电解 - 因此造成的故障和可以应用的补救措施
电解是一个化学分解的过程cal compound by means of an electric current. Electrolysis, in the sense in which it will be discussed here, and in which you are particularly interested, refers to the corrosion of underground metallic structures, such as iron and lead pipes, by stray electric currents which reach these structures and flow to surrounding soil. Soil, when entirely dry, practically does not conduct electric current. Pure water likewise has such a high electrical resistance, compared with ron or lead, that it may be considered a a non-conductor. Water is, however, readily made conducting by the addition of even very small amounts of salts, and conduction through water is, therefore, always electrolytic. Soil in its natural state is always moist, and on account of dissolved salts, such as chlorides, nitrates, etc., which are always present, is an electrolytic conductor. Electric current may be conducted by metallic conduction or by electrolytic conduction. Metallic conduction occurs when an electric current passes through a metal, and is characterized by the fact that no chemical change is produced in the conductor, the only effect being the production of heat. Electrolytic conduction occurp when an electric current passes through an electrolyte. When an electric current flows from a pipe or other metallic structure to surrounding soil, chemical decomposition of the metal will take place resulting in corrosion of the pipe or structure. Concrete, when buried in earth, is moist, and it then becomes an electrolytic conductor, so that an electric current flowing from iron to surrounding concrete will corrode the non by electrolysis. The mass of a metal corroded by electrolysis in a given time depends only on the “current,” and, with the current dcnsilies and other conditions usually found in the case of underground pipes, is equal to that calculated by Faraday’s law. Iron is oxidized by electrolysis at the rate of approximately 20 pounds per year for every ampere of current flowing from the iron to surrounding soil. Under some conditions, particularly with every small current densities, this corrosion may be considerably greater, while with larger current densities than the above, this corrosion may be considerable less than the theoretical rate. The actual rale may vary' in practice from one-half to one and one-half times the theoretical rate. Lead is oxidized by electrolysis under ordinary conditions in soil at a rate equal to approximately 74 pounds for every ampere of current leaving the lead in one year, and this theoretical rate may also vary somewhat in practice. The amount of corrosion produced bv electrolysis is independent of the voltage, except in so far as this determines the amount of current flowing, and the smallcst fraction of a volt can produce corrosion from electrolysis under suitable conditions.
外电流通过电解的快速腐蚀通常是定位的，导致金属蚀。但是，在某些情况下，这种蚀点也可能是由普通的土壤腐蚀引起的，因此腐蚀金属结构的出现本身并不能提供有关是否是通过外部电流电解产生的腐蚀的确定证据。如果地下管道和周围土壤之间的电流方向或多或少连续逆转，则发现在电流从管道流出的时间内发生的腐蚀发生在很大程度上被反向作用所抵消流向管道。由于这种原因，从定期反转的直流电流通过电解而产生的腐蚀比始终朝同一方向流动时要小得多，而且这种腐蚀会降低逆转频率的增加。调查表明，即使在二十四小时内仅发生一次这种逆转，铁的实际腐蚀量仅约为如果始终从管道流向周围土壤的相同量的电流，则会发生的四分之一。当商业频率的交流电流在管道和周围土壤之间流动时，电解产生的腐蚀量为1％或较少的腐蚀，而腐蚀会由相等的直流电流从管道连续流动而产生到土壤。
