DEFORMATION MECHANISMS IN CASE OF DESTRUCTION OF THE TUBING NOZZLE MADE OF FERRITE-PEARLITE STEEL

Abstract

In the work by methods of experimental studies and computer modeling, deformation mechanisms were analyzed during the destruction of the steel suspended branch pipe of the tubing. Tubing rupture occurred during production well operation for 306 days as a result of hydrogen sulfide stress corrosion cracking (SSCC), which was preceded by hydrogen embrittlement of the metal and cyclic action of external forces. Scanning electron microscopy (SEM) shows that the suspended branch pipe is characterized by a ferrite-pearlite structure, and in the area of its fracture, which occurred in the threaded part, there is an increased content of degenerated pearlite grains and traces of hydrogen blisters. Analysis of the crystallographic texture of the original nozzle showed the presence of Br {110} < 112 >, G {110} < 001 >, TG1 {111} < 110 >, TG2 {111} < 011 >, RG {110} < 110 > and RC {001} < 110 > grain texture components. It was found that after operation of the nozzle in well conditions, in the area far from the fracture, the grain orientations related to Cube {001} < 100 >, TG1 {111} < 110 >, TG2 {111} < 011 >, TB3 {331} < 136 > texture components increase. It was found that in the fracture area, in addition to the grain orientations characteristic of the nozzle body, there are also Br {110} < 112 >, G {110} < 001 >, RC {001} < 110 >, RG {110} < 110 >, TC {112} < 110 >, TB1 {111} < 112 > and TB2 {554} < 225 > texture components It is shown that Cube and grain orientation TB3 in the branch pipe after operation accelerate the process of hydrogen embrittlement of metal, and the presence of TB1 orientation indicates the process of return and/or recrystallization in the product. It was found that the process of hydrogen embrittlement led to a decrease in the strength properties and ductility of the steel of the branch pipe. Within the framework of viscoplastic self-consistent (VPCC) model, textures and deformation behavior of samples cut from different sections of the nozzle (before and after operation) were simulated. It was found that at the initial stages of tension the samples of the new branch pipe, the most active is the operation of {110} < 111 > slip systems. In samples of the nozzle after operation, the activity of {110} < 111 > slip systems decreases. At the same time, the activity of {123} < 111 > slip systems increases, and the nature of the operation < 112 > {111} of the slip system does not change. It was found that in all studied states before destruction the activity of {123} < 111 > systems increases ~ 1.4 times. It was concluded that the growth of TG2 {111} < 011 >, {332} < 110 > and {557} < 110 > texture components, as well as the activity of < 123 > {111} slip systems are associated with the effect of shear deformations that generate microcracks in pearlitic grains, and the applied forces contribute to the development of cracks and subsequent destruction of the product. It has been shown that by controlling the crystallographic texture and, accordingly, deformation mechanisms, it is possible to produce new pipeline steels that are more resistant to SSCC.