In this work, we studied the internal flow of viscoplastic liquids through an expansion followed by a contraction, both abrupt and axissymetric, in tubes of circular cross section. Flows like this can be found in many industrial processes such as drawing, displacement of liquids in porous media (as for example, displacement of oil in porous rocks, called reservoirs), among others. We carried through tests for a wide range of the ratio between the lenght and diameter of the tube, and the ratio between the largest and smaller diameter as well as for different flow rates. We observed yielded and non- yielded regions of the fluid for different combinations of these parameters. The yield stress strongly affects the flow pattern through the tube. For low values of the length-to-diameter ratio, the viscoplastic liquid has a border dividing it in two regions: in the external part of the border, a region in which the fluid is not yielded and in the internal part of the border, a region where the yield stress is exceeded and thus, the fluid flows. The phenomenon is known by fracturing. The behavior of the viscoplastic fluid is studied with the aid of the model of Souza Mendes and Dutra (2004).