Papers by Keyword: Corrosion

Abstract: To research the corrosion of clad pipe weld joint, commenting the welding processes of and analysis of the corrosion medium of clad pipe weld joint, using electrochemical impedance spectroscopy carried out the comparative analysis of Nyquist and bode diagram within the time limit of clad pipe weld joint. The results showed that: 316L/20G clad pipe weld joint in the sewage water up to two weeks, because of the passive film thickening, weld corrosion resistance up to the maximum, and then stabilized; Its resistance is slightly decreased, but still has a good corrosion resistance, therefore, 316L/20G clad pipe can be widely used in the sewage pipelines of oil and gas fields.

Abstract: Corrosion attacks steel buildings mainly when the connections wait for welding on site. In the companion paper, the effects were investigated by a series of weld tests. The results show that the surface rust may increase the level of porosity in steel welds, reducing the strength by 5% on average. This paper made a case study, further investigating the effects together with those of workmanship. The seismic risk of the example building has been assessed and compared in detail for acceptable and marginal quality workmanship. The results obtained from the above studies will help develop more sound strategies in construction management and building renovation.

Abstract: Corrosion attacks steel buildings mainly when the connections wait for welding on site. To investigate the effects, a series of experimental and analytical studies have been carried out. This paper summarizes the main results of the experimental studies. The steel welds with and without rust on the welding surfaces were tested and compared in details. The strength of the weld was found to decrease 5% on average. That’s because the rust raised the level of weld porosity. The results obtained above will be considered together with the effect of workmanship in the companion paper, as to assess the seismic reliability for existing buildings with steel moment frames.

Abstract: Biomass has attracted more and more attention in the world as renewable energy. Biomass direct-fired technology is a relatively mature technology with widely application in China. Due to the high content of alkali metals and chlorine in the biomass fuel, biomass direct-fired power plant suffers from ash-deposition and corrosion problems of low-temperature heating surface in boiler, accordingly impact the security and economy of boiler. Based on the literature survey, on-site detection, as well as EDXRF experimental analysis, reasons which resulted in ash-depostion and corrosion problems of air preheater are analyzed for 2×50MW CFB (Circulating Fluidized Bed) boilers in Zhanjiang Biomass Direct-fired Power Plant by Guangdong Yudean Group. Suggestive measures to prevent ash-depostion and corrosion are also proposed in this paper by the analysis of biomass combustion characteristics, ash-depostion and corrosion formation mechanism.

Abstract: The influence of yttrium on the corrosion resistance of four valve steels (X33CrNiMn23-8, X50CrMnNiNbN21-9, X53CrMnNiN20-8 and X55CrMnNiN20-8) in combustion gases of fuel oil containing 10 wt. % of biocomponents has been studied at 1173 K under thermal shock conditions. These experiments have been carried out by rapid heating of the studied materials up to 1173 K and after two hours cooling down to room temperature. These thermal shocks have been repeated hundreds of times, determining after every shock the mass changes of the corroded samples. It has been found that small amount of yttrium deposited on the steel surface using electrochemical treatment considerably improves the scale adherence and consequently corrosion resistance in the case of X33CrNiMn23-8 steel, containing the highest chromium concentration.

Abstract: Electroless Ni-P plating on Mg-7Al alloy by chemical conversion pretreatment was investigated. Morphology of electroless nickel plating coatings and phase compositions were measured by SEM, EDX and XRD. The optimized bath composition parameters were determined through orthogonal design. The morphology of electroless nickel plating coatings on Mg-7Al alloy exhibits a nodular structure and resembles the surface of a cauliflower and the coating is compact and consists of amorphous Ni-P coating. Potentiodynamic polarization curves of the Ni-P coatings in 3.5% NaCl show that the Ni-P coating extensively improves the corrosion resistance of Mg-7Al alloy and the highest corrosion potential reached to -0.54V vs. SCE(saturated calomel electrode). The results of the orthogonal experiment show that Nickel Sulfate of 25 g/L, Sodium Hypopho-sphate of 25 g/L and Citrate 7.5 g/L can be considered as the optimum bath content parameters for electroless Ni–P plating on Mg-7Al alloy and Nickel Sulfate has more effect on corrosion potential than Sodium Hypophosphate and Citrate..

Abstract: The effect of aging on the corrosion property of Al-7Si-0.3Mg Alloy immersed in 3.5% NaCl solution was studied by Tafel polarization curves and corrosion weight loss measurement in this paper. The Vickers hardness of the alloy during aging was measured on Zwick hardness testing machine. The electrochemical behavior of the Al-7Si-0.3Mg alloys after the under aged, peak aged and over aged were analyzed, respectively. The results show that the hardness of the alloy increases at first with the increasing of aging time and gets to the maximum at 4 hour, and descends gradually with the aging time (over aged). Icorr under peak aged status get to the highest value and to the lowest one during under aged status. Correspondingly, corrosion properties under peak aged status are the worst case and the best with under aged status.

Abstract: The present work deals with the formation of Ni-B-W coating on steel by electroless plating process and evaluation of their corrosion resistance after applying heat treatments at different temperatures for 1 h. The Ni-B-W coating was prepared using alkaline borohydride- reduced electroless nickel bath. Scanning electron microscopy of the surface cross-sectional view of the electroless Ni-B-W coating was analyzed and layer characteristics was investigated. Coating structure was investigated using XRD. The study reveals that the Ni-B-W coating is amorphous in their as-plated condition and upon heat treatment at 400 0C for 1 h, Ni-B-W coating crystallize and produce nickel and nickel borides in the coatings. Annealing temperature dependence of the corrosion resistance of the coating was investigated by potentiodynamic polarisation measurements. These results show that the Ni–B-W coating annealed at 650 0C exhibit better corrosion resistance than those of coatings with other annealing temperature. The corrosion resistance increased after the crystallisation of the coating, due to factors like; decrease of porosity and internal stress and the formation of tungsten oxide on the surface acting as a protective layer.

Abstract: The durability of a concrete structure is most significantly influenced by the corrosion of reinforcing bars, rather than by the deterioration of concrete itself. The corrosion of reinforcement bars due to chloride serves as a main deterioration factor at the interface between the bars and the concrete in the concrete structure. Accordingly, the corrosion inhibitors are widely used to improve the resistance to chloride penetration into reinforced concrete. Corrosion inhibitors are generally divided into the anode-type inorganic inhibitors and anode-cathode-type organic inhibitors, in terms of the reaction type. It is known that when the Cl-:OH- concentration ratio exceeds 0.6%, film on passive state metal on the bar-concrete interface is damaged and local corrosion starts regardless of the chloride ion content. In this study, the performance of the corrosion inhibitor was examined using a potentiostat, with chloride ion contents of 1.2kg/m3 (as reference), 2.4kg/m3, and 4.8kg/m3. The variables were the inhibitor type, Cl-:OH- molar ratio according to the addition of anode-type inorganic corrosion inhibitor (four ratios: 0.0%, 0.3%, 0.6% and 1.2%), and ratio compared to the standard anode-cathode-type organic corrosion inhibitor liquid (four ratios: 0.0, norm 1/2, norm, norm 2 times). As a result, with the anode-type inorganic nitrite corrosion inhibitor, the corrosion inhibition performance was verified with a corrosion potential of -0.30V at a molar ratio of 0.3% or higher when the chloride ion content was 1.2kg/m3, and at a molar ratio of 0.6% or higher when the chloride ion content was 2.4kg/m3 or 4.8kg/m3. With the anode-cathode-type organic corrosion inhibitor, the corrosion inhibition performance was very good at half the standard quantity (0.42kg/m3) regardless of the chloride ion content. From the added corrosion inhibitor quantities, the anode-cathode-type organic corrosion inhibitor had a better corrosion inhibition performance than the anode-type inorganic nitrite corrosion inhibitor.

Abstract: This work use the D-gun system to spray the WC-17Co coating. analyzed the microstructure and performance of the coating by SEM, EDAX, XRD, HAXD. It gave a basis for the next research work for the anti-wear coating on aluminum alloy. The hardness of the WC-17Co coating is about HV1100~1300, the average porosity less than 1%. And the max diameter of the single hole is less than 0.012mm. There are no apparent oxide in the coating. The WC particles occurred decarburization during the spraying process and deposited the coating that composed with W2C and Co3W3C phases. The corrosion resistance of the coating is more ideal. But the phase distribution in the coating is not enough uniform.