This paper discusses methods and strategies for combining thermal spray zinc and hot-dip galvanizing to create an all-metallic zinc corrosion protection system. Hot-dip galvanizing is a mature industry and is commonly specified for infrastructure projects, whereas thermal spray zinc and its alloys are gaining traction with many asset owners and departments of transportation (DOTs). This has created questions about how best to combine both systems for exceptional corrosion resistance and material durability. Topics covered include processing variations, application advantages for new versus rehabilitation projects, and how material size influences the preferred processing methods.
Corrosion protection of infrastructure and assets is an area of increasing focus due to increasing financial and safety concerns. On a global scale, corrosion has an annual cost of $2.5 trillion (USD).1 To combat the deleterious effects of this natural phenomenon, specifiers and owners have many choices in terms of materials and protective coatings. Consideration of both initial and life cycle costs has become more important in the age of increased competition and shrinking maintenance budgets.
One of the protective coatings that has performed exceptionally in many types of applications and environments is metallic zinc. With its ability to offer barrier and cathodic protection, a relatively low corrosion rate in atmospheric applications, and along with being maintenance-free, specifiers and asset owners have increasingly specified or considered metallic zinc. Two of the most popular methods for applying this coating include hot-dip galvanizing and thermal spray metallizing. For some applications and material types, these two processes can be combined to create an all-metallic zinc coating system. This paper describes both methods and how to combine them for protecting steel infrastructure and other assets.
There are several types of galvanizing, and the method described in this paper refers to batch or general hot-dip galvanizing. In this process, the material is delivered to a galvanizing plant after fabrication where it is cleaned and coated. It is necessary to have proper vent and drain holes in the metal fabrications since the dip process involves full immersion of the materials into molten zinc, and any trapped air can cause safety issues and possible damage to the material as the air and moisture within it expands as the steel is heated.
