Neutrons can provide information related to the materials with which they interact, that is, to some extent complementary to that provided by X-rays for use in non-intrusive applications. The majority of studies to date have focused on the use of thermal neutrons with there being fewer reports concerning the use of fast neutrons despite the latter being able to penetrate deeper into substances. This record describes an investigation into the use of neutron radiation (from sources such as californium-252 and americium-beryllium) to characterize defects in the walls of oil pipelines. Both sources yield a mixed radiation field of fast neutrons and γ rays which can be collimated and directed towards the steel pipeline under study. Fast neutrons are either transmitted or reflected by the pipe wall. Since the incident radiation flux on the pipeline can be determined and the scattered neutron flux can be measured, the potential exists for an assessment of the ratio of transmitted and reflected fast neutrons to be made. If defects within the pipeline are present, the ratio may be observed to change as a result relative to that of the defect-free alternative. The scattered flux will be measured by an array of organic liquid scintillation detectors, coupled with a real-time, pulse-shape discrimination system. Both γ rays and neutrons are thus retained to provide transmission information about the pipeline sector being tested. A Monte Carlo model is used to simulate a generic pipeline section in order to understand its fast-neutron scattering response under different conditions. For instance, with the pipe filled with crude oil or partially filled with a combination of oil and gas, as well as for different types of effects to its inner structure. The results of these simulations will be presented to justify the choice of scatter arrangement, the optimum angle for the detector deployment and as evidence for the assessment of defects filled with air and for pits filled with oxide-based corrosion residues.