Papers by Keyword: DWTT

Abstract: DWTT (Drop weigh tear test) is an effective way to evaluate the fracture propagation for pipeline steel. The effects of slab reheating temperature, soaking time, single pass reduction ratio during recrystallization zone rolling and transfer bar ratio during non-recrystallization zone rolling on DWTT performance were studied for heavy gauge pipeline steel. And the grain refinement and toughening mechanism were discussed. It was found that the grain in the core of the plate can be refined by reducing the reheating temperature, increasing the single pass reduction ratio during recrystallization zone rolling and setting suitable transfer bar ratio during non-recrystallization zone rolling, which promote the DWTT property improvement for heavy gauge pipeline steel. The 30.9mm heavy gauge pipeline steel plate was industrial produced and the X70 UOE welded pipe with dimension in Φ1219×30.9mm was manufactured. The DWTT 85%FATT (fracture appearance transition temperature) of pipe body is as low as -20°C.

Abstract: The replacement of 22mm thick X80M hot rolled strip for the traditional heavy plate production technology has remarkable advantages in improving the yield, reducing the cost of manufacturing and improving the outer diameter adjustment of pipeline. Low temperature anti Drop Weight Tear Test (for short DWTT) performs one of the key research problems of 2250mm hot rolling line production of this specification. Aiming at the problem of the substandard performance of rolled DWTT development process, the slab fracture morphology of different proportion and slab thickness direction component segregation degree of system were analyzed through the electron microscope. The results showed that the thickness of steel strip was serious segregation and is the main factor affecting the performance of DWTT. By optimizing the caster arc alignment and secondary cooling water, then improving the central segregation effect, the performance of DWTT can be effectively improved, and a stable development and production of 22mm thickness X80M pipeline steel hot rolledstrip can be achieved.

Abstract: Drop Weight Tear Testing (DWTT) method is widely used for determining a materials ability to arrest a propagating crack. The influence factors of DWTT are discussed for X70 thick wall linepipe steel. The effects of nonuniformity of the material, ductile-brittle transition temperature, notch type, evaluation method of the fracture surface, machining method and the test equipments are discussed. Some solutions and recommendations to the problems are proposed.

Abstract: The DWTT fracture toughness of X70 pipeline steel with different content and grain size of polygonal ferrite was investigated. The results show that when the content of polygon ferrite is above 28%, the shear-area percentage of DWTT fracture begins to decrease instead of increase, while polygonal ferrite toughening effect weakens. It is the difference of the polygonal ferrite content that results in the difference of shear-area percentage of DWTT fracture.

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.