Corrosion Cracking Research Articles

Effects of cooling rate on the microstructure and properties of hot-dipped Zn–Al–Mg coatings

Appropriate hot-dip coating process parameters are very important for enhancing the cracking resistance and corrosion resistance of Zn–Al–Mg coatings. In this study, five different Zn–6Al–3Mg coatings were prepared by controlling the cooling rate: ZAM1 (0.1 °C/s), ZAM2 (1 °C/s), ZAM3 (5 °C/s), ZAM4 (30 °C/s), and ZAM5 (400 °C/s). The microstructure of each coating mainly included an Al-rich phase, Zn/Al/MgZn2 or Zn/Al/MgZn11 ternary eutectic, and primary MgZn2 phase. A smaller Zn phase appeared in the ZAM3 and ZAM5 coatings, and there was no primary MgZn2 phase in ZAM5. The surface crack morphology of each coating after the tensile and bending tests was observed using scanning electron microscopy. The cracking resistance of the ZAM5 coating was the highest, followed by those of ZAM1, ZAM2, ZAM3, and ZAM4. The cracking resistance of the coating was correlated to the nucleation quantity of the primary MgZn2 phase, because the primary MgZn2 phase is an intermetallic compound that is difficult to plastically deform. The ZAM2 coating exhibited the best corrosion resistance, as determined by neutral salt spray and electrochemical tests. This result was attributed to its higher ternary eutectic area fraction and lower Al-rich phase area fraction.

Evaluation of Steel Bridge Details for Susceptibility to Constraint-induced Fracture

Historically, reports of significant problems associated with details featuring intersecting welds in steel bridges have been rare. However, there have been several notable cases involving constraint-induced fracture (CIF). CIF is a particular concern since it can occur in a brittle fashion, suddenly and without warning (different from other types of problems, such as corrosion or fatigue crack growth, for example). CIF generally occurs in details that feature a high degree of constraint (leading to a high level of stress triaxiality), in combination with high levels of tensile stress (particularly from residual stresses) and the presence of a notch-like or crack-like planar discontinuity approximately perpendicular to the primary flow of tensile stress. Details subject to a high degree of constraint often feature the intersection of two or three welded structural elements. The distinction between “intersecting welds” and “constraint resulting from the intersection of welded structural elements” is important. This paper summarizes the findings and recommendations of a recently completed report reflecting the current state of knowledge about CIF in steel bridges. The report is based on a review of previous research, industry practices, and the input of a panel of steel bridge industry experts. It provides a review of the fundamental principles of CIF and presents a general procedure for evaluating steel bridge details for susceptibility to CIF, including examples of assessments of commonly used steel bridge details.

Residual flexural capacity of pre-cracked RC beams exposed to chloride penetration at the sea surface temperature

This study deals with the behavior of pre-cracked reinforced concrete beams exposed to a chloride environment. Three-point flexural tests were carried on 14 beam specimens. Damaged and undamaged concrete beams were exposed to chloride ions at different cycles in two manners, wetting–drying cycles and full immersion exposure conditions at the Persian Gulf sea surface temperature (PGSST) for three periods of 63, 125 and 188 days. The variation of crack pattern, crack width, load–deflection curves, corrosion ratio of steel bar, percentage of chloride ion penetration and correlation between crack width and corrosion ratio of steel were examined in the studied specimens. The results showed that steel corrosion ratio was directly correlated with crack width and exposure conditions; also, wetting–drying cycles had more negative effects than full immersion on the studied beam specimens. The free chloride ion content of the samples with wetting–drying cycles was higher than the samples with full immersion. The pre-cracked beam specimens’ flexural capacity and ductility ratio exposed to a chloride environment decreased up to 17% and 40%, respectively.

Corrosion level estimation by means of the surface crack width

Since the concrete cover cracking is the earliest visible manifestation of corrosion, a relationship between crack opening and corrosion level can be a useful non-destructive tool to estimate the degradation level of an existing RC member. In the present paper, the predictive formulations available in the scientific literature estimating the crack width due to a given corrosion level are accurately described and their reliability is evaluated by a statistical analysis of the error in the predictions. At this aim, an extensive dataset on crack openings of artificially corroded RC specimen reinforced with a single bar, or more bars with large spacing, has been collected. Finally, a novel relationship for the assessment of the corrosion degradation from the surface cracking is presented and validated.

Corrosion cracking under main pipelines stress

Stress corrosion cracking (SCC) or stress corrosion is one of the most dangerous types of damage in chemical, oil and gas industry, as well as in processing, nuclear, heat and power, metallurgical, shipbuilding and other industries. Corrosion cracking of pipelines under stress (stress corrosion) is the main source of emergency incidents (emergencies) mainly in gas main pipelines. This type of corrosion is widely known and very dangerous.

Study on surface properties of nanosecond laser textured plasma nitrided titanium alloy

To optimize the surface properties of biotitanium alloy, a nitride layer was prepared on its surface by plasma nitriding process, and then a nanosecond laser was used to prepare microtextures on the surface of plasma nitrided (PN) titanium alloy to optimize its surface wetting properties and biocompatibility. The three-dimensional morphology of laser ablation grooves was observed, and the effects of laser parameters on the width and depth of the ablation grooves. The ablation regulation was investigated to select the optimal parameters for the preparation of microtextures (stripes and grids). It was found that the material removal rate was positively correlated with the laser pulse overlap rate, and the laser overlap rate decreased with the increasing of ablation speed and increased with the increasing of laser repetition frequency. Diffraction peaks of Ti-N-O non-integrable compounds appeared on the ablated surface of microtextured samples. The regular ablation textures appeared on the surface of textured samples, and granular melt products appeared at the edges of the textures. The wettability of microtextured samples was improved, which was beneficial to improve the biocompatibility of PN titanium alloy. Due to the overlapping of scan paths, the ablation morphology of textured samples with scan spacing smaller than the spot diameter was irregular and the depth of ablative groove was smaller, which has better wettability. The electrochemical corrosion tests showed that the corrosion resistance of the samples with 0.05 mm scanning spacing was better than that of the samples with 0.02 mm scanning spacing. In addition, after 30 days of immersion corrosion, only a few corrosion products appeared on the surface of all the textured samples, and no corrosion cracks and holes appeared, so the laser textured PN titanium alloy has better corrosion resistance.

Thermo-hydro-chemo-mechanical coupling peridynamic model of fractured rock mass and its application in geothermal extraction

In this paper, a thermo-hydro-chemo-mechanical coupling peridynamic model of fractured rock mass is proposed to simulate the fluid-driven crack and the characteristics of water pressure and temperature under thermo-hydro-chemo-mechanical coupling condition. Firstly, the coupling model is employed to simulate the thermo-hydraulic coupling consolidation problem of rock samples, and its accuracy is verified by comparing with the analytical solution and the previous numerical results. Secondly, the coupling model is employed to simulate the problems of fluid-driven crack and chemical corrosion, and the present numerical results are in good agreement with those obtained by the phase field method. Finally, thermo-hydro-chemo-mechanical coupling peridynamic model is used to simulate the process of geothermal extraction, and to investigate water pressure and thermal field distribution.

Probabilistic analysis of climate change impact on chloride-induced deterioration of reinforced concrete considering Nordic climate

The impact of climate change on the deterioration of reinforced concrete elements have been frequently highlighted as worthy of investigation. This article addresses this important issue by presenting a time-variant reliability analysis to assess the effect of climate change on four limit states; the probabilities of corrosion initiation, crack initiation, severe cracking, and failure of a simply supported beam built in 2020 and exposed to chloride-induced corrosion. The historical and future climate conditions (as projected by three different emission scenarios) for different climate zones in Sweden are considered, including subarctic conditions where the impact of climate change may lead to large increases in temperature. The probabilities of all limit states are found to be: 1) higher for scenarios with higher GHG emissions and 2) higher for southern than for northern climate zones. However, the end-of-century impact of climate change on the probabilities of reaching the different limit states is found to be higher for northern than for southern climate zones. At 2100, the impact of climate change on the probability of failure can reach up to an increase of 123% for the northernmost zone. It is also noted that the end-of-century impact on the probability of failure is significantly higher (ranging from 3.5–4.9 times higher) than on the other limit states in all climate scenarios.

Research on maintenance and strengthening strategies of concrete structures exposed to chloride environment base on state index

To explore the preventive maintenance and necessity strengthening of service concrete structures suffering from chloride attack, two parameters, the crack width and corrosion depth of reinforcement, are selected as the status indicators throughout the degradation process of cracked concrete structures. Then, based on state index, the maintenance decision-making model of concrete structure in chloride environment is established. The RCM test is adopted to evaluate the effectiveness of several preventive maintenance measures conducted on the cracked concrete element and it is found that the microorganism induced calcium precipitation (MICP for short) sealing method has better redeeming effect. The relevant results can provide certain references for the research on the maintenance and strengthening decision of service concrete structures.

Complex of properties of 2219 alloy weld joint in T62 state under modeling operating conditions

A complex of properties of aluminium alloy 2219 welded joint, made by single-pass welding with a non-fusible electrode along and across the rolled product, and heat-treated to the state T62, in liquid amyl and its vapors at a temperature of 50 °C for 45 days was investigated. Characteristics of plasticity and strength of 2219 alloy welded joints are as follows: in the longitudinal (D) direction – yield strength of the welded joint is (301–317) MPa, of the base metal (295—297) MPa, strength limit of the welded joint (409–415) MPa, of the base metal (422–425) MPa, elongation is (4.0–5.8)% and (17.6–19.1)%, respectively; in the transverse (P) direction – the yield strength of the welded joint is (309–331) MPa, of the base metal (304–307) MPa, the yield strength of the welded joint (392–414) MPa, of the base metal (428–433) MPa, elongation is (2.1–3.3)% and (12.6–15.0)%, respectively. The strength coefficient of welded joints in the longitudinal direction is 0.96, in the transverse – 0.94. Welded joints in the above environment are resistant to corrosion cracking and intergranular corrosion, resistance against exfoliating corrosion is evaluated by grade 2. Resistance of 2219 alloy in T62 state in amyl corresponds to the resistance group «stable», in amyl vapors – the group “highly resistant”. After aging in amyl and amyl vapors, the strength grades of the base metal samples and welded joints in both directions are almost unchanged, the plasticity parameters change ambiguously: the yield strength of the base metal increases by ~ (5–6)%, of welded joints decreases by ~ (6–7)%, the relative elongation of the base metal is reduced by ~ (5–16)%, of welded joints by about ~ 20 %. Independently of the direction of welding relative to metal’s rolling, samples’ fractures are mostly viscous. After the exposing in amyl, the coefficient of the strength of welded joints in the longitudinal and transverse directions is the same and equal to 0.91, after the influence of amyl vapors, it is 0.95 in the longitudinal direction and 0.96 in the transverse direction.

The interplay between corrosion and cracks in reinforced concrete beams with non-uniform reinforcement corrosion

This paper investigates the interplay between corrosion of reinforcement and corrosion-induced cracking in reinforced concrete structures with non-uniform corrosion distribution based on the experimental results of a concrete beam simultaneously subjected to sustained deflection and accelerated corrosion through impressed current. Unlike previous studies, this work encompasses various refined techniques for the measurement of surface cracks, such as digital image correlation and distributed optical fiber sensors, as well as for the assessment of reinforcement corrosion, namely 3D laser scanning, to explore previously hidden aspects of the relationship between the two parameters. The applied techniques proved very effective in providing an unprecedented level of detail of both the crack development and corrosion distribution. More specifically, the formation and propagation of corrosion-induced cracks were accurately and constantly monitored over time and subsequently compared to the distribution of corrosion. The results revealed that determining the maximum corrosion level or even the location of the section with maximum corrosion based solely on visual inspection of the surface crack width may not be possible. However, the width of corrosion-induced cracks was found to increase linearly with the local corrosion level, implying that crack width monitoring can still be used to estimate the rate of corrosion degradation.

The corrosion behavior of HVOF TiAlNb coating in molten Zn-0.2 wt.% Al

Abstract In order to understand the corrosion behavior of high-velocity oxygen-fuel (HVOF) TiAlNb coatings in molten Zn-0.2 wt.% Al, the different kinds of TiAlNb coating were deposited on 316L stainless steel substrate and the corrosion tests in molten zinc were carried out. The coating morphologies, phase composition, and characteristics of HVOF TiAlNb coatings at different stages of immersion time were studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectrometry (EDX). The results indicated that the HVOF sprayed TiAlNb intermetallic compound coatings have excellent corrosion resistance to molten zinc. The corrosion type of the HVOF TiAlNb coatings in molten Zn-0.2 wt.% Al is pitting corrosion and crack corrosion. In the whole corrosion stage of molten Zn-0.2 wt.% Al, the corrosion time has no effect on the phase compositions of the HVOF TiAlNb coatings.

A novel frequency domain feature-based approach for diagnosis of failure faults in complex structures with interconnected joints

A wealth of complex structures with interconnected joints such as steel truss bridges and warehouses commonly exist in civil engineering, while they are easily subjected to joint faults like bolt loosening, breathing crack and chemical corrosion during their service, which would seriously affect structures’ safety, durability and reliability. Therefore, diagnosis of joint faults, especially at an early stage, would be essential and meaningful for complex structures. To overcome some limitations in existing diagnosis methods, a novel frequency domain feature-based approach for joint faults in complex structures is developed in this paper. In the new approach, complex structures are simplified as some simple and discrete unit substructures. Then, corresponding unit dynamic models are obtained for the dynamic analysis by considering effects of potential faults as additional nonlinear loads. Collecting vibration data of complex structures to be diagnosed only under different levels of harmonic excitations, which have different magnitudes but same frequency components, local frequency domain diagnosis features and indicators based on additional nonlinear loads and transmissibility functions are defined, and detailed procedures of the novel approach are shown accordingly. Finally, effectiveness and availability of the novel approach are verified through some experiments on a steel structure with bolted joints. Moreover, results of comparison study and effects of excitation frequency are discussed to show superiority of the proposed approach further.

Methods of Corrosion Testing Used for the Development and Industrial Utilization of Novel Shipbuilding Steels and Alloys. A Review. Part II. Corrosion Cracking and Marine Field Testing

Methods of Corrosion Testing Used for the Development and Industrial Utilization of Novel Shipbuilding Steels and Alloys. A Review. Part II. Corrosion Cracking and Marine Field Testing

Mechanical–transport–chemical modeling of electrochemical repair methods for corrosion‐induced cracking in marine concrete

AbstractReinforced concrete structures exposed to marine environments often experience chloride ingress, reinforcement corrosion, and corrosion‐induced cracking. The electrochemical repair method is a promising concrete rehabilitation technique with advantages of non‐destructive and economic performance in crack repair, chloride removal, and corrosion protection, which is particularly suitable for structures exposed to marine environments. This work presents an innovative methodology for modeling the mechanical, transport, and chemical process during electrochemical treatment for marine concrete structures. The entire process from concrete cracking up to repairing can be successfully reproduced and digitally visualized. The first sub‐model calculates the corrosion‐induced cracking process at the mesoscopic level with the consideration of local mechanical variances of concrete composites. Then, a reactive transport sub‐model is established to reveal the interactions and electrochemical reactions among various species of ions. A crack repair sub‐model is built to visualize the moving interface between chemical deposition and crack surface. Through combining the three sub‐models, the interconnected influencing factors in practical engineering can be quantitively investigated. The calculation results show that, compared with electrolyte concentration, the influence of current density on crack closure rates are more obvious. Other factors such as steel reinforcement diameter and crack distribution pattern, which have not been previously reported are highlighted. These findings can guide the application of electrochemical repair in practical engineering.

Enhancing grain refinement and corrosion behavior in AZ31B magnesium alloy via stationary shoulder friction stir processing

Stationary shoulder friction stir processing (SSFSP) in thick AZ31B magnesium alloy was performed to refine the microstructure followed by evaluating corrosion behavior. The use of stationary shoulder exhibited low heat input and small temperature gradient across the thickness of stir zone (SZ). Moreover, smooth surface morphology with little flash was obtained. The probe-dominated SZ developed fine equiaxed uniform grain structure across the thickness of SZ, which in turn increased the corrosion resistance of SSFSPed alloy as compared to BM. SSFSPed alloy surface confirm uniform corrosion behavior with mud cracking and intergranual corrosion patterns instead of pitting corrosion in BM. This improvement in corrosion was attributed to homogenization of magnesium alloy microstructure by using low-heat-input stationary shoulder tool.

Effectiveness of carbon textile reinforced concrete in shear strengthening short-span corroded reinforced concrete beams

This paper will present the shear behavior of the corroded stirrups reinforced concrete (RC) beams strengthened with textile reinforced concrete (TRC). The shear resistance contributions from the corroded RC beams and carbon TRC at various volume ratios were carefully examined. Eighteen beams were tested, including twelve subjected by an electrochemically accelerated aging technique for 60 and 90 days to obtain the theoretical mass loss in their stirrups of 10% and 20%, respectively. The stirrups were locally corroded in the shear span. After the corrosion accelerating treatment, corrosion cracks on concrete surfaces were marked, and their widths were measured to observe their distributions. A three-point bending test was applied to obtain the shear performances of the corroded beams subjected to the monotonic and repeated loading. Eight corroded RC beams were strengthened using 2 and 3 U-wrap layers of bidirectional carbon textile. The shear behavior will be discussed, including the ultimate capacity, failure mode, load-deflection, load–strain relationship, and crack distributions. Compared to the controlled specimens, the averaged shear strength of corroded specimens decreased by 16.08% and 25.34%, corresponding to the degree of corrosion ranging from 12.3% to 23.6%. The experimental results also demonstrate that the shear capacities of the corroded RC beams strengthened with carbon TRC had been improved 60.6% compared to the severely corroded controlled specimens.

Effect of irregular microcracks on the hot corrosion behavior and thermal shock resistance of YSZ thermal barrier coatings

The durability and service performance of thermal barrier coatings (TBCs) is influenced by its microstructure. One type of yttria stabilized zirconia coating containing irregular microcracks (mc-YSZ) was prepared by atmospheric plasma spraying (APS) method in this study, and the differences in hot corrosion behavior and thermal shock resistance between the conventional YSZ coating and the mc-YSZ coating were investigated. Results showed that the presence of irregular microcracks facilitated the penetration of corrosive salt (V2O5 and Na2SO4) and accelerated the hot corrosion reaction. The deflection effect of irregular microcracks in the early stage of hot corrosion could suppress the propagation of cracks generated by corrosion; but irregular microcracks would merge with corrosion cracks in the later stages of corrosion and aggravate the failure of the coatings. Thermal shock tests showed no significant difference of the thermal shock lifetime between YSZ coating and mc-YSZ coating, which proved that this irregular microcrack could not effectively improve the strain tolerance. The present study provides a reference for the structure design of thermal barrier coatings: when designing the structure of the coating, the appearance of that irregular microcracks should be avoided.

Detection of initiation of corrosion induced damage in concrete structures using nonlinear ultrasonic techniques.

Structural failure caused by corrosion of the reinforcing steel in concrete structures is quite common. In most cases, corrosion cracks appear on the surface at a late stage, leaving inadequate time for taking any measures. This paper investigates the detection of corrosion damage in reinforced concrete elements by using nonlinear ultrasonic (NLU) techniques. Various linear ultrasonic and NLU techniques were adopted to identify the most sensitive technique and ultrasonic parameters for corrosion induced damage detection at its early stage. It is observed that the linear techniques are not very effective in detecting corrosion induced damage. The sideband peak count-index (or SPC-I), a relatively new and promising technique, has been found to be an excellent indicator for the detection of corrosion induced damage initiation. However, its efficacy for detecting corrosion induced damage has not yet been reported. The present study shows that the SPC-I-based NLU technique outperforms (with the highest sensitivity) all other NLU techniques for detecting the onset of corrosion in steel and micro-crack formation in the surrounding material. As the corrosion progresses and cracks appear on the surface of the concrete, the efficiency of the SPC-I slowly weakens and other technique(s) are found to be quite efficient at that stage.

CNN-LSTM network-based damage detection approach for copper pipeline using laser ultrasonic scanning

Copper pipeline is a commonly used industrial transmission pipeline. Nondestructive testing of copper pipeline early damage is very important. Laser scanning has attracted extensive attention because it can realize the visualization of guided wave propagation and non-contact on-line detection. However, the damage points detection in laser scanning imaging method rely on the difference between the damage points signals and surrounding normal points signals. This limits the applicability of laser scanning and may lead to inaccurate in large-area detection. Facing with such challenges, a damage detection method based on CNN-LSTM network is proposed for laser ultrasonic guided wave scanning detection in this paper, which can detect each scanning point signal without relying on the surrounding detection points signals. Firstly, the proposed data conversion algorithm is used to preprocess the laser scanning signals. Next, CNN-LSTM network is used to train the damage detection model. Four 1D Conv channels with different convolution kernel sizes and depths are designed in Convolutional Neural Network (CNN) module. The module can extract the signal time domain features. Then the features are input into the Long Short-Term Memory Network (LSTM) for feature extraction and classification. Finally, the CNN-LSTM is trained using the laser scanning detection data collected on the copper pipeline with crack and corrosion damages, and applied to detect the copper pipeline damage signal. At the same time, the state-of-the-art methods is compared with proposed method. The experimental results show that the detection accuracy of the method is 99.9%, 99.9%, 99.8% and 99.8% for copper pipeline 0.5 mm deep crack damage, penetrating crack damage, corrosion damage and inside crack damage, respectively. The damage location and size can be accurately detected by the proposed method.