Failure analysis and prevention for lng cylinders with 3-d embedded cracks

Abstract

The increase in demand for Liquefied Natural Gas (LNG) has been increasing steadily the past few years due to its environmental benefits as well as low costs. Likewise, the demand for LNG bunkering facilities has increased as well in order to keep up with the higher demand in LNG fuel itself. At the moment, LNG bunkering regulations are yet to be established, hence proper risk assessments have to be done in order to identify potential hazards and ensure the safety of LNG cylinders in the relevant industries.

In this project, ABAQUS 6.10 was used to conduct J-integral analysis on 3 different LNG cylinder pipes, the straight pipe, the elbow joint, and the T-joint. For this analysis, the J-integral values were obtained for through the thickness cracks at various orientations, while varying the pressure, radius-to-thickness ratio and crack length. The results obtained showed that for all 3 types of pipes, under similar loading conditions, longitudinal cracks displayed a larger J-integral value as compared to circumferential cracks of the same size. However, the T-Joint and Elbow joint displayed larger J-integral values as compared to the straight pipe; which suggests that cracks along the T-Joint and Elbow joint have a higher tendency to propagate. This is especially so due to pre-existing flaws as well as residual stresses due to various manufacturing processes such as welding for these two types of joints. Hence, corrective and maintenance work has to be done more frequently at the joint areas to prevent any cracks from propagating.