Residual harmfulness of a defect after repairing by a composite patch

The harmfulness of a defect in a CT specimen made in an API 5L X52 steel pipe is evaluated after being repaired with a composite patch. Due to the fact that the presence of a composite patch improves the fracture resistance but also modifies the constraint, a two-parameter fracture approach is used. More precisely, the stress field at the tip of a notch-like defect repaired by a boron/epoxy bonded composite patch is evaluated by the notch stress intensity factor K_ρ and the effective T-stress T_ef as constraint parameter. An assessment point of coordinates [. T_ef- K_ρ] is reported in the Fracture Toughness-Constraint Diagram{open box} (FTCD). A line from origin O and passing through this assessment point intercepts the Failure Material Master Curve. This procedure allows us to determine a patch repairing index which is a measure of the residual harmfulness of a crack-like defect after repair. The repair with a composite patch reduces significantly the defect's severity and increases the service life.