Corrosion specimen preparation

All data were obtained using corrosion specimens prepared from 12-gage, solution heat-treated sheet. 

Why should the corrosion-specimen surface be re-prepared after a Tafel-extrapolation corrosion-rate measurement before conducting a subsequent measurement ... 

Cotter and Kohler likewise concluded that anodized surfaces produce the most durable adhesive bonds to aluminum. Their study included a comparison of the effects of using bare and clad alloys. In humid conditions, no significant difference was observed in the durability of chromic acid-anodized specimens prepared from the different alloys. In a corrosive environment, however, specimens prepared from the bare alloy proved to... 

G58 Practice for Preparation of Stress Corrosion Specimens for Weldments... 

ASTM G 39, Practice for Preparation and Use of Bent-Beam Stress-Corrosion Test Specimens— This describes methods for design, preparation, and use of bent-beam stress-corrosion specimens. This standard covers apparatus for supporting specimens, basic design of a specimen, stress calculations, test conditions, exposure, and inspection techniques. 

ASTM G 58, Practice for Preparation of Stress Corrosion Test Specimens for Weldments— This covers the manufacture and application of welded test specimens in stress corrosion testing. This practice is used to evaluate a total weldment, weld metal, or presence of notches and stress risers in weldments with respect to SCC in an environment. In addition, ASTM G 58 contains a method for evaluating the critical stress levels that will produce SCC in a weldment. The specimens are evaluated after exposure to an environment by microscopic methods. This standard includes typical specimens (stressed and tension), welding considerations, test specimen preparation, and inspection after exposure. 

Focus here is on service tests that evaluate materials in applications that involve both high-temperature and corrosive conditions. B lsic chemical, thermodynamic, and physical principles are discussed. Specimen preparation, environment synthesis and evaluation are briefly reviewed and, where appropriate, reference is made to more detailed information and studies available in the technical literature. 

Any specimen preparation procedure leaves the surface in some state of roughness. It has been observed that the corrosion on poUshed specimens tends to increase in the first stages of a test, while on rough surfaces the rate decreases. Eventually, both specimens will reach a similar steady state. However, a large real surface area requires more inhibitor for inhibition than a polished one. Thus, surface preparation will affect the determination of the effective inhibitor concentration, particularly in constant inventory tests with a small liquid volume to surface area ratio. 

Corrosion specimens may be unacceptable if they are not prepared properly. One of the major problems is cross contamination during specimen fabrication. Examples of contaminated surface areas of several Grade 702 zirconium specimens from different suppliers are given in Table 1. The specimen preparation can contaminate specimen surface as well when certain operations, such as bending and grinding, are employed. Tools should be clean in specimen-making processes. Surface condition plays an important role in corrosion and is particularly important to zirconium. 

ASTM G 1 Recommended practice for preparing, cleaning and evaluating corrosion test specimens Preparation of test specimens for corrosion testing and evaluation of results... 

Crevice corrosion specimens were tailored as Anderson s assembly. For specimens obtained from tubulars, a milling operation was carried out. Surface preparation involved machining, followed by wet grinding up to 600 mesh. Crevice sites were 16 (only one side) for specimens obtained from... 

Recommended Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens," specification Gl, Annual Book ofASTM Standards, American Society for Testing and Materials, Philadelphia, Pa., 1992. 

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