Dynamic macro modeling for the soil characteristics as a complement for the pre-evaluation step in the external corrosion direct assessment (ECDA) method
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abstract
External corrosion direct assessment (ECDA) includes four steps as a recommended methodology in NACE SP05021. The first is the pre assessment; this initial step considers the recollection of parameters influencing the time-dependent treatment for underground pipelines, feasibility of the method, tool selection for indirect inspection, and region identification. The pipelines as electrochemical cells include physical characteristics (working electrode), soil conditions and environment surrounding the metallic structure (electrolyte and interface) that are not only a function of position, but time. Corrosion as a time-dependent threat is magnitude directly influenced by dynamic parameters, such as the water content and drainage properties in the soils. Dynamic macroscopic changes lead to the collection of more parameters, localized areas where the phenomenon can occur at specific regions, and the technologies that are feasible to apply can be more reliable defining the regions based on evolution and location of water distribution. This study aims to provide a framework on how and what to study in the soil moisture for external pipeline corrosion research. It is composed of three parts: (1) the study of geographical information of the region and the determination of the precipitation pattern, (2) the determination of top soil moisture field capacity from the soil survey information and top soil moisture with the application of water balance method, and (3) applying Richards equation for flow in unsaturated soil to estimate the soil moisture (soil water content) surrounding the pipelines. This work proposes the macromodeling concept based on the water distribution in different regions throughout the year due to the climate, rainfall, and environmental parameters. The watersheds give the location and time for indirect survey deployment. Indirect measurements are considered for a specific region close to the Gulf of Mexico. 2013 by NACE International.
