Analysis of Laminations in X52 Steel Pipes by Nonlinear by Finite Element

Hydrogen induced cracking is of great interest in the mechanical integrity assessment of sour gas pipelines. Multiple stepwise cracks with internal pressure called laminations are often observed in pipelines and their interaction and coalescence may significantly affect the residual strength of the pipes. In this work, the interacting fields of noncoplanar pressurized laminations in the wall of a pipe under pressure are analyzed by nonlinear finite element, considering an isotropic hardening law and the real tensile properties of the X52 steel. The results are presented as the evolution of the stress fields in the interlaminar region as a function of the pressure inside the laminations. It is found that for two approaching stepwise laminations, the critical pressure follows a hyperbolic type law. It is observed that for two cracks with lengths of less than 6.35 mm, the interlaminar region resists a critical pressure between 110 Mpa and 124 Mpa, respectively, for thicknesses 15.8 mm and 25.4 mm. The critical pressure is defined as the pressure inside the lamination that causes plastification of the interlaminar region.