Salt spray corrosion test of micro-plasma oxidation ceramic coatings on Ti alloy

Ceramic coatings were prepared on Ti-6Al-4V alloy in NaAlO2 solution by micro-plasma oxidation （MPO）. The salt spray tests of the coated samples and the substrates were carded out in a salt spray test machine. The phase composition and surface morphology of the coatings were investigated by XRD and SEAM. Severe corrosion occurred on the substrate surface, while there were no obvious corrosion phenomena on the coated samples. The coatings were composed of Al2TiO5 and a little α-Al2O3 and mille TiO2, and the salt spray test did not change the composition of the coatings. The weight loss rate of the coatings decreased with increasing MPO time because of the increase in density and thickness of the coatings. The surface morphology of the coatings was influenced by salt spray corrosion test. Among the coated samples, the coating prepared for 2 h has the best corrosion resistance under salt spray test.

Evaluation of Expansion Process to Improve Corrosion Resistance of Copper Tubes with High Residual Carbon on the Inner Surface

Residual carbon on the inner surface of copper tubes is known to be a cause of pitting corrosion. We showed previously that the rapid filling test was useful to evaluate the pitting corrosion resistance of copper tubes. Immersion tests using the rapid evaluation test solution showed that corrosion occurs on the entire surface of copper tubes with low residual carbon amounts, while those with high residual carbon amounts show pitting corrosion. Therefore, it is necessary to improve the corrosion resistance of copper tubes with high residual carbon amount, which are expected to undergo pitting corrosion. As pitting corrosion occurs when anodes are locally concentrated on part of the metal surface, it has been suggested that anodes be dispersed over the entire surface by the processing of the metal surface. Metal processing methods have various purposes, including changing the shape and properties of metals, and in this case, leading to desirable surface properties (such as expansion and drawing processes). Here, we focused on the expansion process and its effects on corrosion resistance of copper tubes. The results showed that hydraulic expansion has a significant effect on the inner copper surface by improving corrosion resistance as the anode area increases.

Effect of nonmetallic inclusions on localized corrosion of spring steel

Certain inclusions in high-strength 60Si2Mn-Cr spring steel result in poor resistance to localized corrosion.In this work,to study the effect of inclusions on the localized corrosion behavior of spring steel,accelerated corrosion tests were performed by immersing spring steel in 3wt%FeCl_(3)solution for different times.The results show that severe corrosion occurred in areas of clustered CaS inclusions.Sulfide inclusions containing Ca and Mg induced the strongest localized corrosion susceptibility.For the case of(Ca,Mn,Mg)S inclusions,the ability to induce localized corrosion susceptibility is ranked as follows:MgS>CaS>MnS.Moreover,CaS,(Ca,Mn)S,and(Ca,Mn,Mg)S inclusions were mainly responsible for inducing environmental embrittlement.

Laboratory and field testing of bolting systems subjected to highly corrosive environments

The capacity of ground support components which have been affected by corrosion is reduced and may ultimately lead to dynamic failure of the component and the strata. In order to maintain an effective,long-term ground support system, significant campaigns of rehabilitation are often required in corrosion affected areas which also expose the workers to hazardous conditions. The most common corrosion protection for steel ground support utilises sacrificial systems such as galvanising. Galvanising has previously been proven to be susceptible to some corrosion processes. Stainless steel is the most effective in resistance to corrosion, but can be cost prohibitive, and its mechanical properties often make it unsuited to use in ground support components. Providing an outer protective plastic coating to bolts has proven to be an effective means of protecting the inner steel bar from corrosion. However, these support systems tend to be susceptible to coating damage, and require post cement grouting to provide full encapsulation. In comparison to a standard bolt/resin system, they can be slow to install and expensive.These systems have also been shown to reduce overall load transfer performance of the bolting system. In order to provide a higher level of corrosion protection whilst maintaining current installation practices and bolting cycle times, Minova has developed the Enduro^(TM)steel ground support range. The Enduro^(TM) range consists of standard Minova steel ground support components which have been treated with a unique coating process. The Enduro^(TM)coating has been tested in the harshest of conditions, in laboratory controlled conditions and in underground trials. It has been proven to effectively resist or completely eliminate the formation of corrosion, even in the most aggressive environments. This paper explains the process and provides the details of the laboratory and underground corrosion performance testing carried out on Enduro^(TM)ground support products.

Composites Based on GM(1,1)-Markov in the Salt Spray Corrosion Environment

This study was designed to solve the problem of magnesium hazards due to potash extraction in the salt lake region.Using basalt fiber(BF)as the reinforcement material and magnesium oxychloride cement(MOC)as the gelling material,a BF/MOC composite material was prepared.Firstly,the effect of BF addition content on the basic mechanical properties of the composites was investigated.Then,through the salt spray corrosion test,the durability damage deterioration evaluation analysis was carried out from both macroscopic and microscopic aspects using mass change,relative dynamic modulus of elasticity(RDME)change,SEM analysis and FT-IR analysis.Finally,a GM(1,1)-Markov model was established to predict the durability life of composite materials by using durability evaluation indicators.The results show that:when the BF content is 0.10%(by volumetric content),the composites have the best mechanical properties and resistance to salt spray corrosion.However,when the volume of BF content exceeds 0.10%,a large number of magnesium salt crystallization products are observed from the microscopic point of view,and the corrosion of the main strength phase of MOC is more serious.The prediction results of the GM(1,1)-Markov model are highly identical with the raw data.In addition,using the change of RDME as a predictor,RDME is more sensitive to environmental factor compared to the change of mass.Predictions using the change of RDME as a threshold indicate that MOC-BF0.10 has the longest durability life,which is 836 days.The model is important to promote the application of MOC composites in the salt lake region and to promote the healthy development of green building materials.

Galvanic Corrosion of Magnesium Alloy and Aluminum Alloy by Kelvin Probe

Galvanic corrosion on samples of AZ91D magnesium alloy coupled with 2A12 aluminum alloy during neutral salt spray test was investigated.The variations of the surface potential were measured using scanning kelvin probe（SKP）.The results showed that galvanic effect on the corrosion of AZ91D magnesium alloy is closely related to the potential difference between the anodic and cathodic materials.In the initial period,corrosion only occurred in a narrow area at the coupling interface because of the limited distance galvanic current.Then,the corrosion rate of 2A12 aluminum alloy was accelerated due to its poor stability in strong alkali environment,which was attributed to the strong alkalization caused by the corrosion of AZ91D magnesium alloy.With the increase of the potential of 2A12 aluminum alloy as a result of the continuous covering of corrosion products,the potential difference between the two materials was enlarged,which enhanced the galvanic corrosion.

Relationship between Corrosion Form and Elution Behavior of Copper Tubes Surfaces with Different Residual Carbon Amounts

It was well known that residual carbon on the inner surface of copper tubes was a cause of pitting corrosion, and copper tube surfaces with different residual carbon amount were different corrosion forms. In this study, the relation between corrosion form and elution of copper in immersion tests by accelerated corrosion test solutions was examined. Generally, pitting corrosion that occurs in actual machines was reported to observe chloride ion at the bottom of the pitting corrosion of copper tubes. Energy dispersive X-ray (EDX) mapping analysis indicated that chlorine was concentrated in the upper layer of the samples where copper was not detected under conditions of low residual carbon amount, while chlorine was concentrated under part of the micromounds (including the bottom of the pits) under conditions of high residual carbon amount. It was also suggested that the amount of copper eluted was related to the amount of residual carbon.

Electrochemical corrosion failure mechanism of M152 steel under a salt-spray environment

The corrosion failure mechanism of M152 was studied using the neutral salt-spray test to better understand the corrosion behavior of 1Cr12Ni3Mo2VN（M152）, provide a basis for the optimization of material selection, and prevent the occurrence of failure. Moreover, the mechanism was investigated using the mass loss method, polarization curves, electrochemical impedance spectroscopy（EIS）, stereology microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy（EDS）. The results show that M152 steel suffers severe corrosion, especially pitting corrosion, in a high-salt-spray environment. In the early stage of the experiment, the color of the corrosion products was mainly orange. The products then gradually evolved into a dense, brown substance, which coincided with a decrease of corrosion rate. Correspondingly, the EIS spectrum of M152 in the late test also exhibited three time constants and presented Warburg impedance at low frequencies.

Effects of Strain Rate on Stress Corrosion of S355 Steel in 3.5% NaCl Solutions

The stress corrosion of S355 steel in 3.5% NaCl solution under the different strain rates was analyzed with the slow strain rate test（SSRT）, the stress corrosion cracking（SCC） behaviors of S355 steel under the different strain rates in the solution were investigated, and the fracture morphologies and compositions of corrosion products under the different strain rates were analyzed with scanning electron microscopy（SEM） and energy dispersive spectrometerry（EDS）, respectively. The experimental results show that the SCC sensitivity index is the highest when the strain rate is 2×10-6, and the medium corrosion is the main reason resulting in the highest SCC sensitivity index. The SCC sensitivity index is the least when the strain rate is 5×10-6, and the stress is the main reason resulting in the stress corrosion. The SCC sensitivity index is the middle when the strain rate is 9×10-6, the interaction of stress and medium is the stress corrosion fracture mechanism.

湘中溶蚀丘陵区示踪试验——以湖南新化为例

二叠系茅口组灰岩以亮晶颗粒灰岩、泥晶颗粒灰岩和颗粒泥晶灰岩为骨架 ,裂隙溶洞为含水空间的介质类型 ,在以湘中为中心的溶蚀丘陵区普遍存在 ,湖南新化大树——华山一带具有典型代表性。两次示踪试验表明 ,雨季的岩溶水流速快 ,滞后时间和延续时间短 ,而旱季正好相反 ,这是茅口组灰岩岩溶发育和岩溶水特征的反映。近南北向展布的茅口组灰岩东西两侧完整的隔水边界和谷间地块分水岭的存在 ,使每个谷地都具有完整的补径排体系 ,从而形成多个小型岩溶水系统。如果在这些岩溶谷地中修坝建库 ,只要坝址座落于龙潭组砂岩之上 。

Durability problems of lining structures for Xiamen Xiang'an subsea tunnel in China

Durability problem of reinforced concrete for underground structures is a hot issue in the field of structural engineering. For underground structures, the prediction of structural service life and methodology for durability design are needed to estimate structural durability. Taking the case of Xiamen Xiang＇an subsea tunnel as background, which is designed to meet the requirement of lO0-year service life, the influential factors on tunnel lining durability are analyzed. Under the criteria of crack controlling and bearing capacity of linin~ structures, the theoretical service life of Xiamen Xiang＇an subsea tunnel lining is studied. The regulations, which are needed for the diffusion capability of chloride ions in concrete by the relevant diffusion tests, are proposed. After a quick corrosion test, the bearing capacity test on eccentric short columns is implemented to investigate the variation rules in the bearing capacity of models with time. Influence of the corrosion degree of steel bars on the bearing capacity of models is also investigated. Based on the results of model tests, the acceleration ratio between the quick corrosion in laboratory test and the natural corrosion environments is established. Thus, the natural service life of subsea tunnel lining structures can be obtained by means of laboratory tests. Then, the proposed method using this modified model is employed to predict the service life of tunnel lining structures. Finally, the design and construction measures for improving the durability of lining structures of subsea tunnel are introduced. The proposed method in the present study based on a real engineering project is superior to those with only theoretical assumptions, and would be more suitable for similar projects.

Comparison between FAC Analysis Result Using ToSPACE &CHECWORKS Programs and Experimental Result

A number of piping components in the secondary system of nuclear power plants (NPPs) have been exposed to aging mechanisms such as FAC (Flow-Accelerated Corrosion), cavitation, flashing, LDIE (Liquid Droplet Impingement Erosion), and SPE (Solid Particle Erosion). Those mechanisms may lead to thinning, leaking, or the rupture of components. Due to the pipe ruptures caused by wall thinning of Surry Unit 2 in 1986 and Mihama Unit 3 in 2004, pipe wall thinning management has emerged as one of the most important issues in the nuclear industry. To manage the wall thinning of pipes caused by FAC and erosion, KEPCO-E & C has developed ToSPACE program. It can predict both FAC & erosion phenomena, and also be utilized in the pipe wall thinning management works such as susceptibility analysis, UT (Ultrasonic Test) data evaluation as well as establishment of long-term inspection plan. Even though the ToSPACE can predict the five aging mechanisms mentioned above, only the FAC prediction result using ToSPACE was compared herein with the experimental result using FACTS (Flow Accelerated Corrosion Test System) to verify the ToSPACE’s capability. In addition, the FAC prediction result using ToSPACE was also compared with that of CHECWORKS that is widely used all over the world.

Corrosion Behavior of S450EW Low-alloy Weathering Steel in Cyclically Alternate Corrosion Environments

Weathering steel is widely used in various fields due to its excellent mechanical properties and high corrosion resistance. The effect of chromium content on the S450 EW weathering steel in cyclic immersion test was studied. The results indicated that the corrosion resistance of S450 EW weathering steel is closely related to chromium content. The addition of chromium significantly inhibited the weathering steel corrosion. The corrosion rate of experimental steel after 96 h immersion was 1.101 g·m-2·h-1. The rust of S450 EW weathering steel was mainly constituted of Fe OOH and Fe3O4 phase, and the elevation of chromium content promoted the formation of α-Fe OOH. The fine precipitates of the two phases contributed to the formation of dense dust layer of test steel. Furthermore, the increase of chromium is beneficial for the cure of original defects and cracks of the rust layer via the enrichment of chromium. The corrosion potential and the resistance of corrosion process were thus increased, protecting the experimental steel from further corrosion. A S450 EW steel with corrosion resistance more than 1.5 times of Q450NQR1 steel was prepared.

Evaluating the environmental impact of selected chemical de-icers

In this study,the environmental impacts of six commercial chloride-based de-icer products,including Rock Salt and Salt Brine,were evaluated.The nutrients,oxygen demand,heavy metal concentration,corrosion and toxicity of all six de-icers were analysed.With an assumed 500-fold dilution,the test results were compared to the public water-quality criteria.The results show that the selected chemical de-icers have little chance of severely damaging the environment and ecosystem under a normal dilution scenario.However,attention needs to be paid to small water bodies and sensitive receiving water.

Tribological Properties of a Dendrite-reinforced Ti-based Metallic Glass Matrix Composite under Different Conditions

The tribological properties of the in-situ dendrite-reinforced metallic glass matrix composite（Ti42Zr22V14-Cu5Be17）prepared by copper mould casting were analyzed at different normal loads under the dry condition and rainwater.The results showed that the average value of the frictional coefficients and micro-hardness ascended with increasing the normal load,while the wear rate showed a trend of decline under the dry condition.The electrochemical test results showed that the surface of samples was pitting corroded in the rainwater.The matrices were corroded first.Then the dendrites were exposed,leading to the damage of the surface.Both the frictional coefficients and wear rate of the composite in the rainwater were larger than those under the dry condition,primarily owing to the corrosion of chloride ions on the worn surface.The wear mechanisms of composites were mainly adhesive wear,accompanied by the abrasive wear under the dry condition and corrosive wear in the rainwater.The composites have higher wear resistance both under the dry condition and rainwater due to the lower wear rate.