Corrosion testing classification

Fig. 8.97 Classification of pre-cracked specimens for stress-corrosion testing (after Smith and...

All testing has to be related to environmental conditions whose characteristics must be defined. The relation of accelerated corrosion test condition to real service conditions is one aspect while another is defining classes of environment and relating them to characteristic corrosion performance in order to produce useful specification guidelines. BS5493 1977 is an attempt to do this using four categories appropriate primarily to the UK (Table 13.2). Such a classification is clearly an over-simplification, but represents an important step in this particular direction. 

Metals and alloys removal of corrosion products from corrosion test specimens Metals and alloys atmospheric corrosion testing general requirements for held tests Corrosion of metals and alloys. Classification of corrosivity of atmospheres Corrosion of metals and alloys. Guiding values for the corrosivity categories of atmospheres... 

Particular care should also be taken to ensure that the expected in-service corrosion failure mechanism is reflected in the laboratory. Because of the wide range of possible test environments and conditions that may be encountered and used in conducting laboratory corrosion tests, the description of various test methods cannot be exhaustive. The test methods have been grouped into three main classifications ... 

Streicher, M. A., Classification and Application of Corrosion Tests, presented at ASTM Symposium on Application of Accelerated Corrosion Tests to Service Life Prediction of Materials, Miami, FL, 16-17 November 1992. 

The Corrosion Test is being developed to serve as a quantitative test for flux residues. Figure 10 shows the corrosion data for a low solids flux-treated coupon. Based on the data collected for a number of different fluxes, the following corrosion factors are suggested for a 7-day test at 85 °C (185 °F) and 85% RH with the following criteria for flux classification ... 

Corrosion testing procedures yield qualitative and quantitative results that can assess the resistance to corrosion and possibly establish a classification. 

In addition to examining pre-exposure effects, the slow strain-rate testing technique has been used increasingly to examine and compare the stress-corrosion susceptibility of aluminium alloys of various compositions, heat treatments and forms. A recent extensive review draws attention to differences in response to the various groups of commonly employed alloys which are summarised in Fig. 8.57. The most effective test environment was found to be 3 Vo NaCl -F 0.3 Vo HjOj. The most useful strain rate depends upon the alloy classification. 

The effects of corrosion on other properties need similar direct assessment in many cases. However, in the absence of accepted standard tests the BS, DIN, ISO tests for laboratory glassware are often used. At the present time, the British Standard BS 3473 Methods of testing and classification of the chemical resistance of glass used in the production of laboratory glassware is being re-issued in six parts, of which the first five parts are identical to recently revised ISO test procedures. There are also corresponding DIN tests in some cases which are very similar. The current situation is ... 

Two-way analysis of variance (and higher classifications) leads to the presence of interactions. If, for example, an additive A is added to a lube oil stock to improve its resistance to oxidation and another additive, B, is added to inhibit corrosion by the stock under load or stress, it is entirely possible that the performance of the lube oil in a standard ball-and-socket wear test will be different from that expected if only one additive has present. In other words, the presence of one additive may adversely or helpfully affect the action of the other additive in modifying the properties of the lube oil. The same phenomenon is clearly evident in a composite rocket propellant where the catalyst effect on burning rate of the propellant drastically depends on the influence of fine oxidizer particles. These are termed antagonistic and synergistic effects, respectively. It is important to consider the presence of such interactions in any treatment of multiply classified data. To do this, the two-way analysis of variance table is set up as shown in Table 1.24. 

Figure 18.2 A tiered testing strategy for skin corrosion based on the OECD approach to hazard classification.

The tiered approach to hazard classification was evaluated by simulating possible outcomes obtained when a stepwise strategy comprising three alternative tests and one animal test (Figure 18.2) is applied to a heterogeneous set of 51 chemicals (Table 18.7). The decision rules in steps 1 to 3 are based on the CMs for skin corrosion developed above. 

Shading indicates the step where a classification of corrosive potential (C) is assigned to a given chemical, and testing is stopped. 

Goals of Testing and Classification of Test Methods Nonelectrochemical Methods Electrochemical and Electrical Methods Barrier Characteristics of Coatings Adhesion of Organic Coatings Transport Properties of Coatings Other Film Properties Corrosion Resistance of Painted Metals... 

In contrast to the classification of Dangerous Substance Directive 67/548/EEC, a corrosive effect has to be tested on animal skin and additionally at metallic surfaces. As a consequence, many salts are classified in Class 8 in accordance with the ADR regulations but have no corrosive property at the skin. Prominent examples are halogenide compounds, e.g., sodium chloride. 

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