Studi kasus desain upgrading sistem impressed current cathodic protection untuk bagian dasar tanki t 1301 a b c d dan ab rerun tank di PT XX Kalimantan Timur sebagai metode pengendalian korosi eksternal = Case study of upgrading design for impressed current cathodic protection for bottom tank t 1301 a b c d and ab rerun tank at PT XX East Borneo as external corrosion control metode