Cracking Of Steel Research Articles

The synergistic effect of parallel magnetic field and sulfate-reducing bacteria on stress corrosion cracking of buried X80 pipeline steel

In this work, the synergistic effect of parallel magnetic field and sulfate-reducing bacteria (SRB) on stress corrosion cracking (SCC) of X80 pipeline steel in buried soil environments was investigated for the first time by electrochemical experiments, slow strain rate tensile tests (SSRT) and surface characterization. The results showed that the parallel magnetic field suppressed electrochemical corrosion in a sterile environment; the SCC susceptibility decreased with increasing magnetic field strength (0–100 mT). The magnetic field and SRB synergistically promoted the formation of a dense film layer on the surface of the specimen in the inoculated SRB environment. The dense film layer suppresses the local corrosion of the metal and therefore the SCC susceptibility is reduced. The suppression effect no longer increased significantly when the magnetic field strength reached 75 mT. The synergy between the parallel magnetic field and the SRB was responsible for the reduced susceptibility of the SCC. This work contributed to a more in-depth study of the mechanisms of pipeline SCC and the development of pipeline SCC prevention technologies.

The Influence of Repeated Heat Treatments on The Propagation of Fatigue Cracking of Medium Carburized Steel

The issue of metal fatigue emerged as one of the major issues in a variety of engineering designs, and the design engineers were forced to take metals' fatigue resistance into account. In this paper, multiple quenching mediums and varied heat treatments were utilized to examine the effects of various heat treatments on the development of fatigue cracking in steel. The model that was carburized, quenched in distilled water and tempered before being quenched once more in distilled water and tempered a second time had the best outcomes, the fewest cycles needed to cause the model to fail, and a correlation between the rate of fatigue crack propagation and the length of the crack, according to the results. Additionally, the analytical findings demonstrated that this model, as opposed to models with fixed stress intensity factors, has a fatigue crack growth rate. The model that was carburized, quenched in coolant, then tempered and quenched again without performing the tempered appearance failed very rapidly. The high rate of the stress intensity factor with fatigue crack propagation is shown by the data analysis. The results show a reduction in the growth amount tendency of fatigue crack in the linear region mode-III.

The effect of V8C7 size on hydrogen diffusion behavior and hydrogen induced cracking in pipeline steel

This study revealed the relationship between V8C7 size and hydrogen diffusion behavior as well as hydrogen induced cracking (HIC) in pipeline steel. Hydrogen permeation and HIC susceptibility tests were implemented on five conditions with different V8C7 sizes but identical volume fractions. The results proved that with increasing of V8C7 size, the hydrogen effective diffusivity was first decreased and then increased. Increasing the proportion of small size (coherent and semi-coherent) V8C7 increased the effective hydrogen trapping densities, decreased hydrogen diffusion coefficient, improved the distribution of diffusible hydrogen atoms and then the HIC susceptibility of steels was decreased.

Weathering steel bridge structure after 30 years of service ‐ assessment experience

AbstractThe structure of 531.4 m total length bridge was made in early nineties last century and it was regarded as novelty by that time. The interesting point was that the structure was made of original Polish weathering steel prepared for bridge solutions intently. There were several trouble concerning the bridge service, steel cracks and less than expected patina growth due to the unfavorable conditions inside the box girder. Quite recently the bridge was carefully inspected as it was to be an important issue of the modern motorway. There was a question if the bridge is to be demolished, due to the corrosion and structural problems or to be preserved and extended to meet required traffic volume. There was a careful examination performed including metallurgical, corrosion and structural analysis done. The paper is to present the most important outcomes concerning mainly structural issues, but some weathering steel corrosion observation will be provided as well.

Determination of the Existence of Liquid Metal Embrittlement Cracks in Resistance Spot-Welded Advanced High-Strength Steel

Abstract The characteristics of liquid metal embrittlement (LME) cracks combined with the location, amount, and length of the resistance spot-welded joint of galvanized advanced high-strength steel were comprehensively investigated in this study. To better illustrate the features of LME cracks, a multilayer grinding and polishing technique was employed to more comprehensively reflect the existence of LME cracks compared with that of a single-layer technique. Based on the crack observation results of the cross section of the center weld, the longest type-I and type-II cracks were approximately 322.2 and 106.7 μm, respectively. On the contrary, the longest type-I and type-II cracks were approximately 1,062.9 and 194.7 μm, respectively, for the multilayer grinding and polishing technique. The existence of liquid zinc for more time and the resultant tensile stress at the center of the weld can trigger crack propagation, eventually resulting in type-I cracks that are longer than type-II cracks. Similarly, severe LME cracks mainly exist in the central position of the welded joint, implying that temperature and stress can have a crucial effect on the formation and propagation of LME cracks.

Fatigue strengthening of cracked steel plates with bonded Fe‐SMA strips

AbstractPrestressed fatigue strengthening of steel structures has been proven effective by numerous investigations. Bonded iron‐based shape memory alloy (Fe‐SMA) strengthening has shown a great potential in this regard, however, with limited corroborating studies. Moreover, a proper model for fatigue analysis of systems that are retrofitted with bonded Fe‐SMA strengthening is missing. In this study, an analytical model, coupling prestress analysis and fatigue analysis, is proposed. Four steel plates with central through‐thickness cracks were strengthened with use of bonded Fe‐SMA strips, and subsequently tested under fatigue loading after generating prestress via heating and cooling. The fatigue behavior predicted by the proposed model lies in excellent agreement with the fatigue testing results.

Using distributed fibreoptic sensing to monitor repaired structures reinforced with steel‐patches

AbstractAdhesively bonded steel patches present a novel approach to strengthen fatigue cracked steel bridges or similar structures. After the repair, the new weld is covered with an adhesively bonded steel patch, redistributing parts of the load and reducing the overall stress in the repaired structure. Unfortunately, this covers the weld permanently and therefore any form of direct, visual inspection is no longer possible. Hence arises the demand for a technical solution to reliably determine the condition of the repaired weld and its reinforcement. Fibre optic sensors using Rayleigh backscatter offer a spatial distributed strain measurement from which a deformation profile can be generated. This deformation profile allows to determine the load distribution between patch and structure and can be used to identify possible changes in the load distribution which can represent a change in the mechanical properties and therefore a possible defect. Having not only the information about the absolute value of the strain but also its distribution, the expected damage can be located and measured. The deformation profile also allows to separate different forms of failure for example a broken weld, adhesive failure within the patched area or sub surface migrating corrosion.

Metal 3D‐Printing for Repair of Steel Structures

AbstractThis work employs an innovative technique, wire arc additive manufacturing (WAAM) which is a type of directed energy deposition, for fatigue strengthening of cracked steel components. Different steel plates with a central crack were tested under high‐cycle fatigue loading regime, including a reference plate, a plate repaired by WAAM with as‐deposited profile, and a plate repaired by WAAM and subsequently machined to reduce stress concentration factors. Corresponding finite element simulation was conducted to provide a better understanding on the mechanism of WAAM‐repair. The existing central crack in the reference plate propagated and led to a rupture after 0.94 million cycles, while those in the two WAAM‐repaired plates did not propagate, due to the increased net cross‐section and the compressive stresses induced by the depositing process. However, in the second plate, a new crack initiated at the root of WAAM profile as a result of local stress concentration, and the fatigue life reached 2.2 million cycles (2.3 times as the reference plate). The third plate, on the other hand, survived more than 9 million fatigue cycles with no visible degradation, thanks to its smooth machined profile. The findings of this work indicate that WAAM repair shows great potential as a technique to address fatigue‐related damages in steel structures.

Enhancing the SCC Resistance of the Anchor Steel with Microalloying in a Simulated Mine Environment.

This work explored a new idea for enhancing the resistance to stress corrosion cracking (SCC) of mining anchor steel through microalloying. Microalloyed anchor steels with Nb, Cu, Ni, Sb, and C were prepared through vacuum smelting and hot rolling. Electrochemical measurements, slow strain rate tensile (SSRT) tests, and fracture morphology observations were used to study the electrochemical and SCC behavior in the simulated mine environment. The results proved that the microstructure of microalloyed steels varies slightly. Adding Ni, Cu, and Sb can improve the mechanical properties of the anchor steel, while reducing C content decreases tensile strength as a result of loss of the solution-strengthening effect. The addition of Sb, Cu, Ni, and reducing the content of C enhances the resistance to corrosion and SCC by mitigating anodic dissolution (AD), while adding Nb improves SCC resistance by inhibiting hydrogen embrittlement (HE). The combined addition of 1% Ni, 0.5% Cu, 0.05% Nb, 0.1% Sb, and 0.5% C presented the highest SCC resistance, which is a promising prospect for the development of high-performance, low-alloy anchor steels. The combined addition of 1% Ni, 0.5% Cu, 0.05% Nb, and 0.1% Sb resulted in the inhibition of electrochemical reactions and corrosion. As a result of the synergistic effect of the microalloy, both AD and HE mechanisms were simultaneously inhibited, which greatly enhanced SCC resistance.

Analysis of Cracks in Solution-Treated AISI 17-4PH Stainless Steel Observed During Machining of Aerospace Component

Analysis of Cracks in Solution-Treated AISI 17-4PH Stainless Steel Observed During Machining of Aerospace Component

Influence of TiN Inclusions and Segregation Bands on the Mechanical Properties and Delayed Crack in Thick NM550 Wear-Resistant Steel.

The formation mechanism of the delayed crack after flame cutting and mechanical properties in thick NM550 wear-resistant steel are studied by optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and an electron backscattered diffractometer. The delayed crack is formed at the segregation zone (SZ) located in the center of the 65 mm thick steel plate. The strength of the non-segregation zone (NSZ) with a martensite microstructure is slightly higher than that of SZ with a mixture microstructure of martensite plus bainite, and the plasticity of NSZ is significantly better than that of SZ. There exists a more severe segregation in the SZ, and only a slight segregation in the NSZ. The average grain sizes of the segregation bands in the NSZ and SZ are 15.72 µm and 6.76 µm, respectively. The number density of TiN larger than 5 µm in the NSZ and SZ is 0.031 and 1.156 number/mm2, respectively. Therefore, a high hardness segregation band with fine grains and a high dislocation density, along with the large number of coarse TiN inclusions within it, results in delayed cracking. For TiN inclusions close to the crack, microvoids or microcracks around the TiN are formed, and the delayed crack will propagate along the edge of the TiN or through the TiN inclusions.

Weldability study of 304HCu stainless steel using varestraint and “Gleeble” based hot ductility tests

The susceptibilities of 304HCu SS to solidification and liquation cracking are assessed in the current work and the underlying mechanisms are clarified. The development of γ + Nb4C3 eutectic along the interdendritic areas in the fusion zone is attributed for solidification cracking in this stainless steel. To forecast and rank the susceptibility of an alloy to solidification cracking, a novel technique is put forth and experimentally confirmed. Using the measured temperature gradient, welding speed and Scheil's solidification module, a relationship between the liquid fraction and mushy zone width is derived. Liquation cracking susceptibility evaluated using “Gleeble™” based hot ductility test is observed to be high which is attributed to the constitutional liquation of primary Nb(C,N) and secondary M23C6 phases present in the base metal. Further, the influence of phosphorus on the local solidus temperature in the partially melted zone of the alloy is discussed in the context of liquation cracking.

CARBON DIOXIDE STRESS CRACKING IN OIL PRODUCTION

The article describes stress corrosion cracking (SCC) of pipe string elements associated with exposure to carbon dioxide. SCC can occur in solutions containing H2S, CO2, ammonia, nitrates, chlorides, acids, alkalis, etc. The article shows two typical examples of stress corrosion cracking of high-carbon steels of tubular string elements (grades 40X13, 40XH) after operation in field environments whose well products do not contain hydrogen sulfide. The possible mechanism of carbon dioxide stress cracking was analyzed in comparison with carbonate stress corrosion cracking (Carbonate Stress Corrosion Cracking) described in the API 571-2020 standard. It is shown that an integral part of the mechanism of carbon dioxide stress cracking is the growth and development of cracks during hydrogen evolution in the cathodic reaction. The general metallurgical and operational characteristics of steel elements of tubular strings subjected to carbon dioxide stress cracking are given, which are in good agreement with the available foreign literature data. Based on the results of operation, it was confirmed that in «conventional» oilfield systems with carbon dioxide, equipment failures by the mechanism of carbon dioxide stress cracking are possible. Examination of the described failures included the following assessment methods: analysis of the accompanying documentation, visual-measuring control, micro-examinations by light microscopy and scanning electron microscopy, tests to determine the mechanical properties of the metal.Carbon dioxide stress cracking was observed in the presence of the following factors: carbon dioxide environment (in the absence of hydrogen sulfide); high concentration of carbon in steel (0.4 % wt.); increased hardness of steel (from 30.3 to 33.9 HRC); the presence of constant and alternating mechanical loads.

Effect of Thermo-Mechanical Processing on Initiation and Propagation of Stress Corrosion Cracking in 304L Austenitic Stainless Steel

Despite the high corrosion resistance of austenitic stainless steels (SSs), a significant reduction of stress corrosion cracking (SCC) resistance has been reported in cases of high residual stress and metastable microstructural features. In this study, the effect of thermo-mechanical processing (TMP) on the initiation and propagation of SCC in 304L SS was studied. To better understand the SCC mechanisms, three TMPs conditions—welded, solution annealed at 1050 °C for tens of seconds, and straightened—were used. The research focused on analyzing the initial microstructure, residual stress, and hardness along the depth direction to assess SCC resistance and establish correlations with the observed SCC modes. Experimental results demonstrated that transgranular SCC was observed in regions exhibiting elevated residual stress induced by welding and straightening processes. Furthermore, the presence of strain-induced martensite transformation and slip bands formed during plastic deformation were identified as additional factors contributing to the susceptibility of SCC. The study findings highlighted that the magnitude and distribution of residual stresses, in conjunction with microstructural evolution, could be varied depending on the specific TMP condition, leading to different SCC susceptibilities, cracking modes, and directions.

Hydrogen-induced cracking of X70 steel affected by sulfate-reducing bacteria and cathodic potential: experiment and density functional theory study

Submarine pipeline are often exposed to the risk of hydrogen embrittlement from the dual action of marine sulfate-reducing bacteria (SRB) and cathodic protection (CP). In this work, hydrogen permeation test, slow strain rate tensile (SSRT) experiments, and density functional theory (DFT) were used to explain the hydrogen embrittlement (HE) mechanism of subsea pipeline steel under the action of SRB and CP. When the applied CP potential is increased from −850 mV to −1200 mV, the hydrogen seepage current increases 1.8 times. And the tensile specimens pre-charged with hydrogen exhibit significant hydrogen embrittlement behavior. DFT calculations show that the increased concentration of hydrogen atoms on the material surface decreases the diffusion potential barrier, leading to a larger hydrogen seepage current. In addition, the aggregation of hydrogen atoms in the steel weakens the chemical bonds between Fe atoms, leading to hydrogen embrittlement.

Effect of Nb on the Hydrogen-induced Cracking of X80 Pipeline Steel

Nb is a key alloying element added into X80 pipeline steel, and it can enhance mechanical properties by refining grains and introducing precipitates. However, HIC resistance is also one of the most significant performances for pipeline steel served in H2S environment. An all-inclusive recognition of the response of niobium to HIC refusal is important for the appropriate design of the Nb addition amount, the rolling and cooling parameters, and protective techniques to obtain excellent mechanical properties, including strength and ductility and HIC refusal. So in the paper, many test methods, such as EBSD, SEM, and HIC, were adopted to research the response of niobium addition on resistance of hydrogen-induced cracking performance of X80. As the increase in Nb content, grain size decreased and had the strongest trapping hydrogen atom ability. Besides, the percentage of low-angle grain boundaries went up, and more precipitates greatly raised the amount of irreversible hydrogen pitfalls. Nb could greatly promote the HIC resistance, inhibiting crack initiation, and propagation.

The effect of applied potential on stress corrosion cracking of X80 pipeline steel in acidic soil containing sulfate-reducing bacteria

The effect of applied potential on stress corrosion cracking of X80 pipeline steel in acidic soil containing sulfate-reducing bacteria

Combined corrosion and inclination effects on pullout behavior of various steel fibers under wet-dry cycle deterioration

The interfacial bond behavior of corroded fibers in cracked steel fiber reinforced concrete (SFRC) is critical for understanding its structural deterioration performance, while available research focused on aligned straight or hooked-end fibers. This study investigated the combined effects of corrosion and inclination on the pullout performance of various steel fibers bridging artificial cracks exposed to wet-dry cycles of chlorides. Three deformed steel fibers, i.e., hooked-end (H), crimped (C), and milled-cut (M) fibers, with three angles of 0°, 30°, and 45° were examined under both uncorroded and corroded conditions. After corrosion, the average bond strength of H fibers was enhanced due to increased roughness and compact rust layer if the high inclination-induced fracture was avoided, while that of C and M fibers was decreased at various angles because of loose and porous rusts. The highest bond strengths of corroded H, C, and M fibers were discovered at 30°, 30°, and 0°, as a result of the combined mechanisms of snubbing effect, matrix spalling, or corrosion-induced fracture. The ultimate displacement of all fibers increased with angles due to increased matrix spalling area and fiber plastic deformation. The inclination effect of corroded fibers was more significant on energy absorption capacity than average bond strength, regardless of fiber type. A degradation model that describes the snubbing and matrix spalling effects, as well as the corrosion-induced deterioration and fracture was developed, based on which the critical inclination angle was found to decrease with increasing embedded length and decreasing tensile strength.

Crack detection of continuous casting slab by evolutionary topology backbone search

In recent years, computer vision-based methods have been widely used in steel defect detection. Traditional image detection methods mainly rely on manually extracted features, resulting in poor generalization. Deep learning methods are sensitive to the number of samples, and the network structure design relies heavily on manual experience. To address these problems, a backbone network search algorithm based on evolutionary topology is proposed in this paper for crack detection on continuous casting surfaces. Firstly, a variable-length genetic encoding scheme is designed for industrial defect problems with different data complexity, which can improve the applicability of the algorithm and extend the search space. Secondly, to effectively solve the channel redundancy problem in densely connected CNNs, a random pruning strategy for network connection channels is proposed to reduce the topological space and the complexity of the model. Finally, a computational resource allocation mechanism based on a dynamic surrogate model is devised. The surrogate model predicts the individual performance to ensure that computational resources can be concentrated on individuals with better quality. In addition to the steel crack image dataset, the proposed method also uses the workpiece crack image dataset for a supplementary experiment. Experimental results show that the proposed algorithm can achieve better detection performance with fewer computational resources compared to manually designed deep learning algorithms and classical approaches that use evolutionary algorithms to search network architectures.

Experimental study on fatigue behavior of cracked steel plates repaired with adhesively bonded steel patches

Fatigue cracking is prone to occur in orthotropic steel decks (OSDs) due to its complex geometry. To guarantee structural safety and extend the fatigue life of OSDs in steel bridges, the repair technique of adhesively bonded steel patches, which has the advantage of lower cost, easy operation, and not damaging the original structure, is experimentally studied using simplified cracked steel plate specimens. Four repair schemes were considered including bare plate, single-sided patched, double-sided patched, and stop-hole repaired. The failure mode, fatigue crack propagation, and adhesive damage were studied to evaluate the effects of steel patch repair. The morphological analysis was performed to investigate the fatigue fracture characteristics and metal interface performance. The outcomes showed that adhesively bonded steel patches could significantly improve the fatigue life of cracked steel plates and the strengthening was more effective for double-sided patched specimens than single-sided patched specimens. In comparison, the repair effect of the stop-hole method is limited for cracked specimens.