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Several inadequate designs of cathodically polarized offshore and onshore pipelines have been reported in Nigeria owing to design complexity and application of the cathodic protection system. The present study focused on critical and detailed approach in impressed current and sacrificial anode design calculation methodologies for 0.5m diameter and 100000m length of X65 steel pipeline in onshore and 1.2m diameter and 120000m length of X42 steel pipeline in offshore of Niger Delta region of Nigeria. The impressed current design calculation showed 2592150mA of current demand and voltage of 1127585mV required to adequately protect the X65 pipeline with external surface area of 86405m2. The current and voltage requirements were achievable by installing six transformer rectifiers with minimum direct current output of 500amperes and direct voltage output of 200volts. But the sacrificial anode design calculation indicated direct current output of 2262240mA was needed to marginally polarize the X42 pipeline with total external surface area of 226224m2. The computation further showed the current requirement was attainable with connection of 3620 anodes to set up a natural potential between sacrificial anode and pipeline.
Keywords: Cathodic protection, corrosion, impressed current, pipeline, sacrificial anodes