Investigating the effects of salt spray corrosion on mechanical properties of steel sheets of HVAC heat pumps coated with zinc and polymeric substances

Abstract

Steel sheets are extensively used in various industrial applications because of their high mechanical properties, costs, and availability. However, in some applications such as gas, oil, and solar water heaters and heating, ventilation, and air conditioning (HVAC) systems, corrosion properties need to be further improved through new surface coatings for enhanced protection against corrosion, degradation, and abrasion. In many cases, a duplex coating system is used to provide extra protection against corrosion and degradation. In this study, steel sheet samples with varying levels of protective zinc coating thicknesses were individually tested as well as in conjunction with polymeric-based paint coatings through equal exposure times in a salt spray chamber for several days. Corrosion and mechanical testing of varying zinc coatings, especially in duplex systems are hardly available in the literature reviews, and this study reports new findings in the HVAC field. The prepared samples were kept in a salt spray chamber for different time frames (250 -- 1000 hours), and the effects of corrosion damages over time were investigated. Before and after the evaluations, all the sheet samples were subjected to tensile testing to study the changes in mechanical properties. It was discovered that duplex coating systems that involve a zinc coating with an organic polymer-based powder coat or pre-painted finishes on metal sheets (G30, G60, and G90) showed little or no sign of corrosion degradation over time, and therefore experience substantially fewer property changes. However, the surfaces of the uncoated or one-layer coated samples were severely damaged in the salt spray chamber, reducing the lifetime of the HVAC system. It is concluded that the duplex system provided better corrosion and chemical resistance against environmental degradations.