At present, with the development of long-distance transportation pipelines in China and the increasing of transportation distance, there are often fixed piers at the crossing point or along the route in the design process of external transportation pipelines.These weak areas are often protected by external casing, whereas for cathodic protection, these areas are more likely to have a shielding effect on the cathodic protection current and increase the corrosion risk of the pipeline.By analyzing the corrosion cases in the field, it is found that the corrosion usually occurs at the edge of casing.This paper makes a comprehensive comparison of various anticorrosion technologies, and finds out the reason for casing shield to cathodic protection current or the pipeline corrosion, and adopts a series of corrosion protection measures to prolong its life.Based on the investigation of the development status of protection at home and abroad, the rectification measures can be divided into two types: one is to fill the annular space with electrolyte, and the other is to inject the insulating material with good air tightness into the casing.