Grant: Collaborative Research and Development Grants

Hot tap connections of pipelines enable a new pipeline to be connected to an operating pipeline without shutting down the operating pipeline. Since a pipeline can cost hundreds of millions of dollars or more, inconveniencing customers and avoiding the lost income that would be incurred by a shut down is valuable to TCPL. Although the technology to do this for connecting smaller diameter pipes to larger diameter pipes exists, the proposed research will develop state of the art computer models to optimize this technology, to assess the robustness of their existing methodology and extend this technology to connect pipes of nearly equal diameter. Welding is a very complex process that involves complete material processing from melting to solidification and shaping the finished weld pool of roughly 1 cm^3 in times of roughly 1 second. The resulting microstructure controls the weld properties. The convection coefficient and ambient temperature that controls the flow of heat from the weld on the external wall of the pipe to the internal wall of the pipe is dependent on the flow rate, pressure and temperature and type of fluid within the pipe. This controls the cooling rate and microstructure of the weld fusion and weld heat-affected zone in low-alloy pipeline steels. This is particularly important in older pipe steels that have higher carbon levels and ferrite-pearlite microstructure.Current technology uses a cooling rate test that heats a circular patch about 50 mm diameter on the outer wall of the pipe to about 300 degrees C and measures the time it takes to cool the heated area to 100 degrees C and to 15 degrees C above ambient temperature. From these measured cooling times, rules based on experiments are used to judge if the hot tap is likely to succeed. In the proposed research, a computer model will compute the convection coefficient from the cooling rate test data and predict microstructure, hardness, residual stress and distortion in the hot tap weld. We propose to correlate data in TCPL's archives on hot tap welds to validate the computer model.