THE UNDERGROUND structures in a gas-processing complex were provided with impressed-current cathodic protection (ICCP) for protection against external corrosion. The lines were externally coated with coal tar enamel. The installation of ICCP was executed in two phases, in 1993 and 1998. On the basis of on' pipe-to-soil potential (PSP) measurement, it was observed that all the underground pipelines in the slug catcher area were not getting adequate cathodic protection. The available data was analysed, and a survey was also carried out in that area. On the basis of these studies, it was found that certain areas were under-protected. An additional current provided to an anode bed could raise the negative PSP of the lines; however, 'on' PSP still could not be attained to the level more negative than -0.85V for all the lines. Therefore, it was planned to carry out close-interval potential logging (CPL), direct-current voltage gradient (DCVG), and current attenuation test (CAT) surveys to find out the condition of the coating, interference, and current drainage, etc. Due to close proximity of the lines and the other infrastructure of the plant, there was a possibility of interference. The condition of the lines and coating was assessed by excavation of the area; seven locations along the route of the lines were excavated, and it was observed that the coating condition of some of the lines was poor. Thermit welding of one of the lines to a cathode junction box (CJB) was broken, and some of the lines were shorted. Therefore, it has been recommend to recoat those lines which had poor coating, provide proper connection of the lines to the CJB and test points, and provide insulation between the lines which are shorted. For rehabilitation purpose, it has been recommended that a cold-applied, three-ply/two-ply, PE-backed tape system should be used. For the coating purpose, the pipe surface was prepared by sand blasting using a wet nozzle. A three-ply inner wrap and a two-ply outer wrap system, along with a compatible primer, were applied with a total thickness of 3.0mm. After rehabilitation, the PSP values of the lines were even more negative than -1.5V as compared to -0.6 to -0.8 before rehabilitation.
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