Nondestructive Testing of Concrete Structures

Introduction

Nondestructive testing (NDT) of metals is an integral part of the oil and gas, petrochemical, chemical, and process industries. There are well-established methods, codes, and standards within these industries that focus on the NDT of metals to ensure the integrity of piping, vessels, and other equipment. However, there is generally less familiarity in the industry with NDT methods used on concrete structures, despite the prevalence of concrete structures in these facilities. Concrete structures are commonly used for foundations, pipe racks, vaults, blast walls, tanks, spillways and pedestals. Because NDT methods for concrete are generally less known in these industries, they are less likely to be utilized in the inspection and evaluation of concrete structures.

This article will cover three concrete NDT methods and additional considerations will be presented for the use of these NDT methods within process facilities. Four brief case studies will also be presented that highlight the use of these NDT methods in the evaluation of concrete structures in process facilities. This article is geared toward inspectors, engineers, contractors, and others who desire to learn more about NDT tools available to aid in the evaluation of concrete structures in these facilities.

Concrete NDT Technologies

Ground Penetrating Radar

Ground penetrating radar (GPR) is a geophysical technique commonly used to evaluate concrete and geological materials. The method uses electromagnetic waves to assess the internal characteristics of these materials. GPR surveys performed on concrete structures allow for the detection of embedded features such as steel elements (e.g., steel reinforcement, prestressing/post-tensioning stands, anchor rods, metal, and plastic conduit), verification of geometry (e.g., element thickness), and localization of internal defects (e.g., internal voids or poorly consolidated concrete) (Figure 1). The GPR method uses a radar antenna that transmits electromagnetic waves from scans collected at the testing surface. Electromagnetic signals are reflected from material interfaces with varying dielectric properties and collected by the antenna. These signals are then amplified and displayed for subsequent interpretation (Figure 2). Various GPR devices and antenna frequencies can be utilized depending on the specific application and scope of the inspection.