(c) microstructure (e.g., size, shape and orientation of grains, 

 and grain boundaries of a structure!, 



(dl grain size, 



(e) section size, (physical cross-section dimensions}, 



(f) hot and cold working temperature, 



(g) method of fabrication, and 



(h) specimen orientation in relation to working direction. 



Figure 49 presents representative plots of Charpy V-notch absorbed 

 energy curves for several materials used in construction. Fully killed 

 carbon steel made using a fine grain melt practice in the normalized heat 

 treatment has the best notch toughness at lower temperatures of the carbon 

 steels. If sulfide shape control is used during processing, improved notch 

 toughness can be obtained in the transverse (across grain) and through (with 

 grain) section directions. Austenitic stainless steel, type 304, and 9- 

 percent nickel are candidate materials for handling liquefied gases. Notice 

 that gray cast iron exhibits little notch toughness at any temperature 

 shown. 



(3) Wind Erosion . Wind erosion does not have a severe effect on 

 metals. Wind-driven sand, however, can destory paint and therefore increase 

 the formation of rusting on steel structures. Appearance is the property 

 most often affected. 



b. Exposure to Flora . The major effect of flora on metals is a slight 

 increase in corrosion rate where the plants, by their root system, may 

 transport additional moisture to the metal surface. In some soils, aerobic 

 bacteria are present that oxidize sulfur which is either present in the soil 

 or is obtained from decaying organic matter. By oxidation of sulfur, a 

 strong solution of sulphuric acid is formed that reacts with any basic 

 material present. The presence of either anaerobic or aerobic bacteria can 

 cause soils to be corrosive to metals even though a usual mineral analysis of 

 the soil and water does not reveal that a corrosive condition exists. 



c. Exposure to Burrowing Animals . Most metals have high hardness which 

 prevents burrowing animals from penetrating. Animals have damaged the 

 insulation covering of some buried electrical cables, which resulted in 

 failure of the cables. 



d. Exposure to Freshwater . 



(1) General . Exposed surfaces of metals are subject to some degree 

 of corrosion from water. The corrosiveness of water is basically dependent 

 on three factors; acidity, oxygen content, and electrical conductivity. Many 

 rivers are polluted by industrial wastes or runoff from mines causing the 

 water to become acid. Such water may be more corrosive to carbon steel than 

 seawater would be. Rainwater becomes slightly acid as it falls to earth due 

 to saturation with carbon dioxide. As the rain contacts the earth it becomes 

 altered hy reaction with minerals and soil. Depending on the acidity and 



220 



