Corrosion failure analysis of hearing aid battery-spring contacts

Reliability of low power electrical contacts such as those in hearing aid battery-spring systems is a very critical aspect for the overall performance of the device. These systems are exposed to certain harsh environments like high humidity and elevated temperatures, and often in combination with high levels of salt from human perspiration and environmental pollutants. In addition, the design aspects of such systems often call for multi-material combinations of substrate and coatings for catering to various requirements such as electrical conductivity and wear resistance, which in turn enhance the susceptibility of these systems to galvanic corrosion. In this study, traditional behind-the-ear (BTE) hearing aid systems, which failed during service were analysed. Failure analysis was performed on the dome type battery-spring contact systems. The morphology of the contact areas was observed using scanning electron microscopy, and the compositional analysis of the corrosion products and contaminants was performed using energy dispersive X-ray spectroscopy. Wear track morphology was observed on the contact points, and the top coating on the dome was worn out exposing the substrate spring material. The obtained results were correlated to the underlying corrosion mechanism and the failure mode is presented.     

Synthesis and photocatalytic studies of TiO2-clinoptilolite on spent caustic wastewater treatment

Mixed spent caustic is an industrial wastewater that is generated from oil refineries and olefin units. In this investigation, the TiO₂ film was loaded with Clinoptilolite for preparing TiO₂-clinoptilolite photocatalyst. In order to characterize the surface of composite and its microstructure, scanning electron microscopy (SEM) and powder x-ray diffraction (XRD) have been used. Subsequently, this photocatalyst is utilized for the degradation of spent caustic wastewater to determine the photocatalytic efficiency of TiO₂-clinophotocatalyst. Then the photocatalytic degradation of chemical oxygen demand (COD) in spent caustic wastewater has been modeled using the design of experiment method. This procedure was performed in two ways: in the presence of an oxidant agent (H₂O₂) and by minimizing the amount of oxidant. The results show that the maximum degradation efficiency of TiO₂-clinophotocatalyst is 74.3% and 77.3% under the condition of applying limitation and without concerning limitation for the presence of oxidant, respectively.     

多元微通道换热器腐蚀失效分析及预防

对多元微通道换热器的腐蚀进行微观泄漏机制的调查和分析,并使用乙酸盐雾试验（CASS试验）再现腐蚀情况。通过大量的腐蚀再现试验,发现微通道的结构、组成材料间的实际腐蚀电位差以及NOCOLOK（无腐蚀不溶性钎剂）钎焊时的工艺参数对腐蚀试验结果有显著的影响。通过合理调节以上参数,可保证足够的腐蚀裕度。     

Preventing failure in spent nuclear fuel canisters

A spent nuclear fuel canister has been developed with the goal of no containment failure even during accidental drop conditions. This canister was designed to be loaded with U.S. Department of Energy spent nuclear fuel and then used for interim storage, transportation to the nation’s repository, and final disposal at the repository. The design required a high degree of confidence against failure if the canister were subjected to loads (e.g., accidental drop events) resulting in large plastic deformations and high strains. Significant testing of the canister clearly demonstrates that it can safely achieve the intended design goals without failure. The canister skirt and its attachment to the containment boundary are the key engineered elements of the design that allow significant impact damage without failure of the containment. A combination of analytical techniques and physical testing was used to develop and demonstrate the viability of the design. Finite element modeling coupled with scaled drop tests established the design prototype. To validate the design concept, nine full-scale test canisters were fabricated and dropped from various heights and orientations. The nine test canisters experienced varying degrees of damage to their skirts, lifting rings, and containment boundary components. However, all of the tested canisters maintained the containment boundary as evidenced through the results of pressure and selective helium leak testing. Pre- and post-drop finite element analyses were also performed. The analytical results provide accurate predictions of canister responses to the drop tests. The results achieved for the canister can also be applicable to other well-designed containers (canisters, casks, cans, vessels, etc.) subjected to similar loads. Properly designed containers can maintain containment after experiencing dynamically induced high strains, and computer analyses can accurately predict the response of these containers to dynamic loads.     

Corrosion in water supply pipe stainless steel 304 and a supply line of helium in stainless steel 316

A corrosion spreading throughout the 304 stainless steel tubing of a water system to supply various buildings was observed, and also leaks were detected in welding zones. The same place is also crossed by a gas distribution network, with a helium pipe 316 of stainless steel that required periodic repairs more or less every two years, due to the presence of leaks. The tests showed that both types of stainless steel have suffered localized corrosion induced by hypochlorite ion, in a mechanism of dry/wet, and that the welding procedure performed on the 304 stainless steel is unacceptable. Some immediate procedures were undertaken to keep systems running, but recommendations were given for a final resolution of the problems.     

芦笋罐头容器材料内壁腐蚀失效分析

文章对马口铁芦笋罐头容器的腐蚀失效进行了分析和研究。     

Corrosion failure analysis of stainless steel components for maleic anhydride plant

Failures of a flowmeter floater and a spherical valve installed at a pipe transporting maleic acid aqueous solution in a maleic anhydride plant were investigated by means of macroscopic and microscopic examinations, chemical composition analysis, and weight loss tests. The investigation results indicated that the components were made of AISI type 316L stainless steel. The damages of both the floater and the inner surface of the valve were caused by an extensive erosion–corrosion in maleic acid aqueous solution contaminated with sulphuric acid and chlorides, which originated from the feed blending coking benzene and the recycled process water, while that of the back surface of the floater as well as the outer surface of the valve was induced by general and pitting corrosion as a result of formation of a stagnation zone where the acidic chloride-containing solution collected. It was recommended to use a dechlorination device by resin adsorption technique for reducing the content of chloride ions in the maleic acid aqueous solution.     

空调制冷铜管腐蚀失效分析

制冷空调换热器铜管在经过一段时间使用后发生点蚀并引起泄漏。对铜管内外壁腐蚀局部区域使用光学显微镜(OM)、扫描电镜(SEM)进行表面形貌观察,并借助能谱仪(EDS)进行元素成分分析。发现在铜管内壁发生腐蚀的局部区域存在一定量的Cl元素,而在铜管外壁却没有发现Cl元素。由于中央空调循环冷却水使用未处理的生水,而自来水中含有的Cl元素常会引起点蚀发生。Cl~-会破坏氧化物保护层形成易溶于水且不稳定的氯化物,氯化物分解提高局部酸性值,加快金属腐蚀。同时Cu~+、Cu~(2+)通过扩散发生复杂的自催化反应,导致铜管发生点蚀。     

Microscopy of failure mechanisms in filament-wound pipe

Filament-wound pipes pressurized in one of two modes, to give biaxial or uniaxial stress conditions, have been examined using standard microscopic techniques. Whitening of the pipes which develops during testing has been correlated with different types of cracking. A mechanism for weepage in filament wound pipes by the crossing of transverse cracks in adjacent laminae is described. The types of crack present in the pipe at loads up to final failure were found to be consistent with predictions of the stresses acting in the pipe walls.     

Corrosion failure analysis of 20CrMnTi gear in gearbox after oil pressure test

The causes of corrosion failure of 20CrMnTi rusted gear were analyzed by quantitative analysis of the composition, observation of the microstructure, hardness test and electrochemical test. The microstructure characterization showed that the proportion of retained austenite in the rusted gear was slightly higher and the length-width ratio of martensite on the surface of addendum of rusted gear was slightly larger than that of the normal gear. However, the corrosion resistance of the rusted gear surface was similar to that of the normal gear. The lubricating oil of the gear was detected to contain water molecules. Further investigation showed that continuous rainy days during the period from installation to disassembly led to a relatively high humidity environment and also the block cover was not installed at that time. Therefore, the corrosive medium continuously entered the gearbox through the block cover hole and destroyed the protection of lubricating oil film, resulting in serious erosion of the gear near the block cover hole. After securing the problem, the block cover was kept installed all the time and no such corrosion failure occurred again.     

Corrosion failure analysis of high strength grade super 13Cr-110 tubing string

The main reasons for corrosion failure of super 13Cr-110 tubing and couplings have been proposed based on the analysis techniques of Optical Microscopy (OM), Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS) and X-ray Diffraction (XRD). The results show that the composition, structure and mechanical properties of the tubing and the coupling were all in accordance with the corresponding parameter requirements of API Spec 5CT standards. Furthermore, corrosion occurring in the inner wall of joint was caused by the combined impacts of CO₂ corrosion, acid corrosion, erosion corrosion, and crevice corrosion, meanwhile, the synergistic effects of crevice corrosion, and sulfate-reducing bacteria (SRB) corrosion resulted in corrosion occurring in the outer wall of the tubing and the coupling. Finally, to check the quality of the tubing string before well completion, increase torque, install a centralizer, and add bactericide and inhibitor were advised to prevent the types of corrosion failure from taking place.     

Evaluation of an unusual superheated steam pipe failure

An examination has been made of a steam generator outlet pipe that failed locally after some 100,000 h of operation. Failure took place by cracking along preferentially formed lines (or planes) of graphite nodules. Grain boundary decohesion and void formation ahead of the crack tips were very local in nature, voids being formed very close to the propagating cracks only. The graphitization is concluded to have occurred locally because of inhomogeneity in carbon content.     

Corrosion failure analysis of printed circuit boards exposed to H2S-containing humid environments

The corrosion failure of a printed circuit board (PCB) with electroless nickel/immersion gold (ENIG) surface finish in a hydrogen sulfide-containing humid environment was analyzed in this work. To establish a comprehensive mechanism for the damage, the exposed surfaces were characterized by visual inspection, scanning electron microscopy/energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. It was realized that merely copper traces under the edge of soldermasks (on electrical junctions) suffer a galvanic-type corrosion reaction with hydrogen sulfide and moisture adsorbed, forming dominantly copper sulfides and a small amount of copper sulfate and oxide. The creep of the corrosion products on the surfaces of ENIG-plated layers, tin-based solders and adjacent soldermasked areas was also found to be responsible for creating short circuits on the outer layers of the miniaturized PCB.     

Corrosion induced fatigue failure of railway wheels

Two AAR class B rolled wheels for locomotives failed after about two years of service. The fracture surfaces of the failed railway wheels were examined. The examination showed that there were corrosion pits on the back plate surface of the failed wheels. All of the fracture originated from corrosion pits at the wheel plate surface and fatigue propagated to a length and then expanded rapidly by cleavage. Fatigue specimens cut from the wheel plate were corroded with different time duration in an artificial corrosion environment to simulate the corrosion states of the wheels. The fatigue properties of the un-corroded specimens and the specimens corroded with different times were tested in air. Finite element method (FEM) and Sines' criterion were used to evaluate the safety of the wheels. The results showed that the wheel plates without corrosion pits exhibited an excellent resistance to failure. The corrosion pits could promote the initiation of fatigue cracks and drastically lower the fatigue limits of corroded specimens. The real root cause of the failure of the subject wheels was due to the corrosion pits at the wheel plate surfaces. A critical depth of the corrosion pit on the wheel plate 300 μm was recommended. Protection of the wheel plate was important to ensure the safety of wheels and the rust prevention oil was recommended to be applied on the wheel plate regularly.     

Metallurgical analysis of failed SS 304 bolts used in flanged joints of a liquid oxidiser pipe line

Austenitic stainless steel (AISI 304 grade) bolts in flanged joints of a fuel and oxidizer pipeline have been found cracked after 4 years in service. The failed bolts have been studied through standard metallographic techniques to analyse the cause of the failure. Deposits on the bolts were analysed using ion chromatographic techniques. The study revealed corrosive attack from the oxidizing agents, which caused grain dissolution under the stress existing in the assembled bolts.     

乏燃料贮存格架在组件跌落事故中的冲击分析

为解决乏燃料贮存格架在组件跌落事故中的冲击分析问题,对ANSYSLS-DYNA程序在弹塑性条件下的冲击分析功能进行开发,并运用于300 MW压水堆核电厂乏燃料贮存格架受乏燃料组件撞击的仿真分析中,采用应变失效和变形失效的方法对乏燃料贮存格架进行安全评定,证明现有的设计满足安全要求。所应用的弹塑性冲击分析方法,以及对乏燃料贮存格架评定的方法同样适用于其它核电设备。     

Corrosion failure analysis of pure nickel thermocouple sheath used in BaTiO3 hydrothermal synthesis reactor

This paper presents corrosion failure analysis on a commercial pure nickel thermocouple sheath used in BaTiO₃ hydrothermal synthesis reactor. Detailed investigations of the corrosion products have been performed using stereomicroscope, X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. It was found that the corrosion failure of the sheath was mainly due to general corrosion and crevice corrosion of pure nickel, and the main corrosion products were Ni(OH)₂. Many cracks were observed inside the corrosion products and along the interfaces between the corrosion products and metal matrix. BaTiO₃ particles were deposited as parallel white bands along the above cracks inside the corrosion products. Chloride ions also entered the cracks or crevices, resulting in the acidification inside the crevice and aggravated the attack of nickel matrix. Some recommendations to prevent/minimize future similar corrosion failures were proposed.