Electrochemical corrosion behavior of electroless Ni-P coating in NaCl and H 2 SO 4 solutions were studied by potentiodynamic polarization curves and electrochemical impedance spectra techniques, as well as the corrosion morphology was characterized. The results indicate that electroless Ni-P coating with about 25 mm is stable in 30 days immersion in NaCl solution.Although it was corroded with prolonged immersion days, the corrosive medium has not penetrated through the coating. During the H 2 SO 4 concentration ranging from 5 to 10%, the corrosion current density of electroless Ni-P coating increased due to the intensified anodic dissolution process; in 15% H 2 SO 4 solution, electroless Ni-P coating shows obvious anodic passivation effect.

The failure of E230 heat-exchanger in the production of epichlorophydrin (ECH) form dichloropropanol (DCP) was analyzed and material solutions are recommended. The analysis indicates that the combined effect of stress corrosion cracking (SCC) and dissolution of HCl and HClO in the DCP mixture solution in the E230 heat-exchanger chamber to the tube surface and chamber wall contributes to the failure of heat-exchanger tubes and the perforation of E230 heatexchanger chamber. It is recommended to reduce the content of Cl -in the DCP mixture solution and to increase its pH. Titanium, Type 316L stainless steel (SS), and electroless Ni-P coating can be considered as the candidate materials. Also, the process can be divided into two series step with one step heating the temperature from 30 8C to 608C, and the other step heating the temperature from 60 8C to 908C. For the lower temperature step, the Type 316L SS or electroless Ni-P coating can be used. For the higher temperature step, Titanium can be applied. Periodic cleaning of the tube surface and chamber inner surface deposit is necessary. Intensifying the inservice inspection and monitoring is also required.