HOT DIPPED GALVANIZING CHARACTERISTICS ARE THE BEST
The other choices are: CATHODIC ELECTRICAL GALVANIZING, GALVANNEAL ROLLED STEEL, ZINC BASED PAINT BASED COATINGS, and POWERED COAT PAINTS.
FIRST HOT DIPPED GALVANIZING
Hot dip galvanizing actually becomes part of the steel surface and is anodic to the steel substrate at the molecule level. ASTM 123 standard requires a minimum of 4.5 mm of film thickness. The average film thickness from quality galvanizer's is 5 to 7 mils. Greater thickness is available by design
The galvanizing coating is metallurgically bonded to the steel through a series of zinc-iron alloy layers capped by a free zinc layer. A hot dipped galvanized coating is more than just a barrier coating. Because zinc reacts with the atmosphere, the galvanized coating is constantly changing. Zinc reacts with the environment to form zinc oxides, zinc hydroxides and zinc carbonates. These zinc reaction products are known as the zinc patina. The zinc patina actually helps protect the free zinc layer, thus providing additional corrosion protection.
Cathodic galvanizing protection attempts to place a layer of zinc on the steel surface by electrically charging the fabricated piece and drawing the molecules of zinc to the surface.
The MAJOR WEAKNESS of electrically applied zinc IS VERY THIN, TYPICALLY SEVEN TO 1O TIMES THINNER than HOT DIPPED GALVANIZED.
Application of zinc to rolled steel material has it advantages. The major advantage is uniform thickness of the finished product, and low cost.
The FIRST MAJOR WEAKNESS is uneven thickness of the zinc layer on each side of the finished product. During the process of rolling the sheet steel after immersing the sheet steel in the zinc bath it is immediately run through two rollers. The two roller squeeze the sheet steel to a uniform thickness this is good and bad, The good is the sheet steel has uniform thickness. The bad is all of the galvanizing may be on one side of the sheet and little or none on the opposite side. Bottomline during the rolling, the zinc coat may be squeezed out/off one side of the steel sheet.
This is the FIRST MAJOR WEAKNESS of GALVANNEAL. The SECOND MAJOR WEAKNESS of GALVANNEAL is the final coating thickness is significantly thinner than hot dipped.
Paint-based coatings are to some degree, permeable to water and oxygen, even if the paint surface is not nicked or broken. However, when the paint surface is broken down due to abuse, both electrolytes water, and oxygen seep throught the nick and rapidly rust the steel. These electrolyte trapped between the steel and paint promote faster rusting as now they can attack 24 hours per day 7 days a week, rather than air dry during the day. Dump bodies are under constant attack by abuse of the surface paint surface by rocks, stones, sand gravel, all creating nicks in the paint surface, for the electrolytes to attack below the steel surface creating paint boils created by rust behind the paint surface.
Typically the paint coating is BREACHED with the first load of gravel or rock. This explains why paint-based coating systems fail, when a nick in the paint surface allows oxygen, and water, behind the paint surface RUST BOILS GROW RAPIDLY. (2014)
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