海底パイプラインを模擬した水中ラプチャーディスク試験及びガス減圧の数値モデル開発

Abstract

In this research, atmospheric and underwater small-scale pipe rupture disk tests were conducted. Tested pipes with rupture disk were pressurized by pure nitrogen, in which internal pressure changes and external pressure changes were measured by pressure transducers. By comparing results of the underwater tests with results of the atmospheric tests, water effects were clarified: (1) gas decompression in the underwater tests delays due to constrained gas leak by bubble generation and growth as compared to gas decompression in the atmospheric tests, and (2) larger external pressure changes were measured in the underwater tests. In addition, 1D finite-difference based coupled model for gas decompression, in which gas flow inside a pipe and bubble growth are considered, was developed. In the model, governing equations for gas flow inside a pipe and a bubble are derived from mass conservation law and momentum conservation law assuming isentropic changes of gas. Bubble growth is formulated based on Rayleigh-Plesset equation. The calculated results for the rupture disk tests using the model showed good agreements with the experimental results, which analytically clarified the above stated water effects. This research reveals an importance of considering the water effects in evaluating fractures in offshore pipelines. In the future, it is expected that the model is extended to incorporate crack propagation and pipe deformation together with gas decompression and bubble growth.