Mechanical Response Characteristics Of The Paraffin Deposit In Pipelines

The investigation on the mechanical behavior of the paraffin deposits is to study the mechanism of the structural break for the paraffin deposits and analyze the slippage of the paraffin deposits in inclined pipelines, so that the block of the oil pipeline during shut down period can be analyzed as well. Considering the similarity of the mechanical behaviors and mutual actions between gelled crude oil and paraffin deposits, a visco-elastic model and a nonlinear visco-elastic-plastic model were presented on the basis of creep tests under different shear stresses. By analyzing the time-temperature-stress equivalence of creep behavior for gelled crude oil, the main creep curve under reference stress and reference temperature was obtained. A visco-elastic model based upon the main creep curve was also presented. A variaty of methods were applied to analyze the mechanical and rheological behaviors of the paraffin deposits and gelled crude oil in Weijing oil pipeline, for instance, using X-ray diffractometer and polarizing microscope to study the microstructure, using differential scanning calorimeter to study the thermal characteristics, and using rheometer to study the rheological properties. It was shown that the wax crystallization styles of paraffin deposits and gelled crude oil were almost the same, while for the paraffin deposits, the wax crystal was a little bigger and the spaces among wax crystals were larger, resulting in loose structure. Rate-controlled shear tests without thermal treatment were applied to the paraffin deposits by the self-made direct shear apparatus. According to the test data, a visco-elastic model and a visco-elastic-thixotropy equation were presented, and the relaxation modules of the paraffin deposits under different temperatures were obtained. By virtue of ANSYS/LS-DYNA software, a finite element method was applied to analyze the longitudinal shear stress distribution of the paraffin deposits in the slope pipeline. It was shown that, the longitudinal stress distribution was dependent upon the pipeline slope angle, density and thickness of the paraffin deposits. By using ALE coupling-computation method, the slippage of the paraffin deposits in slope pipeline was simulated under conditions of different slope angles, slope distances, pipeline diameters, structural strengths and thicknesses of paraffin deposits. It showed that, the block of the pipeline due to the slippage of paraffin deposits were prone to occur in the cases of large slope angle, large pipeline diameter, large deposit thickness and weak structural strength of the paraffin deposits.