[Discussion Thread] Corrosion by Sodium Hydroxide Solution
Thread Content
Dear teachers, I would like to ask for your advice. Currently, the concentration of sodium hydroxide is 50%, and the temperature is 200 °C. It involves Ni6+Q345R composite plates, and cracks appear in the clad welds of the equipment after just a few months. Even after repairs, cracks reappear after some time. What’s the reason?
After the seam welding was completed, inspections were carried out, including those by third parties, and no issues were found; therefore, it is unlikely that the welds were not done properly.
Is the welding internal stress too high, resulting in stress corrosion cracking due to the alkaline corrosion environment?
The corrosion of nickel by sodium hydroxide is minimal; the material chosen is good. Cracks can only appear under significant force during use, and the mechanism behind crack formation is quite complex. In the use of composite materials, temperature stress resulting from different temperatures is inevitable; welds are weak points in the equipment manufacturing process due to heat cycles, alloying, welding discontinuities, and so on. I suggest conducting stress testing on the weld areas depending on their usage, and then taking another look.