| Hot tapping is a new technology for pipeline maintenance developed during recent decades. It is a technology which welds a branch pipe to an existing and loaded facility such as a pipeline or tank without halting transportation of the pipeline or equipments, and then drills a hole in a sealed cavity. The good economical and social effects make more and more companies to apply this technology.Hot tapping has been taken into use for more than 30 years in Atlantic Region. However, there are only 20 years since hot tapping was applied in China. There is only a little literature reporting the basic theories of hot tapping. In this thesis, the development of application and research of hot tapping were overviewed, the foreground of hot tapping during the next decades were represented. The key problem of hot tapping such as burn-through of in-service welding and strength behavior of in-service welding pipes under internal pressure were studied. The main research work and conclusions are listed below:A measurement system was designed and set up to achieve the temperature fields of manual arc welding as well as TIG welding and in-service welding of T joints. Filter capacitor filtrated the high frequency signal of welding. Welding temperature field was obtained to verify the numerical results. Temperature fields of T joints of plates and orthogonal nozzle during manual arc welding and TIG welding were simulated by finite element method (FEM). It can be concluded from the comparison between the experimental and numerical results that the numerical method is accurate and credible, and stress field can be achieved subsequently.The temperature field and residual stress distribution of discontinuous welding were simulated. It can be concluded that the local high temperature can be reduced effectively using the technique of discontinuous welding, reducing the possibility of burn-through. However, due to continuous alternation of heating and cooling, the thermal cycles of discontinuous welding are...
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