Bare steel pipe and fittings will rust in 4 hours after production or shot blast, if no surface coating. Rust is permeable to air and water, therefore the interior steel beneath a rust layer continues to corrode. Also surface rust is flaky and friable, providing no protection to the underlying steel.
When only temporary protection is needed for storage or transport, a thin layer of oil, grease, or lacquer is applied to pipe surface, which slow or halt rust over 3 months.
