Corrosion Evaluation of Phosphate Coated Fasteners by Ferrotest

Fastener manufacturers and users have been searching for a quick method of evaluating the corrosion resistance of zinc phosphate coated fasteners. Ferrotest was originally developed as a method for rapid evaluation of zinc phosphate coatings on panels that were to be painted. This report examines the use of Ferrotest as a method for rapid evaluation of zinc phosphate coatings on fasteners.

Ferrotest time for evaluating zinc phosphated fasteners was one min. The present method of testing for corrosion resistance of fasteners is 72 hr in a neutral salt spray atmosphere.

Fasteners with different weight coatings and fasteners processed under varying conditions were tested, both with one minute Ferrotest and with a 24 hr salt spray test.

Correlation of the two methods was good, also correlation of coatings between the supplier and user using Ferrotest was good. Ferrotest results indicate a satisfactory method for rapid evaluation of phosphate coated fasteners.