Carbon steel is durable, strong, and has a high resistance to heat, with a temperature range of –65° to 500°F (–54° to 260°C). An alloy of iron and carbon, it is typically alloyed with other metals to improve strength, toughness, and other properties.
External protective coatings such as electroplated cadmium, zinc, and zinc phosphate are applied to carbon steel fittings to extend their service life in corrosive environments. However, in the past decade, cadmium is no longer accepted by most industries due to environmental considerations. Cadmium and zinc corrode sacrificially, protecting the steel substrate from normal atmospheric rusting due to the common presence of oxygen, moisture, and acidic gases. However, they are rapidly attacked by many fluids — including those containing acidic hydrogen, reactive fluorine, chlorine, bromine, iodine, and nitrogen. Zinc-nickel external coating provides enhanced carbon steel protection in ASTM B117 salt spray testing and in fertilizer (urea) applications.