Hydro-testing or hydrostatic testing of metallic equipment such as vessels, piping, valves
etc. is an important method for quality control of parts, after production and during use. When
water is used in these tests, corrosion of the metal, during and after testing is a concern.
Vapor-phase corrosion inhibitors (VCI), when added to water in small concentrations are able
to prevent corrosion during testing, during wet storage and after testing.
The mechanism of amino-carboxylate based vapor-phase corrosion inhibitors is to prevent
corrosion of metals in three phases: within the solution, at the water line, and above the water
line. VCI-based compounds prevent corrosion in the areas which are not reachable with other
corrosion inhibitors. As authorized by the Clean Water Act, the National Pollutant Discharge
Elimination System (NPDES) permit program controls water pollution by regulating point
sources that discharge pollutants into waters of the United States. Generally NPDES permits
exclude heavy metals, oils, and products outside of pH range 5-11. VCI makeup is in
compliance with these requirements. Lab studies and examples of use on various pieces of
industrial equipment will be presented in this paper to show effectiveness of VCI products in
both fresh and salt water applications.
Key Words: Hydro-testing, corrosion, vapor-phase corrosion Inhibitors