Oil Pipeline Steels Research Articles

Modification of Non-Metallic Inclusions in Oil-Pipeline Steels by Ca-Treatment

Corrosion rate in different steel grades (including oilfield pipeline steels) is determined by the presence of non-metallic inclusions (NMI) in steels. Specifically, the effect of different inclusions on the quality of steels depends on their characteristics such as size, number, morphology, composition, and physical properties, as well as their location in the steel matrix. Therefore, the optimization and control of NMI in steels are very important today to obtain an improvement of the material properties of the final steel products. It is well known that a Ca-treatment of liquid steels in ladle before casting is an effective method for modification of non-metallic inclusions for improvement of the steel properties. Therefore, the NMI characteristics were evaluated in industrial steel samples of low carbon Ca-treated steel used for production of oil-pipelines. An electrolytic extraction technique was used for extraction of NMI from the steel samples followed by three-dimensional investigations of different inclusions and clusters by using SEM in combination with EDS. Moreover, the number and compositions of corrosion active non-metallic inclusions were estimated in hot rolled steel samples from two different heats. Finally, the corrosion resistance of these steels can be discussed depending on the characteristics of non-metallic inclusions present in the steel.

Effect of a heat treatment on the cold resistance of steels for oil pipelines

Effect of parameters of heat treatment of steel 20 microalloyed with vanadium on its microstructure and mechanical properties has been studied. It has been shown that the normalization performed before quenching from the intercritical temperature range and high-temperature tempering lead to the formation of an inhomogeneous microstructure with a preferred distribution of cementite particles near the boundaries of ferrite grains. The formation of such a microstructure is accompanied by a decrease in the cold resistance.