Application limits of Ta and Ta-2.5% W for sulfur acid handling

摘要

Long term corrosion test with welded coupons were carried out to determine the application limits of Ta and Ta-2.5% W in sulfuric acid (H{sub}2SO{sub}4). The program included the following two fields of investigation:* Determination of corrosion behavior in 90 through 100% H{sub}2SO{sub}4 at temperatures up to 200℃.* Determination of corrosion behavior in 96 wt % H{sub}2SO{sub}4 comparing recovered nitration-spent acid and technical grade between 150 and 230℃.Mainly immersion tests were performed. A comparison of Ta and Ta-2.5 % W showed that in technical H{sub}2SO{sub}4 the alloy performed better than the metal.Regardless of which material was considered, the higher the H{sub}2SO{sub}4 concentration, the lower the temperature necessary to achieve acceptable corrosion behavior. In technical H{sub}2SO{sub}4, the following application limits were revealed:Ta: 96 wt %/200℃- 97 wt %150℃Ta-2.5% W: 96 wt %/210℃-97.5 wt %175℃.Above 97.5 wt % the corrosion resistance decreased rapidly. The recovered nitration-spent acid led to remarkably lower corrosion rates due to small amounts of nitric acid. In these types of acid-containing oxidizing compounds. 230℃ seemed to besatisfactory, provided the wall of the heat exchanger was sufficiently thick.