Metallography of an Underground Oil Pipeline

The purpose of this article is to show a metallographic analysis of an underground pipeline taken out of operation upon failure. The pipeline had an 8.89 cm (3.5”) diameter and a 7 mm thickness. The study was based on a 45 cm long pipe sample, visibly and entirely corroded, with a fish-mouth crack along its length. The work contributes to finding new ways to prevent structural failure, which has high-impact consequences from the point of view of production, damage to property, pollution, and risks to human live. Through this analysis the knowledge on behavior of failures in terrestrial ducts has been extended. Development of the research included metallographic, chemical, and mechanical tests on the sample in order to know the composition of the material, its strength and its physical conditions upon taking it out of operation. After the analysis of the laboratory tests, the physical and chemical features were compared to existing national and international regulations, which allowed a specific characterization of the conditions of the sample. In accordance with the regulations, the grade of the pipe was between ×65 and ×70. Tensile testing was carried out to obtain mechanical properties in order to corroborate the grade of pipeline steel and complement the metallographic analysis.