Water is generally less corrosive than dichloroethane or a mixture of the two. However, the presence of low level impurities can significantly change the corrosivity of streams such as these. Low levels of chlorides can cause pitting and stress corrosion cracking of austenitic stainless steels. 316L stainless steel is only recommended for dichloroethane if it is dry. The temperature of 250 °C adds to the challenge as corrosion is usually worse at higher temperatures. In addition, a quick look at the references I have shows that many materials are not suitable for dichloroethane at these temperatures if data is available at all. Once the low level impurities in your streams have been identified, a more thorough review of the literature might reveal some possibilities for materials of construction. Or corrosion tests may need to be run at the temperatures and pressures of concern to adequately address the material of construction issues.