Abstract
Accurate corrosion growth predictions are important to determining pipeline integrity verification reassessment intervals and to justify maximum allowable intervals. One existing method to determine a corrosion growth rate is to measure corrosion rate on the basis of linear polarization resistance (LPR) at a dig site where corrosion was identified. This method requires technical improvements to represent corrosivity of a pipeline. Thus, the need was identified to develop an electrochemical testing method which can be employed at the pipeline excavation (dig) sites which will generate corrosion rate data for determining external corrosion integrity verification reassessment intervals. The scope included developing and field-testing of the cells for in-situ corrosion rate measurements. Two cell designs were assembled to enable Linear Polarization Resistance (LPR) measurements in situ in field conditions. Field demonstrations indicate that utilization of the cells facilitates the use of the LPR technique as the basis for determining integrity verification reassessment intervals. The proper approach to corrosion rate calculation requires the use of raw data generated during the LPR test (polarization resistance free from the soil resistance contribution) and direct measurements of the anomaly dimensions (particularly the depth of the anomaly). To estimate the effect of corrosion mitigation due to cathodic protection, the amount of polarization shift must be known and the Tafel behavior of the steel/surface products interface must be either determined during the field measurements or assumed.
