False Galvanization?? 2

[gmf]

I am currently conducting field reviews for a steel railing installation on a roof. The railings are to be galvanized. Following an initial site review we noticed that the vertical members appear to be galvanized, given the typical "flat" grey colour one would expect for galvanized steel. However, the horizontal rails are a shiny silver colour.

Now, given my inexperience with galvanized steel, my question involves the horizontal members noted above. Is it possible for galvanized steel to appear silver? And if so, could this difference in colour be a result of the base metal?

Note, however, the horizontal and vertical steel members contain the same base metal.

 

[SperlingPE]

Yes, freshly galvanized steel can look silver. The dull gray is the result of time. An "oxidation" process takes place.

 

[kenvlach]

The shiny silver color could be zinc electroplating – did you specify hot-dip galvanizing?

Also, gray color could be the result of ‘Galvannealing,’ where additional heating has increase formation of Fe-Zn intermetallics. Better re corrosion, worse re flexibility. Have only seen this on sheet material, though.

For all you ever wanted to know about galvanizing, see
The American Galvanizers Association

http://www.galvanizeit.org/

The GalvInfo Center

http://www.galvinfo.com/

The Galvanizers Association

http://www.hdg.org.uk/

 

[rexastexas]

From what you have provided, it appears that the vertical and horizontals were fabricated from different batches of 'glavanaized' steel. one oxiidized, possibly pickled (light acid bath)for painting, the horizontal one could be 'fresh,' recently galvanized. The spec should control and should be ascertained. Absent a spec or other galavanizg standard to inspect or to follow (usually "x" oz. (or gms) of Zinc (elemental Zn++) per unit length of pipe (or area of)of steel (i.e 1 oz /square foot, or 0.5 oz Zn++ per linealfoot of 2" od pipe.), this basically yields a nominal thickness of zinc, the protecting and sacrificial coating. There are many "standards." For example: if on an interior, air-conditioned, weatherproof walkway in a hotel, the handrail galvanaizing could be minimal. On the other hand, if on an offshore platform ths same handrail will be very heavily Zn++ coated and generally painted as well. Each application should have a specific specifiication based on that industry's standards.

Good luck finding the specification. Specs rule.