Can You Use Galvanized Steel with Glycol-based Heat Transfer Fluids?
However, galvanized steel is not a recommended material of construction for piping in a system using glycol-based heat transfer fluids. The zinc coating on galvanized steel is meant to prevent corrosion at atmospheric conditions, but the components of a heat transfer system often face much more aggressive conditions. As glycols break down, they form organic acids such as glycolic, glyoxylic, formic, carbonic, and oxalic acids. These acids are corrosive to metals such as iron, steel, and zinc. In systems that run at higher temperatures this breakdown is accelerated.
Phosphate inhibitors are commonly added to glycols for a few reasons. They protect against corrosion caused by these breakdown acids by providing pH buffering, which reduces the activity of the acids. Phosphate also reacts with iron and steel to form a protective coating on the metal surface. Unfortunately, phosphates can react with zinc and form a precipitate. This is bad for galvanized steel for a number of reasons.
- Engineering ToolBox, (2003). Working Pressure Copper Tubes Type K, L and M. [online] Available at: https://www.engineeringtoolbox.com/copper-tubes-dimensions-pressure-d_84.html [Accessed Day Mo. Year]