Subsea FRP pipeline performance in external pressure: Failure and external pressure-induced buckling

The Subsea pipelines are subjected to high hoop stresses due to the hydrostatic pressure. When the internal pressure of the liquid has a higher value than the external hydrostatic one, there is a balance of the tensile and compressive stresses. However, during the offshore installation, the subsea pipelines are empty and the compression due to the hydrostatic pressure of the sea is predominant. High compressive stresses in FRP pipelines can cause failure or buckling. In the present work, an investigation of the external pressure-induced failure and buckling is carried out. Analytical formulae and results are provided and discussed.

Structure Partition and Reasonable Width Determination of Waterproof Coal Pillar in Strip Mining

Retaining a waterproof coal pillar is the most effective water conservation method for a roadway close to the gob, and determining a reasonable width of the waterproof coal pillar has been a common problem among mining scholars for a considerably long time. Based on the mining of the 15208 mining face in Xinjing Coal Mine, the structure of waterproof coal pillar is divided into a mine-pressure-influenced plastic zone, an effective waterproof elastic core zone, and a water pressure failure zone. The mine-pressure-influenced plastic zone width is determined by using the limit equilibrium theory, the parabolic strength theory, and the separation variable method. The effective waterproof elastic core zone width is determined by the semi-inverse solution method, and the water pressure failure zone width is determined by considering the infiltration and softening of water. After that, combined with the previous theoretical analysis of engineering examples, the theoretical value of waterproof coal pillar width is obtained. In addition, the physical shape distribution of the waterproof coal pillar is measured by ultrasonic detection technology. The results are consistent with the field measured results. The correctness of the model is verified. Finally, the rationality of the model is verified by comparing with the previous classical models. The research results are applied to the design of the waterproof coal pillar in Xinjing Coal Mine, which could provide a theoretical basis for determining the width of the waterproof coal pillar located close to a gob.

Analytical study on stability of microspheres in syntactic foams structure under hydrostatic compression

This paper analyses prediction methods for failure pressure of microspheres in the structure of syntactic foams, discussing several micromechanical models. The solutions were obtained as per linear elasticity theory and finite-element method. It was investigated how geometric and physical & mechanical characteristic of syntactic foams depend on its components. Pressure failure is much lower if the boundary of the medium is close to the inclusions. This paper suggests an analytical model that yielded conservative estimate of critical pressure for microspheres.

Impact and internal pressure failure of E-glass and S-glass epoxy composite elbow pipe joints influenced by sea water

Consequences of sea water absorption on the impact behaviour of glass/epoxy composite elbow pipe joints were experimentally investigated. Glass-epoxy elbow pipe joints using E-glass and S-glass were fabricated via the hand layup method. The pipe joints were immersed in water as per the current conditions for 0, 3 and 6 months. The relation between the unaged and aged samples was studied by calculating the contact force, displacement and absorbed energy values from the impact tests. Therefore, it is concluded that sea water raised the ageing period of both E-glass/epoxy and S-glass/epoxy fibre-reinforced composite elbow pipe joints which resulted in the degradation between the fibre and resin interface and which was prominent in the elbow joints fabricated with E-glass rather than the one’s fabricated with the proposed S-glass fibre.