Study of corrosion process of surface hardened structural steel for application in petroleum industry

In this Master thesis, the process of corrosion in S235 structural steel in sodium chloride solution, technological condensate of industry, and ammonium hydrogen sulphide was studied. The process of corrosion was investigated by the use of linear polarization resistance method. Surface hardening of the structural steel samples for reducing the corrosion rate such as carburizing and annealing were used during the research. The process of corrosion in the aggressive media like the sodium chloride solution, technological condensate and ammonium hydrogen sulphide was reduced by using two inhibitors, CHIMEC 1839 and Stearin dissolved in Toluene. The hardness of the structural steel samples (annealed, carburized and nitrided) were measured using the Vickers Hardness testing machine and an analysis of each kind of sample with respect to their rate of corrosion in all of the aforementioned aggressive media was studied, leading to a detailed conclusion at the end.

Corrosion is an unavoidable problem in petroleum oil refinery industries due to the complicated work conditions such as high temperature, high pressure, pH value and ion concentrations in aggressive media. As the main construction material for equipment in oil, gas and petroleum industries is steel due to his availability, and low cost. The properties of numerous metals and alloys rely upon the condition of its surface layer. Strengthening (hardening) this layer can further improve the mechanical properties of the material. Thermochemical treatment is a process of saturating the surface layers of metals with one or more elements that alter the chemical composition of the surface layer and get the desired surface properties and microstructure. Thermo-chemical treatment of metal increases its resistance to abrasion and environmental effects (corrosion, high-temperature oxidation, acids).