I have experience with fender piles for submarines. The piles are 90 feet deep. About 45 - 50 feet is embedded in soil. A portion of the fender piles were in ocean water and a part is in open salty air with plenty of chlorides. The following is what I observed during recent upgrades:
1. The potion of the piles that was embedded deep in soil was amazingly clean and no corrosion was observed. As a matter of fact we used these pieces to make up new piles for the client. This has been attributed to lack of oxygen.
2. The portion of the piles that was in the water and splash zones was severely corroded. Keep in mind that marine grade steel (ASTM A690 “High-Strength Low-Alloy Steel H-Piles and Sheet Piling for Use in Marine Environments”) was used for these H piles.
3. The portion that was in the open air suffered medium corrosion.
4. Under the upgrades, we provided inorganic zinc coating and cathodic protection, by using sacrificial anodes. We used aluminum blocks that are supposed to last 15 years. They were over 200 pounds each.
In my practice, I always require specialized coating such as inorganic zinc, hot dip galvanizing or cathodic protection to shield the steel. I have heard of some engineers who increase the thickness of the steel members to account for corrosion. Personally I do not subscribe to this theory simply because you can never estimate the actual loss of section and duration for the loss to take place.
Few years back, I began to add a note to my drawings that in essence puts the onus on owners by stating that structure do require routine maintenance and that they are responsible for doing it to keep the structures functioning properly and for it to retain its structural integrity.
I am not aware of a code that allows or requires thickness increase.
Go to my web site (link below). Then go to the "Steel Sheet Piling & H-Piles" page. Download "NBS Monograph 58, Corrosion of Steel Sheet Piling In Soil"
On the same page, also suggest you download "Bethlehem Steel H Piling". Look on page 27 for more on steel pile corrosion.
Concur with Lutfi about the lack of code requirements on this subject. Use engineering judgement.
