Corrosion features testing

Corrosion fatigue tests under a controlled potential have been conducted in the passive region at the rest potential of the duplex alloy (Eq=- 2Q raVsce) d at a more anodic potential ( anod.=+150 mVsc ) for a given strain rate e=10 s . This strain rate has been chosen because it corresponds to the more marked corrosion fatigue life reduction at both applied potentials. The Coffin-Manson curves under such conditions are given in Fig. 5-36. The following features can be observed ... 

The rich literature on the corrosion of Ni-Cr-Mo alloys in GCR helium is briefly reviewed. Then, we report our preliminary results on the exposure tests of Haynes 230 in GCR representative conditions and we compare resistance of this material to the corrosion features of some reference Ni-Cr-Mo alloys. 

Cinders and acid peaty soils are obviously among the soils most corrosive toward copper. There is, however, no direct relationship between the rate of corrosion and any single feature of the soil composition or constitution". For instance, in the American tests corrosion in several soils with either low pH or high conductivity was not particularly severe, while the British tests show that high chloride or sulphate contents are not necessarily harmful. 

For additional information on some of the features of the salt spray test and its limitations in respect of certain of the purposes for which it may be used, reference should be made to the book Corrosion Testing for Meta Finishing prepared by the Institute of Metal Finishing. 

A feature of corrosion studies which has been stressed recently (2) is the complete failure of laboratory tests on their own to predict how reliable operation of some nuclear steam generators can be maintained. At least a part of this problem is likely to arise from different redox and/or pH conditions imposed by the solution in autoclave tests and in plant conditions and many low level contaminants could be involved. In view of what has been said earlier concerning the role of Mo(VI) in stagnant water it is clear that some data, at least on the thermodynamics of aqueous Mo species, should be sought at high temperatures. 

Some attractive features of radiography are access to interior difficult-to-reach portion, such as valves and pipes, the objects or sample covered with insulation can be tested, reference radiographs can be accessed, the nature and severity of the attack can be assessed with ease, in principle, pit depths can be obtained although laser profilometry is the preferred method in this regard. The main drawback of the method is the whole sample needs to be exposed. Some applications of the method are determination of flaws in weldments and castings to identify sites of initiation of crevice corrosion, valve... 

As in the case of corrosion failures, the sequence of steps involved in analyzing wear failures are initial examination of the failed component including service conditions to establish the mode or combination of modes of wear failure, metallographic examination to check if the microstructure of the worn part met the specification, both in the base material and in the hardened case or applied surface coatings, existence of localized phase transformations, shear or cold worked surfaces, macroscopic and microscopic hardness testing to determine the proper heat treatment, X-ray and electron diffraction analysis to determine the composition of abrasives, wear debris, surface elements and microstructural features such as retained austenite, chemical analysis of wear debris surface films and physical properties such as viscosity and infrared spectral determination of the integrity of lubricants and abrasive characteristics of soils or minerals in the cases of wear failures of tillage tools. 

The simultaneous multielement capability and low detection limits of an ICAP facilitates the analysis of mass-limited samples. Kniseley et al. (9) discussed this advantage with respect to small sample volumes of blood and serum. This feature was indispensable in the analysis of all specimens of human origin. Other areas where limited sample masses have been analyzed relate to materials testing, air particulates, and corrosion testing. Sample masses as low as a few milligrams have been successfully analyzed for 200-/xL volumes. 

Other field tests with proprietary vapour-phase inhibitors [17] in a parking garage with chloride-contaminated precast slabs did not show encouraging results. Corrosion-rate measurements showed a reduction of 60% in areas with initially intense corrosion but also an increase of corrosion rate in areas with low corrosion rates. On structures from 1960 with an admixed-chloride content higher than 1% by mass of cement, already featuring patch repairs, a three-year corrosion rate survey showed lower corrosion rates in the treated areas compared to untreated ones, but cracking and spalling increased also in the treated areas [18]. 

Figure 8.36 Microstructural photomicrographs and X-ray images of a Co-25 wt% Cr-6 wt% Al-0.5 wt% Y specimen after 100 h of cyclic hot corrosion testing at 900 C where 1 mg cm Na2S04—90 wt% NaCl was applied after every 20 h. The structural features at the external scale-aUoy porous-zone interface and at the aUoy porous-zone-unaffected alloy interface are shown in (a) and (d), respectively (b) and (c) are X-ray images of the area shown in (a), and (e) and (f) are X-ray images of the area defined in (d). Note lack of oxygen in particles in porous zone adjacent to the unaffected alloy (f).

Figure 20.57 shows the corrosive effect of CO on various steels in a short-term test with pure CO-H2 mixtures at two CO partial pressures. A striking feature is the shift in the corrosion maximum of the 18-9 CrNi steel at the higher CO partial pressure. This possibly corresponds to the beginning of nickel carbonyl formation, which after a period of time leads to a chromium-enriched and more stable surface layer. 

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