Study On The Internal Corrosion Evaluation Method Of BZ34-6/7 To Underwater Three-way Submarine Pipeline

In the case of submarine pipelines,the consequences are incalculable in the event of an accident.Corrosion is a safe and reliable operation of the most hidden dangers,including CO2 corrosion related accidents accounted for about 25%.The BZ34-6/7 to the underwater three-channel pipeline was put into operation in 2014 and has not yet been tested for CO2 corrosion risk.Therefore,it is necessary to establish an internal corrosion evaluation method suitable for the target pipeline,which can provide the basis for the determination of pipeline internal inspection and pipeline maintenance.It also plays a reference role in the internal corrosion evaluation of similar pipelines.Through data analysis,the corrosion experimental conditions of BZ34-6/7 to underwater three-channel pipeline are determined rationally.The dynamic reaction kettle and corrosion product test Platform(sem/eds)were used to study the effect of CO2 partial pressure,temperature,medium velocity and cl-concentration on the corrosion rate,and the corrosion regularity of the target pipeline was obtained.Based on the experimental data,the adaptive analysis of 4 typical carbon dioxide corrosion rates in Norsok M506,De Waard 95,Cassandra(BP)and DWM model was selected,and the results showed that the 4 models were not suitable for the pipeline.Therefore,the prediction and correction model of carbon dioxide corrosion rate suitable for target pipeline is established by using multivariate regression method.The internal corrosion evaluation method of multiphase flow submarine pipeline containing carbon dioxide is proposed,and the method is applied to the target pipeline.This paper mainly obtains the following 6 conclusions:(1)Carry out the experiment of dynamic reaction kettle corrosion,the results obtained are in agreement with the collected pipeline corrosion data,and the experimental data is reliable.According to the morphology analysis of the corrosion products,the corrosion products of the target pipeline are uniformly dense and not easy to fall off.(2)The results show that Norsok M506,De Waard 95,Cassandra(BP)and DWM carbon dioxide corrosion prediction models have large deviations and are not suitable for target pipelines.(3)Based on dynamic corrosion test data and Arenieu formula,considering CO2 partial pressure,temperature,medium velocity and cl-concentration,the prediction and correction model of carbon dioxide corrosion rate is established.(4)On the basis of the prediction and correction model of carbon dioxide corrosion rate established in this paper,the internal corrosion evaluation method of target pipeline is proposed,And the target pipeline is evaluated.The results show that the pipeline belongs to mild corrosion,and the wall thickness thinning is low wall thickness loss.According to the judging criterion in the internal corrosion evaluation method,the 12m?45m of pipeline is determined as the key point of corrosion monitoring.(5)In order to effectively reduce the risk of corrosion occurring in the submarine pipeline of BZ34-6/7 to the underwater tee,it is recommended to install an effective corrosion monitoring device on the corrosion inhibitor periodically and in the key monitoring pipe segment.(6)It is suggested that the non-contact magnetic stress anomaly detection method or other underwater wall thickness detection method be used for auxiliary judgment and verification,and the corresponding follow-up testing work should be carried out.