AN INVESTIGATION ON THE CAUSES OF CORROSION IN AISI 1009 STEEL PIPE OF THE FIRE LINE IN THE GAS REFINERY

In view of several reported cases of cracking in the piping of the fire extinguishing sector in the oil tanks, a detailed identification of the failure mechanisms was required for the safe continuation of gas processing. Therefore, this study investigated the damage of steel fire extinguishing pipes after a certain period of operation. Severe thinning of the wall thickness was observed in two parts of the pipe. Comprehensive analytical investigations, including optical microscope (OM), quantometer, XRD, FE-SEEM, EDS and microhardness were performed. In addition, the corrosion behavior of the material was investigated by polarization and EIS analysis and the most plausible reactions and corrosion mechanisms were elucidated. The corrosion products on the inside of the pipe included oxide compounds, while on the outside, it was mainly sulfides and oxides. A drastic and slight decrease in microhardness was observed near the inner and outer surfaces, respectively. Electrochemical tests proved the formation of a porous and non-protective layer of corrosion products. The corrosion resistance was found to be weak due to several factors: the nature of the AISI-1009 steel, several micropores, the periodic formation and removal of non-continuous oxide layers and the roughness that accelerated the strong thickness reduction.