Influence Factors of DWTT for High Grade and Thick Wall X70 Linepipe

Drop-weight tear test(DWTT) is an important way to predict the pipeline will crack in brittle fracture way or in ductile fracture way. For the matter of great difference of DWTT results between the specimen with thickness reduced to 19 mm by machining from one surface and the specimen with full wall thickness of 765.2 mm×31.8 mm high grade and large thick wall X70 pipeline, the influence factors of DWTT results for thick wall X70 pipeline were analyzed from inhomogeneity of materials, ductile-brittle transition temperature, evaluation method for shear area rating of the fracture surface, machining method of the specimen with reduced thickness and the test equipments. Some solutions just as carrying the test on equipments with larger energy and using the full wall thickness specimens with Chevron notch were put forwards to avoid the test errors. The research for effects of rods size which supporting the specimens on DWTT results was proposed to carry out, and the rods size of the current criterion was recommended to change from (14.3±1.59) mm to (20±5.0) mm.