Shallow Resistivity Measurements for Subsoil Corrosivity Evaluation in Port Harcourt Metropolis, Nigeria

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Author(s) S.A. Ngah | T.K.S. Abam
Pages 85-91
Volume 3
Issue 2
Date February, 2014
Keywords Resistivity, corrosion, subsurface installations, Port Harcourt, Nigeria.

Variations in electrical resistivity, a diagnostic physical property of geologic materials, have been investigated in Port Harcourt Metropolis using Schlumberger electrode configuration. The aim of the survey was to assess the corrosivity of the subsoil environment with a view to deciding on the components to be installed underground and the appropriate protection measures to be taken against corrosion to achieve expected design life. Depth to groundwater level in the area is shallow necessitating that groundwater be protected from pollution resulting from corrosion. Two geo-electric resistivity layers were distinguished to a depth of 40m based on characteristic resistivity ranges and were interpreted in terms of soil type, water level and lithology. The upper layer with resistivity values between 11 – 53 ohm-m has a thickness of between 5 - 13m. The lower layer has higher resistivity values; 68 – 875 ohm-m. The resistivity values of the upper layer fall within corrosive – moderately corrosive, while the lower layer falls within moderately corrosive – slightly corrosive in the BS Soil Electrical Resistivity Classification. Shallow installations will suffer corrosion from aggressive subsoil if appropriate measures are not taken to protect them. Groundwater quality will be a major casualty of corrosion of unprotected buried steel pipes since groundwater table is shallow to near-surface.

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