CHARACTERISTICS OF WATERJET CUTTING FOR THE OFFSHORE INDUSTRY

Waterjet machining harnesses the kinetic energy of a high velocity waterjet to cut materials. Waterjet cutting for the offshore industry has shown particular interest in recent years. Abrasive Waterjet (AWJ) is seen as an ideal cutting tool for cutting buoys and other structures away from the seabed. The study reported in this paper analyzes certain aspects associated with waterjet cutting in an attempt to improve it as a machining process and to investigate its suitability for offshore use. Specific factors looked at, were the effects of abrasive flow rate on AWJ machining, the performance of waterjet when used underwater, and nozzle design to try and improve the jet focus. From experimentation, cutting while submerged was observed to be possible, although the performance of the jet was slightly stunted due to the interaction of the surrounding fluid. As the nozzle was moved away from the workpiece, thereby increasing the standoff distance, the performance of the jet was found to deteriorate further. An increase in abrasive flow rate was found to aid cutting initially; however at higher flow rates the increase was found to have a detrimental effect on the jets cutting performance. Therefore an optimum abrasive flow rate was found to be between 4.4 g/s & 7.4 g/s. The slope angle of the nozzle axis has no significant effect. The effect of changing nozzle geometry was analysed by computational fluid dynamics. The outcome was that the change in geometry had no effect on the upstream flow.