Validity of Using Fatigue-Based Span Limits in Wave Dominated Environments

Abstract

A subsea pipeline has a unique role to produce oil and gas from an offshore petroleum field, connecting a petroleum facility at the open sea and a near shore terminal at the coast. Pipelines are usually installed on the seabed which have uneven surface. Free spans or suspended spans normally occur in subsea pipelines due to the irregularity of seabed and by scouring phenomena around the installed non-buried pipeline. The span could be as a result of scour, obstruction on the seabed, undulating terrain and topography, sand waves and natural profile. The maximum allowable span is usually considered when design is being carried out. The allowable free span length based on input data and constants given by DNVGL F105 were obtained and compared with the maximum allowable free span length for the response model. The result obtained for the in line and cross flow was 20 m while the maximum allowable span length was 78.2 m. A Mathcad spreadsheet was developed for this calculation and this can be used as an analytical tool for calculating free span. The author would like to compare the results obtained using this spreadsheet with other standard free span softwares in the future.

Copyright 2019, IPPTC Organizing Committee.

This paper was prepared for presentation at the 2019 International Petroleum and Petrochemical Technology Conference in Beijing, China, 27–29, March, 2019.

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