Pigging is widely used in pipelines for wax removal. However, pigging operation relies heavily on "rule-of-thumb." Because of its complexity and lack of methods, the wax removal mechanism is still poorly understood. This work aims to reveal the nature of the wax breaking process and thus promote understanding of wax removal physics. A unique experimental setup is designed and constructed to perform a series of wax removal experiments. The test section consisting of a 50-mm-ID, 600-mm-long, horizontal pipe has an accurate temperature control for wax casting and removal process. Different types of polyurethane pigs without oversize against the test section were used for the experiments to eliminate the influence of friction force between the pig and the pipe wall. Mixtures of crude oil and field wax deposit were cast inside the test section to carry out the experiments. In particular, a novel yield stress measurement was introduced into this study to characterize the wax hardness.The effects of wax thickness, mixing ratio of wax deposit to oil, pipe wall temperature, shape and aggressiveness of polyurethane pig on wax breaking force were investigated comprehensively. In particular, the dependences of wax breaking force on the pig aggressiveness and pipe wall temperature are clarified for the first time. In addition, it is found that the relationship between wax failure stress and yield stress can be well fitted as a linear relation. Furthermore, the dependences of wax breaking force on the wax hardness and pig design being used are revealed quantitatively. Subsequently, it is concluded that there is an overwhelming effect between wax failure stress and yield stress, where the wax failure stress exceeds the yield stress of the same wax deposit during the wax removal process. The findings of this paper are beneficial in determining the optimal de-waxing frequency and evaluating the pigging risks.

Corn starch was dually modified using thermostable α-amylase and pullulanase to prepare resistant starch (RS). The concentration of starch liquid, the amount of added thermostable α-amylase, the duration of enzymatic hydrolysis and the amount of added pullulanase were optimized using RSM to increase RS content of the treated sample. The optimum pretreatment conditions were 15% starch liquid, 3 U/g thermostable α-amylase, 35 min of enzymatic hydrolysis and 8 U/g pullulanase. The maximum RS content of 10.75% was obtained, and this value was significantly higher than that of native corn starch. The degree of polymerization (DP) of the enzyme-modified starch decreased compared with that of native starch. The scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were performed to assess structural changes in native and pretreated starch. The effect of dual enzyme pretreatment on the structure and properties of corn starch was significant. Unlike the untreated one, the pretreated corn starch showed clear pores and cracks. Significant differences in RS contents and structural characterization between starch pretreated and untreated with dual enzymes demonstrated that the dual enzyme modification of corn was effective in enhancing RS contents.

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