Reliability-Based Criteria for Fixed Steel Offshore Platforms

1997 ◽  
Vol 119 (2) ◽  
pp. 120-124 ◽  
Author(s):  
M. Efthymiou ◽  
J. W. van de Graaf ◽  
P. S. Tromans ◽  
I. M. Hines

The key issue addressed in this paper is the accuracy of structural reliability models for the case of fixed steel offshore structures under extreme storm loading. The emphasis is on engineering accuracy for the purpose of use in decision-making, and more specifically to achieve sufficient accuracy to enable the use of reliability models in deriving design criteria for fixed offshore platforms. These reliability models are used to derive partial load factors for use in conjunction with API LRFD to achieve a target reliability level appropriate for permanently manned installations. These load factors are location-dependent. Further load factors are proposed for the design of new, not normally manned installations.

Author(s):  
Geoff Cole ◽  
Annalisa Ernestine ◽  
John Rooney

This paper explores two alternative design philosophies for achieving target safety levels in fixed offshore structures. The first uses a Working Stress Design format, and examines the relationship between the return period of the metocean design criteria and the configured structural reliability. The second uses a Load and Resistance Factor Design format, and considers suitable environmental partial load factors required to achieve acceptable safety levels. An example case study of two unmanned structures demonstrates the importance of local environment and structural configuration in determining reliability. The results indicate that for certain combinations of structural configuration and environment, previously recommended design approaches appear inadequate. This study proposes more appropriate design criteria for two specific configurations on the North West Shelf of Australia.


2018 ◽  
Vol 147 ◽  
pp. 05002
Author(s):  
Ricky L. Tawekal ◽  
Faisal D. Purnawarman ◽  
Yati Muliati

In RBUI method, platform with higher risk level will need inspection done more intensively than those with lower risk level. However, the probability of failure (PoF) evaluation in RBUI method is usually carried out in semi quantitative way by comparing failure parameters associated with the same damage mechanism between a group of platforms located in the same area. Therefore, RBUI will not be effective for platforms spread in distant areas where failure parameter associated with the same damage mechanism may not be the same. The existing standard, American Petroleum Institute, Recommended Practice for Structural Integrity Management of Fixed Offshore Structures (API RP-2SIM), is limited on the general instructions in determining the risk value of a platform, yet it does not provide a detail instruction on how determining the Probability of Failure (PoF) of platform. In this paper, the PoF is determined quantitatively by calculating structural reliability index based on structural collapse failure mode, thus the method in determining the inspection schedule is called Risk-Reliability Based Underwater Inspection (RReBUI). Models of 3-legs jacket fixed offshore platform in Java Sea and 4-legs jacket fixed offshore platform in Natuna Sea are used to study the implementation of RReBUI.


Author(s):  
B. F. Ronalds ◽  
R. Pinna ◽  
D. J. Trench ◽  
D. G. Cosson ◽  
G. K. Cole

Moment magnification in platforms such as monopods and jack-ups may be addressed in a variety of ways in the design process. This paper investigates how differing treatments influence the reserve strength ratio (RSR) and hence structural reliability of sway platforms. Both WSD and LRFD versions of API RP2A are considered, together with several methods of estimating the moment magnification factor. The effect of varying topside weight is also incorporated — increasing topside load increases the second order moments but also increases the amount of steel provided by the Code to resist the loadings. It is found that the RSR varies widely for different structural configurations and may either increase or decrease with increasing topside weight. The RSR is also sensitive to the design approach adopted. As a result, a single set of partial load factors will not succeed in narrowing the spread of reliabilities across different configurations and design philosophies. Indeed, the use of a WSD format may result in more uniform reliability levels than API RP2A-LRFD for certain sway platforms.


2004 ◽  
Vol 31 (4) ◽  
pp. 684-694
Author(s):  
M A Maes ◽  
S Abdelatif ◽  
R Frederking

The present paper describes a recalibration of the loading side of all the design check equations in the Canadian offshore structures standard CAN/CSA-S471, General requirements, design criteria, the environment, and loads (offshore structures). The recalibration was prompted by concerns about changing or improved load–load effect models and new load types and by Canada's intention to harmonize its offshore standards with the new International Organization for Standardization (ISO) offshore codes in the near future. Calibration is performed over wide ranges of combinations consistent with the normal application scope of CAN/CSA-S471. Updated load models are based on a more refined zonation of operational loads into loads of short duration and slowly varying live loads. Frequent environmental load processes and operational loads are modeled using Ferry-Borges–Castanheta pulse load models and infrequent environmental events and are based on point process models. The calibration is performed using a nonlinear optimization of an upwardly restrained safety objective function to result in optimal load factors, companion and combination factors, and optimal specified exceedance probabilities for infrequent load processes.Key words: load combinations, code calibration, pulse load models, safety factors, reliability levels.


Author(s):  
Mehrdad Kimiaei ◽  
Jalal Mirzadeh ◽  
Partha Dev ◽  
Mike Efthymiou ◽  
Riaz Khan

Abstract Fixed offshore platforms subject to wave-in-deck loading have historically encountered challenges in meeting target reliability levels. This has often resulted in costly subsea remediation, impacted platform occupancy levels or premature decommissioning of critical structural assets due to safety concerns. This paper addresses the long-standing industry challenge by presenting a novel structural reliability approach that involves converging the analytical behavior of a structure to its measured dynamic response for assessment. In this approach, called the Structural Integrity Management (SIM) TRIAD method, the platform model is calibrated based on the measured in-field platform natural frequencies using a structural health monitoring (SHM) system, so that the reliability assessment can be performed on a structural model whose stiffness is simulated as close to reality as possible. The methodology demonstrates the potential of unlocking structural capacity of offshore structures by removing conservatism normally associated with traditional reliability assessment methods, thus significantly improving the ability to achieve target structural reliability levels in a cost effective manner. The SIM TRIAD method has been implemented while assessing an existing fixed offshore platform subject to wave-in-deck loads, which is located in East Malaysian waters. It has enabled the facility operator to achieve acceptable target structural reliability and has assisted in developing an optimized risk-based inspection (RBI) plan for ensuring safe operations to end of asset field life. The methodology and findings of the assessment are presented in this paper to illustrate the benefits of the SIM TRIAD method.


1994 ◽  
Vol 16 (2) ◽  
pp. 43-48
Author(s):  
Do Son

This paper describes the results of measurements and analysis of the parameters, characterizing technical state of offshore platforms in Vietnam Sea. Based on decreasing in time material characteristics because of corrosion and local destruction assessment on residual life time of platforms is given and variants for its repair are recommended. The results allowed to confirm advantage of proposed technical diagnostic method in comparison with others and have been used for oil and gas platform of Joint Venture "Vietsovpetro" in South Vietnam.


Author(s):  
S. Raza Wasi ◽  
J. Darren Bender

An interesting, potentially useful, and fully replicable application of a spatially enabled decision model is presented for pipeline route optimization. This paper models the pipeline route optimization problem as a function of engineering and environmental design criteria. The engineering requirements mostly deal with capital, operational and maintenance costs, whereas environmental considerations ensure preservation of nature, natural resources and social integration. Typically, pipelines are routed in straight lines, to the extent possible, to minimize the capital construction costs. In contrast, longer pipelines and relatively higher costs may occur when environmental and social considerations are part of the design criteria. Similarly, much longer pipelines are less attractive in terms of capital costs and the environmental hazard associated with longer construction area. The pipeline route optimization problem is potentially a complex decision that is most often undertaken in an unstructured, qualitative fashion based on human experience and judgement. However, quantitative methods such as spatial analytical techniques, particularly the least-cost path algorithms, have greatly facilitated automation of the pipeline routing process. In the past several interesting studies have been conducted using quantitative spatial analytical tools for finding the best pipeline route or using non-spatial decision making tools to evaluate several alternates derived through conventional route reconnaissance methods. Most of these studies (that the authors are familiar with) have concentrated on integrating multiple sources of spatial data and performing quantitative least-cost path analysis or have attempted to make use of non-spatial decision making tools to select the best route. In this paper, the authors present a new framework that incorporates quantitative spatial analytical tools with an Analytical Hierarchical Process (AHP) model to provide a loosely integrated but efficient spatial Decision Support System (DSS). Specifically, the goal is to introduce a fully replicable spatial DSS that processes both quantitative and qualitative information, balances between lowest-cost and lowest-impact routes. The model presented in this paper is implemented in a four step process: first, integration of multiple source data that provide basis for engineering and environmental design criteria; second, creation of several alternate routes; third, building a comprehensive decision matrix using spatial analysis techniques; and fourth, testing the alternative and opinions of the stakeholder groups on imperatives of AHP model to simplify the route optimization decision. The final output of the model is then used to carry out sensitivity analysis, quantify the risk, generate “several what and if scenarios” and test stability of the route optimization decision.


Author(s):  
Guang Zou ◽  
Kian Banisoleiman ◽  
Arturo González

A challenge in marine and offshore engineering is structural integrity management (SIM) of assets such as ships, offshore structures, mooring systems, etc. Due to harsh marine environments, fatigue cracking and corrosion present persistent threats to structural integrity. SIM for such assets is complicated because of a very large number of rewelded plates and joints, for which condition inspections and maintenance are difficult and expensive tasks. Marine SIM needs to take into account uncertainty in material properties, loading characteristics, fatigue models, detection capacities of inspection methods, etc. Optimising inspection and maintenance strategies under uncertainty is therefore vital for effective SIM and cost reductions. This paper proposes a value of information (VoI) computation and Bayesian decision optimisation (BDO) approach to optimal maintenance planning of typical fatigue-prone structural systems under uncertainty. It is shown that the approach can yield optimal maintenance strategies reliably in various maintenance decision making problems or contexts, which are characterized by different cost ratios. It is also shown that there are decision making contexts where inspection information doesn’t add value, and condition based maintenance (CBM) is not cost-effective. The CBM strategy is optimal only in the decision making contexts where VoI > 0. The proposed approach overcomes the limitation of CBM strategy and highlights the importance of VoI computation (to confirm VoI > 0) before adopting inspections and CBM.


Energies ◽  
2020 ◽  
Vol 14 (1) ◽  
pp. 29
Author(s):  
Mahdi Shadabfar ◽  
Cagri Gokdemir ◽  
Mingliang Zhou ◽  
Hadi Kordestani ◽  
Edmond V. Muho

This paper presents a review of the existing models for the estimation of explosion-induced crushed and cracked zones. The control of these zones is of utmost importance in the rock explosion design, since it aims at optimizing the fragmentation and, as a result, minimizing the fine grain production and recovery cycle. Moreover, this optimization can reduce the damage beyond the set border and align the excavation plan with the geometric design. The models are categorized into three groups based on the approach, i.e., analytical, numerical, and experimental approaches, and for each group, the relevant studies are classified and presented in a comprehensive manner. More specifically, in the analytical methods, the assumptions and results are described and discussed in order to provide a useful reference to judge the applicability of each model. Considering the numerical models, all commonly-used algorithms along with the simulation details and the influential parameters are reported and discussed. Finally, considering the experimental models, the emphasis is given here on presenting the most practical and widely employed laboratory models. The empirical equations derived from the models and their applications are examined in detail. In the Discussion section, the most common methods are selected and used to estimate the damage size of 13 case study problems. The results are then utilized to compare the accuracy and applicability of each selected method. Furthermore, the probabilistic analysis of the explosion-induced failure is reviewed using several structural reliability models. The selection, classification, and discussion of the models presented in this paper can be used as a reference in real engineering projects.


2021 ◽  
Vol 156 (A4) ◽  
Author(s):  
N Hifi ◽  
N Barltrop

This paper applies a newly developed methodology to calibrate the corrosion model within a structural reliability analysis. The methodology combines data from experience (measurements and expert judgment) and prediction models to adjust the structural reliability models. Two corrosion models published in the literature have been used to demonstrate the technique used for the model calibration. One model is used as a prediction for a future degradation and a second one to represent the inspection recorded data. The results of the calibration process are presented and discussed.


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