The Effects of Stress Redistribution Due to Member Failure on Structural Reliability of Offshore Steel Jackets

2002 ◽  
Author(s):  
A. Nelson ◽  
D. J. Sanderson ◽  
A. Stacey
Keyword(s):  
Structural Reliability ◽  
Structural Integrity ◽  
Stress Redistribution ◽  
Periodic Inspection ◽  
Inspection Interval ◽  
Time Period ◽  
Jacket Structures ◽  
Integrity Assurance ◽  
The Impact ◽  
Inspection Schedule

Current practice in providing structural integrity assurance of North Sea Steel Jacket structures relies upon periodic inspection of the sub-structures, with FMD being the preferred method of inspection. The time period between inspections, when employing FMD is dependent upon the structure’s level of redundancy. However, little, if any, consideration is given to the effect a failed member has on the stress distribution within the structure and the probability of a second member failing. A study has been completed that investigated the impact of stress redistribution following failure of a member. The study has considered the impact this has on fatigue lives of adjacent members/joints, and ultimately the impact on structural reliability. The findings from this study suggest that for the type of structures considered, the justification for a given inspection schedule should take due account of the impact of stress redistribution and the possibility that a structure might experience a second member failure during an inspection interval.

The Impact of Stress Redistribution on Structural Reliability Predictions of Deepwater Jackets

2007 ◽  
Author(s):  
Ronald Schneider ◽  
David J. Sanderson ◽  
Simon D. Thurlbeck
Keyword(s):  
Best Practice ◽  
Structural Reliability ◽  
Stress Redistribution ◽  
Correction Factors ◽  
Structural Members ◽  
Jacket Structures ◽  
Effects Of Stress ◽  
Failure Conditions ◽  
The Impact ◽  
Water Depths

Structural reliability predictions for fixed jacket structures often involve calculating the probabilities of structural members failing and the overall collapse probabilities of the jackets existing in the corresponding damaged condition. It is current best practice to consider only single member failure conditions and to ignore multi member failure conditions since the probability of more than one member failing has been considered to be negligibly small. This approach assumes that the failure of a member is in no way related to the failure of another member, which implies that the two events are statistically independent. However, in reality the two events are not statistically independent since the failure of one member changes the stress state and therefore the failure probability of the remaining members. Two studies conducted to investigate the effects of stress redistribution on platform reliability predictions concluded that, by ignoring the effects of stress redistribution, platform reliability predictions could be significantly overestimated. However, they both concentrated on shallow water jackets and consequently a further study was performed to extend the existing work on stress redistribution to consider jacket structures in greater water depths. The study considered single and dual member failure conditions and compared the effects of including and excluding stress redistribution in reliability calculations. The findings of this work suggest that including stress redistribution reduces the predicted platform reliability. From the results, generic correction factors were derived for different inspection intervals, which account for stress redistribution and dual member failure. These correction factors can be applied to the probabilities derived using current best practice to determine a more realistic estimate of a structure’s reliability.

scholarly journals Robotic Model for Unmanned Crack and Corrosion Inspection

2019 ◽  
Vol 9 (1) ◽  
pp. 862-867 ◽  
Keyword(s):  
Structural Integrity ◽  
Oil And Gas ◽  
Processing Technique ◽  
High Rate ◽  
Image Processing Technique ◽  
Destructive Testing ◽  
Periodic Inspection ◽  
The Cost ◽  
The Impact ◽  
Non Destructive

After prolonged usage of materials, the formation of cracks and corrosion initiates due to stress, loading condition, the environment of operation, etc. and this affects the structural integrity of structures. Periodic inspection of structures is usually planned, especially in industries where the impact of failure could be devastating, such as oil and gas pipelines, storage tanks, vessels, and airplanes, etc. which are just a few amongst others. This inspection is often aimed at detecting cracks and corrosion of internal and external components using several forms of non-destructive testing mechanism usually performed by a specialist at a high rate. To reduce the cost of inspection as well as downtime due to inspections and maintenance, deployments of mobile robots with fault tracking and identification purpose are steadily increasing. This paper, therefore, details the implementation of an image processing technique using MATLAB to identify defects of structural elements.

Risk Based Structural Integrity Management Using Bayesian Probabilistic Nets

2006 ◽  
Author(s):  
Roberto Montes-Iturrizaga ◽  
Ernesto Heredia-Zavoni ◽  
Enrique Marcial-Marti´nez ◽  
Michael Havbro Faber ◽  
Daniel Straub ◽  
...  
Keyword(s):  
General Framework ◽  
Structural Reliability ◽  
Structural Integrity ◽  
Suggested Approach ◽  
Annual Probability ◽  
Damage States ◽  
Jacket Structures ◽  
Integrity Management ◽  
Joint Consideration ◽  
Damage Processes

The present paper presents a general framework for integrity management of offshore steel jacket structures allowing for the risk based planning of inspections and maintenance activities with a joint consideration of all relevant deterioration and damage processes. The basic idea behind the suggested approach is to relate the relevant deterioration and damage processes, i.e. the exposure events, to damage states which in turn may be related to the overall integrity of the jacket structural system as measured through the Reserve Strength Ratio (RSR). This facilitates that any state of degradation, irrespective of the cause, can be assessed in terms of their impact on the annual probability of failure for the structure. Taking basis in data as well as subjective information regarding the annual occurrence probabilities of the relevant deterioration and damage processes, together with a probabilistic modeling of the quality of condition control, it is possible to assess the effect of condition control of each type of deterioration and damage phenomena. This then facilitates the development of a general framework for risk based integrity management. In the present work such a framework is formulated using Bayesian Probabilistic Nets (BPN) for evaluating the time varying global structural reliability of jackets subject to progressive deterioration of its members due to the combined effect of different sources of damage.

The Effect of Multiple Member Failure on the Predicted Reliability of Fixed Jacket Structures

2008 ◽  
Author(s):  
D. Sanderson ◽  
A. Nelson ◽  
A. Stacey
Keyword(s):  
Ultimate Strength ◽  
Cross Correlation ◽  
Stress Redistribution ◽  
Design Strength ◽  
Inspection Interval ◽  
Jacket Structures ◽  
Effects Of Stress ◽  
Reliability Assessments ◽  
The Individual ◽  
Large Reserve

Current offshore inspection practice relies on the detection of gross damage, such as flooded member detection. Such an inspection philosophy relies upon the structure’s ability to withstand gross damage for an inspection interval based on the large reserve factors on the jacket design strength in both the undamaged and damaged conditions. This requires a demonstration of the structure’s strength in all of the possible damaged conditions with the most critical member removed. However, the load originally carried by the critical member is redistributed to other neighbouring members which must consequently have an impact on the design fatigue lives of other members and increase the probability of more members failing. Ignoring the effects of stress redistribution due to member failure could therefore result in under-prediction of the probability of a second member failing and hence an optimistic prediction of platform reliability. This paper aims to quantify the effects of stress redistribution on the prediction of platform reliability. Stress and ultimate strength analyses were performed on three platforms in 45m water depth with bracing configurations of varying structural redundancies, namely, single diagonal, inverted K and X-braced, to calculate the stress enhancement in all members due to the individual failure of all other members. These stress enhancements were input into probabilistic fracture mechanics models to calculate the increase in failure probability of these second members due to the failure of a first member. More than 1000 pushover analyses were performed to calculate the ultimate strength of the structures in all single-member failed conditions and many hundreds of dual member failed permutations for each jacket. A cross-correlation of the most significant stress redistribution results and pushover results was used to perform platform reliability assessments. The effect of including stress redistribution and dual member pushover results was shown to reduce the predicted platform reliability for all bracing configurations, mainly due to a number of dual-member failed conditions that weakened the jackets significantly. It is recommended that, in addition to performing single member failed pushover analyses, there is a need to assess dual-member failed conditions that drastically reduce platform strength.

Pushover Load Factors for Fixed Steel Platforms Sensitive to Topside Load and Wave-in-Deck Load

2015 ◽  
Author(s):  
Ramsay Fraser ◽  
Mark Manzocchi ◽  
Richard Gibson
Keyword(s):  
Structural Reliability ◽  
Structural Integrity ◽  
Load Capacity ◽  
Extreme Environments ◽  
Assessment Method ◽  
Assessment Methods ◽  
Performance Criteria ◽  
Reliability Model ◽  
Load Factors ◽  
Jacket Structures

The objective of this paper is to present recent work in the development of a method for the strength assessment of offshore jacket structures subject to storm loading that is consistent across all global offshore regions. Recent developments in the application of response based metocean analysis together with the establishment of a standardized structural reliability model has resulted in an assessment method that can be applied in a consistent manner to all fixed jacket structures in all global regions. Applying this method in the “assessment” stage of the SIM process, as published by API and ISO, would aid global standardization of both the assessment methods and the performance criteria. The assessment methods have evolved over the last 3 years and have been subject to application and testing on several projects involving the assessment of existing offshore jacket structures. They have proven to be capable of discriminating between the differing extreme environments and differing evacuation and unmanning procedures that occur in different regions while being compatible with existing approaches to structural integrity. The paper will describe the standardized structural reliability model and provide examples of load factors for pushover and pushdown analysis for fixed steel offshore platforms that have a storm load capacity that is sensitivity to topside load and wave-in-deck load.

Fitness-for-Service Assessment of Calandria Tube to Liquid Injection Shutdown System Nozzle Contact in a CANDU Reactor

2016 ◽  
Author(s):  
Cheng Liu ◽  
Eric Tulk ◽  
Douglas Scarth ◽  
Larry Micuda
Keyword(s):  
Contact Time ◽  
Regulatory Authority ◽  
Structural Integrity ◽  
Future Time ◽  
Evaluation Period ◽  
Periodic Inspection ◽  
Inspection Interval ◽  
Liquid Injection ◽  
Design Requirements ◽  
Service Inspection

In CANDU1 reactors, calandria tubes are used to separate the fuel channels from the moderator. The Liquid Injection Shutdown System (LISS) nozzles, which contain holes for discharging neutron-absorbing liquid into the moderator, are arranged perpendicularly in the gap between adjacent rows of calandria tubes. Both calandria tubes and LISS nozzles sag during service due to creep, with the more heavily loaded calandria tubes sagging relatively more. When contact between a calandria tube and a LISS nozzle has been detected by in-service inspection, or is predicted to occur, a fitness-for-service assessment is permitted by CSA Standard N285.4 to demonstrate acceptability of continued operation until the end of the next periodic inspection interval, provided that the fitness-for-service assessment is acceptable to the Regulatory Authority. A fitness-for-service assessment has been recently performed for a calandria tube and a LISS nozzle that were predicted to contact at a future time. The assessment has demonstrated that for an evaluation period of three years after the predicted contact time, the structural integrity of the calandria tube and the LISS nozzle is maintained, both components will continue to function in accordance with their design requirements, and their contact will not result in contact between the calandria tube and a pressure tube.

Pipeline Crack Half-Life Versus 1.10 Safety Factor at Next Inspection

2020 ◽  
Author(s):  
Lyndon Lamborn ◽  
Zeynab Shirband ◽  
Ernest Kwok
Keyword(s):  
Safety Factor ◽  
Wall Thickness ◽  
Half Life ◽  
Structural Integrity ◽  
Transportation Systems ◽  
Operating Conditions ◽  
Critical Dimensions ◽  
Periodic Inspection ◽  
Inspection Interval ◽  
Integrity Management

Abstract Periodic inspection is a proven approach to structural integrity management of transportation systems. This is as true for pipelines as it is for aircraft and railways. Setting the re-inspection interval to ensure imperfections cannot grow to critical dimensions prior to the next inspection is a foundational requirement of this maintenance methodology. API 1176 delineates two methods for re-inspection interval criteria for pipeline crack threat management: (1) maintaining a safety factor of 1.10 and at least a 30% of wall thickness remaining ligament depth until the next inspection, or (2) inspect at the half-life of the feature with the lowest remaining life taking the end of life being a 1.00 safety factor. Recent proposed regulatory documents and draft rules have down-selected to Method (1), or at least demonstrating compliance to Method (1), which will require some operators who have only been using Method (2) to safely manage this change. The two methods are compared for every asset of a large North American operator under current actual operating conditions. The relative conservatism of the two methods is directly compared. Sensitivity to a minimum remaining ligament requirement less than the recommended 30% of wall thickness is explored, and leak/rupture threat differentiation is considered. Implications of the change for a liquids pipeline operator in North America are described.

Epigenetic Studies in Psychotherapy: A Systematic Review

2020 ◽  
Vol 16 (2) ◽  
pp. 86-92
Author(s):  
Rafael Penadés ◽  
Bárbara Arias ◽  
Mar Fatjó-Vilas ◽  
Laura González-Vallespí ◽  
Clemente García-Rizo ◽  
...  
Keyword(s):  
Systematic Review ◽  
Dna Methylation ◽  
Mental Disorders ◽  
Epigenetic Modifications ◽  
Symptom Improvement ◽  
Epigenetic Changes ◽  
Main Hypothesis ◽  
Psychological Treatments ◽  
Time Period ◽  
The Impact

Background: Epigenetic modifications appear to be dynamic and they might be affected by environmental factors. The possibility of influencing these processes through psychotherapy has been suggested. Objective: To analyse the impact of psychotherapy on epigenetics when applied to mental disorders. The main hypothesis is that psychological treatments will produce epigenetic modifications related to the improvement of treated symptoms. Methods: A computerised and systematic search was completed throughout the time period from 1990 to 2019 on the PubMed, ScienceDirect and Scopus databases. Results: In total, 11 studies were selected. The studies were evaluated for the theoretical framework, genes involved, type of psychotherapy and clinical challenges and perspectives. All studies showed detectable changes at the epigenetic level, like DNA methylation changes, associated with symptom improvement after psychotherapy. Conclusion: Methylation profiles could be moderating treatment effects of psychotherapy. Beyond the detected epigenetic changes after psychotherapy, the epigenetic status before the implementation could act as an effective predictor of response.

scholarly journals Potential and limitations of finite element modelling in assessing structural integrity of coralline algae under future global change

2015 ◽  
Vol 12 (19) ◽  
pp. 5871-5883 ◽  
Author(s):  
L. A. Melbourne ◽  
J. Griffin ◽  
D. N. Schmidt ◽  
E. J. Rayfield
Keyword(s):  
Climate Change ◽  
Finite Element ◽  
Structural Integrity ◽  
Geometric Model ◽  
Algal Growth ◽  
Coralline Algae ◽  
Rocky Shores ◽  
Element Analysis ◽  
Scan Data ◽  
The Impact

Abstract. Coralline algae are important habitat formers found on all rocky shores. While the impact of future ocean acidification on the physiological performance of the species has been well studied, little research has focused on potential changes in structural integrity in response to climate change. A previous study using 2-D Finite Element Analysis (FEA) suggested increased vulnerability to fracture (by wave action or boring) in algae grown under high CO2 conditions. To assess how realistically 2-D simplified models represent structural performance, a series of increasingly biologically accurate 3-D FE models that represent different aspects of coralline algal growth were developed. Simplified geometric 3-D models of the genus Lithothamnion were compared to models created from computed tomography (CT) scan data of the same genus. The biologically accurate model and the simplified geometric model representing individual cells had similar average stresses and stress distributions, emphasising the importance of the cell walls in dissipating the stress throughout the structure. In contrast models without the accurate representation of the cell geometry resulted in larger stress and strain results. Our more complex 3-D model reiterated the potential of climate change to diminish the structural integrity of the organism. This suggests that under future environmental conditions the weakening of the coralline algal skeleton along with increased external pressures (wave and bioerosion) may negatively influence the ability for coralline algae to maintain a habitat able to sustain high levels of biodiversity.

scholarly journals Development of the Circular Bioeconomy: Drivers and Indicators

2021 ◽  
Vol 13 (1) ◽  
pp. 413
Author(s):  
Maximilian Kardung ◽  
Kutay Cingiz ◽  
Ortwin Costenoble ◽  
Roel Delahaye ◽  
Wim Heijman ◽  
...  
Keyword(s):  
Circular Economy ◽  
Food Production ◽  
Conceptual Analysis ◽  
Green Economy ◽  
Political Agenda ◽  
Analysis Framework ◽  
Stakeholder Consultation ◽  
Time Period ◽  
The Impact ◽  
The Eu

The EU’s 2018 Bioeconomy Strategy Update and the European Green Deal recently confirmed that the bioeconomy is high on the political agenda in Europe. Here, we propose a conceptual analysis framework for quantifying and analyzing the development of the EU bioeconomy. The bioeconomy has several related concepts (e.g., bio-based economy, green economy, and circular economy) and there are clear synergies between these concepts, especially between the bioeconomy and circular economy concepts. Analyzing the driving factors provides important information for monitoring activities. We first derive the scope of the bioeconomy framework in terms of bioeconomy sectors and products to be involved, the needed geographical coverage and resolution, and time period. Furthermore, we outline a set of indicators linked to the objectives of the EU’s bioeconomy strategy. In our framework, measuring developments will, in particular, focus on the bio-based sectors within the bioeconomy as biomass and food production is already monitored. The selected indicators commit to the EU Bioeconomy Strategy objectives and conform with findings from previous studies and stakeholder consultation. Additionally, several new indicators have been suggested and they are related to measuring the impact of changes in supply, demand drivers, resource availability, and policies on sustainability goals.

Sign in / Sign up

Export Citation Format

Share Document