Expansion velocity of metal pipe in underwater explosive welding

The impact velocity is one of the key parameters for underwater explosive welding, which mainly depends on the expansion process of the metal pipe. In present work, a prediction model addressing the expansion velocity of the inner pipe during underwater explosive welding was proposed, in which the detonation properties of the explosive charge and the mechanical properties of metal pipes were considered simultaneously. To improve the accuracy of the model, Henrych's calculating formulae of explosion peak pressure and time constant were modified referring to the numerical simulation results. The expansion velocity predicted by the modified model showed a good agreement with that of the inner explosion experiment of a mono aluminum pipe. Furthermore, the model was employed in designing the explosive charge of the underwater explosive welding of aluminum/steel composite pipe. An impact velocity of 337.5 m·s−1 was chosen firstly based on the weldability window of certain pipes, combining which with the expansion velocity prediction model, the parameters of the explosive were then decided. After the explosive welding, a well-bonded interface of aluminum/steel composite pipe was obtained as expected. The practical impact velocity of the underwater explosive welding measured with the laser interferometry was 325 m·s−1, which was close to the designed velocity. The experimental results demonstrated that the proposed model has good feasibility in expansion velocity prediction and underwater explosive welding design.