Corrosion Protection of Steel Bridges with Thermal Spray Zinc Duplex Coatings – 50 Years Experiences

Since 1969 the specification for corrosion protection of steel bridges in coastal areas of Norway has been to apply a thermal spray zinc (TSZ) duplex coating, and from 1977 this practice also applies for inland bridges. The duplex coating consists of TSZ with a protective paint coating on top. The corrosion protection experiences with these coatings are very good in all environments from C2 to C5. The majority of the bridges with duplex coatings have never had any coating maintenance, although the oldest ones now have a 50 years lifetime. The duplex coating has degraded to varying extent on most of the bridges, though, as must be expected. A statistical analysis of duplex coating performance, as function of exposure environment and age is presented in this paper.