Accelerated exposure testing chapter

This encyclopedia and this chapter are focused on electrochemistry. However, a few words about nonelectrochemical techniques are in order for completeness. Exposure testing of samples to service or accelerated environments is widely used, and there are several ASTM standards describing appropriate methods. Several immersion tests for intergranular and exfoliation corrosion were mentioned in the last section. ASTM G31 describes methods for immersion testing of metals [83]. This standard practice contains mostly common sense, but also has information that will help experimentalists avoid common... 

Section HI covers Types of Tests (H. Hack, Section Editor) includirrg laboratory-accelerated tests, field tests, and service tests. The chapters in this section provide basic principles, describe test techniques and specific considerations such as specimen preparation, test duration and acceleration factors, and cite pertinent standards. Chapters included under laboratory tests are electrochemical, cabinet, immersion, high temperature, and high pressure. Field Tests chapters include atmospheric exposure, seawater, fresh water, and soil. Under service tests are industrial applications and high temperature environments. 

An excellent example of such a progrsun was the one conducted by the automotive industry sponsored by the AISI s Corrosion Task Force in cooperation with SAE/ACAP that was described earlier in this chapter. In this study, ten ma-terisJs (see Table 1) were placed on vehicles operated in the corrosive environments of Montreal, Quebec and St. John s, Newfoundland to determine a performsmce ranking for cosmetic (outside-in) corrosion resistance. These S2ime materials were also exposed in a series of accelerated laboratory tests, at proving grounds, and at other exposure sites. 

There are clear advantages in obtaining direct evidence of performance by exposing the total component or product. This is particularly so in cases involving complex degrading environments and critical applications. Unfortunately this is rarely possible, particularly for accelerated tests, due to limitations of exposure space and costs. When it is possible, it is better to use functional tests on the product to assess the environmental effects, rather than the standard material methods. Increasingly, product specifications include such tests but in many cases it would be necessary to devise methods for the product in question (see Chapter 5). 

The notable exception is the exposure of rubber, including relex ant foams and coated fabrics, to ozone. Many rubbers are susceptable to cracking when exposed in the strained condition to ozone in very small quantities—this is in fact a case of environmental stress cracking discussed above for plastics. Ozone levels in the atmosphere arc generalK no more than the odd part per hundred million, but this is quite sufficient to cause severe damage. Accelerated tests are usually carried out in special ozone cabinets at levels between 25 and 200 parts per hundred million, and the procedures are described in Chapter 15. 

VS4W was started as a 2-year certification study but was subsequently converted to a 10-year VSl study in 2002. A set of readings was taken in 2003, 2005, and 2010, at which time the program was extended to 2015. There are currently 1,524 solid samples and 273 variegated samples on exposure in Florida, Arizona, and Ohio. This group of samples was used as the baseline for the development of an accelerated test protocol that will be discussed later in this chapter. 

---