Zinc, chloride, concentrating paints

Extreme stress corrosion cracking (ESee) occurs when chlorides from the atmosphere, water leaks, or insulation concentrate on the surface of an 18-8 t)/pe stainless steel. Ferric ions from rusted steel flanges will aggravate the situation. ESCC is best combatted by coating vessels and piping over 4 in. using a zinc-free and chloride-free paint system. 

Steel objects, when exposed to humid atmospheres or when immersed in electrolytes, corrode at a rapid rate. For example, abrasively polished, cold-rolled steel panels will show signs of rust within 15 minutes when immersed in dilute chloride solutions with pH in the range of 7-10. One of the methods used to control this rapid corrosion is to coat the metal with a polymeric formulation such as a paint. The role of the paint is to serve primarily as a barrier to environmental constituents such as water, oxygen, sulfur dioxide, and ions and secondarily as a reservoir for corrosion inhibitors. Some formulations contain very high concentrations of metallic zinc or metallic aluminum such that the coating provides galvanic protection as well as barrier protection, but such formulations are not discussed in this paper. 

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