The reboiler tubes at the stripper column are experiencing pitting and cracking from external side which is stripped sour water. The sour water contains typically about 10-15 mg/L chlorides. The tubeside contains MP Steam at around 190 degC. Sour water enters the reboiler at 134 degC. We upgraded the reboiler tube from carbon steel to duplex as the bundle kept leaking every 2-3 years. There's no blowdown so I'm thinking that the chlorides could somehow concentrate on the shellside. The locations of pitting and cracking are directly underneath the top inlet. We've also installed an impingement plate but to no effect. I thought that duplex 2205 could withstand up to 1000ppm chlorides. Appreciate any pointers in mitigating this problem whether metallurgy upgrade (eg. Incolloy 825?) or other suggestions. Thank you! Alani