Hot dip galvanizing is the process of coating pipe and fitting with a layer of zinc alloy in a bath of molten zinc at temperature around 450 °C.
As ISO 1461, ASTM A123, and EN10240, the galvanizing process has its own built-in means of quality control because zinc does not react with an unclean steel surface. So Surface Preparation is a critical step.
Degreasing
A hot alkali solution, mild acidic bath removes organic contaminants such as dirt, paint markings, grease, and oil from the metal surface.
Pickling
A dilute solution by heated sulfuric acid or ambient hydrochloric acid, removes mill scale and iron oxides (rust) from the steel surface.
Fluxing
A zinc ammonium chloride solution, removes any remaining oxides and deposits a protective layer prior to dip steel in bath.
According to ISO 1461, zinc coating thickness follows below form:
Steel thickness mm
Local coating thickness (minimum) μm
Average coating thickness (minimum) μm
Average coating mass (minimum) g/m2
steel ＞6
70
85
610
3＜ steel ≤6
55
70
505
1.5≤ steel ≤3
45
55
395
steel ＜1.5
35
45
325
Galvanizing
Pipe and fittings are completely immersed in a bath of molten zinc. The bath chemistry is specified by ASTM B6, and requires at least 98% pure zinc, to form series of bonded zinc-iron alloy layers.
TPMC is experienced in hot dip galvanizing, testing and packaging conforming to UL request, and supplies high quality galvanizing products to clients.
