Effects of corrosion product deposit on the subsequent cathodic and anodic reactions of X-70 steel in near-neutral pH solution

The effects of corrosion product deposit on the subsequent anodic and cathodic reactions of X-70 steel in a near-neutral pH solution were investigated by localized electrochemical impedance spectroscopy (LEIS), scanning vibrating micro-electrode (SVME) and macroscopic EIS measurements as well as surface analysis technique. It is found that the deposit layer formed on the steel surface is porous, non-compact in nature. The presence of a corrosion product layer would enhance adsorption, but significantly inhibit absorption and permeation of hydrogen atoms into steel. It is due to the porous structure of the deposit that generates a spatial separation of cathodic and anodic reaction sites, resulting in an increased effective surface area for hydrogen adsorption and, simultaneously, a “blocking” effect on hydrogen absorption and permeation. The deposit enhances greatly anodic dissolution of the steel, which is attributed to the adsorption of the intermediate species and the resultant “self-catalytic” mechanism for corrosion of the steel in near-neutral pH solution. In the presence of corrosion product deposit on the pipeline steel surface, pipeline corrosion, especially pitting corrosion, is expected to be enhanced. Stress corrosion cracks could initiate from the corrosion pits that form under deposit. However, deposit does not contribute to hydrogen permeation, although the hydrogen evolution is enhanced.     

Hydrogen permeation behavior of nickel electroplated AISI 4340 steel

The role of the electroplated nickel layer on hydrogen permeation through AISI 4340 steel was investigated by a electrochemical hydrogen permeation test. The permeation test, composed of three steps, was conducted to measure the hydrogen diffusivity and surface hydrogen concentration. A constant current of 20 mAcm^-2 and a constant potential of -100 mV vs. Ag/AgCl electrode were applied to the hydrogen entry and exit cells, respectively. The thickness of the electroplated nickel layer on AISI 4340 steel increased in a linear fashion with an increase in electroplating time. The nickel coated layer contributed to a decrease in the hydrogen permeability of nickel coated AISI 4340 steel specimens. This is due to the fact that the surface hydrogen concentration and hydrogen diffusivity in nickel coated layer were lower than those of AISI 4340 steel substrate. Especially, low hydrogen diffusivity decreased significantly with hydrogen permeability. The critical effective hydrogen diffusivity for barrier of nickel electroplated AISI 4340 steel specimens was higher than the hydrogen diffusivity of AISI 4340 steel specimen. It is proposed then that the thin nickel layer on AISI 4340 steel acts as a barrier for hydrogen permeation through AISI 4340 steel.     

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.     

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 induced cracking (HIC) testing of low alloy steel in sour environment: Impact of time of exposure on the extent of damage

Hydrogen induced cracking (HIC) of line pipe steel was investigated through immersion testing and hydrogen permeation measurements. At constant pH and hydrogen sulphide partial pressure (pH₂S), the extent of HIC was found to depend on exposure time until a stable level was reached. The time to reach this stable value is affected by pH and pH₂S. Results of permeation experiments confirmed that HIC is linked with the increase of hydrogen concentration in the steel. It is also shown that low severity requires longer exposures to reach equilibrium. This must be taken into account for HIC testing in mildly sour environment.     

Amperometric hydrogen permeation measurement in iron using solid polymer electrolyte fuel cells

Electrolytic hydrogen permeation through iron membranes was measured simultaneously by means of a solid polymer electrolyte fuel cell (SPEFC) and standard aqueous-phase hydrogen oxidation. Two configurations of SPEFC were tested: the first included a separate anode for hydrogen oxidation and the second used the iron membrane surface itself, plated with palladium, as the anode. The results showed a limiting hydrogen permeation flux for the first configuration but not for the second, which yielded about 64% of the correct output.     

Double electrolyte sensor for monitoring hydrogen permeation rate in steels

An amperometric hydrogen sensor with double electrolytes composed of a gelatiniform electrolyte and KOH solution has been developed to determine the permeation rate of hydrogen atoms in steel equipment owing to hydrogen corrosion. The gelatiniform electrolyte was made of sodium polyacrylate (PAAS), carboxyl methyl cellulose (CMC) and 0.2 mol dm⁻³ KOH solution. The results show that the gelatiniform electrolyte containing 50 wt.% polymers has suitable viscosity and high electrical conductivity. The consistent permeation curves were detected by the sensor of the double electrolyte and single liquid KOH electrolyte, respectively. The developed sensor has good stability and reproducibility at room temperature.     

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.     

Comparative assessment of electrochemical hydrogen absorption by pipeline steels with different strength

The assessment of ability to absorb hydrogen of three API grade pipeline steels: X52, X70 and X100 have been evaluated. The factors of cathodic hydrogen charging, time of exposure, and applied stress were taken into account. It has been shown that all steels demonstrate the sensitivity to hydrogenating in deoxygenated, near-neutral pH NS4 solution under relatively “soft” cathodic polarisation, although the efficiency of hydrogen permeation in metal is quite low and depends on time of exposure. Applied tensile stress, which equivalent to gross hoop stress in pipe wall under operating conditions, can accelerate the hydrogen absorption in several times. For studied steels the resistance to hydrogen absorption decreases with decreasing of steel strength.     

Effect of microstructure on the sulphide stress cracking susceptibility of a high strength pipeline steel

The sulphide stress cracking (SSC) susceptibility of a newly developed high strength microalloyed steel with three different microstructures has been evaluated using the slow strain rate testing (SSRT) technique. Studies were complemented with potentiodynamic polarization curves and hydrogen permeation measurements. Material included a C–Mn steel having Ni, Cu, and Mo as main microalloying elements with three microstructures: martensitic, ferritic and ferritic + bainitic. Testing temperatures included 25, 50, 70 and 90 °C. Detailed SEM observations of the microstructure and fracture surfaces were done to identify possible degradation mechanisms. The results showed that in all cases, the corrosion rate, number of hydrogen atoms at the surface and the percentage reduction in area increased with temperature. The steel with a martensitic microstructure had the highest SSC susceptibility at all temperatures, whereas the ferritic steels were susceptible only at 25 °C, and the most likely mechanism is hydrogen embrittlement assisted by anodic dissolution.     

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.     

化学镀镍层起泡脱皮原因分析及解决方法

化学镀镍层起泡脱皮会导致无镀层部位的加速腐蚀,在表面处理中是不允许出现的.因此,分析化学镀镍层起泡脱皮原因,找出其解决办法.通过试验得出结论:化学镀镍层有渗氢现象,原子态氢集聚形成气泡.减少施镀时间,降低镀层厚度,解决了镀层起泡脱皮质量问题,保证了化学镀镍零件的防腐性能.     

Effect of post-weld heat treatment on the microstructure and hydrogen permeation of 13CrNiMo steels

The hydrogen trapping characteristics of 13CrNiMo martensitic steel weld metals, with different austenite contents resulting from different post-weld heat treatments, have been analysed. Scanning electron microscopy and X-ray diffraction have been used to study stable austenite resulting from intercritical tempering of these soft martensitic stainless steels weld metals. Austenite contents up to 25 vol.% have been obtained. Hydrogen diffusion and permeation coefficients have been obtained from an analysis of the permeation rate of hydrogen through these materials. A decrease of the hydrogen apparent diffusion coefficient is observed when the tempering temperature is increased in the range ; this decrease is attributed to changes in the martensitic matrix as well as to the increase of austenite content. The role of the austenite phase on trapping is discussed.     

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.     

电化学方法研究高温下氢在碳钢中的扩散

<正> 前言 研究氢在金属中的扩散与渗透,定量的方法主要有阴极过程量气法、电化学测量法、高真空测量法和核物理法。电化学测量法的设备简单,灵敏度高,测量方便、快速、准确,因而被广泛用于氢渗透研究,但到目前为止,一般都只用于温度低于100℃的测量;高真空测量法只适用于氢渗透速率大的体系,不宜用于温度低于200℃的测量。因此,对于100～200℃下氢在金属中扩散行为,目前还缺少合适的测定方法。本工作应用电化学测量法的原理,建立了一套测试装置,研究了100～200℃下氢在碳钢中的扩散行为。     

The hydrogen permeation investigation of API X56 steel in sea mud

It was found that the corrosion rate of steel in the sea mud with sulfate‐reducing bacteria (SRB) could be as high as 10 times of that in the sea mud without SRB. And the hydrogen permeation reaction would occur when metals were corroded. So it is necessary to investigate the effect of living SRB on hydrogen permeation in the sea mud. Cathodic potential was often added to metals in order to protect them. But hydrogen permeation could be affected by the cathodic potential. So it is also necessary to study the effect of cathodic potential on hydrogen permeation. In this paper, the hydrogen permeation actions of API X56 steel in the sea mud with and without SRB at corrosion and cathodic potential were studied with an improved Devanathan‐Stachurski's electrolytic cell. Experimental results showed that during the growth of SRB, the current density curve of hydrogen permeation was accordant with the growth curve of SRB. But the hydrogen permeation current density of API X56 steel hardly changed in the sterilized sea mud. Compared with the hydrogen permeation current density of API X56 steel in the sterilized sea mud, the hydrogen permeation of API X56 steel in the sea mud could be accelerated by living SRB. Experimental results also showed that the hydrogen permeation current density increased rapidly when the cathodic potential was added to the three‐electrode system of the cathodic cell, and then the hydrogen permeation current density could obtain a stable value slowly. So the cathodic potential added to the cathodic cell could accelerate hydrogen permeation.     

Hydrogen entry behaviour of newly developed Al–Mg–Si coating produced by physical vapour deposition

A ternary Al–Mg–Si alloy was prepared by co-evaporation technique and tested with respect to hydrogen entry behaviour as an alternative to conventional zinc coating on steel. Hydrogen entry behaviour evaluated using Devanathan cell showed a smaller hydrogen entry for this new coating than conventional zinc coating. Compared to an unscratched surface, hydrogen entry increased by more than 100 times in the scratched surface, but it was lower than that for the zinc coating with a scratched surface owing to the moderate galvanic corrosion potential of the new coating. This new coating is proposed especially for high-strength steel application.     

Effect of residual stresses on hydrogen permeation in iron

The effect of residual stresses on electrochemical permeation in iron membrane was investigated. Four thermal and mechanical treatments were chosen to obtain different surface states in relation to the residual stresses.Residual stresses were determined by X-ray diffraction (XRD) using the Macherauch and Müller method. The results were completed by the microhardness measurements. For all iron membranes, compressive residual stresses were obtained.Electrochemical permeation experiments using a Devanathan and Stachurski cell were employed to determine the hydrogen permeation behaviour of the various iron membranes. The latter was charged with hydrogen by galvanostatic cathodic polarization in 0.1 M NaOH at 25 °C. The experimental results revealed that hydrogen permeation rate increases with increasing residual stresses introduced in iron membranes.     

Study of the electrochemical permeation of hydrogen in iron

Hydrogen permeation through iron membranes of different thicknesses was studied by the electrochemical permeation technique. The membranes were charged with hydrogen by galvanostatic cathodic polarization in 0.1 M NaOH at 25 °C.The measured build-up and decay permeation current transient had been examined.The experimental results revealed that the diffusion apparently increases with decreasing membrane thickness. This result suggests that the hydrogen transport through membrane was mainly governed by hydrogen trapping at the trap sites present at the grain boundaries.The influence of the passive layer on the hydrogen permeation and its influence on the evaluation of diffusion and trapping characteristics were discussed.     

The effects of sacrificial coatings on hydrogen embrittlement and re-embrittlement of ultra high strength steels

This paper describes an investigation of electrodeposited Zn-14% Ni and aluminium-based SermeTel 1140/962 coatings as possible replacements for cadmium. Slow strain rate tests were performed to measure the extent of direct hydrogen embrittlement of a high strength steel substrate as a result of the coating process and of hydrogen re-embrittlement caused by coating corrosion. The level of re-embrittlement was shown to depend on both the electrochemical potential of the coating and its barrier properties. Zn-14% Ni coatings caused the most re-embrittlement as they had the most active potential and contained through-thickness defects which left the steel exposed to hydrogen uptake. The microstructure of the high strength steel was also shown to be an important factor affecting the extent of embrittlement. AerMet 100 steel was more resistant than 300M steel and this was attributed to the presence of reverted austenite surrounding the martensite laths in AerMet 100, which trapped absorbed hydrogen and prevented a critical hydrogen concentration being reached in the more susceptible martensite phase.