Student Number : 9900051W -
MSc dissertation -
School of Chemical and Metallurgical Engineering -
Faculty of Engineering and the Built Environment / When specifying materials for use in exhaust systems, it is imperative that they exhibit sufficient corrosion resistance for the specific conditionsto which exhaust components are exposed, since up to 80% of all failures is attributed to corrosion and oxidation. It is therefore neccesary to establish the corrosion behaviour of the materials in conditions and environments to which the exhausts would typically come into contact with. Most car manufacturers, exhaust manufacturers and material providers have specific corrosion testing methods which they use to determine the corrosion resistance of candidate materials, but there appears to be no standard procedure. A summary comparing all the existing systems is given in section 2.7. The corrosion testing methods utilise a wide range of conditions, testing temperatures and stages. However, careful investigation of the tests show some similarities, and it was possible to identify eleven key tests, that cover internal corrosion, external corrosion and oxidation for both diesel and petrol engines. Eight of these tests were used to rank the corrosion and oxidation resistance of selected stainless steels, namely AISI type 304, 321, 409, 434 and DIN 1.4509. It appears that the austenitic stainless steels perform better in the cold end conditions, while the ferritic types are more resistant in the hot end high temperature conditions.
Of all the eight test performed, only the electrochemical tests for external corrosion of cold end components did not give reproducible results. The rest of the tests could be used to screen materials for exhaust system applications. In the internal condition of the cold end, the results of the elctrochemical tests indicated that they can be used as a possible replacement for the long exposure tests.
The key tests also highlighted the the presence of NH4+ ions in an exhaust gas is benificial to the corrosion resistance od stainless steels in internal cold end application. Its inhibiting effect was more pronounced for the ferritic stainless steels. The project indicated that external corrosion due to salt environments is not the major cause of the failure of cold end components, but rather that internal corrosion due to the condensate is the most detrimental.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/1682 |
| Date | 14 November 2006 |
| Creators | Nkosi, Zakhele Wonderboy |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 18587320 bytes, application/pdf, application/pdf |
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