Unscheduled Maintenance Research Articles

A Data Driven Prognostic Methodology without a Priori Knowledge

Nowadays systems are more and more complex, there is intense pressure to continuously reduce and eliminate costly, unscheduled maintenance of these systems. In such case, using physics-based damage model is not adequate in term cost/benefit analysis. While, recent technological advances of new sensors, coupled with robust processing algorithms offer an elegant and theoretically sound approach to Condition-Based Maintenance (CBM)/Prognostic Health Management of such complex systems. A new strategy based on forecasting of system degradation through a prognostic data-driven method is required. This paper introduces the development of a data-driven methodology to predict remaining useful life (RUL) of an unspecified complex system. Remaining useful life prediction is performed by recent machine learning techniques without including any system or domain specific informations. The solution is efficient and easy to implement and has the potential to be applicable to a variety of complex systems (automobiles, aerospace systems).

In Situ Observations and Satellite Remote Sensing in SEACOOS: Program Development and Lessons Learned

In situ observing and satellite remote sensing components of the Southeast Atlantic Coastal Ocean Observing System (SEACOOS) implemented from 2002 through 2006 are reviewed and "lessons learned" from the operation of these systems are summarized. The in situ observing program built upon several efforts initiated at academic institutions in the southeast U.S. prior to 2002. The partnership and observing capacity were expanded as the SEACOOS program developed. Sustained near real-time in situ observations were obtained from buoys, offshore towers, pier and shore stations, and mobile platforms (ships, gliders, drifters) using several communications options. The SEACOOS observing program also included several test-bed studies, and a pilot program in regional satellite remote sensing utilized established capabilities at partner institutions to deliver satellite products in near real-time to SEACOOS. Many of the SEACOOS observing activities leveraged personnel and infrastructure resources at partner institutions and support from complementary research projects. The SEACOOS experience provides a number of pragmatic (operational) "lessons learned" that are relevant to the future operation of a Regional Coastal Ocean Observing System (RCOOS). Adequate support of experienced personnel is critical to the efficient, sustained operation of a real-time observing network. Also required are sufficient inventories of spare components, appropriate transportation options to accommodate both routine and unscheduled maintenance, robust communications with sufficient bandwidth and back-up options, and data logging on deployment platforms to minimize gaps in the time-series. RCOOS planning should include mechanisms to ensure effective communications on operational matters among technical personnel within and across regions.

An original multi-objective criterion for the design of small-scale polygeneration systems based on realistic operating conditions

The optimal design and operation of cogeneration and trigeneration systems for buildings applications is a complex issue, which has been investigated by several different approaches. Both the two basic management strategies, namely heat-tracking and electricity-tracking, have advantages and drawbacks in terms of operating results and may lead the plant designer either to undersize or oversize the CHP unit with respect to the optimal lay-out. Experimental works have demonstrated how the actual on-site performance of small-scale polygeneration systems significantly differs from their expected operation, due to the need for a regular plant operation and the effects of outages for scheduled or unscheduled maintenance activities. After pointing out that heuristic approaches based on demand duration curve are weak instruments for plant design optimization, a more refined method is proposed, based on realistic operating conditions. The method integrates results of previous researches, like the proven convenience in using a duration curve of the “aggregate thermal demand” and in adopting flexible and techno-economically feasible management strategies; it is also based on original indicators to be used for the real time optimization of plant operation. The proposed hybrid management criterion represents a good compromise between profit-oriented and energo- environment- oriented solutions, ensuring the combined production system to be eligible for support mechanisms. Finally, the method is applied for demonstrative purposes to a large hotel situated in Italy; implementing the innovative phases of the method by successive steps allowed to recognize what margins for profitability and energy saving each phase provides.

A Prospective Study on the Clinical Performance of Polysiloxane Soft Liners: One-year Results

The aim of the present study was to evaluate the clinical performance of four denture soft liners up to 12 months. Thirty-three edentulous patients who experienced difficulties when using hard denture bases because of changes in denture-supporting tissues were accepted for the study and randomly received Molloplast B, GC Reline Soft, Silagum Comfort, or Mollosil Plus relines. Performance of the materials was evaluated using nine criteria at 3, 6, and 12 months: physical integrity, surface detail, adhesion, color, odor, plaque accumulation, resilience, hygiene, and mucosal condition. A four-point categorized scale (1=poor, 2=fair, 3=good, 4=excellent) was used. Unscheduled maintenance events and the presence of fungal colonization were also recorded. The percentage of patients available at 3, 6, and 12 months were 91%, 91%, and 66%. Main reasons for dropouts and discontinuation were fractured dentures and patient dissatisfaction. At 6 months, 96% of the performance scores were good or excellent and the largest changes were observed for physical integrity, surface detail, color, and fungal colonization. Fungal colonization was the most commonly observed problem and was the only reason of failure at 12 months. The clinical performance of all soft liners was slightly impaired over the 12-month observation. Except for cases showing extensive fungal colonization, the observed changes in clinical performance did not necessitate remaking of the dentures. Mollosil Plus showed a performance comparable to that of Molloplast B, and the other materials had slightly lower performance especially in terms of fungal colonization.

Risk-Based, genetic algorithm approach to optimize outage maintenance schedule

A huge number of components are typically scheduled for maintenance when a nuclear power plant is shut down for its planned outage. Among these components, a number of them are risk significant so that their operability as well as reliability is of prime concern. Lack of proper maintenance for such components during the outage would impose substantial risk on the nuclear power plant (NPP) operation. In this paper, a new approach based on genetic algorithm (GA) is presented for the optimization of the NPP maintenance schedule during plant outage/overhaul, and an optimizer is developed accordingly. The developed optimizer, coupled with the suggested risk-cost model, compromises the cost in favor of maintaining the risk imposed by each schedule below regulatory/industry set limits. The suggested cost model consists of two elements, one considering the cost incurred by maintenance activities and the other incorporating the loss of revenues if needed, but unscheduled component maintenance causes further plant shutdown. The optimizer is developed in such a way that any risk and/or cost models the user desires can be applied. The performance of the developed GA/optimizer is evaluated by comparing its predictions with Monte Carlo simulation results. It is shown that the GA/optimizer performs significantly better.

Innovative Use of the Oil and Gas Regulations

Abstract Applications to amend existing schemes for enhanced recovery of oil by water injection to allow for the intermittent reinjection of raw sour solution gas into the Bashaw D-2G and D-2L pools during times of shutdown was a low cost solution that would allow continuous production while conserving the sour gas. The applications were approved, and the operator is now able to produce oil and gas continuously despite disruptions, planned or unplanned, of the downstream processing or transportation facilities. Introduction Due to third party failures or scheduled and unscheduled maintenance of downstream operations, Key West Resources Ltd. were forced to completely shut-in their oil and gas production in the Bashaw D-2G and D-2L pools (Figures 1 and 2) for a significant number of days each year. This represented a loss in revenue of approximately $81,000 per day (gross 2002 dollars based on Cdn$40/barrel oil and Cdn$4/MSCF gas). Key West was anxious to find a solution that would work within the existing regulatory framework and that would eliminate the pool shut-ins due to third party failures. Key West also required that the solution result in little or no capital expenditure. The application would have to address the EUB's three main concerns: conservation (of the oil), equity and economics. Applications submitted to the EUB, pursuant to the requirements laid out in Guide 65: Resources Applications for Conventional Oil and Gas Reservoirs, June 2000(1), Sections 2.1 and 4.1, requested the following:Amend Approvals 7609 and 7274 for the injection of water to enhance oil recovery from the Bashaw D-2L and D-2G pools, respectively, pursuant to Section 26 (1,a) of the Oil and Gas Conservation Act and Guide G-51, by the intermittent reinjection of raw sour solution gas produced from the pool; and toRe-classify the wells approved for Class II water injection in Approvals 7609 and 7274 to Class III injection (sour gas) wells. The EUB reviewed the initial submission and compiled a list of concerns relating to the suitability and capability of the existing water injection pipeline network to handle the sour gas and the effect of the proposed reinjection on overall oil recovery in the Bashaw D-2L and D-2G pools. The initial and supplemental submissions met all the requirements of Guide 65, while meeting Key West's requirement to maintain production during times of shut-in. Key West was required to compromise on the annual volume they would reinject. The volume approved was a volume that reflected current gas production rates for three consecutive months, rather than a rate based on future development and a catastrophic six month shut-in. Approval to reinject sour gas intermittently into the Bashaw D-2L and D-2G pools, during times when the pools would be shut-in due to third party failures, were granted March 28, 2003 and December 23, 2003, respectively. Discussion Applications #1287609 and #1287472 were submitted to the Alberta Energy and Utilities Board by Fekete Associates, Inc. on behalf of Key West Energy Corporation in December 2002. The purpose of the applications was solely to avoid the loss of production due to plant or pipeline failures, routine maintenance or scheduled turnarounds.

Maintenance alternative integration to prognosis process engineering

PurposeThis paper proposes the extension of a prognosis process by means of the integration of maintenance alternative impacts in order to develop a maintenance decision‐making tool.Design/methodology/approachThe deployment of this extended prognosis process follows a methodology based both on probabilistic and on event approaches.FindingsThe importance of the maintenance function has increased due to its role in keeping and improving the system availability and safety but also the product quality. To support this new role, the maintenance concept has undergone several major developments to lead to proactive considerations mainly based on prognosis process allowing one to select the best maintenance plan to be carried out.Practical implicationsStudies over the last 20 years have indicated that around Europe the direct cost of maintenance is equivalent to between 4 and 8 per cent of total sales turnover. The indirect cost of maintenance is likely to be a similar amount. Thus, in the countries where modern maintenance practices have yet to be well adopted by industry, the potential savings from modern maintenance are massive. These modern and efficient maintenances imply identifying the root‐cause of component failures, reducing the failures of production systems, eliminating costly unscheduled shutdown maintenances, and improving productivity as well as quality. It means, for the companies, migrating from their traditional reactive approach, which is “fail and fix”, to “predict and prevent”. The advantage of the latter is that maintenance is performed only when a certain level of equipment deterioration occurs. This “proactive” maintenance is mainly based on prognosis process often considered as the Achilles heel, while its goal is fundamental for implementing anticipation capabilities. This paper looks into this issue by proposing the development of an innovative prognosis process integrating the modelling of maintenance actions and their impacts on system performances. It leads to offering a maintenance aided decision‐making tool cable of assisting the decision‐maker in selecting the best maintenance plan to be carried out.Originality/valueThe feasibility of this new prognosis is experimented on the manufacturing Tele‐Maintenance (TELMA) platform supporting the unwinding of metal bobbins.

Life cycle cost impact of using prognostic health management (PHM) for helicopter avionics

Case studies were conducted using a stochastic model to predict the life cycle cost impact associated with the application of prognostic health management (PHM) to helicopter avionics. The life cycle costs of systems that assumed unscheduled maintenance and fixed-interval scheduled maintenance were compared to the costs of precursor-to-failure and life consumption monitoring PHM approaches, and the optimal safety margins and prognostic distances were determined.

Multivariate analysis of a simulated prognostics and health management system for military aircraft maintenance

The Air Force logistics operations system is, in general, reactive in nature, with unscheduled aircraft maintenance beginning with a signal for out of tolerance conditions from the aircraft, subsequent fault isolation procedures performed by a maintenance team, and the steps taken to repair or replace the faulty item. The Joint Strike Fighter (JSF) programme has been pursuing an autonomic logistics system (ALS) concept that changes this reactive process into a proactive one, with the employment of technologies such as prognostics and a distributed information network. This paper briefly describes a simulation model of a prognostics and health management (PHM) system employed as part of an ALS for a JSF-type aircraft. The simulation produces a large number of commonly used flight line measures of performance for aircraft availability and mission effectiveness. Multivariate statistical analysis of these outputs provides a means to assess the impact of a PHM system on aircraft productivity.

A maintenance resources capacity estimator

Combat aircraft operations are usually constrained by limits on the logistics resources available. However, models that can compute the logistics resources necessary to support planned combat aircraft activity typically are custom applications that are data-intensive and difficult to use. This paper introduces a method for the Argentine Air Force (AAF) to estimate the mean number of aircraft that can be restored in a given time between consecutive sorties, given specified maintenance resources and base physical geometry. This maintenance resources evaluation technique (MRET) uses an analytical approach to estimate the mean and variance of aircraft unscheduled downtime. These parameters are then used in a Monte Carlo simulation of scheduled and unscheduled maintenance tasks necessary to prepare aircraft for the next sortie. When programmed in a spreadsheet, the MRET combines a high response speed with a moderately detailed scenario description, making the model suitable for the AAF.

Failure monitoring in a high performance hydrostatic actuation system using the extended Kalman filter

This paper describes the development and evaluation of a fault detection strategy for a high performance hydrostatic actuation system, the electrohydraulic actuator (EHA). The approach makes use of the extended Kalman filter (EKF) technique for parameter estimation purposes and changes in the estimated system parameters were related to faults in the EHA. The hydrostatic system has potential applications in the aerospace industry, in robotics, in machining and as such, failures in the EHA can pose a safety hazard as well as result in costly downtime and unscheduled maintenance. Monitoring failures in the hydrostatic system is achieved by estimating two parameters of interest, namely the viscous friction coefficient and the effective bulk modulus. Changes in the viscous friction coefficient in the actuator indicate deterioration of the hydraulic oil or wear in the seals. Lowering of the effective bulk modulus affects the response of the closed loop system, reduces system bandwidth and may cause instability. A simulation study was conducted to investigate the feasibility of the approach as well as the level of accuracy to be expected. The methodology was then verified using experimental results.

Parameter Identification for a High-Performance Hydrostatic Actuation System Using the Variable Structure Filter Concept

Parameter estimation is an important concept that can be used for health and condition monitoring. Estimation or measurement of physically meaningful parameters and their evaluation against predetermined thresholds allows detection of gradual or abrupt deteriorations in the plant. This early detection of faults enables preventative unscheduled maintenance that is of benefit to industries concerned with reliability and safety. In this paper, a recently proposed state estimation strategy referred to as the smooth variable structure filter (SVSF) is reviewed and extended to parameter estimation. The SVSF is applied to a novel hydrostatic actuation system referred to as the electrohydraulic actuator (EHA). Condition monitoring of the EHA for preventative unscheduled maintenance would increase its safety in applications pertaining to aerospace and would reduce its operational and maintenance costs.

‘ODDS ALGORITHM’-BASED OPPORTUNITY-TRIGGERED PREVENTIVE MAINTENANCE WITH PRODUCTION POLICY

In manufacturing field, the planning of opportunistic preventive maintenance actions adapted to minimize the number of useless production stops remains a major industrial challenge. Indeed maintenance decision has to be made in synchronization with the production demands to eliminate costly unscheduled shutdown maintenances and to improve productivity as well as quality. To face with this issue, this paper proposes an innovative approach based on the ‘odds algorithm‘. The objective is to select, among all the production stops already planned, those which will be optimal to develop maintenance actions in time according to the degraded system state. The optimization phase incorporates criteria such as reliability, maintainability and production stops durations. The approach feasibility is shown on an application case.

Applying Analysis of International Space Station Crew-Time Utilization to Mission Design

Science activity on the International Space Station (ISS) has been anecdotally reported to be less than expected, presumably because of excessive time being taken up by habitat maintenance needs. In this analysis, it was determined that each crew member spent an average of 1.9 (or more) h per work day and 1.8 h per rest day performing ISS maintenance tasks. Because of confounding factors associated with insufficient supplies and reduced transport opportunities, the relationship between mission design and actual operations is not necessarily simple or direct, as increased maintenance demands or a lack of up- and downmass for science projects may have both contributed to the crew-time impact. Regardless of the causal mechanisms, however, actual crew time spent on scheduled and unscheduled habitat maintenance on Skylab and ISS exceeded that estimated by design, thus reducing crew time allotted to perform other tasks, although not necessarily science tasks. These impacts would have likely been further exacerbated for ISS if the planned external maintenance tasks had not been reduced during the early design phase. The approach used for assessing external maintenance could be applied for other tasks, such as internal maintenance and science, to establish the amount of time required for mission goals and uncertainty factors. By rigorously addressing parameters such as these early in the design process, crews on future missions to the moon and Mars are less likely to become oversubscribed during actual mission operations.

Aircraft Scheduling with Maintenance and Crew Consideration

In this paper, we propose an integrated approach to combine aircraft routing and crew scheduling problem with the consideration of multiple types of fleets where a crew can only fly the specific type of fleet. This method effectively manages the aircraft and crew because it takes aircraft maintenance into account. A rolling horizon technique is used to capture the uncertainty of demand. The qualitative analysis indicates that unscheduled maintenance posts big impacts on the schedule and results in high operation cost. Special routing and scheduling strategy is provided to reduce the impact from unscheduled maintenance to improve aircraft safety and utilization. The computational results on the real data show that significant benefit can be obtained from the proposed strategy.

Even more price records, new refineries and a technical hitch at the IPE

This section summarizes downstream developments of the previous month. Exploration & Production are covered in 'Upstream Review'. In a final burst before retreating, oil prices once again entered record territory. WTI went to $58.28 a barrel, while Brent shot up to $57.65. In Asia, meanwhile, Malaysia's benchmark Tapis grade climbed above $61.00. The scramble to buy crude oil finally began to show up in stock levels, however, and US inventory figures showing an 8% year‐on‐year rise at the start of April suggested that fears of a crude oil shortage were overplayed. Prices fell sharply leaving Brent and WTI just above $51.00 a barrel. An announcement by OPEC's president, Ahmad Fahad Al Sabah, that the cartel would produce an additional 500,000 bpd in May helped to relax fears further. Product prices remained relatively more robust on a combination of high demand in the US and Asia and unscheduled refinery maintenance in the US.

E-MAINTENANCE IN SUPPORT OF E-AUTOMATED MANUFACTURING SYSTEMS

ABSTRACT Eliminating costly unscheduled shutdown maintenances and accordingly reducing the failures of production systems as a whole help deliver the promises on ordered products. In the exploration of more efficient maintenance and service strategies, the approaches of condition-based proactive maintenance, collaborative maintenance, remote maintenance and service support, provision for real-time information access, and integration of production with maintenance have evolved into a new phenomenon called e-maintenance to meet the needs of the future e-automation manufacturing world. This paper introduces the emerging field of e-maintenance by studying its critical elements in support of the deployment of next generation manufacturing systems; we focus on industrial wireless technology and artificial intelligence, which are two essential technological means in the realization of scalable and agile e-maintenance. The technical issues and challenges involved for applying these technologies in an e-maintenance platform are explained. Finally, a framework for practical implementations is briefly presented.

A PERIODIC-REVIEW INVENTORY SYSTEM WITH SUPPLY INTERRUPTIONS

Supply interruptions resulting from unpredictable events, such as machine breakdowns, order cancellations, unscheduled maintenance, and labor strikes can produce adverse effects on the production/inventory system. In this article, we consider a periodic-review inventory system subject to random demand and unreliable supply. The availability of supply is modeled as an alternating renewal process with general distributions for the durations of the UP and DOWN cycles. We consider the lost-sales case and also discuss the backorder case, for both the discounted and long-run average cost criteria. For the linear cost model, we derive the structural properties and bounds of the optimal policy. We also propose the “end-of-cycle” inventory return contract and show that it may be mutually beneficial to both the firm and the supplier.

Productivity improvement of a BDK process plant via QRA techniques

This paper describes a case study in which Quantitative Risk Assessment (QRA) was used as the background for lay-out modifications to improve the reliability, and thus the productivity, of a batch plant for distilling the production residues of a photo initiator for ecological paints. QRA identified the plant’s critical features. Its reliability was assessed in the light of the literature data coupled with its reported anomaly history. Theoretical improvements in reliability were put into effect through unscheduled maintenance operations. Redundancies, for example, were introduced in the solvent tank level control system and the solvent line valves were replaced with a more reliable model.

Evaluation of a hypermedia maintenance support application

A large hypermedia application has been developed to demonstrate the concept of factory wide hypermedia to support the maintenance of a major process line. As part of its development cycle, the performance of the software and its acceptance by the user community has been fully evaluated. The evaluation method considered in this paper focuses on the subjective opinion of the users and measured the ease with which users could retrieve the information required to perform specific tasks, and is considered suitable for other large industrial hypermedia applications. This research draws together standard evaluation techniques into a methodology for evaluating an industrial strength hypermedia application. The trials undertaken showed that the users were able to find the identical information in approximately one-third of the time when using the hypermedia system, over a paper-based system, which equate to a significant cost savings during unscheduled maintenance periods.