Life Extension Decisions Research Articles

Introduction of a carbon footprint assessment in the oil and gas facility life extension decision-making process

In large oil and gas producing countries, extraction and processing activities, including upstream activities, can represent a large share of domestic emissions. As oil fields approach their expected service life and reach depletion, energy use and GHG emissions increase per unit of produced oil, shifting operations away from their optimal point. Thus, it is paramount that oil field life extension decisions account for energy use and GHG emissions. However, many facilities are having their service life extended without considering this energy inefficiency and previous life extension decision making studies have neglected GHG emissions. Addressing this issue, this paper proposes the inclusion of a carbon footprint assessment within the evaluation of oil and gas offshore production facility life extension. The carbon footprint assessment adds an environmental lens to the evaluation of ageing, formerly evaluated according to material degradation, obsolescence and organizational issues. An eleven-stage framework is proposed to systematize the ageing related carbon footprint assessment and support life extension decision-making: (1) Objective definition, (2) Scope definition, (3) Field conditions description, (4) Scope breakdown into manageable portions, (5) Detailed data collection for each process and subsystem, (6) Input and output definition for each process and subsystem, (7) Process modelling, (8) Methodology definition for energy demand and inefficiency estimate, (9) Monitoring indicator definition, (10) Performance evaluation, and (11) Interpretation of results. The proposed framework is applied to a hypothetical case study, developed with data from a typical oil and gas offshore production platform operated in Brazil. Two LE improvement strategies were simulated, i.e. reducing the number of gas turbines, and increasing the export of natural gas. Both alter the modus operandi of the compression system and do not require additional equipment installation. These strategies resulted in a combined reduction of 922,000 tCO2 during the extended 10-year operation. This outcome demonstrates that by applying the framework opportunities for reducing energy use and GHG emissions during life extension can be identified and quantified, facilitating life extension decision-making.

A dynamic condition assessment model of aging subsea pipelines subject to corrosion-fatigue degradation

Extension of operating lifetime of aging subsea pipelines is of great interest to oil and gas sectors. Corrosion and fatigue are the main causations of the condition degradation of subsea pipelines. A dynamic probabilistic condition assessment model based on continuous dynamic Bayesian network (DBN) is developed to support the life extension decision-making of aging subsea pipeline subjected to the corrosion-fatigue degradation. The methodology is built based on equivalent initial flaw size (EIFS) concept and a time-dependent prediction model implemented using DBN. The complex corrosion-fatigue degradation process is simplified by EIFS concept, and the crack propagation due to corrosion-fatigue is modelled using fracture mechanics model and DBN. A limit state function (LSF) is used to express the failure condition of subsea pipeline due to crack propagation. The dynamic reliability of subsea pipeline is estimated using Monte Carlo (MC) method with the probability distributions of the predicted crack sizes at different time slices. The estimated reliability is compared with the acceptable threshold to decide whether any measures are required to extend the life of subsea pipeline. The methodology is tested by a case study, and it is observed that it can be a useful tool to support life extension decision-making of aging subsea pipelines.

Large-Scale Modeling of Damage and Failure of Nuclear Graphite Moderated Reactor

Abstract The UK Advanced Gas-Cooled reactors (AGRs) have cores made of graphite bricks with dual functions: as structural elements of the core, providing space for and separating fuel and control rods; and as moderator of the nuclear reaction. Nuclear graphite is a quasi-brittle material, where the dominant mechanism for failure is cracking. While cracking of isolated bricks is expected due to operation-induced changes in graphite microstructure and stress fields, these could be tolerated as far as the overall structural function of the core is maintained. Assessment of the whole core behavior has been previously done with whole scale models where bricks have been considered as rigid body elements connected by elastic-brittle springs. This approach does not allow for the realistic assessment of the stresses in the bricks and associated brick cracking. Reported here are results from an ongoing project, which addresses this shortcoming. The proposed model uses deformable bricks with appropriate interactions, allowing for physically realistic whole core analysis. The results are focused on the damage that a graphite moderated reactor develops during a life cycle, how this affects the behavior of the whole core, and how changes in bricks' behavior impacts the core integrity. The proposed methodology is a major step toward high-fidelity assessment of AGRs' fitness for service, required for supporting continuous safe operation and life-extension decisions.

High-fidelity experimental measurements for modeling and simulation of nuclear engineering applications

Modeling and simulation performed with advanced tools are important for thorough understanding of existing power plant response to accidents; for life extension decisions of existing plants; and to support licensing activities for new power plants. The use of computational fluid dynamics (CFD) tool in nuclear R&D has gained significantly due to its capabilities to predict complex flow phenomena at very fine resolutions. High-fidelity numerical simulations including direct numerical simulation (DNS) and large-eddy simulation (LES) have been considered as reliable CFD tools for the development and validation of turbulence models along with experiments. Compared to other CFD techniques, DNS is the most computationally expensive approach, and limited to flow studies at low to moderate Reynolds numbers. LES subgrid-scale (SGS) models require the specification of model coefficients that cannot be generally used to simulate a wide spectrum of flows. Performances of LES with modified SGS model coefficients need to be verified and validated versus high-resolution experimental database or DNS results.In this paper, we present the current state-of-the-art experimental measurements in complex geometries of advanced nuclear reactors, such as turbulent flows in wirewrapped fuel bundle for liquid metal reactors and randomly packed beds for gas-cooled and molten-salt reactors. It is important to achieve an in-depth understanding of flow phenomena and complex flow characteristics within these reactor cores because they are related to the safety and design scenarios. High-fidelity experimental measurements of velocity fields are acquired featuring a combination of time-resolved particle image velocimetry (TR-PIV) and matching-index-of-refraction approaches. Experimental results are obtained at high spatial and temporal resolutions of velocity fields and the first- and second-order flow statistics are suitable for the verification and validation of CFD codes currently used in nuclear engineering applications.

Condition assessment, remaining useful life prediction and life extension decision making for offshore oil and gas assets

Offshore oil and gas assets are highly complex structures comprising of several components, designed to have a lifecycle of about 20 to 30 years of working under harsh operational and environmental conditions. These assets, during their operational lifetime, are subjected to various degradation mechanisms such as corrosion, erosion, wear, creep and fatigue cracks. In order to improve economic viability and increase profitability, many operators are looking at extending the lifespan of their assets beyond the original design life, thereby making life extension (LE) an increasingly critical and highly-discussed topic in the offshore oil and gas industry. In order to manage asset aging and meet the LE requirements, offshore oil and gas operators have adopted various approaches such as following maintenance procedures as advised by the original equipment manufacturer (OEM), or using the experience and expertise of engineers and inspectors. However, performing these activities often provides very limited value addition to operators during the LE period of operation. This paper aims to propose a systematic framework to help operators meet LE requirements while optimizing their cost structure. This framework establishes an integration between three individual life assessment modules, namely: condition assessment, remaining useful life (RUL) prediction and LE decision-making. The benefits of the proposed framework are illustrated through a case study involving a three-phase separator system on a platform which was constructed in the mid-1970s in West Africa. The results of this study affirm the effectiveness of this framework in minimizing catastrophic failures during the LE phase of operations, whilst ensuring compliance to regulatory requirements.

Parametric method of observation results processing with regard to missed data

The matters of ensuring dependable and safe operation of NPP facilities is of significant relevance. That is due to the fact that the proportion of equipment at the end of assigned service life in the nuclear power industry is very high, thus dependability analysis of NPP elements and systems is required. In the process of dependability characteristics analysis a number of problems occur, i.e. evaluation of residual life of equipment, justification of life extension decisions. Also, it is required to provide spare parts for elements and systems, select maintenance strategies, etc. That increases the value of activities aimed at analyzing the dependability of nuclear power facilities and, subsequently, the requirement to develop the methods of analysis of statistical information on the operation of NPP elements, subsystems and systems for the purpose of identifying their performance parameters. At nuclear power plants, activities are organized to collect information on the operation of various facilities, i.e. failures and defects of system components, maintenance procedures, operating modes, storage conditions, etc. The information provided by the NPPs has a number of distinctive features. That is due to the following factors: presence of censorship of failure data, absence of sufficient service hours within the given observation interval and the limited volume of available data. All those factors cause an uncertainty in the resulting evaluations and, subsequently, lower that optimal accuracy on dependability characteristics calculation. In the process of evaluating the dependability of facilities in operation a certain part of facilities and systems often does not fail over the period of observation. In such situations statistical analysis of dependability is required that is based on the so-called right censored samples of which the distinctive feature consists in the fact that the inspected product does not fail within the period of observation. In some cases the operation times of specific facilities are unknown. For instance, at the initial stage of facility operation information on its performance was not collected, and the decision to collect data was taken later. In this case the required method must take into consideration the missing information that was not collected at the initial stage. The limited volume of information is due to the fact that the nuclear energy facilities fall into the category of highly dependable equipment. Failures are rare events. Therefore in order to increase the reliability of dependability indicators estimation all the available information must be used. Thus, taking into account all the available information enables more accurate results that can be used to calculate NPP facility service life. The purpose of this article is to show the application of the method of repeated sample and examine its efficiency. The main focus is on missed data that are to be recovered. The authors provide the results of evaluation of the exponential distribution law parameter subject to right censored and missed data. The suggested method of repeated sample is compared with the bootstrap method and mean substitution method. For evaluation of exponential distribution law parameter the authors suggest using the maximum likelihood method. Statistical characteristics calculation is provided. All the calculations and results are based on test cases.

Development of a techno-economic framework for life extension decision making of safety critical installations

One of the major decisions in management of the industrial assets is to ensure the feasibility of life extension process for safety critical components when they reach end-of-life. Most of the existing life extension decision-making models are restricted solely to either “technical” or “economic” feasibility analyses that may lead to inaccurate results or incorrect conclusions. In this paper, a comprehensive life extension feasibility assessment framework by taking into account both the technical and economic considerations is developed. The proposed techno-economic model for life extension of safety critical elements consists of three phases: preparation, assessment, and implementation. The technical assessment part of the framework incorporates all aspects of data collection and review, screening and prioritization of safety critical elements, condition assessment, estimation of remaining useful life, and risk analysis, while the economic assessment part deals with cost-benefit analysis. The decision to qualify a safety critical element for continuous operation beyond its service life is made based on a “life extension measure (LEM)” which is calculated by combining two indexes of “equipment health condition” and “economic added-value” obtained respectively from the technical and economic assessments. The model is applied to support the life extension decision-making procedure for water deluge systems in offshore oil installations. The results of the study show that the model is highly capable of assisting asset owners to evaluate the technical and economic benefits of extending the service life of components.

Micromechanical modelling of deformation and fracture of hydrating cement paste using X-ray computed tomography characterisation

Cement paste is the basic but most complex component in cement composites, which are the dominant construction material in the world. Understanding and predicting elastic properties and fracture of hydrating cement paste are challenging tasks due to its complex microstructure, but important for durability assessments and life extension decisions. A recently proposed microstructure-informed site-bond model with elastic-brittle spring bundles is developed further to predict the evolution of elastic properties and fracture behaviour of cement paste. It is based on microstructural characteristics of hydrating cement paste obtained from X-ray computed microtomography (micro-CT) with a spatial resolution of 0.5μm/voxel. Volume fraction and size distribution of anhydrous cement grains are used to determine the model length scale and pore-less elasticity. Porosity and pore size distribution are used for tuning elastic and failure properties of individual bonds. The fracture process is simulated by consecutive removal of bonds subjected to surface energy based failure criterion. The stress–strain response and elastic properties of hardened cement pastes with curing ages of 1, 7 and 28 days are obtained. The simulated Young's modulus and deformation response prior to peak stress agree very well with the experimental data. The proposed model provides an effective tool to evaluate time evolution of elastic properties and to simulate the initiation, propagation, coalescence and localisation of micro-cracks.

Establishing a Value Chain for Human Factors in Nuclear Power Plant Control Room Modernization

Commercial nuclear power plants in the United States (U.S.) have operated reliably and efficiently for decades. With a second 20-year life extension of operation beyond the plant's original operating licenses now being considered by many utilities, there are opportunities to achieve even greater efficiencies, while maintaining high operational reliabilities, through strategic, risk- and economically-informed, upgrades to plant systems and infrastructure. The U.S. Department of Energy's Light Water Reactor Sustainability (LWRS) program supports the commercial nuclear industry's modernization efforts through research and development (R&D) activities across many areas to help establish the technical and economic bases for modernization activities. The Advanced Instrumentation, Information, and Control Systems Technologies pathway is one R&D focus area for the LWRS program, and has researchers at Idaho National Laboratory working with select utility partners to use human factors and instrumentation and controls R&D to help modernize the plant's main control room. However, some in the nuclear industry have not been as enthusiastic about using human factors R&D to inform life extension decision-making. Part of the reason for this may stem from uncertainty decision-makers have regarding how human factors fits into the value chain for nuclear power plant control room modernization. This paper reviews past work that has attempted to demonstrate the value of human factors, and then describes the value chain concept, how it applies to control room modernization, and then makes a case for how and why human factors is an essential link in the modernization value chain.

Decision support for life extension of technical systems through virtual age modelling

This article presents a virtual age model for decision support regarding life extension of ageing repairable systems. The aim of the model is to evaluate different life extension decision alternatives and their impact on the future performance of the system. The model can be applied to systems operated continuously (e.g., process systems) and systems operated on demand (e.g., safety systems). Deterioration and efficiency of imperfect maintenance is assessed when there is limited or no degradation data, and only failure and maintenance data is available. Systems that are in operation can be studied, meaning that the systems may be degraded. The current degradation is represented by a “current virtual age”, which is calculated from recorded maintenance data. The model parameters are estimated with the maximum likelihood method. A case study illustrates the application of the model for life extension of two fire water pumps in an oil and gas facility. The performance of the pump system is assessed with respect to number of failures, safety unavailability and costs during the life extension period.

Assessing Long-Term Performance of CANDU®Out-of-Core Materials

As so-called second-generation power reactors are approaching the end of their original design lives, assessments are being made to determine the feasibility and economics of extending plant life. Although components exposed to neutron and gamma irradiation are often those of most concern in terms of in-service ageing and continued fitness for service, ageing of out-of-core components can also limit the possibility of extended service life beyond design life. In CANDU®reactors, life extension decisions occur when the Zr-2.5Nb pressure tubes reach end of life, typically after about 25 years of service for the first CANDU-6 units. At the time of pressure tube replacements, the remaining life predictions for several other major components or systems provide the information required to determine life extension feasibility. Several CANDU reactors are currently being refurbished, with others planned, and experience to date shows that the steam generators, heat transport system piping and various balance of plant piping systems are typically those requiring careful assessment to ensure successful refurbishment. In this paper, we discuss AECL R&D that is oriented towards providing the chemistry and materials inputs required to assess current condition and predict future ageing of CANDU reactor out-of-core components and systems, and in particular steam generators (Alloy 800 tubing and carbon steel internals), feeder pipes and related heat transport system piping (carbon steel flow accelerated corrosion, feeder cracking). Systems and components that may impact future life will also be discussed, along with the related R&D, and this includes balance of plant system piping (feedwater piping and buried piping), cables and concrete structures.

Remaining useful life, technical health, and life extension

Life extension has for a long time been an important and highly discussed issue in nuclear and aviation industries, and has recently attracted considerable attention in the subsea oil and gas industry. Decision-making related to life extension is a multidisciplinary problem, but it primarily depends on the remaining useful life. This paper clarifies the concepts of remaining useful life and technical health, and discusses various influencing factors. An overall model with the capability to handle a heterogeneous combination of requirements, such as degradation modelling, uncertain environmental and operational conditions, uncertain sensor data and expert opinion is suggested for life extension decision-making. It is concluded that a physics-based modelling approach is appropriate for equipment in the subsea oil and gas industry.

PERFORMANCE IMPLICATIONS OF PRODUCT LIFE CYCLE EXTENSION: THE CASE OF THE A‐10 AIRCRAFT

Firms are faced with challenging decisions when capital equipment reaches the end of its designed service life. This research examines the risks of deciding to extend the retirement date of a capital asset in terms of performance and cost and offers recommended actions to mitigate this risk. Through study of the United States Air Force's A‐10 aircraft, the authors analyze one example of decreased performance and increased costs experienced when supply chain implications are not explicitly considered when making service life extension decisions. In this case, the Air Force's efforts to save money through life extension of existing aircraft actually exceeded the seemingly enormous initial investment of acquiring new aircraft. Arguments are presented suggesting the Air Force, in particular, may reap benefits from forming supply chain relationships and creating continuity plans to manage problems such as parts shortages and cost increases when extending the use of capital assets beyond its intended service life.