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Australian Energy Producers Journal Australian Energy Producers Journal Society
Journal of Australian Energy Producers
RESEARCH ARTICLE (Non peer reviewed)

Offshore structures – why all offshore facilities should have a demanning requirement

Matt Keys
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Atkins SNC-Lavalin, 50 St Georges Terrace, Perth, WA 6000, Australia. Email: Matt.Keys@atkinsglobal.com

The APPEA Journal 59(2) 789-791 https://doi.org/10.1071/AJ18109
Accepted: 15 March 2019   Published: 17 June 2019

Abstract

Most offshore structure design codes focus on setting appropriate safety factors to achieve an acceptable annual level of risk. Recent work by Atkins SNC-Lavalin, together with a large number of operators in Australian waters and the North Sea, has discovered that a large number of aging assets are implementing a demanning requirement to limit the risk of platform collapse to personnel, due to changes in loading or degradation of the structure. This work has shown there are two risk scenarios that should drive this requirement. The first scenario which is intended by the codes in limiting the overall annual risk. The second is to limit the collapse risk associated with a known forecast storm, as the level of risk from helicopter demanning is much lower. For all the older offshore fixed and permanently mooring floating structures assessed for a risk level considered acceptable for a forecast storm, this risk level would govern the sea-state demanning criteria. For recently installed facilities that are compliant with current standards, the findings were the same: that all facilities should have a demanning requirement. The level of this demanning sea-state limit has been shown to be lower than expected and is likely to occur only once in the asset’s life; therefore, the cost implications of implementing demanning procedures are minor. This paper presents the basis and range of findings for calculating the risks associated with an annual occurrence and an ‘in a forecast storm’ risk. Further, this paper proposes acceptable demanning limits for facilities designed to current and historical design codes.

Keywords: down manning, structural reliability, structural risk.

Dr Matt Keys is the Global Technical Director for offshore structures at Atkins SNC-Lavalin in the Oil and Gas Division and works with over 250 integrity experts that together service a significant proportion of the world’s aging fleet of offshore platforms. Matt has over 20 years’ experience in the oil and gas industry in both brownfield and greenfield structural analysis, design and integrity management from conceptual through to detailed design, complex reassessments and overall integrity management while operating. His specialist skills include non-linear FEA, structural reliability analysis and fluid structure interaction using CFD. Matt’s experience covers some of the oldest assets in the North Sea, the Middle East, Australia and the Gulf of Mexico to the newest floating facilities recently installed in Australian waters.


References

Energo Engineering Inc. (2007) Assessment of fixed offshore platform performance in hurricanes Katrina and Rita. Final report, prepare for the US Department of the Interior Mineral Management Service Engineering and Research Branch. Available at https://www.bsee.gov/sites/bsee.gov/files/tap-technical-assessment-program/578aa.pdf [verified 9 April 2019]

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NORSOK (2015) Standard N-006: Assessment of structural integrity for existing offshore load-bearing structures. Edition 2, April 2015.