Cementite decomposition in the oil pipelines metal
<i>Background </i>Cementite (Fe<sub>3</sub>C) is one of the basic phases of oil pipeline steels. The mechanical properties of oil pipeline steels depend on the quantity of cementite. <i>Aims and Objectives </i>To determine the quantity of Fe<sub>3</sub>C in the metal of oil pipelines after long-time (33 years) operation. <i>Methods </i>X-ray analysis based on the interpretation of the diffraction lines. <i>Results </i>Cementite decomposition results in the release of a certain number of carbon atoms, part of which comes in the tetrahedral caverns of the body-centered cubic lattice of the ferrite. There is determined the amount of Fe<sub>3</sub>C in the oil pipelines metal (14ГН steel) after long-time operation. The results obtained show that after the 33 years of exploitation 15 % of the 14ГН steel cementite is decomposed.