Is it possible to have steel with chemistry too good for galvanizing?
It is possible to have steel chemistry with levels of silicon and phosphorus that are too low to meet the minimum thickness levels specified in ASTM A123 and ASTM A153. Very low silicon levels are seen more often on pipe though, not plate because aluminum is sometimes used as a deoxider rather than silicon.
For steel with very low levels of silicon and/or phosphorus that cannot meet the thickness requirements of ASTM A123 or ASTM 153, the best option is to blast the steel prior to galvanizing. Blasting the steel increases the surface area of the steel by making it rougher, which gives the zinc more area in which to develop a galvanized coating. Although blasting the steel prior to galvanizing tends to create thicker galvanized coatings, it does not always work well enough to meet the minimum coating thickness requirements of ASTM specifications.
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