管道内壁实施阴极保护时,由于管内空间狭窄,电位分布不均匀。本文讨论外加电流阴极保护采用点状阳极时的情形。这时,管壁电位随着离阳极的距离按双曲余弦函数衰减。文中以大口径输水管的数值运算为例,分析了影响电位分布的各种因素。包括:管内介质的电阻率、管道内径和长度、内壁表面极化电阻以及阳极附近的内壁电位。电位分布随时间趋于均匀是由于极化电阻逐渐增大的结果。
Cathodic protection is generally recommended to control the external corrosion of pipe. Sometimes, however, internal cathodic protection is required. The impressed current protection is usually provided by using discrete inert anodes placed at intervals along the pipe. The characteristics of potential distribution under this condition is perhaps the most importan, aspect because of the limited space inside pipe. Corresponding mathematical expressions were derived. The potential is evaluated as a hyperbolic function of the distance from anode. The relationship has been verified experimentally. The dependence of potential on electrolyte resistivity, polarization resistance of inner surface, pipe diameter and length of pipe is illustrated. The protection current demand was also evaIuated on the basis of non-unlform distribution. Both laboratory investigation and operation experience showed the time-dependence of potential, which could be ascribed to the increase of polarization resistance of the pipe surface. The theoretical consideration presented here would be useful for the design of internal cathodic protection system of pipe in general and for the selection of the inter-anode spaceing in particular.
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