Pressure vessels are subjected to deterioration and damage, which can significantly reduce their strength and loading capabilities. Among several procedures nowadays available to repair damaged steel pipelines, composite-repairing systems have become popular over the past few years to restore the loading capacity of damaged pipelines. This study reports a numerical-experimental investigation performed for a composite-repaired pipeline made of API 5L X60 steel. An experimental burst test was carried out on a 4 m long pipe section, closed by two lateral caps, and tested up to failure by means of high-pressure water. In parallel, the test was numerically replicated through a FEM model of the composite-repaired steel tank, allowing for a cross-comparison of results. It was found that the composite repairing system has almost eliminated both the noteworthy thickness reduction of 80% and the related stress concentrations in the pipe body. These outcomes allow for a better understanding of these repairing procedures in order to drive their subsequent optimization.

In this study, thermal buckling responses of a functionally graded (FG) cylindrical microshell are investigated. Material properties of the FG microshell are considered to be graded through the thickness based on a simple power-law distribution. The governing equations and associated boundary conditions are derived based on classical higher-order shear deformation theory. Size dependence of the FG microshell is properly characterized based on the modified couple stress theory (MCST). Two types of differential quadrature method (DQM) – polynomial based differential quadrature (PDQ) and Fourier expansion based differential quadrature (FDQ) – are adopted to transform the differential equations into algebraic equations. The standard eigenvalue equation in the whole computational domain is subsequently established to obtain critical buckling temperature. The present numerical technique shows very fast convergence speed and is validated by comparison with available data in the open literature. Parametric studies are provided to demonstrate the influences of the temperature distribution profile, edge boundary conditions, length scale parameter, length-to-radius ratio, FG power-law index on the critical buckling temperature. In addition, the values of critical thermal buckling loads predicted by classical and MCST models are compared.

The present research is concerned with the elastic–plastic responses of functionally graded material (FGM) pipe, undergoing two types of loading conditions. For the first case, the FGM is subjected to sustained internal pressure combined with a cyclic bending moment whereas, in the second case, sustained internal pressure is applied simultaneously with a cyclic through-thickness temperature gradient. The properties of the studied FGM are considered to be variable through shell thickness according to a power-law function. Two different designs of the FGM pipe are adopted in the present research, where the inner surface in one case and the outer surface in the other are made from pure 1026 carbon steel. The constitutive relations are developed based on the Chaboche nonlinear kinematic hardening model, classical normality rule and von Mises yield function. The backward Euler alongside the return mapping algorithm (RMA) is employed to perform the numerical simulation. The results of the proposed integration procedure were implemented in ABAQUS using a UMAT user subroutine and validated by a comparison between experiments and finite element (FE) simulation. Various cyclic responses of the two prescribed models of FGM pipe for the two considered loading conditions are classified and brought together in one diagram known as Bree’s diagram.