Offshore Flow Induced Noise

Stoneman Solutions were invited to investigate the problem of fatigue failures and an acoustic phenomenon on the largest semi-submersible gas rig in the world, Asgard B weighing 80,000 tonnes.

With over 30 years of experience in the field of flow-induced noise, Stoneman Solutions were able to attribute the fatigue failures in the pipes and acoustic problems to a vortex shedding process occurring in the corrugated export riser (this is not Vortex Induced Vibration). As the gas was exported an acoustic resonance was generated. A relationship was found between the gas export rate and the stepping frequencies experienced on the rig pipework.

Stoneman Solutions were able to develop many solutions that would reduce or even eliminate the resonances that have been experienced on other rigs. The modifications are to be implemented at the manufacturing stage and the rig will be commissioned in 2005.

Click the links to find out more about the solutions

		Reactive absorber An acoustic blocking device with minimal pressure drop.
		Pipe branching Altering the pipe geometry to position standing wave pressure nodes over pipe junctions.
		Anechoic Termination Absorptive material placed in the pipe to reduce the amplitude of reflections
		Stand Pipes Quarter wave attenuators designed to work at specific frequencies.