External corrosion direct assessment of a 30 inches gas transmission pipeline has been done by the use of direct current voltage gradient in conjunction with close interval potential survey method followed by in-line inspection with magnetic flux leakage tools. The pipe line constructed from API 5L X60 coated with coal tar enamel which 16.5 km length and cathodicaly protected by two cathodic protection station. The result of in-line inspection was used for verification of the external corrosion direct assessment. There was observed a reasonable compatibility. The result of direct inspection of the detected defects showed that the vast majority of coating defects and external corrosion of the pipeline were located on inclined portion of the pipeline. Our investigation showed that cathodic protection of the pipeline was not effective due to interference and shielding effect in the defected area.
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