Hydrogen-induced Cracking Susceptibility Research Articles

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.

Hydrogen-induced cracking of welded X80 steel studies by experimental testing and molecular dynamics modeling

Impact and slow strain rate tensile tests, as well as molecular dynamics modeling, were used to study hydrogen-induced cracking (HIC) of a welded X80 pipeline steel. There is the highest HIC susceptibility at the coarse-grained heat-affected zone, showing an obvious intergranular brittle fracture upon hydrogen-charging. Hydrogen atoms delay dislocation emissions, and the accumulated energy is released mainly through crack initiation. The hydrogen atoms decrease the elasticity of grain boundaries. The locations to initiate cracks in the polycrystalline system are not necessarily the sites with the highest hydrogen atom concentration, but are always at the multi-node grain boundaries.

Effect of Ce content on the hydrogen induced cracking of X80 pipeline steel

In this study, the effect of Ce content on hydrogen induced cracking (HIC) of X80 pipeline steel has been investigated. The results show that as the Ce content increased from 0 wt% to 0.0042 wt%, 0.016 wt% and 0.024 wt%, the HIC susceptibility of tested steels decreased first and then increased. The steel containing 0.016 wt% Ce possessed the lowest HIC susceptibility because Ce modified inclusions, promoted the formation of acicular ferrite, and decreased the number of hydrogen traps and intergranular cracks.

Improving hydrogen induced cracking resistance of high strength acid-resistant submarine pipeline steels via trace-Mg treatment

Hydrogen induced cracking (HIC) is one of the biggest service risks faced by high-strength acid-resistant submarine pipeline steel. In this work, we reported a low-carbon, low-cost and high-efficient method for remarkably improving HIC resistance of the high-strength acid-resistant submarine pipeline steels by trace-Mg treatment. The results showed that the non-metallic inclusions steels were obviously refined, softened, spheroidized and dispersed by trace-Mg treatment, the modified “core-shell” or like “core-shell” structure inclusions had a larger critical size for HIC initiation and a higher saturated hydrogen concentration, and then effectively trapping more hydrogen, dispersing hydrogen pressure and reducing the diffused hydrogen content, thus effectively improving the HIC resistance. With the further increasing of Mg contents, the inclusion modification would be weakened, the hydrogen trapping efficiency decreased, and the HIC susceptibility of the tested steel increased again. In the research range, the tested steels treated with 4 ppm Mg present the lowest HIC susceptibility.

In Situ Investigation of Hydrogen-Induced Cracking Behavior in Linepipe Steel Under Different Environments

NACE MR0175/ISO 15156 provides the severity of a sour environment defined as a function of pH and H2S partial pressure for sulfide stress cracking. Although hydrogen-induced cracking (HIC) is also a major issue of linepipes exposed to a sour environment, the severity diagram does not necessarily correspond to the HIC susceptibility. Recently, from the viewpoint of fitness-of-purpose, the severity diagrams for HIC have been proposed based on the concept of equal hydrogen concentration. From this concept, HIC susceptibility corresponds well to the steady-state hydrogen permeability obtained from the hydrogen permeation test method. In this study, in order to clarify the relationship between HIC susceptibility and hydrogen diffusion behavior, in situ crack inspection during the HIC test and finite element method analysis of hydrogen diffusion were performed. The in situ inspection technique using phased-array ultrasonic testing which can capture the time dependence of crack distribution, and HIC initiation and propagation behaviors were clearly visualized and investigated. It was found that crack initiation and propagation stabilize as hydrogen concentration reaches a steady-state value throughout the specimen and the result was considered evidence that the HIC susceptibility corresponded with the steady value of hydrogen permeability.

Investigation of the hydrogen-induced cracking of E690 steel welded joint in simulated seawater

Hydrogen-induced cracking (HIC) behavior and mechanism of E690 welded joint in simulated seawater were studied via microstructure observations, electrochemical hydrogen charging, slow strain rate tension (SSRT) tests and hydrogen content measurement. The results show that the welded joint of E690 steel has a higher HIC susceptibility than that of base metal, in which the inter-critical heat affected zone (ICHAZ) is composed of polygonal ferrite and granular bainite is the final fracture location in the joint. ICHAZ with the lowest yield strength deformed preferentially under the tensile stress, and subsequently, the proliferating dislocations with the deformation strengthening and the continuously charged hydrogen led to the HIC and brittle fracture at the ICHAZ of the welded joint. Moreover, the HIC susceptibility was linearly dependent on the logarithm of total hydrogen concentration in the steel, and the hydrogen concentration had a more obvious effect on the welded joint than the base metal. The higher density of piled dislocations adjoining the M/A islands in the welded joint exhibited a significant effect on the hydrogen agglomeration and diffusion, which enhanced the HIC susceptibility.

A Comparative Investigation of the Effect of Microstructure and Crystallographic Data on Stress-Oriented Hydrogen Induced Cracking Susceptibility of API 5L X70 Pipeline Steel

In this research, stress-oriented hydrogen induced cracking (SOHIC) test was carried out on a 50 mm thickness of a commercial API 5L X70 steel plate. The evolution of microscopic features such as phase, boundary, interface, grain, and crystallographic data was analyzed before and after SOHIC, in order to comprehend the effect of crystallographic orientation on SOHIC propagation. Chemical composition and previous thermomechanical processing even finish rolling temperature and cooling rate determine the ferrite matrix microstructure. A recrystallized ultrafine ferrite grain with about 3–5% degenerated pearlite dispersed in the microstructure was characterized, called as-received specimen. The average lattice strain and dislocation density was calculated first using multiple Gaussian peak-fitting method from XRD pattern. Electrochemically charged combination mixed H2S-CO2 solution, constant hydrogen injection, and external loading were applied to tensile specimen, in order to simulate the H2S and CO2 environment. The results show that local misorientation and Taylor factor analyses predicted the possibility of hydrogen crack nucleation especially at boundaries and interfaces. Moreover, SOHIC crack propagation occurred along the mid-thickness of the cross section of steel plate along the ferritic boundaries, pearlitic colonies, and ferrite-cementite interfaces. Moreover, the crack propagated along distorted {110} and {001} grains, indicating a strong strain gradient towards the boundaries. The analysis of XRD patterns of SOHIC tested specimen by multiple Gaussian peak-fitting method estimated about 68% increment in micro-deformation and approximately 170% increase in dislocation density.

Sour Environmental Severity for Hydrogen-Induced Cracking Susceptibility

The severity of sour environments has been determined in accordance with the European Federation of Corrosion 16 and NACE MR0175/ISO 15156-2:2015 standards for carbon and low-alloy steels, based on the experimental results of sulfide stress cracking (SSC). However, the severity map obtained from SSC test results cannot be applicable to the hydrogen-induced cracking (HIC) susceptibility. In this study, the hydrogen permeability and crack area ratio of HIC under various pH and H2S partial pressures (pH2S) were measured to establish the link between the sour environmental severity and HIC susceptibility using grades X65 to X80 steels for linepipes. In addition, the hydrogen concentration at the location of the HIC was calculated by the finite element analysis. The results showed that the sour environmental severity map obtained from hydrogen permeation tests changes with time because the hydrogen permeability reached maximum values in the early stage and steady-state values in the later stage. Then, the HIC susceptibility did not correspond to the maximum permeability, but to the steady-state hydrogen permeability. In addition, the hydrogen content at the location of the HIC did not correspond to the maximum hydrogen permeability but corresponded to the steady-state hydrogen permeability, because HIC occurred in the center segregation part and the hydrogen atoms required a certain time to diffuse from the metal surface to the mid-thickness. These results suggest that the HIC susceptibility is dominated by the severity map obtained from the steady-state hydrogen permeability.

Correlation between Microstructure and Hydrogen Degradation of 690 MPa Grade Marine Engineering Steel.

Electrochemical H charging, hydrogen permeation, and hydrogen-induced cracking (HIC) behavior of 690 MPa grade steel substrate and different heat-treatment states (annealed, quenched, normalized, tempered) are investigated by cyclic voltammetry (CV), hydrogen permeation, electrochemical H charging, and slow strain rate tensile test (SSRT). The results show that hydrogen diffuses through the steel with the highest rate in base metal and the lowest rate in annealed steel. The hydrogen-induced cracks in base metal show obvious step shape with tiny cracks near the main crack. The cracks of annealed steel are mainly distributed along pearlite. The crack propagation of quenched steel is mainly transgranular, while the hydrogen-induced crack propagation of tempered steel is along the prior austenite grain boundary. HIC sensitivity of base metal is the lowest due to its fine homogeneous grain structure, small hydrogen diffusion coefficient, and small hydrogen diffusion rate. There are many hydrogen traps in annealed steel, such as the two-phase interface which provides accommodation sites for H atoms and increases the HIC susceptibility.

Investigation into Mechanism of Hydrogen Induced Cracking Failure in Carbon Steel: A Case Study of Oil and Gas Industry

Abstract Although the hydrogen induced cracking (HIC) is recognized as one of the destructive modes for pipeline and component steels serving in sour environments, the behavior of the HIC is still not fully understood. On the other hand, although many efforts have been made to identify the effects of hydrogen on laboratory steel specimens, the study of actual industrial samples has received less attention. In this paper, we have studied the mechanism of the HIC in a damaged pipe of a real case study of the oil and gas industry (finger type slug catcher) using detection, characterization, and microstructural investigation methods. The detection of the HIC in the specimens by advanced ultrasonic techniques, failure analysis using tensile tests, chemical composition analysis, optical microscopy (OM), field emission scanning electron microscopy (FE-SEM), and energy-dispersive spectroscopy (EDS) techniques and their correlation with the microstructure, type, and morphology of the inclusions were conducted. The results indicated that the value of elements, especially carbon (0.13 wt %) and manganese (1.44 wt %), satisfies the requirement of API 5L specification. Furthermore, the inclusions, such as elongated manganese sulfide and spherical aluminum oxide, and the pearlite grains or the interfaces of the ferrite–pearlite phases played an essential role in the HIC phenomenon as nucleation and propagation places of cracks. It was also observed that HIC cracks were mostly initiated and propagated through the center or near the center of a cross-section of specimens. This region was a segregated zone where the center segregation of elements has occurred. Finally, we recognized a linear correlation between the HIC susceptibility and hardness value in steel, where by moving away from the cracks (1800 µm) to the crack edges, the hardness value increased significantly (179–203 HV), confirming the diffusion of hydrogen into hydrogen traps.

Comparative study of non-metallic inclusions on the critical size for HIC initiation and its influence on hydrogen trapping

In the present work, the critical crack nucleation size and the hydrogen trapping capability of inclusion were discussed with a numerical simulation considering the factors of inclusion/matrix heterojunction. The results showed that the inclusion composition had a significant effect on hydrogen capacity and its critical nucleation size of hydrogen-induced cracking (HIC). The MnS inclusions exhibited a larger critical size tolerance of HIC nucleation (approximately 2.5 μm), but for some typical oxide inclusions, it ranged between 0.1 and 0.4 μm. In addition, two sheets of steel containing different composition, morphology, and distribution of inclusions were studied by the standard-based test and thermal desorption spectroscopy (TDS) to evaluate the HIC susceptibility and hydrogen trapping behaviour. The results complementarily demonstrated that when controlling the non-metallic inclusions into the proper size and compound with MnS into the sphere, the HIC resistance of steel could be efficiently improved.

Characteristics of Susceptible Microstructure for Hydrogen-Induced Cracking in the Coarse-Grained Heat-Affected Zone of Carbon Steel

Hydrogen-induced cracking (HIC) susceptibility of the coarse-grained heat-affected zone (CGHAZ) of carbon steel was evaluated using implant tests and the characteristics of susceptible microstructure to HIC was investigated. Three types of carbon steel with different alloying elements were employed as base metals to vary the microstructure of the CGHAZ and implant test assemblies were prepared using an automatic shielded metal arc welding process. A clear difference in microstructure was observed between the CGHAZs of steel with high and low HIC susceptibility; the formation of the primary ferrite in the CGHAZ of carbon steel plays an important role in decreasing the HIC susceptibility.

Effects of Molybdenum on HIC Susceptibility in Normalized Pressure Vessel Steels for Sour Service Applications

This paper discusses a molybdenum-added alloy design for normalized pressure vessel steels, to reduce hydrogen induced cracking (HIC) and inhibit crack propagation. The change in microstructure produced by the modified alloy composition was analyzed to determine its effect on HIC characteristics. The microstructural change was observed by optical microscopy, hardness tests, scanning electron microscopy, and electron backscattered diffraction. The crack length ratio and crack thickness ratio were evaluated using the NACE TM 0284 standard, and ultrasonic testing was used for HIC analysis. The formation of polygonal ferrite and pearlite during the processing of the alloy creates localized areas of high stress concentration at the polygonal ferrite/pearlite interface, due to the expansion/contraction of various structures during the transformation. This results in the generation of potential hydrogen-trapping sites, subsequent HIC, and crack propagation. The addition of molybdenum leads to a decrease in the volume fraction of the pearlite structure in the steel in favor of a more beneficial bainitic ferrite microstructure, which is generated during the normalizing process. This bainitic transformation creates a more favorable expansion/contraction compatibility and reduces/breaks up the ferrite/pearlite banding. The combination of these two characteristics can result in an overall lower stress-intensity state, which can minimize hydrogen-trapping and crack propagation. This study demonstrates that the resistance of normalized pressure vessel steels to HIC can be significantly improved by incorporating molybdenum in the alloy design. Key words: sour service, molybdenum, hydrogen induced crack (HIC), normalizing steel, pressure vessel steel

Important Factors on the Failure of Pipeline Steels with Focus on Hydrogen Induced Cracks and Improvement of Their Resistance: Review Paper

Currently, thousands of kilometers of pipeline steels are transferring hydrocarbon fluids such as oil and natural gas in the world. Due to the fact that these pipes transport corrosive and high-pressure fluids from harsh environments, they are damaged and eventually degraded. Previous studies showed that sulphide stress cracking, hydrogen induced cracking (HIC) and stress corrosion cracking are the main destructive factors in these types of pipes. This paper focused on the HIC related failure in pipeline steel, since the role of texture and grain boundary character has not been completely recognized. Moreover, if pipeline damage is occurred by hydrogen cracks, besides the environmental pollutions, it will cost a lot to repair or replace the damaged pipeline steels. In this research, the factors influencing the initiation and propagation of the HIC cracks, such as hydrogen traps, inclusions, precipitates, microstructure and texture of steel have been investigated. Also, the existing solutions for improving the steel resistance to the HIC have been investigated based on the control of micro-alloy elements, texture and grain boundary engineering. For instance, some special dominant texture components and coincidence site lattice boundaries decrease the HIC susceptibility by providing the resistant path for crack propagation.

A Comparative Investigation of the Corrosion Resistance and HIC Suceptibility of API 5L X65 and API 5L X80 Steels

High strength low alloy (HSLA) steels are used for the construction of pipelines for oil and natural gas transportation. For such applications pipelines must exhibit mechanical resistance and resistance to corrosion and hydrogen induced cracking (HIC). API 5L X65 steels are the main materials used for this purpose. However, for economic reasons, the use of steels of superior grades would be of interest. This work presents a comparative study of the corrosion and HIC resistances of an API 5L X65 and an API 5L X80 steel in deaerated solution A of NACE TM0284 standard. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization experiments were performed in non-sour and sour (H2S-saturated) media, and HIC resistance tests were carried out in the sour medium. Scanning electron microscopy (SEM) and optical microscopy (OM) characterizations of polished and corroded samples were also done. Electrochemical tests showed that the API 5L X80 steel is slightly more susceptible to surface corrosion, which can be probably linked to its higher inclusion content and smaller grain sizes, it was also susceptible to HIC. Mn and S-rich inclusions found in the crack path indicate that this microstructural feature may play a key role in crack propagation and HIC susceptibility

Effect of hydrogen on the fracture toughness of X65 high-frequency welded pipeline

The effect of hydrogen on the fracture toughness of X65 high-frequency welded (HFW) pipelines was investigated both in a hydrogen environment and in air. The hydrogen environment was created by in situ hydrogen charging, using a simulated soil solution as the electrolyte. Four current densities were used, namely 1, 2, 4, and 8 mA/cm2. The fracture toughness was characterized by the crack tip opening displacement (CTOD). The CTOD values of the base metal and weld metal decreased with increasing hydrogen charging current density, and a higher reduction was seen in the weld metal. In addition, the hydrogen permeation and electron backscattered diffraction (EBSD) measurements were also applied to the base metal and weld metal to evaluate the hydrogen-induced cracking (HIC) susceptibility. The results showed that the weld metal had a higher HIC susceptibility than that of the base metal.

Effects of vanadium precipitates on hydrogen trapping efficiency and hydrogen induced cracking resistance in X80 pipeline steel

In this study, the number and size distribution of vanadium precipitates and their effects on hydrogen trapping efficiency and hydrogen-induced cracking (HIC) susceptibility were investigated in X80 pipeline steel. The results showed that as the vanadium content increased, the number of nanoscale vanadium precipitates clearly increased. Furthermore, the amount of hydrogen atoms trapped by vanadium precipitates gradually increased and the hydrogen diffusion coefficient decreased from 4.74 × 10−6 cm2 s−1 in the vanadium-free V0 steel to 8.48 × 10−7 cm2 s−1 in the V4 steel with 0.16% V, according to hydrogen permeation results. It also reduced the possibility of hydrogen atoms diffusing into the sites of harmful defects such as large-size oxides and elongated MnS inclusions, where cracks were caused more easily. In addition, the V3 steel with 0.12% V, containing the largest number of vanadium carbide particles of less than 60 nm, had the lowest HIC susceptibility.

Influence of Thermomechanically Controlled Processing on Microstructure and Hydrogen Induced Cracking Susceptibility of API 5L X70 Pipeline Steel

The effect of different thermomechanical controlled processing routes on susceptibility of X70 pipeline steel to hydrogen induced cracking (HIC) have been studied. Two X70 pipeline steel specimens labelled WE and WD were investigated. These specimens have the same chemical composition, but they were processed with seperate thermomechanical treatments parameters. Microstructural examinations showed that WE consists of mainly acicular ferrite and polygonal ferrite, while WD consists of acicular ferrite and bainitic ferrite. After subjecting both specimens to hydrogen charging for 12 and 16 h in 0.2 M sulfuric acid and 3 g/L ammonium thiocyanate, early onset of HIC was observed in specimen WD. Post-hydrogen charging microstructural evaluation showed the nucleation of discontinuous cracks in WD after 12 h of charging. However, extended charging for up to 16 h resulted in HIC along the mid-thickness region of both specimens. Hydrogen diffusion across specimen WE was better than that of specimen WD. Therefore, hydrogen trapping at grain boundaries, banded deformed grains, inclusions and secondary phases such as martensite and cementite aided initiation and propagation of HIC in specimens. Nevertheless, the adverse effect of these features on HIC risks was more prominent in specimen WD compared to specimen WE. The Vickers microhardness values measured in WD (349.6 HV) and WE (307.4 HV) suggest that WD is harder than WE; and higher kernel average misorientation of 0.66° in WD than in WE (0.58°) shows higher dislocation density in WD. The results from slow strain rate tensile test confirmed that specimen WD was stronger and more susceptible to HIC than specimen WE. It was concluded that microstructural phases developed during thermomechanical processing improved strength in WD at the expense of its crack resistance, while WE with lower strength showed more ductility and higher resistance to HIC.

In Situ Observation of Hydrogen-Induced Cracking Propagation Behavior

Hydrogen-induced cracking (HIC) is one of the major issues of line pipe exposed to sour environments. There are some guidelines on materials requirements for carbon and low alloy steels for H2S-containing environments in oil and gas production. Generally, HIC susceptibility is evaluated after the test duration, typically 96 h, in accordance with NACE Standard TM0284-2016. However, HIC propagation behavior during HIC test has not been fully understood. In this study, a new in situ HIC measurement method has been developed in order to make the connection between HIC propagation behavior and microstructure. This technique is based on the combination of an automatic ultrasonic wave inspection system and a scanning electron microscopy (SEM) observation. HIC propagation rate and HIC propagation behavior of carbon steels with different textures were investigated, using this in situ technique. Texture components of tested steels were changed by controlled rolling process in the alpha-gamma dual phase region. The {100} intensity parallel to the rolling plane was developed with increasing controlled rolling reduction in the alpha-gamma dual phase region. HIC propagation rate increased and crack length of HIC grew in a staircase pattern with time when the {100} texture was highly developed. In addition, HIC propagation behavior could be overlapped with fracture surface, just like a projection mapping. The overlapping could make the connection between HIC propagation behavior and HIC fracture surface. Microstructure and texture just under the HIC fracture surface was also characterized by SEM and an electron backscatter diffraction pattern method. The results obtained in this study showed that HIC propagation behavior was affected by a texture. In addition, the new in situ HIC observation technique, which can make the direct connection between HIC propagation behavior and microstructure, revealed a detailed HIC propagation behavior and an effect of microstructure.

Hydrogen-Induced Cracking Susceptibility and Hydrogen Trapping Efficiency of the Welded MS X70 Pipeline Steel in H2S Environment

Hydrogen-Induced Cracking Susceptibility and Hydrogen Trapping Efficiency of the Welded MS X70 Pipeline Steel in H2S Environment