Effect of H2S on stress corrosion cracking and hydrogen permeation behaviour of X56 grade steel in atmospheric environment

Susceptibility to stress corrosion cracking of X56 steel and its relationship with hydrogen permeation behaviour in atmospheric environment containing H2S was investigated by hydrogen permeation tests at a slow strain rate. The results show that: the fracture strain decreases with the decrease of strain rate under the same experimental conditions; the fracture strain also decreases with the increase of H2S concentration under the same strain rate, and the increased concentration of H2S has no significant effect on the hydrogen permeation in the first wet, etc. dry cycle, however has lead to increased hydrogen permeation in the later cycles. The SEM images of the fractured surfaces show clear evidences of enhanced stress corrosion cracking susceptibility by H2S.

Hydrogen permeation and corrosion behaviour of high strength steel 35CrMo under cyclic wet-dry conditions

Hydrogen permeation behaviours of high strength steel 35CrMo under different cyclic wet-dry conditions have been investigated by using Devanathan-Stachurski's technique. Four electrolytes were used: distilled water, seawater, seawater containing 1500 ppm H2S and seawater containing 0.03 mol L-1 SO2. The corrosion weight loss of 35CrMo in the wet-dry cycles was measured simultaneously. The experimental results show that hydrogen can be detected at the surface opposite to the corroding side of the specimen during wet-dry cycles and the permeation current density during a wet-dry cycle showed a maximum during the drying process. The hydrogen permeation was obviously promoted by Cl- ions, H2S and SO2. The hydrogen permeation in the real marine atmosphere has also been investigated. There is a clear correlation between the amount of hydrogen permeated and the corrosion weight losses. Results show the importance of hydrogen permeation that merits further investigation.

Hydrogen permeation behavior and corrosion monitoring atmospheric of steel in cyclic wet-dry 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.

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 APT 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 APT X56 steel hardly changed in the sterilized sea mud. Compared with the hydrogen permeation current density of APT X56 steel in the sterilized sea mud, the hydrogen permeation of APT 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.

Arc Root Motions In An Argon-Hydrogen Direct-Current Plasma Torch At Reduced Pressure

Arc root motions in generating dc argon-hydrogen plasma at reduced pressure are optically observed using a high-speed video camera. The time resolved angular position of the arc root attachment point is measured and analysed. The arc root movement is characterized as a chaotic and jumping motion along the circular direction on the anode surface.

Effect of mechanical deformation on permeation of hydrogen in iron

Rate of hydrogen permeation was measured under static as well as dynamic mechanical deformation conditions, Cylindrical tensile test specimens were used for the study and hydrogen permeation was measured electrochemically, It was observed that the hydrogen diffusivity decreased as plastic deformation increased for the static deformation experiments while elastic deformation had no significant effect on diffusivity but increased the steady state permeation flux, For the dynamic loading experiment, an elastic deformation increased the hydrogen permeation rate almost linearly. Onset of plastic deformation led a sudden decrease of permeation rate and the reduced rate was rapidly recovered when the plastic deformation ceased. These rapid changes in the permeation rates were explained that the absorbed hydrogen was trapped by dislocations and creation rate and density of dislocations changed drastically when plastic deformation started and stopped.

Hydrogen ion reduction in the process of iron rusting

Since the acceptance of the electrochemical rusting mechanism, oxygen reduction has been considered the main cathodic process, while H+ reduction has been overlooked for the past four decades because oxygen can be readily renewed due to the thin layer Of Solution film formed during atmospheric corrosion. This study shows that measurable hydrogen call be detected at the surface opposite to the corroding side of the specimen during wet-dry cycles, and a clear correlation exists between the quantities of hydrogen permeated through iron sheet and weight loss. Results Suggest the intrinsic importance of H+ reduction that merits further investigation. (c) 2004 Elsevier Ltd. All rights reserved.

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. (c) 2005 Elsevier Ltd. All rights reserved.

热浸镀钢材在海水中的氢渗透行为和脆性研究

氢渗透和拉应力的联合作用对海洋环境中的热浸镀钢材的安全构成潜在威 胁，本文以当前应用最广泛的三种商业化热浸镀钢材（热浸镀锌、锌-5%铝-稀土和锌-55％铝-1.6%硅）为研究对象，采用Devanathan-Stachurski双面电解池测试技术，测试了自渗氢电流密度曲线，研究了镀层与缺陷比例对氢渗透电流的影响，比较了镀层的氢渗透抑制性能及存在缺陷时的自渗氢能力，并结合镀层成分、结构及其腐蚀机理，探讨了其氢渗透机理；通过慢应变速率拉伸实验，获得了热浸镀钢材在不同充氢条件下的应力-应变曲线，比较了其力学性能参数，并配合断口的显微分析，评价了三种热浸镀钢材在海水中的氢脆敏感性，并对其氢脆机理进行了探讨。主要结果如下： (1) 热浸镀锌镀层的氢渗透抑制能力最弱，锌-5%铝-稀土镀层的氢渗透抑制能力较强，镀层存在缺陷时导致的阴极保护能促进氢渗透；锌-55％铝-1.6%硅镀层的氢渗透抑制能力最强，镀层存在缺陷时基本没有氢渗透电流。当镀层存在缺陷时，氢渗透电流密度的最大值随着镀层与暴露的钢材基体的面积比增大而增大。随着镀层中铝含量的增加，镀层结构越致密，镀层的耐腐蚀性能越好，完整镀层的氢渗透抑制能力越强，镀层存在缺陷时的自渗氢能力越弱。 (2) 热浸镀锌和锌-5%铝-稀土镀层钢材在海水中的氢渗透能明显降低材料的断后延伸率和能量密度，使其断裂方式由韧性转变为准解理；锌-55％铝-1.6%硅镀层在海水中对钢材基体进行阴极保护导致的氢渗透虽能显著降低其断后延伸率和能量密度，但其断裂方式以韧性为主，且断口存在局部的准解理撕裂形貌。随着预浸泡时间的增长，材料充氢量的增加，三种热浸镀钢材的氢脆敏感性提高。随着镀层铝含量的增加，热浸镀钢材在海水中的氢脆敏感性降低。

硫酸盐还原菌对热浸镀锌钢材在海水中的氢渗透行为和脆性的影响研究

硫酸盐还原菌(SRB)活动、拉应力和氢的联合作用将对海洋环境中热浸镀锌钢材构筑物的安全带来隐患。本文通过Devanathan－Stachurski双面电解池测试技术，检测了镀层完好及存在缺陷的热浸镀锌钢材在灭菌海水、灭菌培养基及接种SRB的培养基中的氢渗透电流曲线，探讨了镀层缺陷、培养基成分以及SRB对热浸镀锌钢材氢渗透行为的影响；采用电化学阻抗谱测试技术，研究了热浸镀锌钢材在上述介质中的腐蚀机制，并由此讨论了热浸镀锌钢材在不同条件下的氢渗透机制；通过慢应变速率拉伸试验(SSRT)，获得了热浸镀锌钢材在不同腐蚀介质中的应力-应变曲线，比较了其力学性能参数，进而通过断口分析，评价了热浸镀锌钢材在灭菌海水、灭菌培养基及接种SRB培养基中的氢脆敏感性。研究结果表明： (1) 镀层出现缺陷将对热浸镀锌钢材的氢渗透行为起促进作用，这类试样在灭菌海水和灭菌培养基中的平均氢渗透电流密度比镀层完好试样在相同介质中的平均氢渗透电流密度分别提高了250.76%和32.76%；培养基组分对热浸镀锌钢材的氢渗透行为起促进作用，镀层存在缺陷和镀层完好的热浸镀锌钢材试样在灭菌培养基中的平均氢渗透电流密度分别比其在灭菌海水中高181.22%和626.97%；SRB对热浸镀锌钢材的氢渗透行为起抑制作用，镀层存在缺陷及镀层完好的热浸镀锌钢材试样在接种SRB的培养基中的平均氢渗透电流密度分别比灭菌培养基中低90.84%、77.14%。 (2) 电化学测试结果表明，培养基组分能够加速热浸镀锌钢材的腐蚀，使试样表面更容易形成腐蚀缺陷，从而增加其自渗氢能力；活性SRB本身对热浸镀锌钢材的腐蚀和氢渗透起促进作用，但在本文实验条件下，SRB及其代谢产物形成的生物膜以及腐蚀产物组成的致密膜层能够通过阻挡层作用抑制腐蚀，并阻止氢的进入；扫描电镜(SEM)分析结果表明，暴露于接种SRB培养基中的热浸镀锌钢材试样表面有致密的产物膜层，而灭菌培养基中的试样表面没有明显腐蚀产物膜存在。 (3) 培养基组分对热浸镀锌钢材氢渗透行为的促进作用增加了其对氢脆的敏感性，热浸镀锌钢材在灭菌培养基中的断后延伸率和能量密度比在灭菌海水中分别降低了4.97%和5.59%；SRB对热浸镀锌钢材氢渗透行为的抑制作用降低了其对氢脆的敏感性，热浸镀锌钢材在接种SRB的培养基中的断后延伸率和能量密度比其在灭菌培养基中分别高7.78%和8.44%。

35CrMo高强度钢在海洋大气中的氢渗透行为与环境致脆机理研究

海洋大气腐蚀环境是海洋腐蚀环境之一。金属材料在海洋大气环境下会发生环境敏感断裂。在环境敏感断裂中，氢脆是其中的一个重要类型。氢脆是合金中存在过量的氢，并在拉应力协同作用下造成的一种脆断。氢渗透已被证明是金属材料失效的主要原因之一。氢脆导致了材料强度降低，在较低载荷下会导致材料的灾害性破坏，因此研究海洋用钢在海洋大气中的致脆机制与氢渗透行为是十分必要的。本文所做工作主要有以下几点： 一、 采用Devanathan-Stachurski氢渗透技术，研究了35CrMo高强度钢未受 力试样在海洋大气腐蚀环境中的氢渗透及腐蚀失重行为。主要分为两个部分：(1) 干湿循环实验；(2)模拟海洋大气腐蚀实验。实验结果表明，在海洋大气腐蚀环境中，35CrMo 高强度钢存在着明显的氢渗透现象，在不同腐蚀环境中现象有所不同。Cl-离子、H2S、SO2等污染物对氢渗透产生了明显的促进作用。另外，氢渗透量与腐蚀失重存在着明显的线性关系。 二、 采用慢应变速率拉伸实验法(SSRT)，在海洋大气腐蚀环境中对35CrMo试样进行力学性能测试，研究氢渗透对35CrMo应力腐蚀开裂敏感性的影响。实验结果表明，在各种腐蚀条件下，氢渗透会增加35CrMo的应力腐蚀开裂敏感性，使得最大载荷、断裂时间及应变值均减小。 三、 采用Devanathan-Stachurski氢渗透技术与慢应变速率拉伸实验法，进行了35CrMo高强度钢受力试样在海洋大气环境中的氢渗透实验，研究材料形变对氢渗透的影响。实验结果表明，在弹性变形阶段，氢渗透电流逐渐增大，在塑性变形阶段开始后，氢渗透逐渐减小，在塑性变形阶段后期，随着形变的增大，氢渗透电流增大。

Corrosion failure of marine steel in sea-mud containing sulfate reducing bacteria

The corrosion failure behavior of marine steel is affected by stress, which exists in offshore structures at sea-mud region. The sulfate reducing bacteria (SRB) in the sea-mud made the steel more sensitive to stress corrosion cracking (SCC) and weaken the corrosion fatigue endurance. In this paper, a kind of natural sea-mud containing SRB was collected. Both SCC tests by slow strain rate technique and corrosion fatigue tests were performed on a kind of selected steel in sea-mud with and without SRB at corrosion and cathodic potentials. After this, the electrochemical response of static and cyclic stress of the specimen with and without cracks in sea-mud was analyzed in order to explain the failure mechanism. Hydrogen permeation tests were also performed in the sea-mud at corrosion and cathodic potentials. It is concluded that the effect of SRB on environment sensitive fracture maybe explained as the consequences of the acceleration of SRB on corrosion rate and hydrogen entry into the metal.

Hydrogen sensors based on AlGaN/AIN/GaN HEMT

Pt/AlGaN/AIN/GaN high electron mobility transistors (HEMT) were fabricated and characterized for hydrogen sensing. Pt and Ti/Al/Ni/Au metals were evaporated to form the Schottky contact and the ohmic contact, respectively. The sensors can be operated in either the field effect transistor (FET) mode or the Schottky diode mode. Current changes and time dependence of the sensors under the FET and diode modes were compared. When the sensor was operated in the FET mode, the sensor can have larger current change of 8 mA, but its sensitivity is only about 0.2. In the diode mode, the current change was very small under the reverse bias but it increased greatly and gradually saturated at 0.8 mA under the forward bias. The sensor had much higher sensitivity when operated in the diode mode than in the FET mode. The oxygen in the air could accelerate the desorption of the hydrogen and the recovery of the sensor. (c) 2007 Elsevier Ltd. All rights reserved.