Eta layer is the outermost and purest layer of the zinc coating formed during the in-line galvanizing or hot-dip galvanizing process. Its existence and integrity are essential for the finished tube or pipe.
Formation and Function
When steel is galvanized through molten zinc bath, a series of sequential zinc-iron alloy layers (Gamma, delta, zeta) form metallurgically between the steel substrate and the zinc. The eta layer is the final stage:
Composition: It consists almost entirely of pure zinc and contains the least amount of iron.
Location: It is the layer visible on the pipe's surface, giving the classic shiny, spangled appearance of galvanized steel.
Ductility: Because it is nearly pure zinc, the eta layer is the most ductile of all the galvanized layers. This high ductility is crucial as it allows the coating to absorb thermal stresses from cooling and minor mechanical stresses during handling and fabrication without cracking or flaking.
Protection: The eta layer acts as the sacrificial primary defense against atmospheric corrosion.