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Here, we present a numerical approach to analyze the integrity of a vessel that was subject to a weld repair. A Post-Weld Heat Treatment (PWHT) process was implemented to a vessel undergone weld repair due to leakage. Due to the thick wall of the welded bottom head, this welding process must be followed by the PWHT to relieve the residual stress, as well as to improve the material properties. PWHT process was performed by heating the welded area to reach 675 °C temperature. A numerical approach using finite element analysis (FEA) method was performed to analyze the integrity of the vessel. Based on the analysis, the structure is still stable within the applied load. PWHT process does not lead to buckling on the main structure and the load is still lower than the load required for the occurrence of buckling. A sensitivity analysis was also performed with reduced temperatures to 630 °C or reduction of PWHT area width. These changes were found to have negligible effects in reducing the stress and strains in the vessel. After PWHT is completed, the structure is still considered to be safe to be operated, as indicated by its strain that is still below the allowable strain and only relatively small deflection was occurred.

Triethanolamine (TEA), an amine-based corrosion inhibitor, was encapsulated and then embedded into an epoxy coating to provide long-term corrosion protection of aluminum alloy 3003. TEA was encapsulated by means of free-radical polymerization, yielding an average particle size of 450 nm. An applied epoxy coating containing 10 wt % of the nanocapsules successfully protected an artificially defective area for a long period due to TEA adsorption, which resulted in the formation of an inhibiting layer. Electrochemical impedance spectroscopy showed an inhibition efficiency surpassing 85% when the metal experienced mild corrosion in its early stages, and the inhibiting layer started to form by local pH level change, which triggered the release of TEA. On the basis of the results of a scanning vibrating electrode technique, the current density of the metal surface in the presence of an encapsulated TEA coating was significantly lower than that of the control coating with no nanocapsules. Optical microscope and scanning electron microscope images revealed that the sample surface that had encapsulated TEA nearby was considerably less stained after 60 days of testing compared with that of the control sample, which indicated that the metal substrate was protected by an inhibiting layer. Elemental analysis performed by energy-dispersive X-ray spectroscopy further confirmed that the metal surface was well preserved, and a remarkably low oxygen content indicated suppressed metal oxidation. The nuclear magnetic resonance spectra also evidenced a successful release of TEA throughout the experimental period. These findings reflected a spontaneous surface repassivation with the help of encapsulated TEA coating.

The degradation of ultra-fine grained aluminum alloys involves multiple localized corrosion mechanisms at once which make its understanding complex. Here we investigate the electrochemical response of a partially recrystallized ultra-fine grained AA6061 alloy after a low-temperature post-aging treatment. Our results show that the anodic current density, the severity of the filiform corrosion along the shear direction, and the intergranular corrosion are significantly influenced by the precipitation within the shear bands, being the highest at peak aging. Also, passivation is enhanced but the passive film is less stable after ECAP regardless of the low- temperature post-aging treatment. because of the high density of dislocation, precipitates, and grain boundary in the extruded material.

This study introduced an enhanced corrosion performance of an epoxy coated rebar (ECR) embedded with the nanocapsules containing triethanolamine (TEA) as the corrosion inhibitor. Electrochemical corrosion tests indicated a successful protection of the artificially defected area from the sample with encapsulated TEA coating, especially in the initial immersion period, indicating that there was a successful release of TEA from the embedded nanocapsules. A considerably lower surface current density of the encapsulated TEA coating also indicated that the electrochemical reactions were delayed which were further confirmed by surface micrographs that revealed a relatively less degraded artificial defect of the sample with the encapsulated TEA coating. The corrosion product analysis denoted that the inhibiting action has delayed the further oxidation of the exposed surface by having an enhanced barrier protection that helped to maintain a lower O/Fe ratio.

This study introduces enhanced corrosion performance of the Al-Si-Mg coated 22MnB5 boron steel. Structural changes of the coating after hot-dip-aluminizing and hot-press-forming processes with the presence of Mg included compacter surface with Mg segregation and thicker crack-free layer. Electrochemical corrosion tests indicated higher polarization resistance from the Al-Si-Mg sample compared to the reference Al-Si sample, especially in an early period of immersion. Such enhanced anti-corrosion performance can be attributed to the aforementioned structural changes and pore-filling effect of corrosion products. This study depicts that the Al-Si-Mg coating can be considered as another option for hot-press-forming steel by its enhanced barrier protection vs. Al-Si coating.

In this study, corrosion response of the 2060-T8E30 alloy was analyzed in the following environments: EXCO (an immersion test in accordance with ASTM G34), modified EXCO, and modified ASTM acetic a...

We present the preparation and inhibition behavior of rebar in the presence of microencapsulated calcium nitrate (CN) with concentrations of 0.5, 2.0, and 5 wt.% in concrete. From both open circuit potential (OCP) and electrochemical impedance spectroscopy spectra, it was found that an addition of CN corrosion inhibitor-containing microcapsules into concrete beams successfully repassivated or maintained the passivity of the rebar when the concrete was cracked. This corrosion inhibitor healed the rebar by forming a passive layer on the rebar surface under the crack. This healing process was evident by an increase of OCP values to more positive values or by stable OCP values at around -100 mV vs SCE. An increase in phase angle after corrosion activation for CN C 2% clearly showed this healing process. The optimum concentration for maintaining the passivity on rebar in the cracked concrete was found to be 5 wt.%.

It has been documented that the corrosion behavior of AZ91 (Mg–9Al–1Zn, wt.%) alloy is strongly influenced by the morphology, distribution, and volume fraction of secondary phases, however, the proposed corrosion mechanisms are questioned due to new experimental findings. The present study focused on providing a more detailed understanding of the corrosion mechanism of a peak-aged AZ91 alloy exposed to a chloride environment by using scanning Kelvin probe force microscopy, immersion testing, optical microscopy, scanning and transmission electron microscopy techniques and electrochemical microcell technique. It was found that corrosion was simultaneously initiated in the interior of α-Mg grains and in the local α-Mg phase within the α + β lamellar precipitate; furthermore, the lamellar precipitate/α-Mg matrix boundary acted as a barrier for corrosion propagation. The proposed corrosion initiation mechanism is opposed to previous investigations reporting the development of micro-galvanic coupling between the β-Mg17Al12 phase and the adjacent α-Mg matrix, which cannot be supported by our experimental findings. The corrosion propagation in the peak-aged alloy was dominated by the preferential anodic dissolution at the interior of the α-Mg matrix due to its faster corrosion reaction kinetics compared to the micro-galvanic corrosion process between the β-phase and the local α-Mg phase occurring inside the lamellar precipitate.

In this study, we investigated exfoliation corrosion (EFC) of the alloy 2060 T3E80 in an aggressive solution, namely EXCO. The pH value increased from 0.25 at the initial time point to 3.45 after 96 h of testing. In Stage 1 (0.25

A good combination of mechanical properties and corrosion performance is desired when employing Mg alloys in engineering applications. Therefore, it is essential to investigate both the mechanical properties and corrosion resistance of processed Mg alloys to determine the optimum combinations of materials properties. This study investigates the microstructure, mechanical properties, and corrosion resistance of AZ91 (Mg–9Al–1Zn, wt.%) alloys in chloride-containing environments under different processing conditions. The findings revealed that the AZ91 alloy exhibits good mechanical properties combined with high corrosion resistance after microstructure modification through equal channel angular pressing (ECAP). This microstructure was characterized by a bimodal grain structure with the formation of a high volume fraction of well dispersed β-Mg17Al12 precipitates. The superior mechanical properties of the AZ91 alloy after ECAP process were mainly attributed to the combined effect of significant grain refinement and high volume fraction of fine β-Mg17Al12 precipitates that provided grain boundary and precipitation strengthening and promoted a more uniform plastic deformation. The enhanced corrosion resistance of the fine-grained AZ91 alloy was related to the presence of a highly protective oxide layer, the formation of a highly adherent and compact layer of corrosion products, and the development of uniform corrosion with shallow corrosion pits. This simultaneous improvement in strength, ductility, and corrosion resistance of fine-grained AZ91 alloys can serve as a guide for future alloy design and represents a promising alternative for industrial applications.

We studied crevice corrosion of UNS S32003 using a single-boss crevice former. This crevice assembly with a single boss at the center is a modification of the commonly used multiple-crevice assembly (MCA). This design effectively prevents unwanted crevice corrosion outside the crevice of interest. Our single-boss crevice assembly produces comparable repassivation potentials obtained using cyclic potentiodynamic polarization (CPP), Tsujikawa–Hisamatsu Electrochemical (THE), potentiodynamic–galvanostatic–potentiodynamic (PD–GS–PD), and potentiostatic (PS) techniques. Considering the degree of attack, we found that the THE technique is the most powerful for forming a deep, wide, and continuous crevice corrosion site, while the PS technique is the least powerful technique at potentials slightly above the repassivation potential. A galvanostatic hold in step 2 of the THE and PD–GS–PD techniques successfully grows a deep localized corrosion site, as indicated by a deep crevice corrosion attack found in samples tested with these techniques. The PS step (step 3) in the THE technique allows the grown localized corrosion site formed by a previous step (a galvanostatic hold) to propagate inward and along the crevice mouth, creating a wide and continuous crevice corrosion attack along the crevice mouth. Metastable pits play a role in crevice corrosion of UNS S32003 alloy in this study, as indicated by a large number of metastable pits in the crevice region. The ferrite phase is preferentially attacked by metastable pits.

A brine storage tank was reported to have visible and severe localized corrosion 1 year after installation. The material used for this tank was UNS S31603 stainless steel. The corrosion was mainly noticeable at various points/areas along the welded joint, and there was also some pitting on the base metal at the bottom of the tank. Corrosion was also found at the welded joint at the hatch wall. Indications of severe corrosion that resulted in deep metal loss were found at some points along the welded joint. The results of an oxalic acid etch test in the heat-affected zone (HAZ) showed the interdendritic ditches, which are considered to be prone to intergranular corrosion/weld decay. The results of a double-loop electrochemical potentiokinetic reactivation (DL-EPR) test and 3D multiscale images were in agreement with the results of an oxalic acid etch test that indicated the intergranular corrosion susceptibility of the HAZ. The base metal, in contrast, did not show any intergranular corrosion.

We investigate the transpassivity of super-austenitic stainless steel UNS N08367 in 2.5 M LiCl solution by using cyclic potentiodynamic polarization (CPP), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). The CPP curve exhibits negative hysteresis, which indicates a transpassive dissolution process instead of pitting corrosion. The transition from the passive region to the transpassive region is characterized by EIS and equivalent circuit analysis. During the transpassive dissolution of the N08367 alloy, two reactions of adsorbed intermediates are dominant, as indicated by the two inductive loops at the transpassive region. The first inductive loop is associated with the faster reaction, i.e., the adsorption of Fe intermediates. This fast reaction is significantly influenced by the preferential dissolution of Fe during the transpassive dissolution. The second inductive loop is correlated with the adsorption of the Cr intermediate. In contrast to Fe, the Cr content on the surface increases in the transpassive region compared with the content in the passive region. The XPS spectra support the time and frequency domain approach for the preferential dissolution, and the dominant species resulted from the interfacial processes at the transpassive region.

We present the preparation and inhibition behavior of rebar in the presence of calcium nitrate (CN)-containing microcapsules with concentrations of 0.50, 2.00, and 5.00 wt.% in concrete. From both open circuit potential (OCP) and electrochemical impedance spectroscopy spectra, it was found that an addition of microcapsules containing CN corrosion inhibitor into concrete beams successfully repassivated or maintained the passivity of the rebar when the concrete was cracked. This corrosion inhibitor repassivated the rebar by forming a passive layer on the rebar surface under the crack. This repassivation process was evident by an increase of OCP values to more positive values or by stable OCP values at around -100 mV vs SCE. An increase in phase angle after corrosion activation for the sample with 2.00 wt.% microcapsule clearly showed this repassivation process. The optimum concentration for maintaining the passivity on rebar in the cracked concrete was found to be 5.00 wt.%.

A shaft of electric motor fin-fan cooler failed after two years operation. The inspection revealed that the v-belt attached on the electric motor loosed before the failure occurred. Visual investigation results showed the brittle fracture with less plastic deformation. Multiple crack origins observed on the edge of the shaft indicates that the more than one stress concentration generated within the shaft. Microstructure observation revealed fine grain on the edge and become coarse into the center of the shaft. The hardness test results were in good agreement to the microstructure observation where the edge are is harder than the center. Fractography using SEM revealed inclusions located within the shaft and some inclusions are clustered on the area where the cracks initiate to propagate. The presence of intermetallic inclusions was identified by microanalysis using EDS. Inclusions that are brittle in nature become stress concentrations for the operating load since its properties is close to ceramic. The presence of fine grain and inclusions on the edge of the shaft become detrimental to the shaft properties and the presence of fine grain aggravate the failure for its effect according to Hall-Petch theory.

This work presents the interfacial characterization of two UNS corrosion resistance alloys (CRAs), N08367 and S31603 in LiCl and LiBr solutions. The electrochemical nature of these materials in halide solutions demonstrates different mechanisms at the substrate-electrolyte interface. Time and frequency domain electrochemical techniques were used; cyclic polarization tests showed that S31603 was attacked by pitting corrosion for different LiCl and LiBr concentrations. N08367 revealed different mechanisms due to the passivation layer existed under polarization conditions. The current densities increments for the N08367 alloy were attributed to the charge transfer-adsorption mechanism, as evidenced by the EIS data. The pitting potentials of S31603 in LiCl and LiBr solutions were similar. However, the current transients were only found in S31603 in LiCl which might indicate that LiCl had more significant kinetic effect than LiBr. Bias potential was applied for EIS testing to support either active/passive/transpassive behavior for each material. Qualitative analysis could demonstrate the link between EIS and polarization techniques.

The purpose of this research was to study the corrosion behavior of Ti-8Ta-3Nb and Ti-10Ta-10Nb in simulated physiological media in comparison to that of CP Ti and Ti-6Al-4V. In the Ringer's solution, Ti-8Ta-3Nb exhibited a higher passive current density than CP Ti and the other Ti-based alloys. Increasing the alloying additions of Ta and Nb to Ti successfully suppressed the oxygen evolution, lowered the passive current density, and shifted the corrosion potential in the noble direction. While the current densities of CP Ti, Ti-6Al-4V, and Ti-8Ta-3Nb significantly increased at a potential > 1.0 VSSC, the current densities of Ti-10Ta-10Nb tended to remain constant. The deconvolution of the O 1s peaks for Ti-10Ta-10Nb showed the peaks of O2−, OH− and H2O. However, Ti-8Ta-3Nb only showed the peaks of O2− and OH−. The superior property of the passive film on Ti-10Ta-10Nb, in comparison to that on Ti-8Ta-3Nb, was attributed to the presence of the hydrate group inside the passive film.

The use of the finite element in engineering applications has grown rapidly in recent years. Finite element analysis (FEA) is based on numerical computation that calculates all parameters and boundaries given. Supported with powerful computer processors and continuous software development, the finite element method is rapidly advancing. The use of finite element analysis is not limited to the engineering field, as there are also medical and geospatial applications. The early development of the finite element can be traced back to the work of Courant [1], followed by the work of Martin [2], which applied the solutions for structural analyses at Boeing Company in the 1950s. Further work by Argyris, Clough, Turner, and Zienkiewicz developed the governing mathematical equation for the finite element method [3].

A fractured flanged thermowell was received for analysis. The fracture was located at the root of “U” insertion/immersion length which was welded to the flange. The failure of flanged thermowell was attributed to the vortex-induced fatigue. The failure was initiated by the weld failure to withstand the fluctuating load resulted from vortex after years of service. This weld failure then created stress raisers, as evidenced by the ratchet marks and river marks near the outer surface.

A seawater inlet pipe failed in service. The visual examination showed that the backing bar was present inside the pipe and the failure was characterized by leaks at approximately 4–8 o’clock position near that backing bar. The finite element analysis of fluid in the seawater inlet pipe showed that the eddy zone was formed near the backing bar. The leaks and crater-like surfaces were noticed on the inner pipe surface at which the finite element analysis modeled the possibility of the formation of eddy zone.