51314-3850-A Direct Assessment of Effectiveness of Cathodic Protection At Corrosion Defects on Pipelines

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Product Number: 51314-3850-SG

ISBN: 3850 2014 CP

Author: Frank Cheng

Publication Date: 2014

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There have been a large number of factors that are able to affect pipelines integrity such as mechanical defects introduced by manufacturing and construction third-party damage ground movement corrosion etc. In particular corrosion is of great importance because the loss of pipe wall thickness can induce reduction of the pipeline structural reliability and hence an increase in the risk of failure.Cathodic protection (CP) is recognized as an effective method for corrosion prevention. Nevertheless it may become ineffective at corrosion defects such as pits and cracks. Regrettably there has been no relevant work to investigate the effect of defect geometry on CP performance on pipelines. This is partially due to the experimental difficulty and inability of probes or electrodes to access to the environment inside pits and cracks. Also it is worth noting that the CP effectiveness at corrosion defects has not been paid appropriate attention.In this work the CP effectiveness at corrosion defects with varied geometries on pipelines was assessed both experimentally and numerically. A finite element model was developed to simulate distributions of anodic and cathodic current densities at corrosion defects on pipelines under CP. Empirical equations were derived for assessment of local corrosion growth on pipelines under CP. To validate the modeling results a home-made potential microprobe combined with a scanning vibrating electrode technique was used to measure the local potential and current density as well as their distributions in five artificial defects with various geometries existing on an X100 pipeline steel specimen. The implications on pipeline operation and the integrity maintenance were discussed.