Most of the water taps for domestic use are made of copper alloys. Their valve seats occasionally suffer damage due to corrosion and erosion as a result of water quality and seemingly cavitation respectively. The examination of damage mechanism and the development of testing methodology for selecting the durable materials to the attack were requested. In order to understand and solve these problems completely, erosion-corrosion tests were carried out on various copper alloys (five brasses and five bronzes) by using three test methods: (a) the ISO 6509 dezincification test for pure corrosion; (b) the vibratory cavitation test with eccentric stationary specimen for cavitation erosion-corrosion; and (c) the Jet-in-Slit test for flow induced localized corrosion. The materials tested were ranked in different orders of merit according to the results obtained in the three test methods. Among these rankings, the one obtained in the Jet-in-Slit test has agreed upon with the ranking order that had been determined by experiences of field engineers who engaged themselves with the troubles under practical conditions. Hence it was concluded that the damage on valve seats has been caused by the flow induced localized corrosion, and the Jet-in-Slit was recommended as the reliable test method in selecting durable valve seat materials.
The effects of potential and sodium sulfate concentration on the initiation and growth of IGSCC of sensitized 304 stainless steel in 0.01-1kmol/m3 sodium sulfate solutions at 368K have been investigated. A slow strain rate test apparatus was used to make direct observations of crack generation and propagation during the test. The initiation and growth of IGSCC were found to occur for potentials from -500mVAg/AgCl to -200mVAg/AgCl and the IGSCC susceptibility reached a maximum at approximately from -400mVAg/AgCl to -300mVAg/AgCl. The initial crack generation time was a minimum around -400mVAg/AgCl and the crack growth rate increased monotonously with increasing potential. Therefore, the SCC test results indicated that the maximum IGSCC susceptibility emerged at approximately from -400mVAg/AgCl to -300mVAg/AgCl, suggesting that the susceptibility of IGSCC must be determined as a function of the synergistic effect of the crack generation frequency and the crack growth rate. The initial crack generation time decreased with increasing sodium sulfate concentration. The crack growth rate was independent of the crack generation time and showed approximately a constant value. The crack generation time were distributed at random. Therefore, it was considered indispensable to evaluate IGSCC resistance of various austenitic stainless steel by statistical methods.
Pinhole defects of TiN coated stainless steels were evaluated electrochemically in deaerated 0.5kmol⋅m-3 H2SO4+0.05kmol⋅m-3 KSCN solution at 298K. The TiN films formed by an activated reactive evapolation method exhibited the columnar structure with ‹111› orientation, which contained more or less pinhole defects. The critical current density for passivation, icrit, in the TiN-coated stainless steels decreased with an increasing film thickness, and the resulting corrosion resistance was improved remarkably by TiN-coating. The area fraction of pinhole defects was evaluated by the ratio of icrit of a coated and a non-coated specimen. Thus, the result coincided well with the ‘true’ area fraction based on the optical micrographs before or after polarized anodically. Consequently, such electrochemical measurement is superior as an evaluation method for the pinhole defects of corrosion-resistible coating.
When stainless steels are immersed in natural sea water, biofilm begins to develop on their surface to make electrode potential (Esp) of the steels ennobled up to approximately 400mV vs. SCE, which enhances possibility of localized corrosion. In this paper, effect of environmental factors on activity of biofilm on the steels in natural sea water was investigated. Firstly, steels were immersed in natural sea water for 14-16 or 30 days from 1991 to 1994 to measure Esp vs. time of steels in various seasons. Attained value of Esp in winter was lower than that in the other seasons. Under conditions where sunlight was allowed to illuminate steels, Esp decreased by about 100mV around noon every day and returned to their stationary ennobled value at night. This effect of sunlight was observed for 316 steels with Esp values more noble than 200mV vs. SCE. Different from sunlight, a fluorescent lamp for cultivating plants made no significant effect for the Esp. Therefore, following experiments were carried out under the condition of turning on the lamp. To study effect of other environmental factors on activity of biofilm, ennobled steels were immersed in abiotic sea water adjusted to various temperatures (5-95°C), pH (2-10), salinities (3-45‰) or applied potentials (-500-300mV vs. SCE). As the next step of experiments, the samples were transfered to abiotic sea water under natural condition and subsequent behavior of Esp was measured to examine whether Esp of them were maintained after these treatments. Ennobled Esp of the steels was not maintained in abiotic sea water adjusted to temperatures higher than 60°C for 24 hours, pH 2 and 3 for 24 hours, salinity of 45‰ for 96 hours or applied potential of -500mV vs. SCE for 5 hours.
Various electric materials applied in computers and peripherals are used under sever atmospheric environment, which is the cause of atmospheric corrosion related with humidity and various additional factors. So, these materials corrode and electric systems take damages such as electric-shorts, electric-disconnection. In this paper, we review some examples related with atmospheric corrosion factors as the effect of air polutant gases, the degases from plastic materials and so on.