The invention relates to a petrochemical cracker having piping comprising a portion wherein the centerline of the portion follows a substantially helical path, wherein the amplitude of the helix is less than or equal to one half of the internal diameter of the piping. When fluid flows in such piping, it is made to swirl. This provides a number of advantages, such as improved in-plane mixing of the fluid, enhanced uniformity of residence time, and so on.
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