Abstract
In this research, we aimed to investigate the level of damage occurred in the steel tube material grade CK45 (AISI 1045) after a short period of service in an output desalination unit of an oil refinery industry. Visual examinations revealed that the material of the failed tube had significant thickness reduction and also localized corrosion damage. Energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction spectrum show that the corrosion products mostly consist of oxygen as the main element and slightly sulfur. Metallographic observations on the failed sample show that the observed pinholes were initiated on the inner surface of the tube sample where the surface was exposed to a possible mixed corrosive gas of H2S, CO2, and naphthenic acid. It is assumed that a severe thickness reduction has been initially taken place from the inner surface of the tube, and consequently the condensation of byproducts led to development of a localized corrosion and formation of pinholes due to flow stream of corrosive exhausted gases in output oil–gas separator vessel of the desalination unite. Presence of metallic elements in the EDS analysis such as calcium, magnesium, potassium, aluminum, manganese, silica, and zinc confirmed the possibility of condensation of corrosive compounds on the inner surface of the carbon steel tube grade CK45 in output oil–gas separator vessel of desalination unit. Microhardness measurements confirm that the steel tube has no hardness change in its core and outer surface. However, slight reduction in hardness is noticed near the inner surface of the tube sample which can be attributed to the presence of the pinholes. Electrochemical corrosion studies were carried out in the corrosive media filled up with a NACE ID 182 solution. Electrochemical investigations revealed that the corrosion products formed are typically porous which cannot provide a protective layer on the surface of the steel tube sample. Finally, recommendations mainly include application of protective coatings on the inner surface of the tube sample, and/or substitution of more resistive alloys with lower susceptibility to corrosive environments. Moreover, operational conditions such as temperature, water to oil ration and addition of any emulsifiers should be precisely controlled in order to decline any unpredicted fluctuations in output desalination unit’s products.
Published Version
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