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Firstly, we shall look at the corrosion resistant alloys. Within corrosion resistant alloys there are three main sub groups, B-alloys, C-alloys and G-alloys. Those Hastelloys® with high nickel and molybdenum have a high resistance to pitting and crevice corrosion, and those with high chromium percentages thrive in highly oxidizing environments. Generally, C-alloys are the most versatile of all the Hastelloys®. Common to all C-type alloys are their ability to resist the formation of boundary precipitates in the weld heat-affected zone (inter-granular corrosion-weld decay). The most commonly used C-type alloy in industry is the C-276. If we take a look at C-type alloys we see that Stainless Steel fails more often than Hastelloys® due to pitting and crevice corrosion as well as from general corrosion (see figure 1). The table below (figure 1) shows how the Critical Crevice Temperature and the Critical Pitting Temperature of some Hastelloys® and types of Stainless Steel. Hastelloy® C-22 alloy has a Critical Pitting Temperature greater than 140˚C whereas stainless steel type 316L only has a Critical Pitting Temperature of 15˚C. This shows that C-22 is a far better at resisting corrosion at higher temperatures than its Stainless Steel counterparts. The same applies to C-276; which is due to them containing a higher composition of carbon and molybdenum than that of Stainless Steel, Mild Steel and Iron. A specific advantage of C-22 is that it can be easily welded. C-22HS has the same resistance as C-22 but it has double the yield strength. Alloy Critical Crevice Temperature ˚C Critical Pitting Temperature ˚C Hybrid-BC1 125 >140 C-4 50 100 C-22 80 >140 C-276 55 >140 C-2000 80 >140 316L 0 15 254SMO 30 60 625 40 100 Figure 1- Table ... ... middle of paper ... ...ure 2- Table showing Hastelloys® against Stainless Steel in terms of Cracking A large number of Hastelloys® have low carbon contents, which reduces the carbide precipitation during welding. This also makes Hastelloys® more preferential over stainless steel. Hastelloys® which have a high composition of chromium are used in strong oxidizing mediums. For a range of physical properties of corrosion resistant Hastelloy see figure 4. Works Cited 1. Haynes International, Available at: http://www.haynesintl.com/ (Accessed: 24th February 2014). – most information came from their Company website. 2. CSI Alloys, Available at: http://www.csialloys.com/about_advantages.php (Accessed: 21st February 2014). - C-22 -> About C-22 -> Advantages  Figure 1 3. Megamex, Available at: http://www.megamex.com/hastelloy.htm (Accessed: 20th February 2014).Hastelloy® -> Hastelloy® C-276

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