Development and application of models for the stability analysis of Australia’s offshore pipelines

Offshore subsea pipelines are used to export oil and gas from the field to platform and then from the platform to the mainland. As they are the sole conduit for the hydrocarbons their stability and integrity are of critical economic and environmental importance. With more than 80 per cent of Australia’s gas resources in deep, remote, offshore areas, the ability to realise their full potential relies on the development of safe and economically viable solutions to transport them. Pipelines offshore of Australia must maintain structural integrity and continuous supply of products across hundreds of kilometres of seabed. This paper discusses one aspect of this challenge. It concentrates on how to design for stability of untrenched pipelines under storm conditions. Force balance methods commonly applied are first described before the benefits of using a dynamic time domain approach are shown by way of example. Novel macroelement plasticity models that describe the force-displacement behaviour of a vertically and laterally loaded pipe in Australian soils are outlined. Their application is shown in the design example.