LIFETIME EXTENSION OF AGEING OFFSHORE STRUCTURES BY GLOBAL ULTIMATE STRENGTH ASSESSMENT (GUSA)

Malaysia is the second largest oil and gas producer in Southeast Asia. Majority ofjacket platforms in Malaysia have exceeded their design life with various types of underwaterstructure irregularities. Therefore, it is essential to address the reliability of the jacket platformsin Malaysia due to ageing, increasing environmental loading and demand to prolong theproduction for a further 25 years. The main purpose of this analyses is to determine thestructure’s risk level over its remaining service life which is a vital information in managingageing facilities to cater for the demand of continuous production. Global Ultimate StrengthAssessment (GUSA) methodology was used to support detailed reassessment applied inmanaging safety, integrity analyses and reliability by evaluating the existing platform’s loading.It is a tool for high-end analysis of structures for Risk-based Assessment (RBA). In this paper,the reassessment of an ageing platform over 30-year-old, still in production is presented todemonstrate GUSA capability to perform the platform’s life extension evaluation. The outcomefrom these analyses can effectively assist in understanding the structure platform’s failuremechanism and correctly identify mitigation actions required. As part of the analyses, non-linearanalysis and probabilistic model as practiced in the industry were used in order to get ReserveStrength Ratio (RSR) and Annual Probability of Failure (POF) results. The accuracy andcomprehensiveness of this method will assist the industry, especially oil and gas fields’ operators,in decision-making, specifically in identifying problem-oriented-solutions as part of theirbusiness risk management in managing ageing facilities.

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Comparative Study of Structural Reliability Assessment Methods for Fixed Offshore Structures

10.20944/preprints202108.0099.v1 ◽

2021 ◽

Author(s):

E. Mat Soom ◽

M.K. Abu Husain ◽

N.I. Mohd Zaki ◽

N.A. Mukhlas ◽

S.Z.A. Syed Ahmad ◽

...

Keyword(s):

Structural Reliability ◽

Oil And Gas ◽

Offshore Structures ◽

Mitigation Strategies ◽

Life Extension ◽

Risk Level ◽

Long Distance ◽

Design Assessment ◽

Integrity Assessment ◽

Structural Deterioration

The oil and gas sector has recognised structural integrity assessment of ageing platform for prospective life extension as a rising concern, particularly in encountering the randomness of the harsh ocean environments. This condition leads to uncertainty in wave-in-deck load estimates and a high load level being imposed on offshore structures. This emphasises the necessity of enhanced reliability, as failure might result in inaccessibility because of the uncertainties related to long-distance services, such as accuracy of predictions of loads and responses. Even though the established guidelines present a fundamental assessment, additionally, comprehensive rules are required. This paper performed a reliability analysis incorporating practical approaches that can more accurately represent time-dependent structural deterioration. The following two procedures have been adopted by a majority of significant oil and gas operators to monitor the safety and integrity of these structures: a) Ultimate Strength Assessment (USA) method and b) Reliability Design Assessment (ReDA) method. A comparison of these two reliability approaches was performed on selected ageing jacket structures in the region of the Malaysian sea. The comparative findings, namely, reserve strength ratio (RSR) at various years of the return period (RP) and ratio value for risk of failure regarding the probability of failure (POF), provided a check and balance in strengthening confidence in the results. The findings showed that the structural components might safely survive either using the USA and ReDA method in such conditions, as the reliability indexes were determined to be satisfactory compared to allowable values from ISO 19902 design specifications. Therefore, these evaluations were determined to control the risk level of the structure during the remaining of its lifetime and undertake cost-effective inspections or mitigation strategies when necessary.

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Results From Model Testing of Ice Protection Piles in Shallow Water

Volume 2: Ocean Engineering and Polar and Arctic Sciences and Technology ◽

10.1115/omae2006-92100 ◽

2006 ◽

Cited By ~ 2

Author(s):

Arne Gu¨rtner ◽

Joachim Berger

Keyword(s):

Model Test ◽

Oil And Gas ◽

Offshore Structures ◽

Full Scale ◽

Offshore Structure ◽

Oil And Gas Fields ◽

Ice Loads ◽

Drifting Ice ◽

Ice Model Test ◽

Gas Fields

The development of oil and gas fields in shallow icy waters, for instance in the Northern Caspian Sea, have increased the awareness of protecting offshore structures by means of ice barriers from the impacts of drifting ice. Protection could be provided by Ice Protection Piles (IPPs), installed in close vicinity to the offshore structure to be protected. Piles then take the main loads from the drifting ice by pre-fracturing the advancing ice sheet. Hence, the partly shielded offshore structure could be designed according to significant lower global design ice loads. In this regard, various configurations of pile arrangements have been model tested during the MATRA-OSE research project in the Ice Model Test Basin of the Hamburg Sip Model Basin (HSVA). The main objective was to analyse the behaviour of ice interactions with the protection piles together with the establishment of design ice loads on an individual pile within the pile arrangement. The pile to pile distances within each arrangement were varied from 2 to 8 times the pile diameter for both, vertical and inclined (30° to the horizontal) pile arrangements. Two test runs with 0.1 m and 0.5 m thick ice (full scale values) were conducted respectively. The full scale water depth was 4 m. Based on the model test observations, it was found that the rubble generation increases with decreasing pile to pile distances. Inclined piles were capable to produce more rubble than vertical piles and considerable lower ice loads were measured on inclined arrangements compared to vertical arrangements. As initial rubble has formed in front of the arrangements, the rubble effect accelerated considerable. Subsequent to the build-up of rubble accumulations, no effect of the pile inclination on the exerted ice loads could be observed. If piles are used as ice barriers, the distance between the piles should be less than 4D for inclined piles and 6D for vertical piles to allow sufficient rubble generation. Larger distances only generated significant ice rubble after initial grounding of the ice had occurred.

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Accounting for Climate and Typology of Reuse of Offshore Structures with a Change of Function

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.713-715.205 ◽

2015 ◽

Vol 713-715 ◽

pp. 205-208 ◽

Cited By ~ 2

Author(s):

Ilya Vladimirovich Dunichkin ◽

Pavel Kirillovich Kalashnikov

Keyword(s):

Theoretical Model ◽

Oil And Gas ◽

Offshore Structures ◽

Environment Protection ◽

Offshore Structure ◽

Oil And Gas Fields ◽

Offshore Oil And Gas ◽

Gas Fields ◽

Offshore Oil ◽

Oil And Gas Companies

The new typology of marine facilities deals with the problem of offshore oil and gas fields’ infrastructure usage after their elimination. The influence of climate on offshore structures and the authorities’ requirements in the matter of natural environment protection create huge costs for oil and gas companies, if the abandoned platform will be at sea. The concept of oil platform reconstruction with the change of functionhas allowedto create theoretical model of offshore structure and to identify the most relevant functions for the reconstructed objects. It has led to the following basic groups of architectural typology.

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Methodologies on Hull Girder Ultimate Strength Assessment of FPSOS

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4001957 ◽

2011 ◽

Vol 133 (3) ◽

Cited By ~ 4

Author(s):

Xiaozhi Wang ◽

Haihong Sun ◽

Tetsuya Yao ◽

Masahiko Fujikubo ◽

Roger Basu

Keyword(s):

Ultimate Strength ◽

Structural Design ◽

Oil And Gas ◽

Economic Aspects ◽

Strength Assessment ◽

Hull Girder ◽

Oil And Gas Fields ◽

Offshore Oil And Gas ◽

Gas Fields ◽

Offshore Oil

Floating production, storage, and offloading systems (FPSOs) have been widely used for the development of offshore oil and gas fields because of their many attractive features. They are mostly ship-shaped and either converted from existing tankers or purpose-built. However, FPSOs have their own unique characteristics, including various operational requirements. In addition to that, the expectation of safety and economic aspects of FPSOs require an optimized structure to be designed. This calls for reliable structural assessment methodologies. One of the most important aspects of FPSO structural design and assessment is the hull girder ultimate strength. In this paper, different methodologies of hull girder ultimate strength assessment will be introduced and numerical calculations of hull girder ultimate strength will be presented based on six different FPSO designs. The results will then be analyzed in terms of their differences, and conclusions will be made based upon reliable methodologies for hull girder ultimate strength assessment of FPSOs.

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Methodologies on Hull Girder Ultimate Strength Assessment of FPSOs

Volume 2: Structures, Safety and Reliability ◽

10.1115/omae2008-57899 ◽

2008 ◽

Author(s):

Xiaozhi Wang ◽

Haihong Sun ◽

Tetsuya Yao ◽

Masahiko Fujikubo ◽

Roger Basu

Keyword(s):

Ultimate Strength ◽

Structural Design ◽

Oil And Gas ◽

Economic Aspects ◽

Strength Assessment ◽

Hull Girder ◽

Oil And Gas Fields ◽

Offshore Oil And Gas ◽

Gas Fields ◽

Offshore Oil

Floating production, storage and offloading systems (FPSOs) have been widely used for the development of offshore oil and gas fields because of their many attractive features. They are mostly ship-shaped, and either converted from existing tankers or purpose-built. The hull structural scantling design for tankers may be generally applicable to FPSOs. However, FPSOs have their own unique characteristics, including various operational requirements. In addition to that, the expectation of safety and economic aspects of FPSOs require an optimized structure to be designed. This calls for reliable structural assessment methodologies. One of the most important aspects of FPSO structural design and assessment is the hull girder ultimate strength. In this paper, different methodologies of hull girder ultimate strength assessment will be introduced and numerical calculations of hull girder ultimate strength will be presented based on six different FPSO designs. The results will then be analyzed in terms of their differences, and conclusions will be made based upon reliable methodologies for hull girder ultimate strength assessment of FPSOs.

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Analysis of Ice Loads on Offshore Structures for Okhotsk Sea Oil and Gas Fields

Volume 2: Structures, Safety and Reliability ◽

10.1115/omae2011-49596 ◽

2011 ◽

Cited By ~ 2

Author(s):

Alexander T. Bekker ◽

Olga A. Sabodash ◽

Aleksey Yu. Kochev

Keyword(s):

Comparative Analysis ◽

Probabilistic Model ◽

Sea Of Okhotsk ◽

Oil And Gas ◽

Offshore Structures ◽

Okhotsk Sea ◽

Oil And Gas Fields ◽

Ice Conditions ◽

Ice Loads ◽

Gas Fields

In the study, the results of a statistical modeling of ice loads from drifting ice features on the ice-resistant platforms in Piltun-Astohsky and Lunsky oil&gas fields of “Sakhalin-I” and “Sakhalin-II” Projects are investigated. The authors made a comparative analysis of ice loads on various types of gravity-based concrete structures in ice conditions of the Sea of Okhotsk according to the standards, procedures and guidelines from different Codes of design. And also the probabilistic model of ice loads, developed by the authors in the previous studies, was considered for comparative analysis.

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