Why cannot steel and aluminum radiators be used simultaneously in the same hot water system?

This post was last edited by ylb913 on 2015-11-13 06:33. Mixing radiators made of different materials can lead to various safety hazards; this is especially true for aluminum radiators. It is essential to be careful and avoid installing them alongside products made of other materials. Firstly, since the resistance coefficients of different materials vary, this approach will disrupt the balance of the existing heating system, creating a potential difference. As a result, radiators with lower potential may develop holes due to electrochemical corrosion, leading to leaks. Secondly, in general, lightweight radiators have relatively small diameters; if used together with cast-iron radiators, it can easily lead to hydraulic imbalances in the system, resulting in insufficient heating heat. 1. China’s heating systems operate in an open manner; when heating is stopped, the system is emptied, resulting in high humidity inside the radiators. In conditions with sufficient air supply, the corrosion rate is much higher than in an atmospheric environment. Experts and scholars at home and abroad have spent many years studying the corrosion mechanisms of steel radiators, and it is believed that, based on an analysis of the corrosion conditions, oxidative corrosion and various types of oxygen concentration cell corrosion (such as crevice corrosion, intergranular corrosion, pitting corrosion, and under-scale corrosion) are the main causes of corrosion and leakage in steel radiators. 2. Chlorine or bleaching powder is commonly added to tap water in China for disinfection, which introduces chloride ions into the water. Cl- is an active anion with high permeability, and it accelerates the corrosion of both steel and aluminum. 3. In some areas of China, the water quality is poor – it has high hardness and is alkaline, which facilitates the formation of scale. This scale accelerates the corrosion of aluminum radiators. To reduce corrosion of the boiler and pipes during operation, heating boilers often contain a certain amount of alkaline corrosion inhibitors, which can cause corrosion to aluminum radiators ； At the same time, to reduce scaling on the inner walls of boilers and pipes, alkalis are often added to the boiler water in order to adjust its pH value. Practice has shown that when the pH value of the water in the boiler is around 9.0, scaling agents such as calcium and magnesium ions find it difficult to form precipitates, which helps to reduce scaling on the inner walls of boilers and pipes and is beneficial for the proper operation of the boiler. 4. Aluminum radiators have strong oxidation resistance, but are prone to alkali corrosion and chloride ion corrosion. When the water quality in the heating system is alkaline (with a pH value above 7) or has a high chloride content (high salinity), the radiators are at risk of corrosion and leakage. Furthermore, since aluminum alloys are more reactive than other commonly used metals and are prone to electrochemical corrosion, it is necessary to avoid mixing aluminum alloys with other materials during installation.

Because using products made of two different metals in the same water system theoretically creates a chemical galvanic cell, resulting in electrochemical reactions; the metal with more reactive chemical properties will corrode more rapidly.