temperature, and chlorination. When employing such control measures, the 

 corrosion performance of the base metals must be considered. 



In addition to biofouling, there are several organisms (such as limnoria, 

 teredo, and termites) common in the marine environment that cause deteriora- 

 tion of structures through boring. Because metal structures are impenetrable 

 these organisms do not cause deterioration usually found on marine pilings 

 constructed of wood. 



g. Wave and Current Effects . Fouling diminishes as water velocities in 

 contact with a structure reach the 1- to 2-meter-per-minute (3 to 6 foot) 

 range. Pitting of the more noble materials slows down and may even cease. 

 As velocities continue to increase, stainless steel and nickel base materials 

 remain passive and inert but corrosion barriers are stripped away from carbon 

 steel and copper alloys. Although wave or current velocity are seldom too 

 high to allow the use of carbon steel, velocity is a factor to consider in 

 the design of equipment such as piping and pumps. 



h. Abrasion. Abrasion to metal structures is caused by the movement of 

 the elements in the coastal zone and their ability to transport particles 

 with force against all structures. Significant particle transport is 

 caused by wind and water. Structures in windswept beaches and shores are 

 subject to severe abrasion from the wind-driven sand with substantial force 

 and can result in significant metal wear in the case of steel or other metal 

 structures. For steel pile structures, abrasion to piles at the mud line 

 increases the metal loss far in excess of loss from corrosion. For some 

 structures, usually on land or for structural elements located above the 

 waterline in the ocean, added abrasion resistance can be provided by addi- 

 tional protection in the form of concrete, wood, or hard-surfaced alloys 

 Most hard-surfaced metals require special heat treating and the addition of 

 small amounts of other elements such as manganese. 



The latest improvement in steel piling was the development of mariner 

 steel for seawater exposure. Mariner steel was developed primarily to 

 improve the corrosion resistance of steel in seawater by alloying about 0.5 

 percent each of copper and nickel in addition to about 0.1 percent of phos- 

 phorous (ASTM Standard Specification A 690-77). While mariner steel has a 

 somewhat improved strength, its hardness is little different than that of 

 normal steel piling and abrasion resistance is also little different. 

 Although cathodically protected steel structures in seawater usually take on 

 a calcareous coating (chemicals deposited from the seawater) this coating is 

 too soft to offer any resistance to abrasion. 



i. Seismic Effects . Metals are well suited for marine construction in 

 areas of seismic activity. They possess high tensile strength, good duc- 

 tility, and, when properly specified, good toughness. In addition, metals 

 can consistently meet specified minimum seismic requirements. Steel, the 

 most economical of the metals for construction of harbor facilities, is 

 available in several shapes. The inherent high-bending strength of steel H- 

 piles permits the development of required resistance to lateral forces, when 

 used in foundation designs where resistance to seismic forces is required. 

 The ability of metals to be loaded in shear, compression or tension within 

 calculated limits facilitates the design of earthquake-proof structures. 



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