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Yield stress is a key rheological parameter of dense paste. Considering practical utility and to estimate the possible slipping flow, yield stress measurements were carried out using the curve extrapolation method and vane method with rheometer in both controlled shear stress (CSS) and controlled shear rate (CSR) model. All measured yield stresses show to increase exponentially with concentration in different scale. The vane method yield stresses are both higher than the extrapolation curve yield stress. For the coal slurry used in this paper, the extrapolation curve yield stress is lower by 17–30% than the dynamic yield stress that obtained under test model CSR. It indicates that wall slip exists in pipeline transportation; meanwhile wall slip can reduce transportation resistance of dense paste to some extent.

The yield stress is a key rheological parameter of thick paste and critical design parameter of the high pressure pipeline system. Take coal slurry as an example, whether using vane method or curve extension method, the yield stress both exponentially increase with concentration increasing, but the data of yield stress in two methods is different. For pipes with different diameters, the yield stress showed in pipeline transportation varies during the extension of rheology curves. By contrasting the results of curve extension method and vane method using pipelines with different diameters, it comes that with a certain concentration and a certain range of diameter, yield stress with vane is bigger than that with curve extension, due to the effect of wall slip in pipe flow test.