The term hot-dip galvanizing is defined as the process of immersing iron or steel in a bath of liquid zinc to produce a corrosion resistant, multi-layered coating of zinc-iron alloy and zinc metal. The coating is produced as the result of a metallurgical reaction between the liquid zinc and the iron in the steel. The coating forms an equal thickness on all surfaces immersed in the galvanizing kettle. This process, similar to the one seen in Figure 1, has been in use since 1742 and has provided long-lasting, maintenance-free corrosion protection at a reasonable cost for many years. The three main steps in the hot-dip galvanizing process are surface preparation, galvanizing, and post-treatment, each of which will be discussed in detail.
Steel structures with visible evidence of corrosion are pictured in the series of photos in Figure 2. Rust and corrosion can be expensive for business owners and taxpayers because buildings, roads, and bridges, without sufficient corrosion protection, may need to be repaired often or even rebuilt.
The process is described in more detail later in this section. It is inherently simple, and this simplicity is a distinct advantage over other corrosion protection methods.