Assessment of reinforced concrete structures in marine environment: a case study

This paper presents the results of a series of investigations that were performed on a reinforced concrete bridge structure exposed to marine environment in subtropical weather. Data were obtained by assessing the structural conditions using visual observations, nondestructive evaluations, and laboratory testing in order to define the cause and the level of concrete deterioration due to corrosion. In addition, a probabilistic methodology was used to compute the time of corrosion initiation focusing on reinforced concrete subjected to a similar chloride environment. The initial service life was predicted with a method that employed the use of statistical models of the governing parameters obtained from field data. Results show that this approach could be utilized for assessment of existing and new constructions and/or as a tool for decision-making process during the structural design phase.

A Uniform Linear Multi-Coil Array-Based Borehole Transient Electromagnetic System for Non-Destructive Evaluations of Downhole Casings

Borehole transient electromagnetic (TEM) techniques have been proven to be efficient for nondestructive evaluations (NDEs) of metal casings using eddy-current properties. However, physical limitations and bad borehole conditions restrict the use of eddy-current sensors, which makes downhole casing inspections very different from those of conventional NDE systems. In this paper, we present a uniform linear multi-coil array-based borehole TEM system for NDEs of downhole casings. On the basis of the borehole TEM signal model, a numerical multi-coil array approach using the Gauss–Legendre quadrature is derived. The TEM response can be divided into two independent parts related to the transmitting-receiving distance (TRD) and the observation time and casing thickness. Using this property, the signal received by the multi-coil array is weighted to cancel the influence of the TRDs of the different array elements to obtain the optimal response according to the linearly constrained minimum variance criterion, which can be shown to be identical to that of achieving the maximum signal-to-noise ratio. The effectiveness of the proposed method was verified by applying the uniform linear multi-coil array to a borehole TEM system for NDEs of oil-well casings. Field experiments were conducted, and the results demonstrate the effectiveness of the proposed method.