This paper describes a method for evaluating the discharge of a solid plug from the flow path of a jacketed piping system. The practical application of a finite difference technique known as the Godunov method is employed to provide a numerical solution to the nonlinear hyperbolic conservation laws, more commonly recognized as the conservation of mass, momentum, and energy in the gas dynamics discipline. The purpose of this paper is to provide technical insight into the engineering investigation of a solid polyethylene plug that may be dislodged from within a high-pressure polyethylene (HPPE) process unit. Due to the nature of the process gas, a steam pipe jacket encompasses the inner process pipe except in areas where valves and fittings are heated with steam tracing. It is suspected that in the regions in or around the two in-line control valves that are located immediately downstream of each product receiver vessel, the product may solidify during abnormal transient operations that result in a loss of heating to the process pipe. when this occurs, a solid "plug" of undefined size forms, thereby blocking the flow path between the product receiver outlet and the vent stack that is located downstream of the two in-line control valves. On occasion, unit operators employ pressures up to 3500 psig upstream of the solid plug in an attempt to clear the flow path and resume normal operations. The plug blow operation problem was subdivided into two main areas of concentration. The first part of the problem entailed defining a solution technique that would allow for the mathematical modeling of the plug blow itself, i.e., a scheme by which the size of the plug did not influence the major effects on the process pipe and its associated jacket pipe. In addition, the technique had to allow for the separation of a relatively high-pressure region upstream of the plug (approximately 3500 psig maximum) and an atmospheric pressure downstream of the solid plug. Once the resulting pressures, densities, and other functional parameters from the mathematical model were obtained, the resulting reaction forces from the plug blow operation were calculated. The second part of the problem entailed a more standard piping stress analysis on both the existing pipe geometries and a modified system that would accommodate the anticipated shock loads as a result of the plug blow operation. The fact that the shock loadings were generated within a jacketed pipe system, however, added to the complexity of the problem at hand The analyses that were performed included, but were not limited to, one-dimensional computational fluid dynamics and various structural finite element analyses. A summary of the results of the technical analyses, investigative calculations, and technical conclusions are presented in the following paragraphs of the subject paper.
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