Corrosion aspects in indirect systems with secondary refrigerants

Sammanfattning: Aqueous solutions of organic or inorganic salts are used as secondary refrigerants in indirect refrigeration systems to transport and transfer heat. Water is known for its corrosive character and secondary refrigerants based on aqueous solutions have the same tendency. The least corrosive from the aqueous solutions are glycols and alcohols. Salt solutions, such as chlorides and potassium salts, are much more corrosive. Nevertheless, it is possible to minimize corrosion risks at the beginning stage while designing system. Proper design can significantly help in improving system performance against corrosion. There are several aspects which need to be taken into account while working with secondary refrigerants: design of system, selection of secondary refrigerant, proper corrosion inhibitors, compatible materials used to build the installation and proper preparation of system to operation. While choosing proper materials it is advised to avoid the formation of a galvanic couple to reduce the risk of the most dangerous type of corrosion. Oxygen present in installation is another important factor increasing the rate of corrosion. Even small amounts of oxygen can significantly affect the system lifetime. The methods of cleaning, charging the system with refrigerant, and deaeration procedures are extremely important. The purpose of this thesis work is to present the problems of corrosion occurring in the indirect systems with secondary refrigerants. The thesis describes the mechanism of corrosion and its different types, most commonly used materials in installation, different corrosion inhibitors used to protect system. This thesis also lists the available secondary refrigerants on the market and briefly describes them. Further, it describes the important aspects related with designing, preparing and maintaining of indirect systems. This thesis is giving some clues and shows what should be done in order to reduce risks of corrosion.