62589751-Manual-de-Simulador-Pipe-Phase.pdfSphering (Pigging) Sphering of a wet gas pipelines is a common operating practice to improve the flow efficiency of the pipeline. PIPEPHASE uses a modified form of the Barua-modified-McDonald-Baker (MB) pigging model to simulate the sphering process. The MB model is a successive steady state model. Normal two-phase flow is represented in Figure 32. The pig is launched after steady state flow has been reached. After the pig has been launched four distinct zones of flow occurs in the pipeline - the re-established two phase flow zone, the gas flow zone, the liquid slug flow zone and the undisturbed two-phase flow zone. The model assumes that the inlet flow rate remains constant at the steady state rate after the pig has been launched.Re-established liquid Slug Zone Undisturbed Two-Phase Flow Two-Phase Flow Zone PIPEPHASE predicts the pressure profile, length of each zone and the position of the sphere as a function of time. In addition, when the liquid slug reaches the end of the pipeline a special slug delivery model is used to model the slug delivery when the liquid slug accelerates. Next calculation continues after slug delivery is completed to calculate the time it takes for steady state flow to be re-established in the pipeline. The first sphere must be launched at the inlet of the first pipe. Subsequent pigs may be launched from downstream pig launching stations when the upstream pig(s) reach the downstream pig launching station. To model the pigging process the pig diameter must be specified in the first pipe.To specify downstream pig launching stations, specify the pig diameter for the corresponding pipe. The program interprets the launching station to be the inlet of the pipe. Setting the Calculation Tolerances For networks that require iterative calculations, you can set the pressure convergence tolerance for the solution. For instance, if you do not specify a tolerance pressure value, PIPEPHASE allows for a tolerance of 2 psi. It will then perform the required iterations until it reaches a pressure that is within 2 psi of the desired value. Setting tighter tolerances results in more accurate solutions, at the expense of more calculation time. The tolerance should commonly range between 0.5 to 5 psi for pressure. If you anticipate a large drop in pressure, then it may be appropriate to set a higher tolerance. Conversely, for small pressure gradients, you should set a tighter tolerance value.PIPEPHASE allows you to specify tolerances for other parameters, as well. When using the MBAL method, you can specify the flow tolerance, with the units depending on the fluid type (bbl/day for liquid and black oil, MM ft3/day for gas and gas condensate, and MM lb/hr for compositional fluids and steam). You can also specify temperature tolerance for MBAL networks.For PBAL network solution methods, in addition to the pressure tolerance, you can also specify the rate to improve convergence in networks with chokes in critical flow..