Papers by Author: Chun Yong Huo

Abstract: The cooling medium choice is restricted due to no detailed regulations for temperature control as the specimen with gaseous cooling medium in the API, ASTM and the standards or specifications of China. The analysis and calculating are made to the physical process of the cooling. The preservation hold time are provided for DWTT specimen at different temperature in the gaseous cooling medium. It provide primary sustaining base to control the cooling process of gaseous cooling medium. The essential point of the precise means of temperature testing is brought forward at the same time.

Abstract: The delamination cracks and its effects on the fracture of pipeline steel are investigated experimentally by using of Drop-Weight Tear Test (DWTT). The delamination cracks are produced by the stress perpendicular to the weak interfaces before main crack beginning or accelerating, no new delamination crack is produced during the stabile propagation of fracture. The quantity, splay degree of delamination crack and the space between two delamination cracks are influenced by the stress state of the crack tip at beginning or accelerating point of main crack and the length of delamination crack is influenced by the stress state of the crack tip during the propagation of fracture. The surface of delamination crack is cleavage fracture appearance with large cleavage facet. There is no delamination crack on the brittle fracture surface below the brittle-to-ductile temperature or on the brittle fracture region of mix-mode fracture surface with ductile and brittle region. The part of fracture surfaces with delamination crack ought to be evaluated as the shear area because the delamination cracks are produced only on the ductile fracture surface or on the ductile part of fracture surface.

Abstract: Preventing pipeline from rapid crack propagation is a critical issue to avoid casualties and disasters. In this paper, by combining the energy balance theory with FEM simulation and arrest criteria, the numerical analysis is developed to solve the problem of crack dynamic propagation in gas pipeline. This simulation, in combination with the full-scale blast tests, provides a broad prediction of the dynamic fracture process. The crack tip opening angle (CTOA) criterion is consummated through the comparison between CTOA in FEM calculation and the critical value of (CTOA)C obtained by the experiment. The result of the simulation for the crack speed and location is consistent with data by Alliance and Japanese full-scale blast tests.

Abstract: The effects of thickness, notch orientation and delamination cracks on the impact toughness of X70 pipeline steel are investigated experimentally by use of the instrumented Charpy impact tests at different temperatures. The couple effect of delamination cracks, thickness, notch orientation and temperature is discovered. The delamination cracks have certain direction, and their amount and size are related to the temperature and the specimen thickness. Though the delaminating orientations of T-S and T-L specimen are not same, the reasons for both T-S and T-L specimen delaminating are that the weak interfaces in the specimens are pulled apart by the stress perpendicular to them. The delamination cracks can improve the actual impact toughness of X70 pipeline steel both T-L and T-S specimens. The effect of delamination cracks on the actual impact toughness changes with the thickness and the temperature. The couple effect of wall thickness, defect orientation and working temperature of pipeline must be taken into account in safe assessment of pipeline.