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This technical bulletin will consider four methods of protecting carbon steel pipe support components from corrosion; painting, zinc coatings, hot dip galvanizing, and combinations of these. Painting has an advantage when appearance and choice of color are important. Modern painting systems may be appropriate protection in certain environments. Paint provides “barrier” protection to a metal surface. The ability of zinc to provide cathodic protection for carbon steel in addition to barrier protection is a fundamental advantage. In most cases the reduction in life-cycle costs justifies the small additional cost of galvanizing. Indeed painting and galvanizing together can provide a synergistic benefit which may be justified in some cases.

The use of zinc and galvanizing has a long history. The early patents for hot dip galvanizing were issued in France and England in 1836 and 1837. This technology was quickly adopted and was widely used in the late-1800s. In the United States we have bridges more than 100 years old which have galvanized structures. In addition, we have transmission towers and substation structures that are over 70 years old. A pipe rack at a petrochemical plant near Houston was studied after 28 years of service. Measurements of the zinc thickness remaining provided a forecast of another 60 years of service life. Pulp and paper mills use galvanized materials in most of their critical environments. It is important to understand the fundamentals which make this “old” technology so cost effective in such a wide variety of applications.

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