F-Files: Mechanisms of Failure
Problems with galvanizing

From JPCL, June 2015

by Jayson L. Helsel, P.E., PCS, KTA-Tator, Inc. Richard A. Burgess, PCS, KTA-Tator, Inc., Series Editor

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Tagged categories: Bridges; Case History; Coating failure; Coating Materials; Failure analysis; Galvanized steel; Steel; Surface preparation

Comment from Rahrig Phil, (6/25/2015, 10:15 AM)

The galvanizing industry recognized the issue of flaking of the coating due to reactive steels about 15 years ago and developed a solution to prevent the phenomenon for a significant range (<0.22%) of silicon content in the steel. Adding a small amount of nickel to the molten zinc bath effectively minimizes and regulates the reaction of the molten zinc and iron in the steel due to the presence of silicon used to kill the steel. Nickel has been utilized by the industry for the last 10 years and the incidence of excessively thick galvanized coatings has been reduced significantly. The rapid corrosion you mention on the underside of the bridge is created by a constant wet cycle related to a design flaw in the bridge where water is improperly directed to the support beams and not away from the bridge itself.

Comment from Mario Colica, (11/30/2015, 5:25 AM)

As the long lasting resistance against corrosison depends on the thickness of Zinc ; for long cycles life I suggest the Zn Thermal spray whose thickness can reach more than 300 um (i.e. 12 times more than HDG ).Other benefit is the easy paintbility of Zn coating.

Comment from Antonio Leal, (12/4/2015, 10:05 AM)

In the same way that are followed in industrial painting, cleaning and blasting pattern, atmosphere conditions, dry film thickness, adhesion test, etc. Plating on these parameters are not always followed and depended on Company Conceptualized in the market, if this is not followed we know what will be the results.

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