SUBSEA PEC: The NDT Diverless Robotic System for the Pipeline Corrosion Inspection

Abstract

Abstract PEC (Pulsed Eddy Current) is an NDT system applied to many sectors, and nowadays it plays an increasingly significant role in the maintenance of the offshore structures. The operational principle is based on eddy currents created by a magnetic field induced in a metal structure. Through the reverse principle it is possible to analyze their behavior: we obtain information related to the average wall thickness and therefore of the corrosion status. Salient feature of PEC system is that it operates without removing, modifying or pre-treating the protective coating of the steel structure to be inspected. The physical human presence for the system utilization has been essential in the standard practice. In the offshore world this requirement is very expensive, risky to comply with and often even physically impossible to achieve. For these cases, the subsea technology has allowed developing systems aiming to replace the human presence if this is not achievable or economically not viable. The "Subsea PEC" technology has been strategically developed for deep offshore inspections; a completely diverless machine mounted on WROV is deployed on the pipeline. The machine operations are remotely controlled from the surface on board the vessel and underwater module is employed on the pipe. The system automatically performs all the placements along the pipe length in order to carry out sectional scanning and obtain corrosion status readings around entire pipe perimeter (360degree readings). A single placement of the system allows detailed scan around the targeted pipe section and includes inspection of one further meter in length along the pipe. This technology allows complete mapping of the pipeline corrosion status without production interruptions since no destruction or pre-treatment of the protective coatings is required. Subsea PEC has already achieved considerable success with encouraging results during inspections carried out in the Mediterranean Sea, Red Sea, the South China Sea and the North Sea.