The offshorepipeline market remains a large segment of oil and gas expenditure inAsia-Pacific and is forecast to continue apace. Design and installation ofpipelines in Asia and Australia is generally no more arduous than usual butthere are some distinctive characteristics of the continental margins withinthis region that are not commonly found in other oil and gas producing areas. In particular, the continental margins of the South China Sea and NW Australiaare much wider, and can be far more topographically uneven than those found elsewhere. This has a profound impact on pipeline design and integrity with specificrespect to spans. Of interest tothis study are: the underlying causes of on-bottom roughness, pipeline routing, critical span predictions and, from an installation perspective, spanrectification measures. It is not uncommon for on-bottom roughness and spananalyses to significantly over-predict quantities of critical spans in theearly design stages. Many of these will be marginal and in all likelihood neverappear once the pipeline is laid. Effort to eliminate these at the earliestpossible stage is worthwhile. This paper firstfocusses on the physical features of the continental margin that give rise toon-bottom roughness to help understand what are the particular soils and seabedfeatures that cause the spans which is information vital to the selection andapplication of span mitigation measures. The study then considers how thenumber of predicted spans can be reduced through a process of preliminary routeoptimisation and other measures including recommendations for optimisationsthat can be applied to input parameters used in span analyses. Lastly the paperconsiders the challenges of remedial work in the field. There are many spanrectification methods available but none are appropriate for all circumstances. The technology is reviewed and a matrix is presented assigning levels ofsuitability to each method depending on seabedconditions and water depth. Bothpre-lay and post-lay rectification measures are considered. Improvements in pipelinerouting and span analysis should result in more reliable predictions of therectification required and provide more realistic scopes of works for planningand costing.

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