Hydrogen-induced Cracking Research Articles

Bayesian Correlation Prediction Model between Hydrogen-Induced Cracking in Structural Members

Background: A quantitative model was developed and applied for analyzing the correlation between hydrogen-induced corrosion cracking in both main cable wires and degraded stiffening of the girders of a cable suspension bridge, considering maintenance effects across time and space. Method: Bayesian inference is applied for predicting the correlations among the wires in the main cables owed to hydrogen-induced cracking (HIC) in the cable wires of a steel bridge, by using the improved hierarchical Bayesian models proposed here. Results: The simulated risk prediction under decreased strength of cable wires, due to the corrosion cracking, yields posterior distributions based on prior distributions and likelihoods. The Bayesian inference model can be applied to the design and maintenance of highly corroded and correlated components Data are updated through analyzed information from previous crack steps. A numerical example including not only reliability indices but also probabilities of failure for cable wires, damaged by HIC, is then presented. Compared with a conventional linear prediction model, the one herein developed provides highly improved convergence and closeness to the analyzed data. Conclusion: The proposed model can be used as a diagnostic or prognostic prediction tool for the performance of corroded bridge cable wires with crack propagation, allowing the development of maintenance plans for mechanical components and the overall structural system.

Evaluation of hydrogen-Induced cracking resistance of the In625 laser coating system on a C-Mn steel substrate

Abstract The corrosion of C-Mn steels in the presence of hydrogen sulfide (H2S) represents a significant challenge to oil production and natural gas treatment facilities. The failure mechanism induced by hydrogen-induced cracking (HIC) in a Inconel 625 coating / C-Mn steel has not been extensively investigated in the past. In the present work, an API 5CT steel was coated with In625 alloy using laser cladding and the HIC resistance of different regions, such as the coating surface, the substrate and HAZ, were evaluated. SEM observations illustrated that all HIC cracks were formed at the hard HAZ after 96h of exposure. No HIC cracks were observed in the substrate and the In625 coating after the same exposure duration. Pitting was recorded in the substrate caused by non-metallic inclusion dissolving.

Evolution of MnS inclusions in Ti-bearing X80 pipeline steel

Studies show that manganese sulfide (MnS) inclusions in pipeline steel affect the lateral performance of steel in its rolling deformation, as well as the hydrogen-induced cracking and sulfide stress corrosion cracking resistance performance. To inhibit the precipitation of MnS and its effect on pipeline steel, a quenching experiment and a diffusion couple experiment, which investigated the evolution of MnS inclusions in Ti-bearing X80 pipeline steel, were conducted. The experimental results show that the transformation of the MnS inclusions during solidification is as follows: MnS→ titanium sulfide (TiS) → Ti4C2S2. The transition temperatures of MnS to TiS and TiS to Ti4C2S2 are 1673 and 1273 K, respectively, and the overall size of the sulfide decreased as well. Thermodynamic calculation results confirm that the transition temperatures of MnS to TiS and TiS to Ti4C2S2 are 1623 and 1203 K, respectively. When the sulfur content in the X80 pipeline steel is 0.0015%, all the sulfur in the steel can be converted into Ti4C2S2 with a titanium content of more than 0.02%.

A focus on different factors affecting hydrogen induced cracking in oil and natural gas pipeline steel

In this research, hydrogen induced cracking (HIC) behavior of an API X70 pipeline steel has been studied. In order to create HIC cracks, an electrochemical hydrogen charging experiment was carried out on X70 steel by using 0.2 M sulfuric acid and 3 g/l ammonium thiocyanate for 8 h. Moreover, SEM, EDS and EBSD techniques were used to characterize the as-received (AR) steel and investigate the different aspects of HIC phenomenon as well. The results showed that the inclusions and precipitates which play a key role in HIC phenomenon have been distributed randomly through the cross-section of tested steel. However, the concentration of them was higher at the center of cross-section than other areas. All HIC cracks initiated and propagated through the center of thickness where center segregation of elements has occurred. It is also observed that HIC cracks were initiated from several special types of inclusions and precipitates such as manganese sulphide and carbonitride precipitates. EBSD results showed that the dominant local texture of center of thickness in RD-TD plane was {001}//ND and {111}//ND. Moreover, HIC cracks propagate through differently oriented grains where the local texture is random.

Hydrogen diffusivity and tensile-ductility loss of solution-treated austenitic stainless steels with external and internal hydrogen

The effects of external and internal hydrogen on the slow-strain-rate tensile (SSRT) properties at room temperature were studied for ten types of solution-treated austenitic stainless steels containing a small amount of additive elements. The hydrogen diffusivity and solubility of the steels were measured with high-pressure hydrogen gas. The remarkable tensile-ductility loss observed in the SSRT tests was attributed to hydrogen-induced successive crack growth (HISCG) and was successfully quantified according to the nickel-equivalent content (Nieq), which represents the stability of the austenitic phase. The relative reduction in area (RRA) of the steels with a larger Nieq was influenced by the hydrogen distribution, whereas that of the steels with a smaller Nieq was not. This unique trend was interpreted with regard to the hydrogen distribution and fracture morphology (HISCG or microvoid coalescence).

Heat-Affected Zone Formation in Electrospark-Deposition Additive Manufacturing on Ultrahigh-Strength Steel

Electrospark deposition (ESD), an additive microweld-surfacing process, is typically used as a new or repair technology to enhance wear and corrosion resistance for build-up and special surface modifications. ESD employs short-duration, high-current electrical pulses that result in a fused metallurgical bond to the substrate. The pulse microsecond duration splat transfer produces micro- and nanostructures and a very narrow heat-affected zone. The limited corrosion and hydrogen-induced cracking resistance of conventional ultrahigh strength 4340 type steel, greater than 1500-MPa yield strength, led to the development of precipitation-hardened, corrosion-resistant, ultrahigh-strength steel alloys such as Custom 465 and Ferrium S53. Additive surface repair technologies of these alloys in the heat-treated condition are very limited. Preheating requirements, distortion, heat-affected zones, and post-additive heat-treatment requirements prevent surface treatments in the heat-treated condition. This paper characterizes ESD applied to ultrahigh-strength steel with respect to the heat-affected zone and the deposit–substrate mixed zone through micro- and nanohardness measurements and through microstructural and microchemical characterization. The additive alloy was Stellite 21, a cobalt-based, high-chromium alloy capable of developing high hardness and high corrosion resistance. Results show that, properly applied, the heat-affected zone width ranged from 8 to 15 μm. Microhardness analysis revealed a drop in hardness within this zone. The weld dilution zone width in the deposit is on the order of 8 to 10 μm within the first two deposit layers.

Stress corrosion cracking of L360NS pipeline steel in sulfur environment

Slow strain rate test (SSRT) and tensile fracture observation are applied to study the stress corrosion cracking (SCC) of L360NS pipeline steel. 5.0 wt. % sodium chloride solution containing elemental sulfur and 0.5 wt. % glacial acetic acid solution containing elemental sulfur are used. The results show that brittle fracture mainly occurs on the samples in high sulfur environment. In the sulfur suspension solution, the SCC sensitivity of L360NS pipeline steel increases along elemental sulfur content. In sulfur melting cladding condition, obvious corrosion can be observed with a large amount of corrosion pits appearing on the gauge section of the sample. The corrosion products are Fe1+xS, black easily detached, and H2. In sulfur suspension and sulfur melting cladding conditions, stress oriented hydrogen induced cracking (SOHIC) is the main cracking, which is caused by the joint effect of SCC and hydrogen induced cracking (HIC).

Corrosion Behavior of API X100 Steel Material in a Hydrogen Sulfide Environment

Recently, the API X100 steel has emerged as an important pipeline material for transportation of crude oil and natural gas. At the same time, the presence of significant amounts of hydrogen sulfide (H2S) in natural gas and crude oil cause pipeline materials to corrode, which affects their integrity. In this study, the effect of H2S concentration on the corrosion behavior of API X100 in 3.5% NaCl solution is presented. The H2S gas was bubbled into saline solutions for different durations, and the corrosion tests were then performed using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) techniques were used to characterize the corroded surface. The results indicate that the corrosion rate of API X100 steel decreases with increasing H2S bubbling time due to the increase in H2S concentration in 3.5% NaCl solutions. It is noticed that an accumulation of a critical amount of hydrogen in the metal can result in hydrogen-induced crack initiation and propagation. It was further observed that, when the stress limit of a crystalline layer is exceeded, micro-cracking of the formed protective sulfide layer (mackinawite) occurs on the API X100 steel surface, which may affect the reliability of the pipeline system.

Diffusible Hydrogen Level in Deposited Metal and Their Effect on Tensile Properties and Flexural Strength of P91 Steel

In a “very high-temperature reactor” (VHTR), the Nb–V-modified 9Cr–1Mo creep strength enhance the ferritic (CSEF) steel which is the chosen material for fabrication of reactor pressure vessels and piping because of its excellent high temperature thermal and mechanical properties. In such CSEF steel weldments, the hydrogen-induced cracking (HIC) is a critical issue. In the present work, the different levels of hydrogen have been induced in P91 CSEF weld metal to study their effect on HIC. The HIC susceptibility of P91 steel welds has been studied by carrying out the tensile test and flexural test for the different level of diffusible hydrogen. The hydrogen levels in deposited metals have been measured by using the mercury method. The fracture tensile and flexural test samples have been characterized based on the field-emission scanning electron microscope (FE-SEM). It is concluded that higher the level of diffusible hydrogen in deposited metal, more is the susceptibility of P91 steel to HIC. The minimum flexural and tensile strength are 507.45 MPa and 282 MPa, respectively, for 12.54 ml volume of diffusible hydrogen in 100 g of deposited weld metal.

Effect of Grain Orientation and Boundary Distributions on Hydrogen-Induced Cracking in Low-Carbon-Content Steels

Hydrogen-induced cracking (HIC) causes considerable economic losses in a wide range of steels exposed to corrosive environments. The effect of crystallographic texture and grain boundary distributions tailored by rolling at 850 °C in three different steels with a body-centered cube structure was investigated on HIC resistance. The x-ray and electron backscattered diffraction techniques were used to characterize texture evolutions during the rolling process. The findings revealed a significant improvement against HIC based on texture engineering. In addition, increasing the number of {111} and {110} grains, associated with minimizing the number of {001} grains in warm-rolled samples, reduced HIC susceptibility. Moreover, the results showed that boundaries associated with low {hkl} indexing and denser packing planes had more resistance against crack propagation.

Investigating the influence of hydrogen on stress corrosion cracking of 2205 duplex stainless steel in sulfuric acid by electrochemical impedance spectroscopy

AbstractAs a nondestructive and sensitive method, electrochemical impedance spectroscopy (EIS) can be used to investigate the passivation and breakdown of passive films on steel. In this study, EIS, combined with slow strain rate test and scanning electron microscopy, was employed to study the stress corrosion cracking (SCC) behavior of 2205 duplex stainless steel in 0.5 m sulfuric acid solution under hydrogen-charging conditions. Results showed that the corrosion resistance of passive film on the hydrogen-charged specimen was lower than that for the specimen with no hydrogen charge. Hydrogen-induced cracking was evident after the specimens had been charged for 24 h. The phase shift in EIS, calculated from frequencies between 0.1 and 10 Hz, could be used to monitor the SCC process.

Stress corrosion cracking behavior of PH13-8Mo stainless steel in Cl– solutions

The stress corrosion cracking (SCC) behavior of PH13-8Mo precipitation hardening stainless steel (PHSS) in neutral NaCl solutions was investigated through slow-strain-rate tensile (SSRT) test at various applied potentials. Fracture morphology, elongation ratio, and percentage reduction of area were measured to evaluate the SCC susceptibility. A critical concentration of 1.0 mol/L neutral NaCl existed for SCC of PH13-8Mo steel. Significant SCC emerged when the applied potential was more negative than —0.15 VSCE, and the SCC behavior was controlled by an anodic dissolution (AD) process. When the applied potential was lower than —0.55 VSCE, an obvious hydrogen-fracture morphology was observed, which indicated that the SCC behavior was controlled by hydrogen-induced cracking (HIC). Between —0.15 and —0.35 VSCE, the applied potential exceeded the equilibrium hydrogen evolution potential in neutral NaCl solutions and the crack tips were of electrochemical origin in the anodic region; thus, the SCC process was dominated by the AD mechanism.

Effect of bainite in microstructure on hydrogen diffusion and trapping behavior of ferritic steel used for sour service application

Abstract

Role of crystallographic texture on the improvement of hydrogen-induced crack resistance in API 5L X70 pipeline steel

The purpose of this work was to improve the resistance of hydrogen-induced cracking in API 5L X70 steel by engineering the crystallographic texture and grain boundary distributions via different rolling temperatures. Hydrogen-induced cracking and electrochemical hydrogen charging tests were carried out in two different conditions: commercially produced and isothermally rolled at 850 °C in laboratory. The results showed that the development of dominant {011} grains parallel to the normal direction, and a small number of {001}//ND grains obtained by isothermal rolling at 850 °C, increased the hydrogen-induced crack resistance; while the hot rolled sample with sharp {001}//ND textures was highly susceptible to cracking.

Effect of arc distance on HAZ thermal cycles and microstructural evolution 10CrNi3MoV steel

Double-sided double GTAW and GMAW (DSGTAW and DSGMAW) have been proposed to reduce hydrogen induced crack (HIC) susceptibility in recent years. This paper is mainly to investigate the effect of arc distance on thermal cycles and microstructural evolution of HAZ. To clarify this, DSGTAW and single gas tungsten arc welding (SGTAW) were employed in backing welding of 10CrNi3MoV low-alloy high-strength steel. The thermal processes were studied by numerical simulation in this paper. The heat input of each pass was 21.7 kJ/cm. The thermal cycles of SGTAW and DSGTAW with different arc distances (d) were compared and analyzed. The microstructural evolution of coarse grained heat affected zone (CGHAZ) of SGTAW and unaltered coarse grained heat affected zone (UACGHAZ) of DSGTAW was observed by confocal laser scanning microscope (CLSM). The results show that DSGTAW can significantly decrease the cooling rate of HAZ. As the arc distance increases, the trough temperature (T t ) between the two peak temperatures induced by the fore and rear arc will decrease and the HAZ temperature gradient of rear pass will increase which can lead to the change of thermal cycles. When arc distance increases to 60 mm, brittle intercritically reheated CGHAZ (IRCGHAZ) will form.

Displaced hardness peak phenomenon in heat-affected zone of welded quenched and tempered EM812 steel

Investigations of microstructural and hardness gradients in the heat-affected zone (HAZ) of quenched and tempered (Q&T) steels have indicated that peak hardness does not occur in the grain-coarsened heat-affected zone (GCHAZ) adjacent to the fusion boundary, which is typical of ferritic steels, but corresponds more closely to the grain-refined region (GRHAZ). This phenomenon, the displaced hardness peak (DHP) effect, is considered to arise when the hardenability of the steel is high enough to result in the same microstructure in the GC and GR heat-affected zones, except for significant refinement of the microstructure of the GRHAZ, which increases the hardness and strength above those of the GCHAZ. The current paper concentrates on the effect of grain size on hardness in the HAZ of a boron-containing low-carbon martensitic steel subjected to bead-on-plate welding. Thermal simulation experiments were used to clarify the relationship between prior austenite grain size and the hardness gradients in the actual HAZ. The simulation work demonstrated that peak hardness in simulation samples occurred in regions of lower austenite grain size, supporting the proposed origin of the DHP effect in actual welds. Implications regarding hydrogen-induced cold cracking (HICC) susceptibility of the GRHAZ are discussed.

Improvement of strength and toughness: The effect on the weldability of high-strength steels used in offshore structures

The effect of strength and toughness on the weldability of high-strength steels is very vital consideration in the offshore oil and gas industries. Improved impact toughness of high-strength steels in offshore structures enables viable exploitation of hydrocarbons in technologically challenging conditions. This article reviews improvements in the weldability and impact toughness of high-strength steels. Steels with high strength are associated with high carbon content and addition of alloying elements as they induce hardness which leads to a higher risk of brittle fracture and hydrogen-induced cracking needs. The combination of high strength with high toughness was studied by examining the toughening mechanism of thermomechanical-controlled processing steels, which have higher strength than conventional steel plates but meet the conflicting requirements of strength, toughness and weldability. The thermomechanical-controlled processing production process entails controlled rolling process combined with accelerated cooling or direct quenching to ensure stable mechanical properties of thermomechanical-controlled processing products in welded constructions. It is concluded that due to their very fine grain size and refined heat-affected zone structure, thermomechanical-controlled processing steels can be an effective cost-saving means for fabrication of offshore structures, particularly in shipbuilding, offshore platforms and pipelines for high-operating pressures.

Failure of mounting bolt of helicopter main gearbox support strut

Abstract The mounting bolt of helicopter main gearbox support strut was fractured into two pieces during the flight mission. The fracture occurred at the root of the first engaged thread of the bolt-nut assembly. Visual inspection of the fracture zone revealed cracks, formed by interlinking of corrosion pits, at the almost all thread roots of the bolt. Energy dispersive spectroscopy disclosed significant damage of the cadmium plating as well as the presence of large amounts of corrosion products at the bolt threads. Through the fractography and metallography analysis, it was found that the mounting bolt failed due to hydrogen-induced intergranular stress corrosion cracking (HI-IGSCC). The finite element (FE) analysis confirmed that the crack origin was located at the area with the maximum tensile stress in the bolt.

Effect of Cu Addition in Pipeline Steels on Prevention of Hydrogen Permeation in Mildly Sour Environments

In this study, the influence of Cu addition on hydrogen entry behavior was investigated with the aim of preventing hydrogen-induced cracking (HIC) in mildly sour environments in which the solution pH is more than 5.0, and a mechanism related to the formation of a protective layer which contributes to the prevention of hydrogen entry was discussed. A hydrogen permeation test was conducted in a solution with a strong pH buffering capacity under 0.1 MPa H2S and 10−3 MPa H2S. In order to clarify the relationship between hydrogen entry and the microscopic structure of corrosion products, corrosion products were characterized by focused ion beam scanning electron microscopy and scanning transmission electron microscopy combined with energy dispersive x-ray spectroscopy. The results indicate that hydrogen permeability, diffusible hydrogen, and the corrosion rate all decreased as a result of Cu addition at 0.1 MPa H2S, and Cu tended to be locally enriched in the inner layer of corrosion product within 100 nm from...

Simulation of Environmentally-Assisted Material Degradation by a Thermodynamically Consistent Phase-Field Model

Environmentally-assisted material degradation involves mass transport and mechanical processes interacting in the material. A well-known example is hydrogen-induced stress-corrosion cracking. One major challenge within this scope is the quantification of the coupling mechanisms in question. The computational modeling of environmentally-assisted cracks is the key objective ofthis investigation and realised within the theory of gradient-extended dissipative continua with length-scales. The modeling of sharp crack discontinuities is replaced by a diffusive crack model based onthe introduction of a crack phase-field to maintain the evolution of complex crack topologies. Withina thermodynamical framework allowing for mechanical and mass transport processes the crack phase-field is capable to model crack initiation and propagation bythe finite element method. As complexcrack situations such as crack initiation, curvilinear crack patterns and crack branching are usuallyhard to realise with sharp crack models, they can be assessedwithout the requirement of a predefinedcrack path within this method. The numerical modeling of a showcase demonstrates a crack initiationas well as a crack propagation situation with respect to the determination of stress-intensity factors; acrack deviation situation with a curvilinear crack path is modeled by the introduction of a geometricalperturbation and a locally enhanced species concentration