CORROSION AND PROTECTION OF STEEL PILING IN SEAWATER 

 Section I. INTRODUCTION 



Steel piling is widely used in building marine structures. Steel 

 sheet piling is often used in seawater to retain earth and prevent its 

 erosion by water at such structures as bulkheads, quay walls, seawalls, 

 and cellular construction for breakwaters and jetties. Steel H and 

 cylindrical piles find wide use in seawater as supports for docks and 

 offshore drilling platforms. They are also used in such structures as 

 dolphins to resist lateral loads. 



Althoiogh steel has many advantages as a material for marine con- 

 struction, it has the disadvantage of corroding in seawater if not 

 protected. 



A number of factors may affect the rate at which steel corrodes in 

 seawater. Some of the more important ones are the water temperature, the 

 amount of dissolved oxygen, salinity, water velocity, abrasive materials 

 in suspension, and the amount and type of marine organisms present. 

 Effective methods of protecting steel from corrosion are to isolate the 

 steel from the corrosive environment by a protective barrier or protect 

 it by causing an electric current to flow to the steel from another source 

 such as from another metal which is anodic to steel or from sources such 

 as batteries or rectifiers. The latter method is known as cathodic pro- 

 tection. Barrier type protection consists of organic and inorganic 

 coatings and concrete encasement. 



Concrete jackets of good quality concrete and workmanship have a 

 reputation for being effective in protecting steel from corrosion. However, 

 the initial cost of this method is relatively high. No test data has been 

 located from which to determine the protective life of concrete jackets 

 on steel piling installed in seawater. 



Tests conducted by the U. S. Naval Civil Engineering Laboratory in- 

 dicate that some of the relatively new coatings are performing fairly well 

 on pile specimens in seawater. Tests data on these coatings have been 

 incorporated in this report. Indications are that the initial costs of 

 most of these coatings are considerably higher than the short-lived as- 

 phaltic and coal-tar coatings commonly applied to steel piling in the past. 

 Once the life spans of a number of the more durable coatings have been 

 established, an analysis of the cost per year of protection will be very 

 beneficial to designers and maintenance personnel. 



Better techniques and materials are being continually developed for 

 cathodic protection and if properly designed and installed, it can be 

 very effective for protecting steel piling below the water level. Steel 

 above the water line must be protected by one of the other methods since 

 submersion in seawater is required to complete the electrical circuit for 

 cathodic protection. 



