There are various sources for this information and it will depend on several factors - besides distance from the ocean, pollution (industrial)and location, location and location will effect the rate.
From ASM Handbook, Volume 13C
the rate of low carbon steel (similar to A 36) in a marine environment can vary from 0.53 mils/yr (rural) to 3.57 mils/yr (industrial), 5.73 mils/yr(mild) to 20 mils/yr (severe).