Wyniki 1-1 spośród 1 dla zapytania: authorDesc:"Markus BÜCHLER"

AC-corrosion on cathodically protected pipelines: A description of the involved processes, the risk assessment and a new normative approach DOI:10.15199/40.2018.8.1

  1. Introduction Within two extensive DVGW research projects [1, 2] the interference values specified in ISO 18086 were confirmed by laboratory and field investigations. Unfortunately satisfying the current density requirements at increased ac-interference levels, high protection current demand of the pipeline, heterogeneous soil resistivity, and dc-interference conditions was found to be challenging in the practical application. This is mainly a result of the required less negative on-potentials (Eon) that do not leave room for required adjustment of the rectifiers. This inherently bears the risk that the shifting of the Eon to less negative values results in an important decrease of the accorrosion risk, but increases the risk of not meeting the requirements of EN 12954 and ISO 15589-1 with respect to cathodic protection (CP) effectiveness. Hence, controlling ac-corrosion can readily result in corrosion due to insufficient CP. Within the DVGW research projects corrosion rates higher than 100 mm/year were observed on electrical resistance coupons (ERcoupons) demonstrating that the control of ac-corrosion has highest priority. However, these high corrosion rates were never present for longer periods of time on these pipelines, since they were operated for several decades under these conditions and would have shown leaks. This discrepancy between coupon data and operation experience was attributed to the specific geometry of the polymer adjacent to the ER-coupons or temperature effects caused by the discharge of high current densities. However, further investigation made clear that neither effect can explain the relevant difference in corrosion rate on the coupon and the pipeline. Only more recent investigations based on the numerical description of the effects taking place under cathodic protection, provided a conclusive explanation for this discrepancy [3-5]. These model calculations result in two key conclusions: AC-corrosio[...]

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