Chilled water is a popular cooling medium in HVAC system, which is always distributed to air handling units through the pipes. However, a seriouscorrosion problem has been found for the piping system if no preventative measure is taken. In order to mitigate the corrosion of pipes, the application of corrosion inhibitor and laser surface melting on black steel were attempted. Black steel samples were immersed in tap water medium at various temperatures (5 and 13 oC), and various concentrations of sodium nitrite-based corrosion inhibitors for investigation. This study concerns the assessment of the inhibition effect by using potentiodynamic polarization method and microstructure analysis. In this thesis, sodium nitrite-based corrosion inhibitor was found to be significantly reduced the corrosion rate of specimens in tap water and formed a protective coating in-situ by the reaction between the solution and the steel surface. In addition, it was observed that this improvement was related to the concentration of inhibitor and optimum concentration was evaluated. On the other hand, influence of laser surface melting of black steel on both hardness and corrosion behavior was also studied. The microstructures of the as-received and laser-treated samples were characterized by using optical and scanning electron microscopy with hardness testing techniques, in various experimental conditions: with different laser beam density and scanning speed. Furthermore, investigation was also carried out on the corrosion characteristics of laser-treated specimens in 0.9 wt% NaNO2 solution and tap water at 13 oC In the case of laser surface melting, most of specimens show improved corrosion resistance and refinement of microstructure with hardness increment. In fact, the hardness and corrosion characteristic of all laser-treated specimens are strongly dependent on the scanning speed and power density of the laser beam, which in turn result in different microstructures.