It is relatively easy to alloy other metals with iron in making steel. 

 Low alloy steels contain up to 1.5 percent of elements such as manganese and 

 silicon. Medium alloy steels contain 1.5 to 11 percent of alloy elements and 

 high alloy steels, including both ferritic and austentic stainless steels, 

 contain more than 11 percent of alloy elements. 



Most coastal structures using steel as a principal construction material 

 use certain steel shapes in the following manner: 



(a) sheet piles for caisson walls, cutoff walls, bulkheads, and 

 groins; 



(b) "H" sections for bearing piles and beams; 



(c) pipe or tubing for bearing piles, conduits and handrails; 



(d) solid rods for tiebacks or tension members; and 



(e) reinforcing bars for concrete. 



(2) Aluminum . Aluminum, being a light metal in its high purity 

 form, is soft and ductile but does not possess sufficient strength for 

 structural applications. The addition of alloying elements imparts strength 

 to the metal. Elements used as alloys in aluminum are copper, magnesium, 

 zinc, silicon and small amounts of other elements such as chromium, usually 

 with copper to obtain high strength structural shapes. 



(3) Copper . Copper has several unique properties that make it a 

 very useful material. In addition to its high thermal and electrical con- 

 ductivity it has high corrosion resistance and can improve other elements by 

 being readily alloyable. The most corrosion resistant of the copper alloys 

 to seawater are aluminum brass, inhibited admiralty brass, and the copper- 

 nickel alloys. 



(4) Use in Coastal Structures . Steel is used as structural shapes 

 in most types of coastal structure. It is used as well in composite struc- 

 tures, for example as rebar in concrete construction. Steel alloys have 

 found many uses as bar stock, wire and wire fabric. Many alloys of aluminum, 

 due to their high corrosion resistance as well as strength-to-weight ratios 

 have also found many applications in marine structures. Copper, in addition 

 to uses as pipe and sheathing, has a high alloying capability in bronze and 

 brass that makes it a very useful element in the marine environment. 



In the use of steel, alloys and other metals in the coastal environment, 

 care must be taken to avoid direct contact of dissimilar metals that can form 

 a galvanic couple. When dissimilar metals are in electrical contact with 

 each other and immersed in an electrolyte, a potential difference is estab- 

 lished; an electric current will flow and rapid corrosion will take place. 

 If two dissimilar metals must be joined, then several precautions must be 

 taken such as insulating the metals, avoiding unfavorable effects by keeping 

 the cathode area small, placing a more anodic third metal in contact with the 

 other two to provide sacrificial protection and investigating other possible 

 solutions to protect the structure. • , 



380 



