Abstract
Cathodic protection systems for offshore petroleum production platforms have commonly been designed for 20 years; however, because service life has been extended beyond this in many cases, retrofitting is required. A fundamental parameter needed for efficient, effective design of such retrofits is the structure current demand or maintenance current density at the time of the cp redesign. Five possible methods are identified for assessing this parameter, including 1) polarization of the structure, 2) anode potential measurements, 3) field gradient measurements, 4) the potential difference - modified Dwight equation (Δϕ-MDE) method, and 5) gaussian ammeter measurements; and test facility experiments were performed using the latter three. Based upon results from these, the Δϕ-MDE and gauss meter methods were utilized comparatively in conjunction with a newly proposed inspection protocol to perform cathodic protection surveys on three Gulf of Mexico platforms. The results from these are presented along with an assessment of the advantages and disadvantages of each current demand assessment method.
