Remote electrode (remote earth ) . The potential of a structure-to-earth 

 will change rapidly near the structure, and if remote earth is reached, 

 there will be little or no variation in the voltage. Remote earth is any 

 location away from the structure at which the potential gradient of the 

 structure to earth is constant. 



Resistivity . The specific resistance of a material. It is defined as 

 the resistance in ohms of a centimeter cube of material, measured across 

 opposite faces. Since the resistance of a material varies directly with 

 length and inversely with area, the resistance (R) can be written in an 

 equation R = p(l/a). By rearrangement solving for p, p = R(l/a); where R 

 is in ohms, 1 is in centimeters and a is in square centimeters. Thus the 



. , _ • J. • • 4. ohm X cm. ^ , 



units of resistivity are or ohm-cm. 



cm. 



Rusting . Corrosion of iron resulting in the formation of products on 

 the surface, consisting largely of hydrous ferric oxide. 



Scaling . The formation of partially adherent layers of corrosion products 

 on a metal surface at high temperature. 



Season cracking . Cracking resulting from a combination of corrosion and 

 internal stress. A term usually applied to stress-corrosion cracking of 

 brass . 



Self-corrosion . (See local action. ) 



Slushing compound . A nondrying oil, grease, or similar organic compound 

 that, when coated over a metal, affords at least temporary protection 

 against corrosion. 



Spalling . The chipping or fragmenting of a surface or surface coating 

 caused, for example, by differential thermal expansion or contraction. 



Stray current corrosion . Corrosion caused by an electric current through 

 paths other than the intended circuit or by an extraneous current in the 

 earth. 



Stress corrosion . Corrosion of a metal accelerated by stress. 



Stress corrosion cracking . Cracking resulting from the combined effect 

 of corrosion and stress. 



Subscale formation . (See internal oxidation. ) 



Tarnish. Discoloration of a metal surface as the result of formation of 

 an adherent continuous film of corrosion products. 



Tuberculation . The formation of localized corrosion products scattered 

 over the surface in the form of knoblike mounds . 



B-9 



