Effect of environmental and metallurgical factors on hydrogen induced cracking of HSLA steels

Hydrogen induced cracking (HIC) resistance of two high strength low alloy (HSLA) steel plates equivalent to API X70 grade was evaluated in various test solutions with different H₂S partial pressures and pH values. Results showed that H₂S partial pressure is the key parameter affecting HIC resistance. Hydrogen permeation rate was affected by both H₂S partial pressure and pH of test solutions, whereas the apparent hydrogen diffusivity was determined mainly by pH value in case of H₂S partial pressure less than 0.1 atm. HIC in the steels primarily nucleated at inclusions and/or clusters containing the Al and Ca oxides. HIC resistance was determined by diffusible hydrogen amount with different microstructures.     

Effect of microstructure on the hydrogen trapping efficiency and hydrogen induced cracking of linepipe steel

The hydrogen trapping efficiency in different microstructures is compared, and the critical hydrogen flux for hydrogen induced cracking (HIC) is determined for API X65 grade linepipe steel. By controlling the start cooling temperature (SCT) and the finish cooling temperature (FCT) in thermomechanically controlled process (TMCP), three different kinds of microstructure such as ferrite/degenerated pearlite (F/DP), ferrite/acicular ferrite (F/AF), and ferrite/bainite (F/B) are obtained. A modified ISO17081(2004) standard method is used to evaluate the hydrogen trapping by measuring the permeability (J_ssL) and the apparent diffusivity (D_app). Microstructures affecting both hydrogen trapping and hydrogen diffusion are found to be DP, AF, BF and martensite/austenite (M/A) constituents. The hydrogen trapping efficiency is increased in the order of DP, BF and AF, with AF being the most efficient. HIC is initiated at the local M/A concentrated region when the steel has such microstructures as F/AF or F/B. Although the trapping efficiency of bainite is lower than that of AF, bainite is more sensitive microstructure to HIC than to AF.     

The effect of grain size and aging on hydrogen embrittlement of a maraging steel

Notched tensile tests were conducted under a slow displacement rate to evaluate the influences of grain size and aging on hydrogen embrittlement (HE) of T-200 maraging steel. In addition, an electrochemical permeation method was employed to measure the effective diffusivity (D_eff) and apparent solubility (C_app) for hydrogen of various heat-treated specimens. The results indicated that the aged (482 °C/4 h) specimens comprised of numerous precipitates led to a raised C_app and a decreased hydrogen diffusivity as compared to those of the solution-treated ones. The solution-treated specimens were resistant to gaseous HE, whereas aged specimens were susceptible to it, implying the strength level was the controlling factor to affect the HE susceptibility of the specimens. Nevertheless, all specimens suffered from sulfide stress corrosion cracking (SSCC) severely but to different degrees. The aged specimens were more likely to form intergranular (IG) fractures in H₂S but quasi-cleavage (QC) in H₂. For the solution-treated specimens, a fine-grained structure was susceptible to HE in H₂S and revealed mainly QC that differed from the IG fracture of the coarse-grained one. The fracture mode of the specimens could also be related to the transport path and / or the supply of hydrogen to the plastic zone of notched specimens in hydrogen-containing environments.     

Hydrogen permeation behavior in pure nickel implanted with phosphorus, sulphur and their mixture

The entry and transport of hydrogen in phosphorus (P)-, sulphur (S)- and their mixture (P + S)-implanted nickel specimens with a fluence range of 1 × 10¹⁵ to 1 × 10¹⁷/cm² have been investigated using an electrochemical permeation technique and etching treatment (0.2% HF solution). From the hydrogen permeation transients obtained, the effective hydrogen concentration (C_H), apparent hydrogen diffusion coefficient (D_lag) and breakthrough time (t_lag) were estimated by using the time lag method in addition to the steady state permeation current density (P_∞). It was found that at a fluence of less than 1 × 10¹⁶/cm² almost all hydrogen permeation transients of the implanted nickel specimens were affected by the defects (vacancy, compressive stress and so on) generated during ion implantation process. At a high fluence of 1 × 10¹⁷/cm² the hydrogen permeation transient had a specific behavior because of the formation of amorphous phase for P, the structure change from fcc-structure to bcc-structure for S and both of them for the mixture (P and S). However, a synergistic effect of P and S was not observed on the hydrogen permeation transient. The behavior of these parameters depending on fluence and implanting element was discussed in terms of an amount of hydrogen entry site, the degree of defects, the properties of amorphous phase and structure and so on.     

Hydrogen embrittlement susceptibility and permeability of two ultra-high strength steels

Slow displacement rate tensile tests were carried out in a saturated H₂S solution to investigate the effect of hydrogen embrittlement on notched tensile strength (NTS) and fracture characteristics of two ultra-high strength steels (PH 13-8 Mo stainless steel and T-200 maraging steel). Hydrogen permeation properties were determined by an electrochemical permeation method. The results of permeation tests indicated that over-aged specimens showed a lower diffusivity/hydrogen flux and higher solubility than those solution-annealed. The great increase in reverted austenite (irreversible hydrogen traps) together with numerous precipitates at the expense of dislocations (reversible) in the over-aged specimen led to such a change in permeability. Ordinary tensile tests indicated that four tested specimens had roughly the same yield strength level. Hence, the hydrogen embrittlement susceptibility of the material could be related to their permeation properties. The uniform distribution of strong hydrogen traps in over-aged specimens instead of weak traps in the solution-annealed impeded the hydrogen transport toward the strained region, thus, the resistance to sulfide stress corrosion cracking was improved in over-aged specimens.     

Notch tensile properties of laser-surface-annealed 17-4 PH stainless steel in hydrogen-related environments

Slow displacement rate tensile tests were performed to determine the notched tensile strength (NTS) of 17-4 PH stainless steel with various microstructures in hydrogen-related environments. Solution-annealed (SA), peak-aged (H900), over-aged (H1025), and laser-annealed (LA) specimens were included in the study. Based on the results of NTS in air, the NTS loss in both gaseous hydrogen and H₂S-saturated solution was used to access the detrimental effects of hydrogen in 17-4 PH steel subjected to different treatments. Electrochemical permeation tests were also employed to determine the hydrogen permeation characteristics of the 17-4 PH steel plate with various microstructures. The result indicates that all the specimens have low NTS loss in gaseous hydrogen but significantly suffer from sulfide stress corrosion cracking (SCC), especially for the soft SA specimen. It was deduced that high hydrogen diffusivity and less trapped hydrogen atoms in the SA matrix provided rapid transport of massive hydrogen atoms into highly stressed region, and deteriorated the NTS tested in the saturated sulfide solution. On the other hand, H1025 specimen consists of the blocky austenite together with Cu-rich precipitates uniformly distributed in the grain interior; dense and coarse precipitates are also observed along prior austenite grain boundaries. Hydrogen atoms tend to be trapped along grain boundaries, and lead to the formation of intergranular fracture for H1025 specimen tested in the H₂S solution. Fine and homogeneously distributed precipitates in the H900 matrix result in uniformly trapping of hydrogen atoms, so it behaves superior properties than other specimens. The decohesion of precipitate/matrix interfaces induces quasi-cleavage fracture of the H900 specimen tested in H₂S solution. Finally, the application of laser-annealing treatment on the H900 specimen cannot improve its resistance to sulfide SCC, because the laser-annealed zone is susceptible to hydrogen embrittlement in the H₂S solution.     

Effects of hydrogen on the fracture toughness of a X70 pipeline steel

Effects of hydrogen on the fracture toughness of a X70 pipeline steel were investigated in the cases of hydrogen pre-charging and dynamic hydrogen charging in 0.5 mol/L H₂SO₄ solution under slow strain rate tensile testing. Under the hydrogen pre-charging, the fracture toughness decreased in a linear relationship with the hydrogen concentration as the hydrogen concentration was more than 1 ppm in weight. The fracture surfaces were characteristic of dimples. Under the dynamic hydrogen charging, the fracture toughness for hydrogen-induced cracking decreased linearly with logarithm of the hydrogen concentration without stress. The hydrogen-induced fracture had the appearance of cleavage facets.     

Film properties and stability influence on impedance distribution during the dissolution process of low-carbon steel exposed to modified alkaline sour environment

In this work, we characterized the anodic dissolution and the hydrogen transport within carbon steel (SAE 1018) samples immersed in alkaline sour solutions (CN⁻, polysulfide-base inhibitor and H₂S(aq)). The evolution of interfacial and transport processes could be quantified by Electrochemical Impedance Spectroscopy (EIS) and hydrogen permeation measurements. EIS experimental data were analyzed and fitted by using Transmission Line Model (TLM); this latter helped to propose the mechanisms through the porous layer of the corrosion products formed. The area influencing the dissolution and the mass transfer process was quantified by the pores number, pores thickness and the interfacial passive electrical elements describing the mechanisms in different regions within the pores of the corrosion product layer. The TLM was used to analyze the active-mass transport processes occurred at different spatial positions of the porous layer, such as the mass transfer at the wall and the active-mass transfer at the base of the cylindrical pore of the non-stoichiometric Fe_xS_y.     

Hydrogen permeation behavior and corrosion monitoring of steel in cyclic wet–dry atmospheric environment

Hydrogen permeation of 16Mn steel under a cyclic wet–dry condition was investigated by Devanathan–Stachurski's electrolytic cell with a membrane covered on the exit side by a nickel layer and the weight loss was measured for each wet–dry cycle. The results show that hydrogen permeation current change with different atmospheric environment: distilled water, seawater, and seawater containing 100 ppm H₂S. The results show that seawater can induce an increase in the hydrogen permeation current due to the hydrolyzation reaction. And after the increase, equilibrium is reached due to the equilibrium of hydrolyzation reaction effect and the block of the rust layer. On the other hand, H₂S contamination also can induce an increase in the maximum hydrogen permeation current due to the hydrolyzation reaction. And H₂S contamination delays the time that hydrogen permeation is detected because of the formation of the FeS_(1?x) film. The FeS_(1?x) film can block the absorption of hydrogen onto the specimen surface. The surface potential change and the pH change of the metal surface control the hydrogen permeation current. And a clear linear correlation exists between the quantities of hydrogen permeated through the 16Mn steel and the weight loss. Based on the linear correlation, we monitored the corrosion rate by monitoring the hydrogen permeation current by a sensor outside. Good coherences were shown between results in laboratory and outside.     

Characterization of inclusions of X80 pipeline steel and its correlation with hydrogen-induced cracking

In this work, the microstructures of an X80 pipeline steel were characterized, and their susceptibilities to hydrogen-induced cracking (HIC) were investigated by hydrogen-charging, electrochemical hydrogen permeation and surface characterization. It is found that the microstructure of X80 pipeline steel consists of a polygonal ferrite and bainitic ferrite matrix, with martensite/austenite (M/A) constituents distributing along grain boundaries. The inclusions existing in the steel include those enriched with Si, Al oxide, Si–ferric carbide and Al–Mg–Ca–O mixture, respectively. The majority of inclusions are Si-enriched. Upon hydrogen-charging, cracks could be initiated in the steel in the absence of external stress. The cracks are primarily associated with the Si- and Al oxide-enriched inclusions. The diffusivity of hydrogen in X80 steel at room temperature is 2.0 × 10⁻¹¹ m²/s, and the estimated hydrogen trapping density in the steel is as high as 3.33 × 10²⁷ m⁻³.     

Hydrogen entry into pipeline steel under freely corroding conditions in two corroding media

Hydrogen permeation through API 5L X65 pipeline steel was studied under freely corroding conditions in NACE solution (simulated seawater) and poisoned 1 N H₂SO₄. A steady state condition with regards to permeation flux is not obtained due to the presence of corrosion product, changing sample dimension and a possible change in hydrogen availability on the corroding surface. A unique way of calculating the sub-surface hydrogen concentration (C₀) under non-steady state freely corroding conditions has been developed. The C₀ has been evaluated as a function of exposure time in NACE solution and poisoned H₂SO₄ solution. The sub-surface hydrogen concentration (C₀) increased initially but then decreased with increasing exposure to the corroding solutions, after demonstrating an early maximum. The changes in C₀ have been explained taking into consideration the corrosion products that developed, the possible anodic reactions, the changes in sample thickness and other issues in the dynamic system.     

Scanning photoelectrochemical analysis of hydrogen permeation on ASTM A516 grade60 steel welded joints in a H2S containing solution

Hydrogen permeation through a welded joint of an ASTM A516 grade60 steel immersed in a H₂S solution was investigated using the scanning photoelectrochemical microscopy, an in situ technique providing images of the spatial distribution of hydrogen diffusion in real time and with good resolution. The paper presents images of hydrogen spatial distribution in the material including the base metal and heat-affected zone. Electrochemical impedance measurements were also performed in order to complement the information obtained.     

The effect of pressure on the permeation of hydrogen through steel

A cell is described which provides a means of studying the permeation of hydrogen through steel at elevated pressures. It has been shown that the significant factor in permeation is the partial pressure of hydrogen, p_H2, and not the applied pressure, P, and that reproducible results can be obtained provided the solution is agitated so that the hydrogen generated cathodically is dispersed into the bulk solution. The permeation of hydrogen through steel has been studied in 0.1 mol dm^?3 NaOH and in 0.05 mol dm^?3 H₂SO₄ under conditions of constant current density and applied pressure and at various constant partial pressures of hydrogen, and it has been shown that in all cases (?J/?p_H2) > 0. In 0.1 mol dm^?3 NaOH linear J vs $\text{i}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and J vs p_H2 relationships have been observed, whereas in 0.05 mol dm^?3 H₂SO₄ although J vs $\text{i}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ is linear at low current densities the curves follow linear J vs log i and J vs log p_H2 relationships at higher current densities. The results in NaOH and H₂SO₄ have been explained in terms of the effect of p_H2 on the rate constants k₂, k_?2 of the chemical desorption step of the h.e.r. A decrease in k₂ and an increase in k₂ will increase the coverage, θ_H, with a consequent increase in the rate of permeation. The effect of p_H2 on permeation may be of significance in systems where the steel is enclosed so that hydrogen is discharged cathodically at high partial pressures, e.g. high-strength steels used for reinforcing bars and prestressing cables in concrete, which are adventitiously connected to a cathodic protection system.     

Hydrogen entry into steel during atmospheric corrosion process

Hydrogen entry and permeation into iron were measured by an electrochemical method during atmospheric corrosion reaction. The hydrogen permeation was enhanced on passive films because the hydrogen adsorption increased by the hydrogen evolution mechanism which is different from that on a bear iron surface. The permeation rate during a wet and dry corrosion cycle showed a maximum in the drying process depending upon the surface pH and the corrosion potential. The pollutant such as Na₂SO₃ which decreases the pH and the corrosion potential causes an increase in the permeation rate. The mechanism of the change in the permeation rate during the wet and dry cycles is explained by the polarization diagram of the electrode covered by thin water layer.     

Measurement of steady-state hydrogen electrode reactions on Alloys 600 and 690 tubes

The steady-state polarization measurements for HER and HOR were carried out in order to obtain the effects of hydrogen pressure, solution pH, and temperature on the current densities of Alloys 600 and 690, respectively. Optimization was performed to obtain the electrokinetic parameters of HER and HOR on Alloys 600 and 690 such as forward and reverse transfer coefficients and equilibrium corrosion densities. From the optimization process, the activation energies, E_ac, of both hydrogen reactions on the surfaces of the Alloys 600 and 690 tubes were obtained as 30.5 kJ/mole on the surface of Alloy 600 tube and 35.6 kJ/mole on Alloy 690 tube. Furthermore, the equilibrium exchange current densities of hydrogen electrode reaction, i₀(H₂), on the surface of the Alloys 600 and 690, respectively, were proposed as functions of hydrogen pressure, solution pH, and temperatures.     

Hydrogen-induced cracking of pure titanium in sulphuric acid and hydrochloric acid solutions using constant load method

The hydrogen-induced cracking (HIC) of the commercial pure titanium (Ti) has been investigated as functions of applied stress and test temperature in sulphuric acid and hydrochloric acid solutions by using a constant load method. From the results obtained, HIC was hydrogen embrittlement (HE) related to the fracture of hydride. We have also found that the steady state elongation rate obtained from corrosion elongation curve becomes a relevant parameter for predicting time to failure and a criterion to assess whether HIC takes place or not. A parameter, t_sst_f⁻¹ was also found to become an indicator to assess whether HE takes place or not. Furthermore, it was deduced that HIC was qualitatively explained in terms of hydride formation and a localized deformation, which was basically based on a hydride formation-rupture event at crack tips.     

Hydrogen permeation in high strength steel under load in aqueous environment

Abstract

The hydrogen assisted cracking problem is one of the major causes of the failure occurring in the high strength steel structures used in various industries. In aqueous environment, hydrogen is generated by the hydrogen reduction reaction on the steel surface. With depletion of the high quality resources in oil and gas industry, the hydrogen assisted cracking problem becomes severe in sour environment, which contains high amount of H₂S. Understanding on the hydrogen permeation behaviour is crucial to deal properly with the hydrogen related problems since they are primarily determined by the hydrogen uptake and transport in the steel. The Devanathan–Stachurski method is widely used to evaluate electrochemically the hydrogen permeation behaviour. This method has been successfully used for the steel with no load. Under loading condition, this electrochemical test method has been modified to accommodate the externally applied load. However, the data require careful examination to validate the technical importance because of the stability and homogeneity of palladium layer coated on the steel surface under load. In this paper, the hydrogen permeation test method under loading condition will be reviewed for the high strength steels used in oil and gas industry. The factors affecting the hydrogen permeation in the high strength steel will be discussed in terms of the applied stress level and the sulphide film forming on the steel surface in sour environment.     

Sintered stainless steels: Fatigue crack propagation resistance under hydrogen charging conditions

Monophasic and multiphasic (two and three phases) sintered stainless steels were prepared both considering premixes of AISI 316LHC and AISI 434LHC stainless steels powders and using a prealloyed duplex stainless steel 25% Cr, 5% Ni, 2% Mo powder. Their fatigue crack propagation resistance was investigated both in air and under hydrogen charging conditions (0.5 M H₂SO₄ + 0.01 M KSCN aqueous solution; applied potential = −700 mV/SCE), considering three different stress ratios (R = 0.1; 0.5; 0.75). Fatigue crack propagation micromechanisms were investigated by means of fracture surface scanning electron microscope (SEM) analysis.For all the investigated sintered stainless, fatigue crack propagation resistance is influenced by hydrogen charging and an increase of crack growth rates dependent on the steel microstructure is obtained. Experimental results also allow to identify the sintered stainless steel obtained from the prealloyed 25% Cr, 5% Ni, 2% Mo powder as the most resistant to fatigue crack propagation in air and under hydrogen charging conditions.     

The effect of H2S concentration on the corrosion behavior of carbon steel at 90 °C

The electrochemical behavior of SAE-1020 carbon steel in 0.25 M Na₂SO₄ solution containing different concentrations of H₂S at 90 °C was investigated using the methods of weight loss, electrochemical measurements, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that the corrosion rate of carbon steel increased significantly with the increase of H₂S concentration. H₂S accelerated the corrosion rate of SAE-1020 carbon steel by a promoted hydrogen evolution reaction. Severe corrosion cavities were observed on the carbon steel surface in the solutions containing H₂S due to cementites stripped off from the grain boundary. The loose corrosion products formed on the steel surfaces were composed of mackinawite.     

Electrochemical and surface analytical studies on hydrogen permeation with Fe-Cu alloys in sulfuric acid with and without H2S

Cathodic and anodic polarization curves and hydrogen permeation have been determined for Fe, Fe-0.5Cu and Fe-3.4Cu in sulfuric acid. During cathodic polarization at potentials more noble than -400 mV (NHE) a black layer consisting of metallic Cu and Fe-oxides or -hydroxides is formed on the surface of the alloys by preferential dissolution of Fe. The black layer acts as a barrier for hydrogen diffusion and a catalyst for H₂ evolution, the layer reduces the permeation rate by a factor of two compared to pure Fe, in the presence of H₂S the reduction is by a factor of six. Addition of H₂S and/or an increase in pH can shift the cathodic polarization curve to more negative potentials where the scale is not stable. Under such conditions the permeation rate is faster on the alloys than on Fe.