This study dealt with the capacity of the inline technique to upgrade steel-pipe-based hydraulic systems with respect to magnitude attenuation and pressure-wave oscillation period expansion. This technique consisted in replacing a short-section of the induced transient pressure region with another of plastic material type, including high- or low-density polyethylene (HDPE or LDPE). The method of characteristics was implemented to discretize the extended one-dimensional water-Hammer Equations, embedding the Ramos et al. formulation. The comparison of the numerical solution with the observed data, quoted in the literature, and alternative numerical solution demonstrated the accuracy of the developed solver. The test case addressed a transient flow involving the cavitation onset. Results showed that the HDPE plastic-short-section-based layout of the inline technique provided the best tradeoff between magnitude attenuation and pressure-wave oscillation period expansion, in comparison with the LDPE plastic-short-section-based layout and the HDPE or LDPE material-based main-pipe systems.