Failure analysis and electrochemical testing of ammonium chloride corrosion in a heat exchanger in a diesel hydrotreating unit of a petroleum refinery

•Application of the method for evaluating the corrosive behavior of different austenitic stainless steel samples exposed in aqueous ammonium chloride medium;•Investigation into the formation of ammonium chloride salts in the oil and gas industry, especially in hydrotreatment units for petroleum products such as diesel;•Comparison between the most widely used corrosion evaluation techniques in electrochemical corrosion studies of metallic materials, the potentiodynamic polarization curves technique and electrochemical impedance spectroscopy;•Use of failure analysis methodology and non-destructive testing in the evaluation of the corrosive process in a heat exchanger of an oil refinery, thus providing the managers of the industrial plant and the maintenance teams with more comprehensive and valuable information;•Providing the design and material selection teams with the best and most indicated solutions in the choice of the most resistant steels to the exposure media in ammonium chloride corrosive environments. Crude oil is a complex mixture of hydrocarbons and can contain various impurities, which vary depending on the source and geographical location from which it is extracted. These impurities include sulphur, nitrogen, some metals, asphaltenes, non-condensable gases and salts. Salts in oil are typically found in the form of ions, which means that they are dissolved in the water present in the crude oil, or in the form of solid salts that are later deposited in equipment, pipes, and ducts. These salts can be harmful because, when the oil is processed, the water present in the oil can separate from the hydrocarbons and cause corrosion of equipment in the oil refining plant. In addition, salts can form solid deposits that can obstruct equipment. It is therefore important to remove or reduce the presence of salts in oil during the refining process to avoid operational problems and problems with the quality of the refined product. Several occurrences are reported in the specialized literature of equipment failures in the oil refining industry involving corrosion by salts, especially ammonium chloride salts. Basically, ammonium chloride, whose chemical formula is NH4Cl, is an inorganic chemical compound consisting of ammonium ions (NH4+) and chloride ions (Cl−), It is known by several names, including “ammonium salt” or “ammonium salt” due to its composition. The aim of this paper is to investigate the failure of a shell-and-tube heat exchanger in the charge p