Thermodynamic Characteristics Investigation of the In-situ Gas Pipelines Welding Process

The major safety problem of in-service welding municipal gas pipelines is burn-through and hydrogen induced cracking. In this paper, a numerical model to analyze the thermodynamic characteristics (temperature field and allowable stress)during the welding process at different working conditions is established.. This model is then applied to a testing case: the leakage section of the Harbin-Yilan long distance transmission pipelines. In this case, the impact of working parameters during the welding process (pipe-wall casing thickness, welding energy input and velocity of the flow medium) on the temperature field and allowable stress is analyzed. The optimal working parameters to avoid burn through and hydrogen induced cracking are also derived. The testing case shows that the model developed in this paper is useful in providing technical support for online welding process, and therefore can be applied widely in practice.