually lead to localized corrosive attack, deteriorating the TWIP steel performance. In order to protect the surfaces during processing, a new kind of extremely formable coating for TWIP steels is proposed in this study. Thin polyelectrolyte films are deposited on the TWIP surfaces by a dip coating process. Different film conditions are established and the corresponding damage evolution is characterized. In order to precisely determine the reasons for local film cracking, a thorough characterization of the deformation behavior and the surface evolution of the TWIP steel substrates have been conducted and the suitability of the polyelectrolyte-based coatings for future applications has been demonstrated.

Selection of inhibited preservative materials for corrosion protection of gage parts (level transmitter torque tubes in primary and secondary oil processing units) and experience in application of such materials

The reasons of initiation and development of local corrosion attack which is the most hazardous form of destruction of thin-walled tubes in level transmitters at oil processing units are examined. The protective effect of oil-based preservation materials with respect to nickel and copper-nickel alloys in hydrocarbon media containing chlorides and sulfur compounds has been studied. Laboratory studies and industrial tests have shown that the highest protective effect is provided by M-1 inhibitor at 5 mass% concentration in PES-5 silicone oil. The formulation is successfully used for the protection of torque tubes in liquid level transmitters at primary and secondary oil processing units.

Study of sulphate-reducing bacteria corrosion in the weld joint for API X-70 steel

The corrosion behavior originated by sulfate-reducing bacteria (SRB) was studied in two regions of welded API X-70 steel pipeline. The studies were focused on base material (BM) and heat affected zone (HAZ), from the internal region of the pipe. SRB were extracted from oil and grown in a Postgate medium. Corrosion was evaluated at 60 °C for times between 5 and 64 days. Potentiodynamic polarization curves, obtained by electrochemical techniques, indicated surface activation at short times. Structural and morphological characterizations were carried out by scanning electron microscopy (SEM) and optical microscopy (OM). H2S concentration and pH were also measured. Results showed an important increase in the corrosion damage up to 20 days, influenced by the SRB activity, which lead to a maximum of H2S (pH minimum). It was found a localized corrosion attack in the HAZ in a higher quantity compared to BM; and the formation of a thin film on the steel surface, originated by corrosion products and bacterial activity.

Assessment of Intergranular Corrosion Attack in Austenitic Stainless Steel Using Ultrasonic Measurements

The structural materials of reprocessing and waste management plants are made from AISI Type 304L (UNS S30403) grade austenitic stainless steels and are prone to localized corrosion attack like intergranular corrosion (IGC). It is very important to detect and characterize this attack non-destructively. An ultrasonic-based, non-destructive evaluation technique has been developed to detect and estimate the depth of IGC attack in Type 304 (UNS S30400) stainless steel grade plate. Samples with varying degrees of IGC attack were generated in laboratory and used for this study. Ultrasonic measurement involved determination of sound velocity in longitudinal mode, longitudinal to shear velocity ratio, sound attenuation measurement, and spectral analysis. The elastic modulus measurement using a nano-hardness tester was carried out to formulate the basis of change in sound velocity in the IGC-attacked samples as compared to the virgin sample. This paper gives the details on the sample preparation method used for generation of IGC attack in Type 304 stainless steel plate and reports the results of ultrasonic measurement on the characterization of IGC attack. The results are compared with maximum depth of IGC attack estimated by microscopic examination.

In vivo degradation performance of micro-arc-oxidized magnesium implants: A micro-CT study in rats

Biodegradable Mg alloys are of great interest for osteosynthetic applications because they do not require surgical removal after they have served their purpose. In this study, fast-degrading ZX50 Mg-based implants were surface-treated by micro-arc oxidation (MAO), to alter the initial degradation, and implanted along with untreated ZX50 controls in the femoral legs of 20 male Sprague–Dawley rats. Their degradation was monitored by microfocus computed tomography (μCT) over a total observation period of 24weeks, and histological analysis was performed after 4, 12 and 24weeks. While the MAO-treated samples showed almost no corrosion in the first week, they revealed an accelerated degradation rate after the third week, even faster than that of the untreated ZX50 implants. This increase in degradation rate can be explained by an increase in the surface-area-to-volume ratio of MAO-treated implants, which degrade inhomogeneously via localized corrosion attacks. The histological analyses show that the initially improved corrosion resistance of the MAO implants has a positive effect on bone and tissue response: The reduced hydrogen evolution (due to reduced corrosion) makes possible increased osteoblast apposition from the very beginning, thus generating a stable bone–implant interface. As such, MAO treatment appears to be very interesting for osteosynthetic implant applications, as it delays implant degradation immediately after implantation, enhances fracture stabilization, minimizes the burden on the postoperatively irritated surrounding tissue and generates good bone–implant connections, followed by accelerated degradation in the later stage of bone healing.

Localized Corrosion of Friction Stir Spot Welds in Magnesium AZ31 Alloy

A scanning reference electrode technique (SRET) apparatus has been designed and commissioned to investigate the corrosion of friction stir spot welds (FSSW) made in AZ31 magnesium alloys. The operational parameters of the apparatus have been calibrated to give adequate spatial resolution. By combining the SRET data with material flow data and immersion test data it was found that the FSSW process causes the formation of distinct noble and active regimes within the weld area. The noble region is aligned with the stir zone (SZ) and is caused by a dynamically recrystallized grain structure which are void of dislocations/twins, and β Mg17Al12 . Localized corrosion attack was observed in both SRET and immersion testing along the thermo-mechanically affected zone (TMAZ). The same effect was consistently observed with a flat versus concave shoulder tool, and dwell times of 1s and 4s.