발전용 플랜트 배관의 강도 및 변형에 미치는 내/외부 감육의 영향

Abstract

Fracture behaviors and strengths of pipes are very important for the integrity of energy plants, ocean structures, and so on forth. In pipes of energy plants and ocean structures, sometimes, the local wall thinning may result from severe erosion-corrosion damage. Recently, the effects of local wall thinning on fracture strength and fracture behavior of piping system have been well studied. In this paper, the monotonic bending analyses were performed on full-scale carbon steel pipes with local wall thinning on the inside. A monotonic bending load was applied to straight pipe specimens by four-point loading at ambient temperature without internal pressure. The elasto-plastic analysis was performed by FE code ANSYS on straight pipes with wall thinning. We evaluated the failure mode, fracture strength and fracture behavior from FE analysis. Also, the effect of the axial strain on deformations and failure modes was estimated by FE analysis. Experiments for effects of location of thinned wall on the fracture behavior of pipes were carried out, and were compared with the analytical results. Local wall thinning for the bending test was machined with the various sizes on the outside of pipes in order to simulate the metal loss due to erosion/corrosion. Accurate simulations of fracture behaviors of outer wall thinning, were possible by three dimensional elasto-plastic analyses and then FE analysis for the pipes with local wall thinning on the outside made a comparative study with that of inside. Fracture type obtained from the experiments and analyses could be classified into ovalization, local buckling and crack initiation depending on the thinned length and thinned ratio. From the results, the fracture behaviors of pipes with the outer wall thinning were showed that can be applied to estimate the fracture behaviors of pipes with the inter wall thinning. Monotonic bending tests were performed on full-scale welded carbon steel pipes with local wall thinning to compare unwelded ones. A monotonic bending load was applied to straight pipe specimens by four-point loading at ambient temperature without internal pressure. The observed failure modes were divided into four types; ovalization, crack initiation/growth after ovalization, local buckling and crack initiation/growth after local buckling. Also, the strengths of welded and unwelded piping system with local wall thinning were evaluated.