Cathodic Protection Potential Detection And Condition Assessment For In-service Subsea Pipelines

Subsea pipelines are the integral part of offshore oil and gas energy gathering and transmission.Subsea pipelines are highly susceptible to corrosion when fully exposed to the complex environment of the sea.According to the statistics of submarine pipeline accidents in China and abroad.Corrosion is the main factor of submarine pipeline failure.Once a pipeline fails,huge economic may losses and irreparable environmental may damage.The combination of external anticorrosive coating and sacrificial anode cathodic protection is generally used in subsea pipeline corrosion protection projects.As the service life of the pipeline increases and the surface anticorrosive coating continues to break down,and the sacrificial anode is used in a considerable quantity,which may lead to the cathodic protection system facing failure.Accurate detection and effective assessment of the cathodic protection status of subsea pipelines is therefore key to preventing accidents due to corrosion on subsea pipelines.The purpose of this study is to assess the validity and accuracy of the in-service submarine pipeline cathodic protection potential detection method for the remote reference electrode potential difference measurement in a real sea environment.Based on the existing work,a live sea trial of probable detection of undersea pipelines under unburied and 1m/0.5m buried conditions were conducted.Secondly,cathodic protection status of undersea pipelines is assessed based on the undersea pipeline potential detected by the method.The assessment includes the rate of coating breakage,the working condition of the sacrificial anode and the remaining quality of the sacrificial anode in relation to the impact of the cathodic protection condition.This paper firstly introduces the corrosion mechanism of submarine pipelines in the marine environment,and elaborates the principle of submarine pipeline cathodic protection potential detection method based on remote reference electrode potential difference measurement,and introduces the theoretical basis of numerical simulation method and artificial neural network.Based on the existing test model of a real-life subsea pipeline with a total length of 114 m and an integrated potential detection device carried by an ROV,the probable detection test was carried out in the actual sea environment.A detailed design of the methods and processes for the implementation of unburied and buried conditions in the vital sea environment.Results of empirical tests in the acutal sea environment prove that the probable detection method based on the potential difference measurement of the remote reference electrode has a high detection accuracy in the sea and can be used in the actual subsea pipeline cathodic protection potential detection project.In order to evaluate the cathodic protection status of in-service submarine pipelines,numerical simulation of cathodic protection was carried out based on a real sea test model.And the correlation between the electric field of cathodic protection and the parameters influencing the cathodic protection status of the pipeline was conducted.A Bayesian regularized BP neural network model was designed by using Matlab software,and programed an interface for Submarine Pipeline Cathodic Protection Condition Assessment.The data from the real sea potential detection was input into the evaluation program for testing,and the evaluation results were generally consistent with the actual situation,proving the effectiveness and feasibility of the numerical simulation-based and artificial neural network methods in the assessment of the cathodic protection status of submarine pipelines.