Failure analysis on abnormal wall thinning of heat-transfer titanium tubes of condensers in nuclear power plant Part II: Erosion and cavitation corrosion

In Part I of the failure analysis on abnormal wall thinning of heat-transfer titanium tubes used in condensers in nuclear power plant, we analyzed the causes and mechanisms of abnormal thinning that commonly happened at the contact part between the tubes and the support plates. This kind of failure was the mainstream failure type in our case and the main causes were found to be eccentric contact wear and three-body contact wear rooted in processing defect of internal borings, corrosion products deposit and sagging, and foreign particles. However, there were still some individual failure tubes with different failure sites and modes and were located under the bypass pipes at the shoulder of the tube tower instead of in its lower part, obviously telling another failure story. In Part II of the failure analysis, material analysis, metallographic examination, mechanical performance tests, macro- and microstructure analysis and composition analysis were conducted. The failure causes were found to be erosion and cavitation corrosion and the synergetic effect of them. Finally, corresponding countermeasures were suggested.     

连续式热压烧结金刚石制品的研究

烧结是决定金刚石制品性能的关键环节。通过对比分析普通电阻式热压烧结工艺和连续式热压烧结工艺所获得的锯片试样,阐述了连续式热压烧结工艺制备金刚石制品的优越性。结果表明:连续式热压烧结工艺能降低产品的气孔率,提高致密度和质量稳定性;改善金属胎体对金刚石的包镶状况;减少烧结过程中的能耗和烟尘,对金刚石制品行业节能减排具有积极推动作用。     

Electrochemical study of the corrosion of different alloys exposed to deaerated 80 °C geothermal brines containing CO2

Corrosion of metallic engineering materials accounts for problems during geothermal operation in the Upper Rhine Graben (URG). Herein, we study the electrochemical behaviour of various metal alloys in an 80 °C simulated geothermal environment by using potentiodynamic polarisation and open-circuit potential measurements. Two different natural geothermal waters from URG geothermal sites were used for the experiments. The measurements reveal spontaneous passivation to be a key process for all alloys. This ennoblement protects more noble alloys from significant corrosion (e.g. titanium gr. 2, alloy 625) and brings less noble alloys to failure, mostly due to pitting corrosion (e.g. 316L).     

Meso-scale numerical investigation on cracking of cover concrete induced by corrosion of reinforcing steel

Concrete cover cracking induced by corrosion of steel reinforcement is a major influencing factor for durability and serviceability of reinforced concrete structures. Here in this study, the influence of concrete meso-structure on the failure pattern of concrete cover is accounted for. The concrete is assumed to be a three-phase composite composed of aggregate, mortar matrix and the interfacial transition zone (ITZ). And a concrete random aggregate structure is established for the study on the mechanical behavior of radial corrosion expansion. In the present simulations, the plasticity damaged model is used to describe the mechanical behavior of the mortar matrix and the ITZ, and it is assumed that the corrosion of steel reinforcement is uniform. The cracking of concrete cover due to steel reinforcement corrosion is numerically simulated. The simulation results have a good agreement with the available test data and they are between the two analytical results. The failure patterns obtained from the macro-scale homogeneous model and the meso-scale heterogeneous model are compared. Furthermore, the influences of ratio of cover thickness and reinforcement diameter (i.e. c/d), the location of the steel reinforcement (i.e., placed at the middle and corner zones) and the concrete tensile strength on the steel corrosion rate when the concrete cover cracks are investigated. Finally, some useful conclusions are drawn.     

Electrode surface treatments in sludge electro-osmosis dewatering

The sewage sludge dewatering produced by wastewater treatment plants (WWTP) is a multifaceted process due to the presence of colloid fractions. Electro-osmosis could be a suitable technique to reduce the water content of the final sludge. Electric fields of 10, 15, and 20?V/cm have been studied for electro-osmosis tests under the pressure of a static or rotating piston, obtaining a dry solids content up to 40–45%, with respect to 25–30% obtained by mechanical methods. In order to optimize the process, the corrosion behavior and the wear of the anodic material appear to be the main critical aspects, due to the high circulating current density and the use of a rotating electrode. We compared the efficiency and the corrosion resistance of dimensionally stable anodes (DSA) with respect to bare stainless steel (AISI 304) and stainless steel coated by PVD technique with TiN, AlTiN, and DLC. Characterization of the anode surfaces by SEM and potentiodynamic tests show that DSA is the most suitable material for our application. However, efficiencies of the electro-osmosis processes have been found comparable, in terms of developed current densities and total energy consumptions, for short-test duration.     

Effect of probe orientation on hot‐film / CTA velocity measurements in stirred tanks and a simplified measuring method

Abstract

To solve the difficulty of selecting the hot‐film probe orientation in velocity measurements in aerated or nonaerated stirred tanks, the effects of probe orientation on mean and rms fluctuating velocity measurements were studied and the feasibility of using substituting simplified measurements was investigated.

Experimental results of velocity measurements inside or outside of the impeller stream in an aerated or nonaerated stirred tank indicated that the directional sensitivity of the hot‐film probe is insignificant due to the vortices in the tank, and three velocity values obtained by placing the probe in the radial, tangential, and axial direction were proportional to the “true” value obtained by the traditional method.

Using a simple model of re‐combination of velocity components and analyzing the data with statistical regression method, good correlation was obtained when three velocity values obtained in radial, tangential, and axial directions or when the first two were consisted in the model, which can therefore be used as reliable and practical substituting methods.     

Laminated aluminum thin-films as low-cost opaque moisture ultra-barriers for flexible organic electronic devices

Flexible aluminum moisture barrier films are shown to meet ultra-barrier requirements with water vapor transmission rates as low as 1*10⁻⁴ g/m²/day at 38 °C and 90% R.H. These low transmission rates are achieved by lamination of two films that are independently processed on individual substrates. The integration in organic electronic devices like organic solar cells or OLEDs is particularly easy in a single lamination step, since an existing aluminum electrode can be utilized as one half of the moisture barrier. The resulting laminate maintains flexibility of the device and improves the barrier quality by an order of magnitude compared to conventional stacking of two barriers. Organic solar cells with this type of encapsulation are manufactured and aged in controlled climate. They do not exhibit significant extrinsic degradation.     

Crack growth model for pipeline steels exposed to near‐neutral pH groundwater

This paper postulates a crack growth model for pipeline steels in near‐neutral pH soil environments, on the basis of the experimental results reported in literature and the fundamental understanding of the corrosion fatigue crack growth dominated by hydrogen embrittlement mechanism. The comparison with the laboratory data indicates that this model can provide reasonable predictions for the dependence of the crack growth rates on the stress intensity factor, stress ratio, loading frequency, solution pH and electrochemical potential.