Question

Question 3 (20 marks) Two 304 stainless steel plates are welded together at their ends as shown. During operation, the plates are exposed to a wet chloride environment and subjected to tensile forces as shown in Figure Q3. After a period of time, the plates are found to have failed at the weld joint as a result of stress corrosion cracking. weld 304 stainless steel plate 304 stainless steel plate applied force applied force Figure Q3 (a) Explain what is meant by the heat affected zone (HAZ) in a weld (3 marks) (b) Explain how sensitisation occurs in an austenitic stainless steel such as the 304 stainless (5 marks) steel (c) Propose TWO different grades of austenitic stainless steel to prevent sensitisation during the welding process. Discuss briefly how sensitisation is prevented in these grades and give a disadvantage of each of the two grades (6 marks) (d) It has been proposed to replace the welded joint with a lap joint bolted together by carbon steel nuts and washers as shown in Figure Q3(d). The carbon steel is more reactive and is found lower in the galvanic series than the 304 stainless steel. Discuss the potential corrosion problems related to this new joint. (6 marks) carbon steel nut and washer 304 stainless steel plate Figure 3(d)

Answer 1

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