scholarly journals Structural Integrity of Fixed Offshore Platforms by Incorporating Wave-in-Deck

2021 ◽  
Vol 9 (9) ◽  
pp. 1027
Author(s):  
Nurul Uyun Azman ◽  
Mohd Khairi Abu Husain ◽  
Noor Irza Mohd Zaki ◽  
Ezanizam Mat Soom ◽  
Nurul Azizah Mukhlas ◽  
...  
Keyword(s):  
Structural Integrity ◽  
Limit State ◽  
Pushover Analysis ◽  
Offshore Structures ◽  
State Equation ◽  
Air Gap ◽  
Wave Crest ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
The Impact

The structural integrity of offshore platforms is affected by degradation issues such as subsidence. Subsidence involves large settlement areas, and it is one of the phenomena that may be experienced by offshore platforms throughout their lives. Compaction of the reservoir is caused by pressure reduction, which results in vertical movement of soils from the reservoir to the mud line. The impact of subsidence on platforms will lead to a gradually reduced wave crest to deck air gap (insufficient air gap) and cause wave-in-deck. The wave-in-deck load can cause significant damage to deck structures, and it may cause the collapse of the entire platform. This study aims to investigate the impact of wave-in-deck load on structure response for fixed offshore structure. The conventional run of pushover analysis only considers the 100-year design crest height for the ultimate collapse. The wave height at collapse is calculated using a limit state equation for the probabilistic model that may give a different result. It is crucial to ensure that the reserve strength ratio (RSR) is not overly estimated, hence giving a false impression of the value. This study is performed to quantify the wave-in-deck load effects based on the revised RSR. As part of the analysis, the Ultimate Strength for Offshore Structures (USFOS) software and wave-in-deck calculation recommended by the International Organization for Standardization (ISO) as practised in the industry is adopted to complete the study. As expected, the new revised RSR with the inclusion of wave-in-deck load is lower and, hence, increases the probability of failure (POF) of the platform. The accuracy and effectiveness of this method will assist the industry, especially operators, for decision making and, more specifically, in outlining the action items as part of their business risk management.

Developing the Structural Integrity Management System for Ageing Fixed Offshore Oil Platforms in Indonesia

2017 ◽  
Vol 862 ◽  
pp. 265-270
Author(s):  
Raditya Danu Riyanto ◽  
Murdjito
Keyword(s):  
Management System ◽  
Structural Integrity ◽  
Offshore Structures ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
Element Analysis ◽  
East Kalimantan ◽  
Ranking Criteria ◽  
Life Years ◽  
Integrity Management

Offshore structure, particularly fixed offshore structures, should be kept in the performance for the fit-for-purpose condition during their operating lifetime. For fixed offshore structures that exceed their designated life years, the proper Structural Integrity Management System (SIMS) should be developed and applied. Despite the fixed offshore platforms have their service life, there are still platforms that continue to operate exceeding their service lifetime. These ageing platforms should be taken care thoroughly to avoid the consequences that could take casualties. This paper will propose the proper initiation of SIMS development for ageing fixed offshore platforms in Indonesia, by taking an example at Bekapai Field Platforms in East Kalimantan. Using HAZID technique and several ranking criteria, the platforms are assessed and ranked. Platforms that categorized in critical condition are grouped based on similarities in geometry and function. The highest rank is analyzed in computer Finite Element Analysis (FEA) Software with modification based on latest inspection result. This method is proven to be a proper method to be used as a maintenance program for ageing fixed offshore platforms in Indonesia.

Experimental Study of Air Gap Response and Wave Impact Forces of a Semi-Submersible Drilling Unit

2006 ◽  
Author(s):  
Saeid Kazemi ◽  
Atilla Incecik
Keyword(s):  
Experimental Study ◽  
Offshore Structures ◽  
Model Tests ◽  
Air Gap ◽  
Scale Model ◽  
Offshore Structure ◽  
The Caspian Sea ◽  
Wave Impact ◽  
Impact Forces ◽  
The Impact

An experimental study for predicting the air gap and potential deck impact of a floating offshore structure is the main topic of this research. Numerical modeling for air gap prediction is particularly complicated in the case of floating offshore structures because of their large volume, and the resulting effects of wave diffraction and radiation. Therefore, for new floating platforms, the model tests are often performed as part of their design process. This paper summarizes physical model tests conducted on a semi-submersible model, representing a 1-to-100 scale model of a GVA4000 class, “IRAN-ALBORZ”, the largest semi-submersible platform in the Caspian Sea, under construction in North of Iran, to evaluate the platform’s air gap at different locations of its deck and also measure the impact forces in case of having negative air gap. The model was tested in regular waves in the wave tank of Newcastle University. The paper discusses the experimental setup, test conditions, and the resulting measurements of the air gap and the wave impact forces by using eight wave probes and three load cells located at different points of the lower deck of the platform.

scholarly journals An Overview of classifications and incidents/accidents in offshore structures: Oil and gas

2020 ◽  
Vol 1 (4) ◽  
pp. 13-18
Author(s):  
Jean Pierre Lukongo Ngenge ◽  
Abdallah M.S. Wafi
Keyword(s):  
Oil And Gas ◽  
Offshore Structures ◽  
Research Topic ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
The Past ◽  
Wide Range ◽  
Advanced Knowledge ◽  
Construction Accidents ◽  
The Impact

Offshore platforms are considered among the most significant structures in the world that humans have ever built, having to function in a wide range of extremely challenging environments and have a major impact on the economy and industrial progress of countries. It is extremely important to properly plan, design, construct, transport and install such offshore structures. In the absence of commitment to this, the consequences could be severe in both economic and environmental terms. An overview of offshore structures is presented in this paper, and its purpose is to offer a consistent vision for the various types of offshore structures to be used for the extraction of oil and gas. In addition, the paper focuses on the expected accidents that may occur during and after construction. Accidents do not only cover the difficult environment where these structures are to be built, but they also cover the impact of climate change on these structures. The approach considered in this paper involves a systematic literature review that deals with reviewing different studies done on the similar research topic. The results found in this study determined that the type of offshore structure to be built or fixed at a particular location in water, depends mainly on the water depth and also on the past and present environmental records. Nonetheless, the outcomes of this study are still general; thus, further studies have to be completed in order to acquire more advanced knowledge in this particular field.

scholarly journals Numerical Assessment of FPSO Platform Behaviour in Ship Collision

2020 ◽  
Vol 9 (2) ◽  
Author(s):  
Ozgur Ozguc
Keyword(s):  
Structural Integrity ◽  
Energy Levels ◽  
Offshore Structures ◽  
Offshore Platforms ◽  
Hull Girder ◽  
Analysis And Design ◽  
One Year ◽  
Criteria For Evaluation ◽  
Vessel Impact ◽  
The Impact

Offshore platforms may potentially collide with vessels of various types, including visiting ships such as supply ships and passing ships. The most critical and relevant conditions, including the analysis and design approaches are introduced. Different ship types having different displacements and structural designs exert different vessel impact loads on impacted structures. This paper presents the findings of collision impact analyses of the side shell panel, bow and stern structures of Floating Production Storage Offloading (FPSO) platforms in case of impact, e.g. by a supply vessel or methanol tanker. As collision impact simulations continue to be conducted conservatively, the colliding positions of the striking vessel are presumed to be  bow and stern only, with side force. In order to assess hull strength in collision events, non-linear FE simulations were performed by means of the MSC / DYTRAN tool, as these collision events result in more complex reactions. The degree of hull damage suffered by an FPSO vessel in different collision scenarios and at varying impact energy levels was determined in accordance with the NORSOK N-004 standard guidelines. Post-collision analyses were conducted to establish the structural integrity of the damaged hull after being exposed to environmental conditions for one year. The reduction of hull girder strength associated with the worst damage was evaluated and accounted for in the present study, providing no further damage occurs. Furthermore, the acceptance criteria for evaluation and corresponding consequences are calculated and discussed in detail. Finally, the findings from the present paper will help clarify the impact response of offshore structures and evaluation approaches and give valuable guidance for the design and operation of FPSO platforms.

Integrity Management System for Fixed Offshore Structures Inspection Strategy

2004 ◽  
Author(s):  
Mohamed A. El-Reedy
Keyword(s):  
Management System ◽  
Offshore Structures ◽  
Assessment Method ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
Structure Comparison ◽  
Actual Structure ◽  
Existing Structures ◽  
Integrity Management

The GUPCO offshore structure management system was developed as a part of an integrated infrastructure management system. This paper presents a case study of providing an integrity management system for inspection, evaluation and repair of the fixed offshore platforms in Gulf of Suez. The management system procedure is presented focusing on the first step for defining the highly risky weight to the lower risky weight structure based on API criteria for assessment of the existing structures. The risk analysis methodology for developing design and assessment criteria for fixed offshore structure based on consequence of failure is illustrated. In our case study the assessment method is applied for a number of fixed offshore structures. The above methodology is performed after theoretical assessment and then verifying by using ROV subsea inspection for the fixed offshore structure. Comparison between the actual structure performance and the predicting risk assessment for the structure from the model will be studied. The overall management system will be illustrated in scope of predictive maintenance philosophy and reliability for all offshore structures.

Wave Impact Load and Corresponding Nonlinear Response of a Semi-Submersible

2019 ◽  
Author(s):  
Yinghao Guo ◽  
Longfei Xiao ◽  
Handi Wei ◽  
Lei Li ◽  
Yanfei Deng
Keyword(s):  
Spatial Distribution ◽  
Structural Integrity ◽  
Impact Load ◽  
Wave Crest ◽  
Impulsive Effect ◽  
Offshore Platforms ◽  
Wave Impact ◽  
Global Response ◽  
Local Wave ◽  
Incident Waves

Abstract Offshore platforms operating in harsh ocean environments often suffer from severe wave impacts which threaten the structural integrity and staffs safety. An experimental study was carried out to investigate the wave impact load and its effect on the global response of a semi-submersible. First, two typical wave impact events occurring successively in the wave test run are analyzed, including the characteristics of incident waves, relative wave elevations and the spatial distribution of the wave impact load. Subsequently, the corresponding global response of the semi-submersible under these two wave impacts are investigated in time domain. It reveals that compared with the incident wave, the relative wave elevation has a more straightforward relationship with the wave impact load. The relative wave crest height is associated with the spatial distribution of the wave impact load, while the local wave steepness matters more in the magnitude of the wave impact load. The impulsive effect of the wave impact load on the motion behaviors is not obvious. But severe wave impacts can introduce excessive horizontal accelerations and nonlinear behaviors like ringing in the acceleration response.

Wave Load Prediction on a Stationary Bergy Bit Near a Fixed Offshore Platform

2017 ◽  
Author(s):  
Dong Cheol Seo ◽  
Tanvir Sayeed ◽  
M. Hasanat Zaman ◽  
Ayhan Akinturk
Keyword(s):  
Water Level ◽  
Offshore Structures ◽  
Air Gap ◽  
Offshore Platform ◽  
Load Prediction ◽  
Wave Load ◽  
Offshore Structure ◽  
Cfd Simulations ◽  
Simulation Performance ◽  
Fixed Offshore Platform

Offshore oil and gas operations conducted in harsh environments such offshore Newfoundland may pose additional risks due to collision of smaller ice pieces and bergy bits with the offshore structures, including their topsides in the case of gravity based structures particularly in extreme waves. In this paper, CFD (Computational Fluid Dynamics) prediction for wave loads acting on a bergy bit around a fixed offshore platform is presented. Often the vertical column of a gravity based structure is designed against ice collisions, if operating in such an environment. In practices, topsides are usually protected by being placed sufficiently high from the still water level, away from the reach of the bergy bits. This vertical clearance between the still water level and the topside deck is known an air gap. Hence, the amount of the air gap planned for such an offshore structure is an important factor for the safety of the topsides at a given location. In this study a CFD method is applied to estimate the dynamic response of the bergy bit and provide a reliable air gap to reduce the potential risk of the bergy bit collision. In advance of more complex collision simulations using a free-floating ice for the airgap design, CFD analysis of wave load prediction on a stationary bergy bit is carried out and reported in this paper. In the experiments and CFD simulations, the location of the bergy bit is changed to quantify the change of wave load due to the hydrodynamic interaction between the bergy bit and the platform. Finally, the results of the CFD simulations are compared with the relevant experiment results to confirm the simulation performance prior to the free floating bergy bit simulations.

Structural Integrity Control of Ageing Offshore Structures: Repairing and Strengthening With Grouted Connections

2013 ◽  
Author(s):  
S. M. S. M. K. Samarakoon ◽  
R. M. Chandima Ratnayake ◽  
S. A. S. C. Siriwardane
Keyword(s):  
Structural Integrity ◽  
Oil And Gas ◽  
Load Transfer ◽  
Fatigue Loading ◽  
Offshore Structures ◽  
Future Research ◽  
Offshore Platforms ◽  
Historical Evidence ◽  
Design Service Life ◽  
Pros And Cons

Structural integrity control (SIC) is an increasingly important element of offshore structures. Not only is it used in newly built and existing offshore structures (e.g. oil and gas (O&G) production & process facilities (P&PFs), wind turbine installations, etc.), but SIC is also essential for ageing offshore platforms which are subjected to an extension of their design service life. In these cases, SIC programs must be performed to assess the platforms. If any significant changes in structural integrity (SI) are discovered, then it is essential to implement an appropriate strengthening, modification and/or repair (SMR) plan. Currently, welded and grouted repairs are mostly used for SMR. Although a welded repair may typically restore a structure to its initial condition, if the damage is due to fatigue loading and welded repairs have been carried out, then historical evidence reveals that there is a high potential for the damage to reappear over time. On the other hand, mechanical connections are significantly heavier than grouted connections. Consequently, grouted repairs are widely used to provide additional strength, for instance, to handle situations such as preventing propagation of a dent or buckle, sleeved repairs, leg strengthening, clamped repair for load transfer, leak sealing and plugging, etc. This manuscript examines current developments in grouted connections and their comparative pros and cons in relation to welded or mechanical connections. It also provides recommendations for future research requirements to further develop SMR with grouted connections.

scholarly journals Risk Based Inspection of Jackets Submitted to Through-Wall Cracks

2003 ◽  
Author(s):  
Franck Schoefs ◽  
Mustapha Rguig
Keyword(s):  
Decision Aid ◽  
Structural Integrity ◽  
Offshore Structures ◽  
Probability Of Detection ◽  
Non Destructive Testing ◽  
Destructive Testing ◽  
Probability Of False Alarm ◽  
The Impact ◽  
Non Destructive ◽  
Rational Process

The actual challenge for the requalification of existing offshore structures through a rational process of reassessment leads to state the importance of Risk Based Inspection methodology. This paper points out the inspection results modelling and their contribution to decision aid tools. The study of the impact of through cracks on structural integrity of jacket platforms is still a challenge. The detection of large cracks is first addressed. In order to minimize inspections and maintenance costs, all the available data from inspection results, such as probability of detection and probability of false alarm, must be addressed, as well as the probability of crack presence. This can be achieved by the use of the decision theory. These capabilities of Non Destructive Testing give a first input for the risk study. A cost function is suggested to introduce this modelling into a risk analysis and is devoted to help rank the NDT tools. The case of large through-wall cracks is specifically addressed.

Experimental Investigation of Ice Mass Hydrodynamic Interaction With Offshore Structure in Close Proximity

2015 ◽  
Author(s):  
Tanvir Mehedi Sayeed ◽  
Bruce Colbourne ◽  
Heather Peng ◽  
Benjamin Colbourne ◽  
Don Spencer
Keyword(s):  
Hydrodynamic Interaction ◽  
Impact Load ◽  
Numerical Study ◽  
Numerical Models ◽  
Offshore Structures ◽  
Ocean Engineering ◽  
Offshore Structure ◽  
Area Of Interest ◽  
Close Proximity ◽  
The Impact

Iceberg/bergy bit impact load with fixed and floating offshore structures and supply ships is an important design consideration in ice-prone regions. Studies tend to divide the iceberg impact problem into phases from far field to contact. This results in a tendency to over simplify the final crucial stage where the structure is impacted. The authors have identified knowledge gaps and their influence on the analysis and prediction of iceberg impact velocities and loads (Sayeed et. al (2014)). The experimental and numerical study of viscous dominated very near field region is the main area of interest. This paper reports preliminary results of physical model tests conducted at Ocean Engineering Research Center (OERC) to investigate hydrodynamic interaction between ice masses and fixed offshore structure in close proximity. The objective was to perform a systematic study from simple to complex phenomena which will be a support base for the development of subsequent numerical models. The results demonstrated that hydrodynamic proximity and wave reflection effects do significantly influence the impact velocities at which ice masses approach to large structures. The effect is more pronounced for smaller ice masses.

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