Branch connection to existing hydrocarbon pipelines are often attached by welding on the pipe while liquid or gas products are contained in or flowing in the pipe when it is not feasible, or impractical, to take the piping out of service. This procedure is called hot tapping. A problem, so-called “burn-through”, will occur when welding onto a pressurized pipe if the un-melted area beneath the weld pool has insufficient strength to contain the internal pressure of the pipe. It is reported by Battelle Institute that this burn-through problem will occur when inside surface temperature is in excess of 982 degree C regardless of internal pressure [1]. From the safety view points, this problem shall be avoided. In addition, the piping or equipment base metal thickness must provide support for the new connection and hot tapping machine. From these reasons, the minimum base metal thickness of approximately 5mm (to be precise 4.8mm) is recommended [2]. In this study, the validity of the minimum base metal thickness of 5mm was confirmed by means of “Thermal Analysis Computer Modeling for Hot-Tap Welding” developed by my company to confirm the effectiveness of the Thermal Analysis. This thermal Analysis can calculate the cooling rate and temperatures faithfully using heat elastoplastic finite element analysis. After the confirmation of that, we can determine the welding conditions and conduct the hot tapping operations safer. Prior to applying this thermal analysis tool to hot tapping models, reliability of this thermal analysis tool was confirmed by a preliminary experiment.

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