RIASSUNTO
ABSTRACT
The present work was carried out with the objectives of supplying to CP designers data collected insitu, in the actual environment in which the protected structure is deployed. Sensors arrays have been deployed at six different sites from 35 m to 900 m depth. The measurements are based on the deployment of a CPC sensor which records the coupling current between a cathode and an anode, and the cathode potential. The effect of temperature and pressure on calcareous deposit properties was put into evidence and was useful to explain the different pseudo polarization curves. For carbon steel: The results are broadly quite in a good agreement with standard and recomendation1,2. For stainless steel: The initial current was independent of the location; the steady state current demand at -600 mV/Ag.AgCl depends strongly on the environment ; the current demands tent to decrease with time in tropical and arctic zones, but increased in sub-tropical area and the current demand at - 950 mV/Ag.AgCl does not depend on the location.
INTRODUCTION
The durability of metallic structures exposed to natural seawater is often linked to the efficiency of protective systems which consist mainly of cathodic protection. Unsuitable cathodic protection may induce higher costs of installation and services, loss of performance of the structures, etc. The design of a cathodic protection system involves many calculations. The results are dependent on the structure (materials, surface area exposed to seawater, etc.) and environmental parameters. These parameters are connected to the properties of the interface metal/seawater and are specific to the structure (alloy, surface state, coating, biofouling, etc.) and the marine environment (salinity, dissolved oxygen, temperature, flow rate, etc.). The most common way to select current demand for a cathodic protection design consists in applying data available in the literature1,2. In case of inaccurate data with regards to actual parameters, this can result in an over/under-protection of the installation and therefore an over-cost or underestimated lifetime of the cathodic protection. An alternative way is to apply data collected in situ, in the actual environment in which the protected structure is deployed. Against this background, a project entitled “ICP-DATA” has been initiated with the participation of the following industrial partners: Statoil(1), Technip(2) and Total(3) The French Corrosion Institute and Ifremer carried out this joint industrial project, with the objectives of supplying data to cathodic protection designers such as: - Cathodic current demand and potential versus time exposure, - Environmental parameters. - Efficiency of galvanic anodes This paper covers the results obtained at different sites namely: Ormen Lange, Snøhvit (Norway), Tchibouela (Congo), Alwyn Platform (UK), Matterhorn (USA) and Bekapai (Indonesia).
EXPERIMENTAL PROCEDURE
The measurements are based on the deployment of a CPC sensor which records the coupling current between a cathode and a sacrificial anode, and the cathode potential versus a pseudo-reference electrode (pure zinc) as a function of time (Figure 1)