Immersion testing

In many commercial brochures, chemical resistance is indicated as excellent, good, fair, or poor. Although the test method is usually outlined, wide interpretation is possible. Immersion tests are usually described in this manner. Hydrolytic stabiUty is tested by salt-spray cycling or autoclave cycling. 

The primaiy use of this laboratoiy technique today is as a quick check to determine the order of magnitude of a corrosion reaction. Sometimes the calculated rate from an immersion test does not look correct when compared to the visual appearance of the metal coupon. 

As was cited in the case of immersion testing, most SCC test work is accomplished using mechanical, nonelecdrochemical methods. It has been estimated that 90 percent of all SCC testing is handled by one of the following methods (1) constant strain, (2) constant load, or (3) precracked specimens. Prestressed samples, such as are shown in Fig. 28-18, have been used for laboratory and field SCC testing. The variable observed is time to failure or visible cracldng. Unfortunately, such tests do not provide acceleration of failure. 

Nickel-iron alloys are more resistant than iron to attack by solutions of various salts. In alternate immersion tests in 5% sodium chloride solution Fink and De Croly determined values of 2-8, 0-25 and 0-5 g m d for alloys containing 37, 80 and 100% nickel compared with 46 g m d for iron. Corrosion rates of about 0.4 g m d are reported by Hatfield for Fe-30Ni alloy exposed to solutions containing respectively 5 Vo magnesium sulphate, 10 Vo magnesium chloride and 10% sodium sulphate the same alloy corroded at a rate of about 1.2 g m d in 5% ammonium chloride. 

A rapid immersion test in a hot aqueous solution containing sulphur... 

Tests for quality of sealing of anodic coatings have become internationally standardised. They include dye spot tests with prior acid treatment of the surface (ISO 2143 1981 and BS 6161 Part 5 1982), measurement of admittance or impedance (ISO 2931 1983 and BS 6161 Part 6 1984), or measurement of weight loss after acid immersion (ISO 3210 1983 and BS 6161 Part 3 1984, and ISO 2932 1981 and BS 6161 Part 4 1981). Of these the chromic-phosphoric acid immersion test (ISO 3210) has become the generally accepted reference test. 

Table 19.S). In particular, they have established that the presence of dissolved O2 enhances passivity thus causing E, to become more positive, and consider that this explains the failure of France and Greene to obtain accord between controlled potential tests in hydrogen-saturated chloride solutions and immersion tests in oxygenated chloride solutions at the same potentials. 

Skin tolerance was tested on rabbits. A 1 % alkanesulfonate solution applied five times did not produce any irritation on the rabbits skin. The same results were obtained by the closed patch test carried out with human test subjects in a hospital. The good dermatological properties were also confirmed by the Polano test (arm immersion test). 

Diffusion rates for liquids in an elastomer are easily measured by absorption (immersion) testing, a simple process as indicated in Figure 23.6. An initially weighed immersed sheet sample of elastomer is removed from the liquid periodically, rapidly dabbed with tissue paper, reweighed, and replaced. A plot of mass increase versus root time is drawn (also see Figure 23.6), root time being chosen due to the form of appropriate solutions of Fick s laws. 

FIGURE 23.6 Immersion testing outline—an absorption plot. 

Our goals in designing the immersion testing system were (i) to emulate or improve upon operations as specified in the manual immersion test method, (ii) to increase sample throughput, (iii) to improve the precision and accuracy of measurements, (iv) to establish procedures for testing materials in hazardous liquids, and (v) to provide sufficient flexibility to handle different types of specimens and enable future expansion of operations. 

The objective of the immersion test is to determine the moisture content (percent weight gain) of a material as a function of its immersion time. To interpret immersion test data, moisture diffusion through the thickness of a test specimen can be described using a one-dimensional Fickian equation... 

Figure 6. Immersion testing of a polyester/glass fiber laminate in distilled water at 60 C.

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