Studies and Research on Determining the Cause of the Cracking of X60 Pipeline in the Expanding Operation

Résumé

In this paper was followed the determination of the cause of pipe cracking in the expansion operation. The metallographic analysis of a sample taken from the X60 pipeline was performed to determine the cause of pipe cracking. The structure of the material presents the following defects: linear macro-inclusions type silicates fragile, which layer the material and affect virtually all the thickness of the board; linear segregations in carbon, thickness 0.4-1.5 mm; segregations area in sulphur, and linear segregation in sulphur at the half thickness of the board; in the area of the fissure, the presence of hard particles, with the hardening structure, which influenced the normal flow of steel to deformation. The presence of hard particles, with the hardening structure, in the rift area influenced the normal flow of steel to deformation. The presence of the overlay formed in hot lamination on the surface of the board indicates the existence of a material defect, which changed the normal flow of the material during deformation. At the expansion operation, in the area of overlap of the material, due to these structural inhomogeneities, the limit of breaking resistance was exceeded, and the material was cracked on about 90% of the thickness of the table.