Effect of Variables on Corrosion Tests

Effect of Variables on Corrosion Tests It is advisable to apply a factor of safety to the results obtained, the factor varying with the degree of confidence in the applicabihty of the results. Ordinarily, a factor of from 3 to 10 might be considered normal. 

This chapter presents a discussion of the fundamentals of aluminium alloy corrosion applicable to the wet storage of spent nuclear fuel throughout the world. It examines the effects of variables on corrosion in the storage environment and presents the results of corrosion surveillance testing activities at SRS, as well as discussions of corrosion at fuel m storage basins at other production sites of the USDOE. Aspects related to the corrosion of aluminium clad fuel at SRS apply to research and test reactor fuel worldwide. 

Chemical corrosion tests focus primarily on resistance to surface and selective corrosion. In general, the effect of material and corrosive medium variables can be understood with these methods. The variable potential, on the other hand, is more or less undefined and can experience time changes depending on the properties of the various partial reactions involved in corrosion. The fluctuation range of the potentials found in practice cannot be taken into account in the immersion test. Often, therefore, the results obtained in chemical corrosion testing using electrochemical methods must be further differentiated to take account of the variable potential. If the corrosion rate determined in chemical corrosion testing depends heavily on the potential, and has little to offer, but if there is only a little potential dependence it is more reliable. 

Autoclave corrosion tests are a convenient means for laboratory simulation of many service environments for the purpose of evaluating the corrosion resistance of materials and for determining the effects of metallurgical, processing, and environmental variables on corrosion processes. The reason for such tests is to more closely recreate the high temperatures and pressures commonly occurring in commercial or industrial processes. 

In all field testing, the effects of variability in the composition of the stream being studied on the corrosion processes must be considered. Since small changes in the composition in organic solutions can have dramatic effects on the corrosion rate as well as the stability of passive films. 

The eff ect of velocity on corrosion and mass transfer is not apparent at this time. This is mainly due to a lack of tests in which velocity is the only ariable. Correlation between the pump loops and thermal convection loo))s suggests that velocity has little effect on mass transfer other than on the type of plug formed, provided conditions for cavitation do not exist. However, results from tests now under way should definitely evaluate this variable. 

In some instances it may be possible, though it is usually very difficult, to undertake laboratory corrosion tests under conditions that will be the same as those encountered in some practical application, and thus to secure some directly applicable data. More often, the conditions of service are so variable or so difficult to appraise accurately and duplicate in the laboratory that it is impractical and probably unwise to attempt to do so. A better procedure is to examine the individual effects of the several controlling factors by varying them one at a time so as to provide a picture of their influence on the... 

J. J. Noel, Effects of metallurgical variables on aqueous corrosion, in ASM Handbook, Vol. 13A, Corrosion Fundamentals, Testing, and Protection, ASM International, Materials Park, OH, 2003, p. 259. 

Some understanding of the corrosion of aluminium alloys used as cladding on research and test reactor fuel has been obtained from the CRP. Aluminium corrosion is extremely complex and the variables affecting localized corrosion (pitting and crevice corrosion) act both independently and synergistically. Additional information about the effects of deposited particle composition on the corrosion behaviour of aluminium alloys is needed. Surface finish affects the corrosion of aluminium alloys, and more information is required with respect to this parameter. Additional data on the effects of certain impurity ions in basin water on localized corrosion behaviour are necessary to better identify the ions that cause corrosion. A goal would be to develop an equation for pitting as a function of water chemistry parameters. 

Section V on Testing in Environments (H. Hack, Section Editor) includes chapters on outdoor and indoor atmospheres, seawater, fresh water, soils, concrete, industrial waters, industrial chemical, petroleum, high-temperature gases, organic liquids, molten salts, liquid metals, corrosion inhibitors, in-vivo, and microbiological effects. Each chapter provides a descriptive overview of the environment and factors and variables affecting corrosion rates and mechanisms. 

One variable frequently overlooked in designing tests for selecting materials for industrial chemical applications is the presence of small quantities of chemicals present as contaminants that is, chemicals that are there unintentionally. Often these chemicals have no effect on corrosion behavior and can be safely ignored. However, eJl too often this is not the case. Consider, for example, the effect of a few... 

The problem with corrosion testing for crude oil environments is the wide variability in the composition of the crude oils and the resulting variability in their effect on... 

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